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1906 Multimeter Service Manual

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4. SER 5V 11 E 10 8 GBIBSET GPIBSEL IEEE488 3 IC A14 i CONNECTOR SN75161 e JUGOSZERE GPIB SER 5V 1 aK A15 5 ES EZ UPD7210 2 18 25 48 _ PJ1 17 O REN Q REN VCC R W 74HC1Q PJ1 a 3 18 24 20 z i 5 O p cede e qQ GND SER av RZW E E Pjf B O 5 A gt 18 37 NDAC CLK E 22 28 Bji 7 O NRFD zg Q NRED RST RESET IC4 A SER PJI 6 O EDAM pav OUT 7 74HCQ5 OE CE 7 1 38 Do EM i Re ia iR 2g Q 6 28 E T a MAS E gt Q ATN M 14 AB At A2 JE PE PJI 18 A SRO INT a o Q sro c7 a 1EB bovan 18 SER BV ig 8000 PJI 12 TE BE 15P 5383R Ag O 8 4 9152MHZ a 14 g Bg da R W CER MP 117A1 n O m wa P312 BZW P12 A2 15 saa gt PJ1 19 O igen BEN OW 2 DE GPIBSEL ca P13 A3 18 f yo O TRZ
5. CTRL15A 3V AN as A BC559 U Wi LPR au HI 4 RL 1 a pas 12 OS A 5 470K m SENS 3 12 11 R122 R1 L 228K 228K Cy a2 FUSIBLE FUSIBLE sM CTRL 1 PAS D as C8 4216 CTRL18 R93 8 BC549 1UN m 4 220K lt N FUSIBLE CTRL19A B SE Ss E 5 X at AG RL3 AC 3 R192 R11 4K7 AG W2 1K FUSIBLE 5 AAMA V 018 12 0 AN a ES BC559 a HI SJ 4 ETRL18 i CONT DET GUARD mi R29 A e SIGNAL R75 22K 1 7 8 C61 vi 338K L 1 mer N CONDITIONING EBM PTCI DC 2 RP4 D IC20 D IC11 A LM324 KME RER R28 0P482GP NE v2 1 IC7 A 220 R78 5V AN 1053 DG 4 330K 13 WSZ API A 4016 gan 12M T 7 av R27 11 14 CTRL19A v3 OHM RE 5 CTRL2 ICB A Mh 35 EUN 2 ETRLTOA 2K2 L n II pon g R77 12 1202N AG 12 RA RL2 330K x 4 AB R105 13 R45 R46 i 7 IC51 33 K 188K 5 CTRL2 14 180 UE D8 NI ADZ11 CTRL21 1 2 1 2 BHM 1N4148 3 11 CQ mmm 5 d 6 13 dh E Pd IC5 A IC4 A 18 CTRL5A iv 4016 4016 BV R 2 C64 C4 Cg tav R117 3 5 398 iu C62 m _1C12 IC5 E 3 3N3 IC1 B C78 1N4148 1 C74 100N 108U IC D p i 034 c i IC5 D 4016 T 12 5 216 122
6. 2 LM324 C35 7 1 47U 25V 2 1 IC23 A 1 DAN 2 LM324 ISS 12 RA 3 dr zb 1 11A IC21 B Pune 3 H A MA 5 ETRE AC23 B o 7 LM324 CTRL2A 8 n CTRL2 5 C36 7 H OHMS 1C21 C 47U 25V 2 RL2 CTRL14 5 LO 3 gt LAH a IC23 C PJ2 5 FS5 8 CTRL18A 18v 3 NLMa24 Eg BRI IC41 8 I U 10 C37 RL3 CTRL1Q I 8 378 W22G 7815 pos 47U 25V 2 1 18 1 I P 3 15V D eg 5V DAN 5V ST Ba IC21 D 2 2 1047 18 Q0U20B11 58B2 I 13 1av 13 D C43 C48 3 R 3 74AC573 1g 478U 2 188 14 CTRLIGA 14 ISPLAY KEYBOARD li E ER 25y 4 17 B1 I PJ2 4 35V 12 12 D1 A av A 1C23 D Q R 11 LM324 5 5 C44 B2 PJ2 3 1 100 BV R D2 5 a MAIN PCB 478U tav iav I O 35V 25V IC5a i EGG 2 1 P 3 15V 1C22 A 7 8 13 B3 l 8 375A 78 68 5V AN 2 L M324 R A D3 5V CTRL15A 3 1 BE z 3 CTRL5A T E ON OFF MAINS B7 CTRL5 Bou e 4 CTRL15 R 5v FUSE 1C22 B E CAL gt pa IC24 B i u s 2 m 2 5V A D amp M LM324 1N4148 5 LM324 11 r PJ1 1 AE 1 SWI h at ENABLE TF 41 pas 7 CTRL15 7 CTRL18A PORT 1 DG O Ifi 57 L49 BV 56 BI PJ1 18 J2 18 28 5 U 75A CTRL16 5 ry a ME t IZP 3 CTRL6 5 OY PIEREK pace ka Wu MEI l m B 7P IC22 C IC24 C CAL ENABLE O A ale PJ2 1 amu mt 2 18 ees D
7. 1 0 00 O0 0 0 00 0 0 0 200uA 2mA 0 1 0 i Q Q9 9 00 1 10 10 x 20mA 200mA 10A ab a x x 1 0 1 00 0 AMPS AC Li A 0 A 0 A 1 A TiO x x x x x x x 0 0O 1 00 0 O O 0 0 0 0 0 0 0 0 O0 20048 2mA 20mA 0 0 1 A 1 1 1 0 A O Oo A O Oo A O 1 0 O x 1 200mA 10A 0 O OHMS 200 2k 20k A x A A 1 X A A 1 0 0 1 1 1 10 0 1 1 1 0 A Aa i 0 A 1 1 0 w 1 1 k 0 D D 0 X A A 1 x A A 1 O A 1 1 200k 2M Li Sq 1 4 x A A 1 0 Q 0 20 high low state 1 0 A x active toggling according to measurement sub reading not set according to function range Fig 6 Table of Control Signals vs Function Range 18 Calibration The instrument is software calibrated and retains its calibration constants in EEPROM The calibration procedure is programmed into the ROM and simply has to be stepped through by front panel key presses or by remote interface commands The magnitude of the required calibration signal for each range and function is also programmed into the ROM and is displayed as a calibration prompt at each step The calibration point can however be changed by remote command There is no facility for changing the
8. IC31 CNY17 3 27001 0020 C14 Cap 10u 35V 23557 0647 Cap 1u 63V 23620 0256 C18 Cap 100N 63V Cer 23438 0007 Cap 100N 63V P E 23620 0246 C19 Cap 100N 63V P E 23620 0246 Cap 47U 25V 23557 0659 C63 Cap 100U 16V 23557 0530 Cap 100U 10V 23557 0657 C64 Cap 1U 63V P E 23620 0256 R1 Res 470k Fusible 23225 4470 Res 220k W75 23209 4220 R93 Res 220k Fusible 23225 4220 Res 220k W75 23209 4220 R122 Res 220k W75 23209 4220 R127 Res 1 23202 2100 R32 Res 10MOF 23202 6100 Res 100kF 23202 4100 FS3 4 7 Pcb Fuse 375mAT 22315 0440 FS5 6 Pcb Fuse 750mAT 22315 0451 PJ4 16 way header 22575 0103 10 way header 22575 0062 RS232 IEEE Pcb IC8 R6 and R9 are no longer fitted The connector assembly changes from 16 way 43172 1060 to 10 way 43171 1460 The part number of the new complete assembly is 44812 0580 was 44812 0560 Mechanical The transformer changes from 20661 0240 to 20661 0241 the electrical specification is the same as before but the new transformer is wound differently to simplify manufacture and has a different pin out The rear panel also changes to accommodate the revised transformer and is now printed instead of using labels the new part number is 33331 2010 was 33331 1950 Ferrite sleeves 22040 0030 quantity 2 used on mains wiring and safety earth and 20040 0040 used on input socket leads were added to improve conducted emissions and RF immunity emissions respectively Circui
9. D2 D 18 38 21 14 4 7 10 14 IEEE ENABLE 18 nu TinnzT Alo Ata 23 Ata z3 4 7 12 EEPROM DATA asa A11 A A11 2 CONT DET 20 37 A12 E A12 die P53 HALT A12 26 Bibi T DIGO cora 21 toe na E ALS A13 ALS PES 13 DIG 22 BSS X4 d 35 A14 18 HI 2 1c39 17 STEZ 11 FOLE pa Da pa 17 RZY 3 16 P56 A15 12 SEN r Tm DIG3 COL3 24 D1 D1 16 2 P57 13 15 N 5 14 DIG I Da D2 DIGS 25 ta 53 14 6 13 O SER 5V CB ENABLE P68 D1 D3 16 DIG6 SER 5V F4 CTRL15 26 D2 D4 D4 13 7 12 STE a 18 27 7 ps 74HCB73 12 8 2803 11 PJ4 1 10K P62 D4 D5 m SER 5V y 28 Es LE DE g 18 2 CIBET P63 D3 D6 w R58 jes SER V O ETAT 28 oe a gt m Log 2 LO sa ake AP4 3 2 LATCH ENABLE 1 sle P65 D6 A14 A14 RAW LATCH ENABLE 1 O PJ2 28 DG SER 31 a Py4 4 LATCH ENABLE 2 PEE 07 RIG 47k 8 14 a LATCH ENABLE 3 32 BEZ T 27 8 3 er GND GND D15 1C26 B 14 C4 6 By 15 A15 DG WR C66 D dh K R 1N4148 ko 7 O P M SER 5V g 5V up 4148 35V SER av PJ4 7 5V e 2 t 2 la 2 a 2 SER BV IC3 R101 d DG M aas 3swg 3 swiat 3owi44 IC27 A PJ4 8 CNY17 3 100K D14 DG Sd U 1N 1489 LE 1 5 IEEE ENABLE as SK 4148 D11 R21 KRI i a SE BC559 1N Ah 100K i 3 14 10 R127 SU 1 2 1 2 1 Z g a O 1K m Kaski 4148 B f f W a a R57 R7Q VBAT 3 swa SW7 SWi1 SW15 an 1QK 4K7 K3 D17 B DE 8 4 7 m BAT TEST
10. RES 100RF W25 MF 25PPM RES 910RF W25 MF 25PPM RES 100K 1 25ppm MF RES4K7C W25 MF 50PPM RES 301KC W25 MF 50PPM RES 330KF W60 MF 50PPM RES 2KOOF W125 MF 10PPM RES 18KOF W125 MF 10PPM RES 1KOJ FUSIBLE RES 100K FUSIBLE RES 220K FUSIBLE RES 470K FUSIBLE RES ORO1G 4 TERM 30PPM PBV RES NETWK SIL 10K X 48 PREC VOLT DIV NETWK 1776 C4 PREC CURRENT NETWK 1787 41 RES MATCHED SET Position R47 R10 48 67 96 106 R68 R32 115 116 R52 R8 R4 7 R113 R43 R35 R34 37 R23 R18 38 103 R42 R17 55 63 109 R108 R24 R41 R40 R78 R13 121 R119 R120 R37 R36 R75 76 77 R31 R30 R11 R94 95 R93 R1 R74 RP3 4 RP1 RP2 R15 22 107 25 PCB ASSY MAIN 44812 0540 continued Part Number 23386 9201 23388 9103 23427 0254 23427 0268 23427 0328 23427 0357 23427 9206 23557 0647 23557 0655 23557 0657 23557 0658 23557 0659 23557 0677 23620 0236 23620 0246 23620 0255 23620 9007 23647 0527 23648 0002 23649 0001 23685 0006 23984 0005 25021 0901 25115 0907 25211 9302 25341 0214 25341 0215 25380 0229 25383 0506 25386 9901 25601 0001 25601 0400 25601 0410 25601 0420 27001 0020 27103 0020 26 Description VARISTOR THERMISTOR CAP1NOK 100V CER MED K P2 5 CAP22PG 100V CER NPO P2 5 CAP10PC63V CER RD870 6NPO1 CAP33PG63V CER N150 P2 5 CAP15PG 100V CER NPO P2 5 CAP 10U 35V ELEC RE2 P2 CAP 470U 35V ELEC RE2 P5 CAP 100U 10V ELEC RE2 P2 CAP 100U 25V ELEC RE2 P2 5 CAP 47U 25V ELEC RE2 P2 CAP 470
11. C and F5 F7 is turned off by a low CTRL12f or all DC Voltage measurements The input impedance on the 200mV and 2V ranges is determined by R78 and RP1 B When LOZ is selected these resistors are connected in parallel by IC8 B and IC1 A and the combination is connected to the HI input terminal via RP1 A RL3 and R11 giving an input impedance of 11 MQ All other gates which could contribute to this impedance are turned off When HIZ is selected IC8 B and IC1 A are turned off so that the input impedance effectively becomes infinite On 20V DC ranges and above RL1 is switched to pin 5 to isolate this sense line from incoming high voltages and the input multiplexing takes place between IC4 A and IC4 B IC4 A senses the output from the input attenuator via R46 R45 and IC5 A IC5 B and IC5 D are turned off for all DC voltage measurements The two element DC input attenuator is formed by RP1 A in series with RP1 C RP1 D or RP1 E in the 20V 200V and 1kV ranges respectively The measurement 7 current is fed to the bottom element of the attenuator via IC1 A in the 20V range and via IC1 D plus the appropriate gate in IC2 in the 200V and 1kV ranges The voltage across the bottom of the attenuator is sensed via IC1 C or IC 1 B and IC2 The gate selection in IC2 is controlled by CTRL6 and CTRL7 which select the gates according to a binary code with CTRL6 the LSB CTRL7 CTRL6 IC2 gate 0 0 0 i e 0 1 1 1 0 2 1 1 3 The bottom of the attenuator is co
12. KEYBOARD MAIN REAR PANEL ASSY 46812 0500 Part Number 20030 0263 20030 0266 20037 0301 20037 0304 20037 0401 20038 9501 20038 9502 20210 0101 20210 0102 20234 0011 20234 0012 20234 0028 20234 0029 28 Description WASHER M3 ZPST WASHER M4 ZPST WASHER M3 SHK PROOF I T ZPST WASHER M4 SHK PROOF I T ZPST SOLDER TAG SHAKEPROOF 4BA WASHER M3 Spring WASHER M4 Spring NUT M3 ZPST NUT M4 ZPST SCREW M3 X 10 PNHDPZ NPST SCREW M3 X 8 PNHDPZ ZPST SCREW M4 X 10 PNHDPZ ZPST SCREW M4 X 12 PNHDPZ ZPST Position SW1 SW2 16 FOR DISP1 2 LINKS R81 88 R25 26 27 R89 92 R16 R21 C66 C4 C60 C59 D11 14 18 LED1 21 DISP1 2 IC39 IC38 Position AC RECEPTACLE EARTH AC RECEPTACLE TRANSFORMER BLANKING PLATE BRACKET OUTER EARTH AC RECEPTACLE TRANSFORMER BLANKING PLATE BRACKET MAINS RECEPTACLE BLANKING PLATE BRACKET MAINS RECEPTACLE REAR PANEL TRANSFORMER SPACERS BLANKING PIECE BRACKET EARTH REAR PANEL ASSY 46812 0500 continued Part Number 20661 0221 22115 0240 22300 9301 22315 9401 22520 0140 22520 0500 22538 9404 22575 0203 22575 0205 23386 9201 31334 0120 31342 0140 33111 9030 33331 1950 37541 0860 Description SPACER Hex M3 x 20NPBR TRANSFORMER FUSEHOLDER Panel Mounting FUSE 1A Fast Blow HBC AC RECEP FUSED C19271 MS3 DPS FUSE DRAWER 230 115 CL19274 BOOT INS FOR FUSED IEC SKT SKT3W 156 20AWG Yellow IDT SKTSW 156 20AWG Yellow IDT VARISTOR BLANKING PIECE 2
13. add it to the timer count from the second conversion phase to obtain a number accurately representing the measurement current Buzzer The programmable buzzer is driven by a square wave from IC14 buffered by Q17 The buzzer is turned on by a high 19 signal Power Supply The power supply consists of two sets of linear regulators driven from the mains transformer One set of regulators IC41 1C42 IC43 and IC50 supplies the measuring circuitry which requires to be completely floating relative to earth ground The measuring circuitry includes the CPU keyboard and display components The other set of regulators IC44 and IC45 supplies the remote interfaces via supply signals designated SER 5V SER 0V and SER 5V SER OV is connected to earth ground The transformer provides the necessary isolation between the supply groups Signal isolation is provided by opto couplers see remote interface section Note that care must be taken with the insulator between the three terminal regulators and the rear panel as this insulator must withstand flash testing to 3kV AC It is possible to puncture the insulator with sharp device corners In addition it must be positioned so that there is maximum possible material surrounding all sides of the regulator tabs This means positioning it hard against the clamp screws and centralising the regulators across its width CPU Keyboard and Display refer to main circuit diagram sheet 2 The CPU sectio
14. current for the transmit LED in IC28 Incoming serial data is received by IC27 D and passed to the SIO via IC30 The serial interface conforms to the ARC standard IC26 C thus relays incoming RS232 signals on to other instruments further down the RS232 chain IC27 C receives RS232 data from devices further down the chain and relays them back to the RS232 controller via IC26 A GPIB Interface refer to both the main CPU Keyboard Display and GPIB circuit diagrams The GPIB interface operates via the RS232 interface The source and destination of the RS232 signals are selected on the main board as follows IC26 B is used as a logic gate to inhibit RS232 data reaching the GPIB board when RS232 is selected Similarly IC26 A inhibits output to the RS232 connector when GPIB is selected The RS232 receivers IC27 B and IC27 D are DC controlled via pins 12 and 5 respectively so that the source of incoming RS232 data may be switched between the RS232 connector and the GPIB board A low level on these pins turns the receiver off and drives its output to a high impedance which allows the two output to be wire ANDed IC26 B IC26 A IC27 B and IC27 D are controlled by DC signals generated by IC4 on the GPIB board according to the state of the RS232 GPIB selection switch The GPIB interface proper is held on the GPIB board and consists of a remote processor IC6 which communicates with the GPIB via the GPIB controller IC18 and with the processor on the main boa
15. flows through the relay coils so little power is dissipated in them The supply to IC22 is raised a Vbe by D22 This is to guarantee that CTRL4A swings positive enough to turn on MOSFET F3 which switches in the 200mA current shunt Fig 6 presents a complete list of control signals and their states for each meter function and range Input Signal Conditioning Guard Tracks All input sense paths which would be susceptible to board leakage are protected by a guard track driven by IC20 D The guard track is driven with a voltage which approximates to the mean buffer input The guard track can be identified on the PCB by the absence of solder resist over it Input Signal Conditioning DC Volts refer to the main circuit diagram sheet 1 Each complete measurement requires two sub readings representing the incoming signal HI either direct or attenuated and the incoming signal LO connected to AG Analogue Ground The displayed measurement is calculated from these two sub readings and the regularly updated reference sub readings On the 200mV and 2V DC ranges the input voltage is passed to the buffer unattenuated via R93 R1 RL1 R44 and IC4 D RL1 is switched to pin 4 by a low going CTRL1A signal Input protection on this sense line is provided by Q5 and Q6 which limit the voltage to approximately 3 6V The input multiplexer switches between IC4 D and IC4 B the analogue common being sensed as for all DC Volts ranges via IC4 B IC7 B IC6
16. for every function 10 options including optimised default values for each range and function Reading is held when stable Displays deviation from entered reference value dB Displays measurement in dB relative to 1V 1mA 1kOhm or user entered value or in dBm Ax B Linear scaling of results with offset Limits Reading displayed with H L or P pass with respect to user defined high and low limits Min Max Minimum and maximum reading stored Data Logger Manual or automatic storage of 100 measurements INTERFACES RS232 Complies fully with the ARC Addressable RS232 Chain interface standard Address selectable from the front panel Baud rates 9600 1200 and 300 GPIB Optional Fully complies with IEEE 488 2 POWER REQUIREMENTS AC Input 110 120 Volts AC nominal 50 60Hz or 220 240 Volts AC nominal 50 60Hz by rear panel adjustment The instrument will operate safely and meet specification within normal AC supply variations viz 99 132 Volts AC and 198 264 Volts AC respectively Power Consumption 25VA max Safety This multimeter DMM is a Safety Class I instrument by IEC classification it has been designed to meet the requirements of both IEC348 and IEC 1010 1 This multimeter has been designed for use in a Pollution Degree 1 environment in the temperature range 5 C to 40 C 20 80 RH non condensing It has been designed for Installation Category Il measurement use to 600VDC rms and Installat
17. of the main conversion period is the measurement current C29 is therefore charged by the measurement current and the emitter of Q13 rises When the integrator output reaches the input threshold of IC12 B the output of IC12 B is allowed to go high The high is gated through IC13 A on its next clock which turns off D19 and allows Q12 current to flow into the integrator The integrator is now charged by the measurement current minus the Q12 current The value of Q12 current is designed to be just greater than twice the largest measurement current so the integrator output is always forced down at a rate which guarantees it will reach the input threshold of IC12 B within one clock period When the integrator output reaches the input threshold of IC12 B again the output of IC12 B is forced low which is gated through IC13 A at the next clock and so turns on D19 to divert the Q12 current from the integrator once more Because the Q12 current has flowed into the integrator for exactly one clock period a known amount of charge has been removed from the integrator capacitor With the Q12 current switched out the integrator is again charged positively by the measurement current only thus forming a relaxation oscillator The cycle repeats for the duration of the main integrate period The CB PULSES out of IC13 A are counted by a hardware counter within the CPU At the end of the main conversion period this count represents the amount of charge which had to be re
18. 000 000mA 200 000uA 2 00000mA 20 0000mA 200 000mA AC Amps Calibration Ohms Calibration 22 Step No 1 2 3 4 Step no 1 CON OA R N Input Value 200 000uA500Hz 2 00000mA500Hz 20 0000mA500Hz 200 000mA500Hz Input value 000 0000hms 0 00000kOhms 100 0000hms 1 00000kOhms 10 0000kOhms 100 000kOhms 1 00000MOhms 10 0000MOhms Comments s coni p ditto ditto Comments Comments o cinput Comments Comments s c HI to LO on signal and SENSE i ps ditto 4 terminal mode 4 terminal mode 4 terminal mode 4 terminal mode Fig 8 Table of Standard Calibration Values Remote Calibration Commands VDC start calibration of DC Volts function ADC start calibration of DC Amps function A10DC start calibration of DC 10Amps function VAC start calibration of AC Volts function AAC start calibration of AC Amps function A10AC start calibration of AC 10Amps function OHMS start calibration of Ohms function STEPCAL calculate the calibration constant for this step and move on to the next step invokes response of P or F if first attempt to step calibration no response if step has already failed READ return the next reading once the reading is stable operation mode specific to calibration routine but returned value is as described in the operating manual SETCAL set the calibration prompt to the value lt nrf gt value rounded to an integer representing the display value S
19. 053 8 R9 2K7 B 85V po a CTRLS X gt 100 15V IC46 A F6 3 FS1 1A wa ZVN33Q6A ON Aa 2 1 5V R52 MA KU g ILEIN LL 1 Q7 300 3 2 337 1av CTV CTRL 13 CEB R15 2 16 v5 350 a CTRL3A Lan ZARA 1C9 B LM324 na Ed RP2 25V 4053 nta 4040 7 4R7 15V R36 reta D n 1 2 KA R18 301K dz ZVN33Q6A 1 6KB ji 5 I gag p C21 C56 R37 T 03 C33 Ses 2QQUA 18 15 47U E 47U 4K7 tau pa e R22 CTRL18 L SEVO 35v AGB 1 2288MHZ O 04 5 BY Eis 2 MORSE ares 1 BQN BKB 05 CTRLBA Em LET 4 017 DI D4 1 p F2 X C2 V REF AG SESEG 11 13 4880 V IN4aan a VN E 188N i a DG R125 2 R34 5 IC28 C 011 12 1M BV D3 EI 3 R107 4K7 AN BC558 012 n8 Tm IN4000 yy STAR Ien pon 8 mee ce os Jes BV A D CTRLBA 2 k ed 8 BRINE ata 528HZ R124 rte R59 2 MA 1a C57 c78 1 aye LM339 Toe a LA 47U D19 22P ait 7 3 BA 4 V REF R17 s ANE TH 8 1KB Ahles 1 BK W 1 DISCHARGE COMPLETE STP3 DG 6 W Ak pm NEBBE A LZY AE 4 As me 5 6 6 95 E UNTTAB a SAW OHMS REF GK R35 8 11 LO aca C79 R120 AG AG av JAG 3 1 17 C 5KB L hy cza EET w4 IC17 B 3N3 18 R23 V REF 5V 7 s t T T R24 3 4 5 t2 7 a 3 CB PULSES 15K DISCHARGE ENABLE 18 A A D 3 E i 5V AN 11 8 z DISCHARGE COMPLETE c31 eu T IC12 B a QS IE13 A at 15V H2 E22 1av BIB IE12 C QU 159 CB ENABLE Ama 74HC11 R 74HC74 R84 BC549 i 437 47
20. 0U 25V ELEC RAD P7 5 CAP 1NOK 100V P E 435 1 P5 CAP 100NK 63V P E P5 CAP 3N3K 63V P E P5 CAP 10NK 100V P EP5 CAP68PF 630V P S CAP 330PF 630V P S CAP1NOF 63V P S RADIAL CAP 3N3J 63V P P FKP2 P5 TRIMCAP 2 22P P P 107 2831 022 DIO 1N4148 B R DIO 1N4002 B R RECTIFIER BRIDGE W02G TRAN PNP ZTX214L BC559 TRAN PNP ZTX550 L BC327 TRAN NPN BC549 TRAN NPN BC337 TRANMOUNTING CLAMP TRAN FET DNJ BF245A TRAN MOSFET N CHAN ZVN3306A TRAN MOSFET N CHAN ZVN2106A TRAN MOSFET N CHAN BUZ71A OPTO COUPLER CNY17 3 IC LM339 Position V1 2 3 4 PTC1 C61 C70 C75 C81 C38 39 C14 31 32 33 34 40 41 58 67 C43 44 47 C12 69 71 80 C13 49 53 66 68 C21 22 35 36 37 56 57 C45 46 C72 C2 10 11 15 16 19 20 24 28 30 42 48 54 55 62 63 65 73 74 76 79 C9 C8 C6 C1 C7 C29 VC1 2 3 D6 7 8 9 10 12 14 19 20 21 22 D1 5 13 BR1 2 3 Q2 5 9 10 11 12 14 15 16 17 Q8 Q1 3 4 6 13 18 Q7 HEATSINK F4 F1 6 F2 5 7 F3 28 30 IC18 PCB ASSY MAIN 44812 0540 continued Part Number 27106 0506 27106 0624 27106 0626 27106 0704 27160 0009 27160 0011 27160 0012 27160 0013 27160 0020 27161 0040 27164 0502 27165 0400 27226 0161 27226 0400 27226 0520 27226 0530 27231 0000 27231 0110 27231 0270 27231 0740 27231 5730 27231 5740 27234 5730 27240 9404 27250 0050 27250 0160 27400 0100 27401 0020 27410 0420 28151 0010 28500 0800 35555 1750 Description IC LM324N IC AD711JN IC AD548JN IC MC34184P IC
21. 15P P14 A4 17 B RZL 1 23 A2 EER 3 ExrAL 18 E RS2 P15 A5 PJI 22 1 14 TR TE 22 AB Q SER V 5 1 A1 40 p 13 4 RS SER V E E 16 A6 230 21 AG E AB BJ1 24 TE PE IC2 RSA RESET 5 g RES P17 A7 28 3 A7 AE O 2 Tr 19 28 19 py SER 5V 7g 518 as 23 AS a O B Q nro MSD mu 4 X NMI 28 24 PJ 2 O 3 18 23 18 pe O A8 O B2 D2 Q pioz SER 5V 5 a aan 27 21 Pit 3 4 17 38 17 ps INT 0 TRO Ata O B3 D3 Q p103 SEEDA ati 28 23 PJI 4 5 15 31 18 p4 R W A11 O B4 D4 Q 0104 H7 38 Jas A12 25 2 PJ1 13 5 15 32 15 pa m A12 B5 D5 Q DI05 182K F 24 26 PJI 14 7 14 1 pg 7 A13 O ai BTOB 8 P2 TIN A14 23 A14 PJI 15 A B 13 EsiE 13 Di BJt 16 ME g 7 zi 12 35 DLOZ S P21 TOUT At5 22 A15 11 Bs O B8 DB Q p108 LSD 18 1922 SCLK BB 75160 RB SER IN 11 P23 RX D Ag 37 13 raak SER OUT 12 P24 TX DizAt 38 FE a mm 35 16 SER 5V SER BN SER 5V D4 SER V D3 A3 34 17 BE 1EB R6 21 VCC D4 A4 33 18 D6 CNY17 3 100 28 20 14 D5 A5 32 18 1 PIZ A VCC VCC D7 d ICI IC2 IC4 GND D6 A5 3 A14 VRP ss PI2 2 3 j O 5N75161 SN7516 IC5 D7 A7 38 GND GND SER V A14 27 SER 5v 12 7 6 nee DI PART No R2 R4 R6 R9 ice SER BV SPR 5 44812 0569 t k 1oaK 1ga MK dNY17 3 F D4 44812 0589 10K 100K PZ D5 44812 0639 1aak 220K R9 Q Jci 6 DB 7 1K es P T FITT PJ2_9 NOT FITTED Q SER OUT
22. 1906 Multimeter Service Manual Part Number 48511 1110 55 2 Table of Contents Specification 2 Safety 5 General Overview amp Principles Operation 6 Detailed Circuit Operation 7 Calibration 19 Parts List 24 Circuit Diagrams 33 Specification Accuracy Accuracies apply for 1 year 18 C to 26 C Temperature coefficient outside these limits is lt 0 1x quoted range accuracy per C Warm up time to rated accuracy is 1 hour DC VOLTS Range Accuracy Input Impedance Max Input 200Mv 0 017 3D 10MQ or 1kV DC or 2V 0 012 3D gt 1GQ AC Peak 20V 0 019 3D 10MO any range 200V 0 019 3D 1000V 0 019 3D RESISTANCE OHMS Range Accuracy Max Measuring Current Max Input 200 0 025 4D 1 5mA 2k 0 019 3D 1 5mA 300V DC or RMS 20k 0 019 3D 0 4mA continuous 200k 0 019 3D 40uA any Ohms input 2M 0 022 3D 4uA any range 20M 0 07 3D 400nA Max open circuit voltage 3 5V Audible continuity check available on all ranges TRMS AC VOLTS Range Accuracy Range Accuracy 45Hz 5kHz 5kHz 10kHz 10kHz 20kHz 20kHz 50kHz 200mV 0 296 150D 0 296 250D 3 500D 2V 0 2 150D 0 2 250D 0 5 300D 3 1500D 20V 0 2 150D 0 2 250D 0 5 300D 2 1000D 200V 0 296 150D 0 2 250D 0 5 500D 750V 0 296 150D Additional error at crest factor 3 typically 0 796 Input impedance 1MOhm 100pF an
23. 4 IC35 13 Put 19 PJ2 19 DE 120 8 O O SE n 25V ANE 8 CTRL3A ona CTRL18A 74AC573 1g O 12 B5 LITU aon DG CTRL3 ta 4 1N4148 R12 D5 4 17 T E LED TIE 2 75 15V 5K6 5 16 LEDS LED17 DIGO O Bes IC44 Sb BENI 4341B 6 15 SC B PIS 2 Wa2G S d e gt C88 R123 BV Z 1 rp 3 SER 8 188U 3x3 R av 7 14 A E 5V 1N4148 ES ay E 2 4 4 D7 DG 13 LED2 C46 C52 LE N F 3 12 LED18 LED18 DIG 2 BV 4 14 I 4700U EEE 108 CTRL4A LE OE PJ5 3 25V 25V T 12 SER BV 1 CTRL4 12 IC22 D 2 BV O M 9 11 11 1 i l RP4 A a E 1 a LED3 I B47 7 LM324 PORT E I PJS 1 ragau EE 18V 1av LED11 LED19 DIG2 mE 120 O 16V 1 b YU 25V 2 BZ 2 1C36 19 CTRL1 7 ka 74HC573 75A 1 P 3 SER 5V 5 2 BV BI 3 18 CTRL2 2 Ld OZP B2 4 17 CrAL3 LED12 LED2Q DIG3 IC45 RP4 B B3 5 16 4 CTRL 79LQ5 1 k B4 5 15 CTRL6 2 4 B5 7 14 8 S 7 B6 13 pi LED5 AR 8 CTRL7 LED13 LED21 DIG4 B7 3 12 CTRLB 7 LE OE D28 BV 8 O A AB w wow 18 8 1 LATCH ENABLE 2 11 L LEDG id E PORT e g IC32 8 b IC23 C DG LED14 DIG5 Ag Jou 1 2288MHZ 11 J 2 e KK 74HC11 2400 27FF KK A11 1 12 Y LED7 5V A12 2 IC19 A IC28 B LED15 DIGG a 13 A1 A10 2 19 8 C28 J BZ 1C37 CTRL 8 CAL ENABLE 122N zanci1 74HC573 1g AE 74HC27 Bi 3 CTRL1Q z VCC R98 7 Tag pa 33 A14 B2 4 17 CTRL 1 1 LEDS PR 5 E Eg A15 18 erga ss 83 5 16 cTRLI2
24. 4W IEEE SW INSULATOR REAR PANEL BRACKET MOUNTINGS REAR PANEL LABEL EARTH BOND POINT FRONT PANEL ASSY 46812 0510 Part Number 10233 0102 20030 0263 20037 0401 20038 9501 20038 9502 20210 0102 20234 0012 20234 0027 20612 0011 22225 0221 22225 0400 22571 0800 22571 0810 22571 0820 33331 1890 33331 1900 Description TUBING H S 4 8MM ID 08886F WASHER M3 ZPST SOLDER TAG SHAKEPROOF 4BA WASHER M3 Spring WASHER M4 Spring NUT M4 ZPST SCREW M3 X 8 PNHDPZ ZPST SCREW M3 X 6 PNHDPZ ZPST WASHER FIBRE M3 PUSHBUTTON PB09 50 000 GREY 6 SWITCH PUSH PUSH PBMS 6018 SKT 4MM SAFETY BLACK SKT 4MM SAFETY RED SKT 4MM SAFETY WHITE FRONT PANEL OVERLAY FRONT PANEL Position REAR PANEL TRANSFORMER FOR FS1 FS1 FOR FS1 Position KEYBOARD SWITCH FRONT PANEL STUD KEYBOARD FRONT PANEL SWITCH FRONT PANEL STUD FRONT PANEL STUD KEYBOARD SWITCH KEYBOARD FRONT PANEL KEYBOARD ON OFF SWITCH 29 CASE PARTS Part Number 10220 0100 10232 0305 20010 0253 20030 0263 20030 0264 20037 0301 20038 9501 20062 9303 20065 0030 20210 0101 20234 0011 20234 0025 20234 0027 20234 0038 20234 0042 20612 0011 20661 9301 20661 9402 20662 0540 22315 0239 22491 0010 22491 0020 22491 0010 25386 9901 31336 0250 31346 0160 31547 0320 33536 0810 33536 0820 37511 0480 37511 0490 37511 0510 37523 0170 37541 0830 30 Description GROMMET STRIP HEAT RECOVERABLE SLEEVE H20 X 20MML BLACK RIVET SNAP LO
25. 6 regulates at 6 95V The 6 95V from IC16 is divided down by R15 R22 and R107 to produce 2V and 200mvV references which are selected by IC9 B according to the meter function and range The signal CTRL18 controls IC9 B such that 200mV is selected when 18 is high and 2V is selected when it s low The table in fig 6 shows which reference voltage each meter function and range uses The selected reference voltage is further selected in IC7 C During resistance measurements IC7 C is switched to LO SENSE and in all other functions it s switched to the reference voltage Sos R18 ras lp ee 55 IC18 A x ase R48 ISS Ste z IC20 C mia pasa T GI Ay Joa lz DISDE BUBLE 20127 w DIONE TOFFTETE CB PULSES IC10 cz j gt s el be T avwan CTRL 8 t MO AMPLIFIER eS y TE 1c47 D Fig 4 Simplified Schematic of A D Converter 12 307 a ENABLE 4 o MAIN CONVERSION PERIOD DISCHARGE Ll 1 ENABLE I II DISCHARGE COMPLETE 100 20m5 e 1 gen IC12 PINS THRESHOLD INTEGRATOR DUTPUT CB PULSES 3 26u5 Fig 5 A D Converter Waveforms not to scale The A D Converter refer to simplified schematic fig 4 a
26. 73 0041 22574 0430 23185 1100 23185 2100 23185 3100 23185 4100 23427 9206 23557 0612 23620 0246 25021 0901 27001 0020 27163 1600 27163 1610 27231 0050 27231 0100 27240 9403 27250 0410 27400 0080 28500 0800 31343 0020 35555 1890 43172 1060 Description WASHER M3 ZPST WASHER M3 SPRING SCREW M3 X 10 PNHDPZ NPST SWITCH SLIDE RA PCB MTG DPDT HEADER2 WAY STRAIGHT SKT 24W RA IEEE RC10 24R LNA RES 100RJ W25CF RD25S B R RES1KOJ W25CF RD25S B R RES10KJ W25CF RD25S B R RES 100KJ W25CF RD25S B R CAP15PG 100V CER NPO P2 5 CAP 1UO 50V ELEC RE2 P2 CAP 100NK 63V P E P5 DIO 1N4148 B R OPTO COUPLER CNY17 3 IC 75160 IC 75161 IC 74HCO5 IC 74HC10 IC HD6303RP IC UPD7210C GPIB IC 27C256 32Kx8 EPRM 200ns XTAL 4 9152MHZ MICROPROCSR INSULATOR IEEE INTRFC PCB IEEE INTERFACE CONN ASSY IEEE MAIN Position Position INSULATOR PCB INSULATOR PCB INSULATOR PCB SW1 LK1 PJ1 R6 R9 R1 2 3 5 10 R4 7 8 C7 8 C9 C1 2 3 4 5 6 D1 2 IC8 IC2 IC1 IC4 IC5 IC6 IC3 IC7 XTL1 31 Manufacturing Changes 32 From December 1995 a number of changes were made to improve performance particularly the settling time on AC measurements and to ensure full compliance with EMC and LVD Directives The main pcb became Issue 4 the IEEE interface assembly used the same pcb but without IC8 and with a different cable assembly and the transformer was changed These parts are not interchangeable with earlier versions At the same
27. As for the DC attenuator the measurement signal is gated via IC1 D and the sense is routed via IC1 B to the amplifier input IC8 B and IC D are turned off so that R78 is not in circuit IC3 B is turned off so that R120 is not in circuit RP 1C gives the amplifier a gain of approximately 1 10 for the 2V range with VC2 allowing frequency trimming Similarly RP1 D and RP1 E are used in the 20V and 200V ranges respectively In the 750V range F7 is again switched off and IC2 selects R13 to give a gain of approximately 1 10 000 Input Signal Conditioning AC Current 10 refer to main circuit diagram sheet 1 The AC current shunt operation is the same as for DC current The AC current sense signal is routed from IC6 B to the RMS converter via IC6 A IC8 A isolates the AC current sense line from the filter R44 and C8 which would otherwise represent an unacceptably low impedance when connected in parallel with the higher value current shunts TO A D BUFFER CTRL10A SI TO A D BUFFER ICS A REF SENSE LO OHMS REF O IC1 B Fig 3 Resistance Measurements Simplified Schematic Input Signal Conditioning Resistance Measurement and Continuity Check refer to simplified schematic fig 3 Resistance measurements are made using a ratiometric method The same measurement current is passed through a reference resistor and the resistance to be measured X For each complete reading a sub reading is made of the voltage at each end of the refe
28. BE N R2 2 1 2 5V RP3 B RP3 D pe 2 ul 2 Dm L RP3 A 1 k 12K 3 4 3 4 3 4 3 swi6 By 12K atis dh D12 S WA swe 5W12 R111 R112 BC549 1N4148 ep is E SER YOU 5 3 4K7 8 D18 C55 EH C4a R68 R99 R59 R3 1N4148 GUARD ud nea 100N ke 2M2 IC18 B 18K 1K8 CERES BATT PI lez 2 I a ye 2 CNY17 3 EI 5V IC28 A T N ui a 358 ils l si aj M S C88 IC28 4 Q 2 RX By 14 14 LM338 SW5 Swg CNY17 3 5 PJ3 2 R62 u T T g 13 RES 1 5 5 56a 4 m PJ3 3 13 11 LK2 M RESET 1a IC18 D Z PJ3 4 R69 C41 2 LM3393 2 4 O IC27 D 5 DG D13 ized 18U E 41 PJ3 5 1488 1N42002 35V RES O RP3 C 2 PJ1 16 53 16 SER BV OD R56 6 Hu 1 aK mie pig 7 X Balls EDLA PJ S P22 15 B 18 A BEEN av Sieg elio EOS PJ1 4 E 14 G is 7 T Bit 18 13 IC27 C Siara 11 Bi 015 G 13 VBAT BV SA BC553 ET IC26 C 5V a Oo 14C88 EE C42 R PJ3 11 C65 gm 192N C24 C68 ojola O 100N 122N 1828U DG M 25V DG DG DG 14 14 20 DE 5V 45V VCC VCC VEC IC35 T SER BV 1518 1532 1C36 IC28 IC37 VCC GND GND GND SK L 3C88 Jicso IC38 7 7 18 DG mE 100N 74HC373 DB DG GND DG 10 DG DG
29. C36 IC37 and IC38 and the fourth byte which drives the display segments is retained in IC47 and IC35 PORT 1 is updated regularly in the NMI routine at 600Hz The PORT 1 writing process is as follows Data is first written into IC47 and IC35 and then latched from their outputs into one of the secondary latches by LATCH ENABLE 1 LATCH ENABLE 2 or LATCH ENABLE 3 which are themselves output port data lines driven from within the CPU under software control The third byte is latched by LATCH ENABLE 1 into 1C38 which is on the display PCB and drives the display digits The fourth byte is then written into IC47 and IC35 to turn on the segments The output enable of IC38 is driven by LATCH ENABLE 1 delayed by R16 This ensures that each digit is not driven until the correct segment information is latched into IC47 and IC35 which thus avoids spurious segments appearing on the display C66 is present to remove glitches injected by cross talk in display cable D14 D11 R21 and C4 delay turn on of the display at instrument switch on until after the software has started the display multiplex IC36 and IC37 store the current hardware control lines CTRL1 CTRL13 In addition the front panel LED indicators are driven from IC37 The LEDs and the main display are multiplex driven 15 The main display is driven one digit at a time by open collector driver IC39 under control of latch IC38 The LEDs are arranged in a row and column matrix with the three ro
30. CK PLSTC 8x2 5MM WASHER M3 ZPST WASHER M2 5 ZPST WASHER M3 SHK PROOF I T ZPST WASHER M3 SPRING SCREW NO 6 X 0 5 PNHDPZ ST AB SCREW NO 4 X 3 8 PLASTT PNHDPZ NUT M3 ZPST SCREW M3 X 10 PNHDPZ NPST SCREW M3 X 12 PNHDPZ ZPST SCREW M3 X 6 PNHDPZ ZPST SCREW M3 X 40 PNHDPZ ZPST SCREW M3 X 30 PNHDPZ ZPST WASHER FIBRE M3 SPACER HEX STUD M3 x 25ZPST SPACER RND HEX ST 1 5 LPlas FOOT MOULDED GREY 543 248 FUSE 125MA TL HRC MAINS LEAD 2M RA IEC SKT STRPENDFOR 240V WORKING MAINS LEAD 2M RA IEC SKT EURO MAINS LEAD 2 2 5 IEC SKT USA TRANMOUNTING CLAMP HANDLE BENCH INST CASE STD SCREEN PCB LOWER SCREEN UPPER CASE UPPER BENCH INST STD CASE LOWER BENCH INST STD LABEL GPIB LABEL RS232 LABEL RS232 GPIB SELECTOR LABEL HANDLE LOGO BENCH INSTR LABEL REAR PANEL 1 AMP FUSE Postion SCREEN UPPER SCREEN LOWER FEET REGULATORS SCREEN LOWER PCB SCREEN SPACERS FEET REGULATORS PCB SCREEN UPPER SCREEN LOWER IEEE PCB PILLAR PCB IC S PCB SCREEN FOR IC44 FOR IC41 42 43 SCREEN UPPER CASE UPPER LOWER TRANSFORMER PCB MAIN SCREEN PCB IEEE PCB MTG OR FOR 220V WORKINGOR FOR 120V WORKING FOR IC41 42 43 CASED PARTS continued Part Number 37541 0840 48581 1070 48581 1071 58231 0050 Decription LABEL REAR PANEL MAINS FUSE INSTRUCTION BOOK ADDENDUM TO INSINS BOOK TEST LEAD SET DMM SAFETY PCB ASSY GPIB INTERFACE 44812 0560 Part Number 20030 0263 20038 9501 20234 0011 22218 0212 225
31. LEDI6 DIG7 PE PROM VEC 11 Da 2 1C48 19 3 4 EEPROM DATA 4 9152MHZ AVS B4 6 18 CTRL13 Bee A DI Da 1C25 6303X BE 7 14 P31 10 PJ2 1g E cs 2 Fir m QBj2 11 R26 2 4 17 2 C38 XTAL E 1 2288MHZ B6 8 13 A 8 D2 SK IC49 15P 3 ESTA An pE g 12 PJ1 12 7 TPIZ 12 R27 16 B7 Ob B3 5 GND 835558 mim 55 4 52 RE LE OE e Li 6 15 EP MPa RK e WR 22 28 z 14 5 MP 1 R W 11 1 x 8 13 Raz s RES 5 5 LIR Oza a8 LATCH ENABLE 3 DG C81 L cia CC 122N VEC gt l o KOU BV g Qstey BA 100N 4 14 W RES LE DE GND DG 5a 18 ta a 11 1 DISCHARGE COMPLETE 2 TINI AB P AB g Aa g A A x DISCHARGE ENABLE EX P2 TOUT A A1 g g Ba BO ae 2 RB 1 A I DISP1 LAN DISP2 11 8 A2 OQ 11 feo ee eee A2 E ze gt LIE 33 e RBA D4 D3 D2 DI c B D4 D3 D2 RX A3 A3 Pit 4 Y R83 C 8 mu deu E s 0 Gaz dE pe IEEE TX P24 TX g 4 1C34 zai 1533 B3 PAR c ORIS EB R84 3 5 D 14 5 AB O29 13 CIRETS P25 TQUT2 PEN aki ae gt gt BE REJ gt F Evo E gue A ETHEZI Lb P26 AG 88 AB z B B5 FIA yo 94 PIZ 7 R86 T2 o ES o o 9 43 3 G 1 CB PULSES P27 TCLK A7 A7 E A7 32K 8 B6 X FIZ B R87 G 16 5 5 4 as AB RAM pc R88 DP 15 B7 PJ1 8 5 2 9 P DP Aa 24 B4KXB 24 D 1 D4 D3 D2 D1 CAL ENABLE S lobo TIROTYT AS Ag 21 148 O D4 D3
32. N 4 tav av 114016 5 CTRL R4 6 3 Lo E AB 5K1 AG C15 C16 4 m BV AN R115 R116 5 CAV in ETRLIGA 4 x LL a tenn ay 4 12M 12M BIN IOUT CTRL4A 8 1 r4 ta A 8 16 C13 R32 1a R5 V 02 ZZ 1c2 vDD E Bs 18V 188U AG 188K BOUT igis RE R47 BC559 2K2 A CTRL7 81 AUS GND DG nes 25V 4 AD636 7 5568K g TF VEE 7 VIN DB AG 1c4g 15V 13 5 R119 7 OPA130PA tbe AG X x an Iz la a t 2s tav Il 91g AG E19 COM z AKA A AKA KA KA R33 47U IC11 B 7 E C25 ee VY sis 27 ICt A IC1 C DG 69 69 69 69 C9 C9 V9 V9 CTRLJA 5 nba 18K 25V E 5 5 0P482GP TM 3 102 2K2 N 4016 BC543 1 5 2 4 12 14 M5 H1 C AG 5y AG IC3 B 5 7 8 CONV I P By AH CIB 3 4 228 122N 5 2 3V L CTRL3A a 4 R7 R121 a s I 192K AG AG C5 taa 3 18 C28 NOT SLEY 122N 5 12 FITTED 18v 1C8 D 4 5 UL B AG 4216 av R 4016 qe 3 REG RP1 D 6 NOT C27 tak Ts pr S FITTED 1B N RP1 B RP1 E 228 1M1 1K I R13 KA 12 R78 7 e vez e cs 188 I ET XxX 12M 2 505 M C7 pe N B 14 R38 E 18K IC7 B KA IC6 C ABES CTRL18A Ed T E 4053 OY cTRL12 J CTRL 20 gt S R48 bea R31 IC46 D 4 5 4053 13 7 1M 2K 2 5V EN 15 4 3 F5 14 a ZVN21Q6A 2 5V B ju LO SENSE 3 OO 3 ERE 18 LO IC46 B d C73 AG IC4 B CTRLB 12 A A MA LM324 EE gan g 4 AC 72 4816 AB AG EA CTRL2 L lt y N 15V AG e L L 7 IC6 B 4
33. Pe D2 SER 5V 1N4148 PIZA SER 5V A 2 RS232 IC4 C e gt SER IN T RESET PJ2 12 4 1 74HC85 e i RAN SUED 5 6 IC4 D PJ2 13 Ria R2 Ze IC5 A 12K SWI Of O 10K 10K 74HC1Q PJ2 14 SER BV 1 m m 8 R3 10K 12 3 4 IEEE 11 po P42 15 A St RESET 13 12 PJ2 16 SER BV IC4 B SER BV e coocs m LK1 1C4 F sav SA AS27232 CONNECTOR SER av Hl cia Thurlby Thandar Instruments Ltd Glebe Road Huntingdon Cambridgeshire PE29 7DR England Telephone 44 01480 412451 Fax 44 01480 450409 e mail sales tti test com web site www tti test com Book Part No 48581 1110 Issue 2
34. RES 100KJ W25CF RD25S B R RES 330KJ W25CF RD25S B R RES 470KJ W25CF RD25S B R Parts List Position SCREEN LOWER SCREEN SPACERS SCREEN LOWER SCREEN SPACERS SCREEN LOWER SCREEN SPACERS SCREEN SPACERS PJ3 BATT RL1 2 3 FOR FS2 FS2 LK2 3 PJS PJ2 PJ3 PJ1 PJ4 B RR19 20 R9 65 105 110 R28 R117 R56 62 R2 R49 64 R59 R5 6 27 58 R14 R123 R3 51 R70 102 111 114 R12 100 R33 50 57 66 99 101 R29 R39 53 118 R46 69 97 98 104 112 R45 R44 PCB ASSY MAIN 44812 0540 continued Part Number 23185 4560 23185 5100 23185 5220 23185 6100 23187 1300 23187 1620 23187 2510 23202 2200 23202 2240 23202 2390 23202 2470 23202 2620 23202 2680 23202 2750 23202 3100 23202 3140 23202 3150 23202 3360 23202 3510 23202 6100 23203 1100 23203 1910 23203 9608 23204 2470 23204 4301 23206 4330 23208 2200 23208 3180 23225 2100 23225 4100 23225 4220 23225 4470 23296 0030 23301 0416 23310 0010 23310 0510 23339 0203 Description RES 560KJ W25CF RD25S B R RES1MOJ W25CF RD25S B R RES2M2J W25CF RD25S B R RES10MJ W25CF RD25S B R RES 300RJ W25CF RD25S B R RES 620RJ W25CF RD25S B R RES5K1J W25CF RD25S B R RES 2K00F W25 MF 50PPM RES 2K40F W25 MF 50PPM RES 3K90F W25 MF 50PPM RES 4K7OF W25 MF 50PPM RES 6K20F W25 MF 50PPM RES 6K80F W25 MF 50ppm RES 7K50F W25 MF 50PPM RES 10KOF W25 MF 50PPM RES 14KOF W25 MF 50PPM RES 15KOF W25 MF 50PPM RES 36KOF W25 MF 50PPM RES 51KOF W25 MF 50PPM RES 10MOF W25 MF 50PPM
35. TORECAL store calibration constants of any successfully calibrated functions AUTO remove the calibration prompt from the display and show the current reading using default calibration constants Safety Tests The following tests will be necessary to ensure that the instrument meets the specified safety standard if the instrument has been damaged or repairs have been carried out Equipment required high voltage generator providing 1k5V and 3kV 50Hz earth continuity tester operating at 25A Test 1 Earth Continuity Check that the resistance between the earth pin of the mains input socket and any exposed metal part is less than 0 5 Ohm corresponding to 12 5V at 25A Test 2 Breakdown Between Mains Live Neutral and Safety Earth Remove all connections from the measuring inputs Using a special mains input lead with the live and neutral connections joined together check that there is no breakdown at 1k5V between the live neutral wires of the power cord joined together and the earth wire in the cord Test 3 Breakdown Between The Measurment Inputs and Safety Earth This test is particularly necessary if the mains transformer or opto isolators have been replaced or the insulator between the rear panel and the IC regulators has been disturbed This test should be carried out after Tests 1 and 2 if they are also required Remove the mains cord from the instrument Connect the 3kV source between the LO input terminal and the head
36. U BESSER R 35V av 1aak N 2 ki 25V 1K P 1W 8 1Qv 6 av 013 ALBA 10A mimi a 4 Rig BC549 2 gt 5 ana 8 as QV REF R D a 1 3 ET 5V A D 2 TNR KA R67 R42 VAN ata 3 gt 6 Pak n Jks 10 dd F4 s 25333 ap RES IC46 C av v BF245 av R LO SENSE 5 TN M En IC13 B IC12 A LO AU R LM324 3 74HC74 SENS P QV REF 15 gt C32 1 y 1 Qk 15V av 1 Ba 12U RB tw 4 OKA c38 35V 620 R188 R189 CONV I P 13 IC11 D 192N 14K 12K a IC17 A cde 15V FA 6 95V r CA3088 FS2 18A i s 2 7 18A nu 7 0P482G av G 18V Ld d 6 LM324 v4 358 7 ss CTRL2A B tau 5 i Ri1Q l 4 22 188 R4Q Si R41 AG R39 36K av REF 47K 8 14 Q 5V AN 5V AN FOU SAY R103 R63 12 Tr 3 18 14 ICi 14 C54 BKB 1aK tav iUUN IC11 C 5V AN 5V AN 5 C68 IC8 VEC 13 vDD vDD IEF 4 IC17 D OP482GP 1aau R53 VDD 6 Icg lt IC28 A E EJ SOSE 4053 4016 TEAMS av 47K Eg 4053 IC5 GND 2 LM324 B B B 2 av i VSS VEE VEE IC12 74HC11 GUARD AROUND 7 1 ede VSS VEE DG 8 gt 7 Ice 7 L A D COMPONENTS 1 3 i2 5 15 15 DG 8 7 AG 10y av 3 R65 d DG 18V DG 18y C40 AG 18 3 i 27 IC3 A 1282N 4216 IC3 D IC3 C IC8 C R V REF GUARD AG MAINS SOCKET NO 1C21 A
37. V REG 7805 TO220 IC V REG 78L05 TO92 IC V REG 79L05 TO92 IC V REG 7815 TO220 IC V REG 7915 T0220 IC LM3999Z IC CA3086 IC AD737JN IC CD4016 IC 4040B IC 4052B IC 4053B IC 74HCOO IC 74HC11 IC 74HC27 IC 74HC74 IC 74HC573 IC 74HC574 IC 74AC573 IC HD6303XP IC 14C88 IC MC1489P IC 27C512 64Kx8 EPROM 200ns IC 93CS56 2K 128X16 SER EEPROM IC 32Kx8 CMOS RAM 120ns BUZZER C amp D TRANSDUCER 40TGPC XTAL 4 9152MHZ MICROPROCSR PCB MAIN Position IC20 24 46 IC10 51 IC40 IC11 IC43 44 IC50 IC45 IC41 IC42 IC16 IC17 IC15 IC1 3 4 5 8 IC14 IC2 7 9 IC32 IC12 29 IC19 IC13 IC36 37 IC48 IC35 47 IC25 IC26 IC27 IC34 IC49 1C33 BUZZ XTL1 27 PCB ASSY KEYBOARD ASSEMBLY 44812 0550 Part Number 20105 0510 22225 0220 22226 0140 22573 0056 23185 0000 23185 0330 23185 0820 23185 3100 23185 3470 23185 4100 23427 0324 23557 0647 23557 0657 23620 0246 25021 0901 25061 0200 25061 9503 27164 0506 27231 5730 35515 1140 43171 0070 Description INSERT THREADEDKF2 M3 ET SWITCH PUSH PUSH KEYSWITCH DARK GREY HEADER 16 WAY STR SIL RES ZERO OHM RES33RJ W25CF RD25S B R RES82RJ W25CF RD25S B R RES10KJ W25CF RD25S B R RES47KJ W25CF RD25S B R RES 100KJ W25CF RD25S B R CAP56PG 100V CER N150 P5T CAP 10U 35V ELEC RE2 P2 CAP 100U 10V ELEC RE2 P2 CAP 100NK 63V P E P5 DIO 1N4148 B R LED T1 ROUND 3mm RED DISPLAY 4 DIGIT LED IC ULN 2803A IC 74HC573 PCB KEYBOARD CONN ASSY
38. able writing This input is driven by the software The battery backup supply VBAT is generated by the lithium battery BATT When the instrument is switched on Q18 and Q9 are turned on and VBAT is pulled to within 200mV of the 5V rail As the 5V rail falls at power off Q18 and Q9 turn off and D14 holds VBAT up until D12 starts to conduct and the battery takes over at about 3 3V The CPU reset circuitry uses three of the comparators in IC18 The reset period RES bar low is determined by the charge time of C41 via RP3 A At power on the open collector output of IC18 B is turned off CA1 has no charge so RES bar is driven low by IC18 C C41 charges up via RP3 A until it reaches the 2 5V threshold of IC18 C set by RP3 B and RP3 C and RES bar is driven high C40 starts with no charge at switch on and then charges down to 25mV as defined by R68 and R69 The output of IC18 C is therefore held open circuit until the 5V rail starts to drop at switch off The rail drop is AC coupled to the input of IC18 B by C40 and the reset capacitor is immediately discharged driving the processor into reset D13 allows fast discharge of CA0 when the instrument is switched off ready for immediate switch on again Serial Interface 16 The CPU contains an SIO port which provides the RS232 communication via the serial remote interface The serial interface is opto isolated from the processor and measuring circuitry by IC28 and IC30 Q15 supplies the drive
39. an be selected remotely to initiate calibration See the list of remote calibration commands Stepping through the calibration is achieved using the STEPCAL command which is equivalent to pressing the RANGE UP key in manual mode The STEPCAL command generates a response which is P if the step calibration was successful and F if it failed Note that in GPIB or addressed RS232 operation the meter is held up until the response is taken by the controller If the response is F it is necessary to send another STEPCAL in order to move to the next calibration step There is no response to be taken from the second STEPCAL After successful calibration of a function the calibration constants may be stored using the STORECAL command which is equivalent to pressing the STORE key A facility only available via the remote interface is to set the point at which the calibration of individual steps is performed This is achieved using the SETCAL command The syntax of the SETCAL command is SETCAL followed by the value of the required calibration input which is rounded to form an integer corresponding to display reading ignoring the decimal point For instance if the new calibration point for the 20V DC range is to be 18 0000V then the value sent should be 180000 in any nrf format The calibration value can only be sent once the meter has been stepped into the range concerned If the SETCAL command is not sent then the inbuilt calibration value will be
40. ay be pressed to store the new constants for this function New calibration constants are stored and old constants over written only when the STORE key is pressed following a successful calibration Calibration constants are stored for all functions that have been successfully calibrated since calibrate mode was entered and the STORE key was last pressed If calibration of a function is unsuccessful then no new constants can be stored for that function If pressing the STORE key results in new constants being stored then CAL donE is displayed If no new constants are stored then no CAL is displayed When all required functions have been calibrated exit calibrate mode by releasing the CAL switch the CAL LED will turn off If the CAL switch is released before the new constants have been stored using the STORE key they will be lost Remote Calibration 20 The user is referred to the instrument operating manual for instructions on how to use the remote interfaces There are some commands which are only used for calibration while other commands are common to normal operation Note that the READ command is common but it operates differently in calibrate mode and normal mode It is possible to perform the calibration procedure over either of the remote interfaces The procedure is essentially the same as described above for manual calibration The instrument must first be put into calibration mode manually after which the required function c
41. calibration point from the front panel Each meter function can be calibrated separately however certain calibration constants are calculated during the DC Volts calibration procedure and used by other functions It is therefore necessary to know that the DC Volts function is calibrated before any other functions may be calibrated The calibration status of each function is recorded in a series of flags one for each meter function see table below The flags can be displayed when in calibrate mode CAL switch latched in CAL LED on by pressing the LOG key The flags are shown as a series of 1 s and 0 s across the main display All flags are set to O when a default calibration is performed and the appropriate flag is set to 1 when true calibration constants are stored for each function DIGIT 7 DIGIT 6 DIGIT 5 DIGIT 4 DIGIT 3 DIGIT e DIGIT 1 DIGIT O D DEFAULT CALIBRATION DHMS 10A 1DA mA mA V V AC DC AC DC AC DC 1 TRUE CALIBRATION Fig 7 Calibration Flags Calibration Equipment It is recommended that calibration equipment with accuracy five times that of the instrument is used for DC Volts and Ohms and four times the specification for all other functions AC Voltage and current calibrations are performed at 500Hz In addition frequency trimming of the AC input attenuator is necessary at 200mV 20kHz 2V 10kHz and 20V 50kHz Ohms calibration is performed in four terminal mode so the calibration equipment must provide a rem
42. e fuse body which could therefore result in instrument damage D1 to D5 prevent overvoltage from damaging the current switches and shunts and result in FS1 blowing if sufficient current is drawn Input Signal Conditioning AC DC Converter refer to main circuit diagram sheet 1 The AC DC conversion is performed by true RMS converter IC15 The signal to be measured is input to pin 2 and negative DC appears at pin 6 The input signal is AC coupled via C19 with bootstrapped DC bias supplied by IC11 C and R32 for good LF performance The source of the signal is selected by IC6 A pin 13 of IC6 being the AC Volts input and pin 12 being the AC current input C12 is the converter s averaging capacitor which averages a logarithmic voltage at pin 5 R106 is switched across the averaging capacitor by IC4 C for inputs below 1 200th of full scale to allow the reading to reach zero for zero input The converter s output is switched into the A D buffer via IC5 D and IC4 A with post filtering of the converter s output performed by IC11 B and associated components FEBE e R115 R116 A C75 VC1 R118 Fig 2 AC Volts I P Simplified Schematic Input Signal Conditioning AC Volts Attenuation refer to simplified schematic fig 2 The AC voltage readings require one sub reading The LO terminal is sensed via AG and is measured during the regular reference updates IC4 A is therefore switched on permanently except during the reference sub readin
43. gs The AC DC converter works in the range 0 200mV RMS input signal so all AC inputs are first converted to this level For AC Volts measurements the multimeter uses an active attenuator centred around the amplifier IC51 configured as an inverting amplifier with the virtual earth node pin 3 biased via IC7 A at one Vbe above analogue common The signal is AC coupled into the amplifier s inverting input by C76 with DC stabilisation provided by feedback resistors R115 and R116 D21 and D6 prevent large transients on the input causing latch up The AC attenuator presents a constant input impedance on all ranges of nominally 990kOhms consisting of R75 R76 and R77 In the 200mV range the input resistors are connected to the amplifier inverting input by IC8 B IC8 D and IC5 B IC1 D and IC1 B are turned off R120 is the 200mvV feedback resistor around IC51 The output from IC51 is divided by about ten at the junction of R119 and R121 and the feedback is taken from this point This gives a nominal overall gain of one whilst maintaining a relatively low feedback resistance for better HF performance It is essential for HF performance also that F7 is turned off in the 200mV range as this isolates spurious capacitive feedback through RP1 and associated gates R117 provides current limiting for IC6 A s input protection diodes if the output of IC51 goes more positive than 5V In the ranges 2V 20V and 200V F7 is turned on and IC2 selects the feedback for IC51
44. h instrument The optional GPIB interface works via the RS232 The display consists of multiplexed 7 segment LEDs The front panel LEDs are also driven via the main display multiplexing and the keyboard is scanned by the CPU using the display multiplexing signals Detailed Circuit Operation The following sections describe the detailed operation of the circuit blocks outlined in the general overview Refer to the main circuit diagrams where information is not presented on simplified schematics Measurement Control Signals and Signal Drivers The CPU is responsible for setting up all the measurement signal paths implemented using CMOS analogue gates and MOSFETS In addition the CPU controls the A D conversion process in real time The CPU controls all instrument functions using signals at two different levels All control signal names start with CTRL followed by the signal number and if the signal swings nominally between 5V and 10V it is suffixed with A 5V logic signals have no suffix All 5 10V level control lines are translated from their logic level equivalents by the amplifiers in IC21 IC22 IC23 and IC24 Note that the signals CTRL1A CTRL2A and CTRL10A are used to switch relays RL1 RL2 and RL3 All three relays are bistable latching types which require pulses of positive polarity to switch one way and negative polarity to switch the other way This is achieved by ac coupling the control lines via C35 C36 and C37 No dc current
45. ion Category measurement use to 1000V DC rms General Environmental Operating Range 5 C to 4 C 20 to 80 RH Environmental Storage Range 40 C to 60 C Size 260 W x 88 H x 235 D mm excluding handle and feet Weight 2 2kg Safety When operating the instrument with the covers off the users attention is drawn to the fact that the measurement circuit analogue common is capable of being driven up to 1kV above earth ground All measurement circuits are therefore potentially hazardous including the CPU section of the main board and the display keyboard mounted behind the front panel Instrument safety in normal use with the cover on is dependent on the safety earth connections to the front and rear panels and to the remote interface section of the main board It is therefore essential that these connections are only disturbed when absolutely necessary and are then replaced correctly In this case the safety tests at the end of this manual should be carried out to ensure that the meter still meets the specified safety standard Mains Fuse The mains input is protected by a fuse located in a drawer beneath the mains input socket This fuse should only be replaced with one of the type specified on the rear panel label Note that the fuse drawer orientation selects the mains voltage required to power the instrument Current Range Protection Fuses The mA ranges measuring currents up to 200mA are protected by a 1A 20mm HRC fu
46. moved from the integrator capacitor in order to balance the charge delivered by the measurement current and maintain the output of the integrator close to the threshold of IC12 B It is therefore a coarse measure of the measurement current itself At the end of the main conversion period there remains an unknown amount of charge in the integrator capacitor To determine how much charge is left the integrator output is discharged down to AG by the Q11 current source and the time taken for the discharge is measured using a timer within the CPU The timer is started when the CPU drives DISCHARGE ENABLE high DISCHARGE COMPLETE bar is already held high by the high output of IC18 A so IC17 C is turned on and Q11 current flows into the integrator When the integrator output reaches AG the comparator IC18 A switches DISCHARGE COMPLETE bar low to stop the Q11 current and thus hold the integrator output at AG ready for the next conversion cycle DISCHARGE COMPLETE bar also stops the timer in the CPU The timer is clocked by the 1 2288MHz E clock generated within the CPU which is 4x the frequency of the clock used for the main conversion period Thus because the Q11 current is 1 64th the Q12 current it is known that the charge removed from the integrator capacitor during each of the timer clock periods is 1 256th of that removed during each clock period during the main conversion period It is therefore possible to multiply the CB PULSES count by 256 and
47. n features a 6303 processor with battery backed RAM to store instrument set ups and the current hardware configuration when the instrument is switched off In addition an EEPROM retains calibration constants which are stored during the calibration procedure Default calibration constants are stored in the main EPROM and may be recalled at any time overwriting any existing calibration constants in the EEPROM The CPU IC25 controls all the input signal conditioning circuitry the A D circuitry the keyboard and the display The CPU contains a timer counter which is used to count CB PULSES from the A D hardware and another timer which is used to time the final discharge of the integrator capacitor at the end of each conversion period see A D section This represents the time difference between DISCHARGE ENABLE going high and DISCHARGE COMPLETE bar going low In addition the CPU contains an integral serial port which is used for the remote control serial interface Most hardware control lines the 7 segment display the front panel LED indicators and the keyboard scan are driven through a single external port PORT 1 Six hardware control lines CTRL14 CTRL21 CTRL15 CTRL16 CTRL17 and 18 are driven directly from output ports within the processor chip PORT 1 is memory mapped at address 0400H and consists of latches IC47 and IC35 Four bytes of information are stored in Port 1 Three bytes of information are stored in secondary latches I
48. nd waveform diagram fig 5 IC40 provides a x1 or x10 input buffer to the converter R10 filters out HF noise picked up on the extremely high impedance node feeding 1C40 Analogue multiplexer IC9 A switches the feedback to change the gain under control of signal 18 1C40 is switched to x10 for all AC functions 200mV DC and for all current measurements It is switched to x1 for Volts DC ranges 2V and above and all Ohms ranges except the 200Ohm range where it is switched between x1 and x10 depending upon the sub measurement under way The output from 1C40 is bipolar ranging between 0 and 4V for the Ohms measurements and between x 2 1V for all other functions R55 IC11 D and F4 form a transconductance amplifier with output current proportional to the output voltage of IC40 The magnitude of the measurement current is determined by R55 R40 and R41 represent constant current sources which are added to the measurement current This offsets the measurement current so that the current out of F4 is unipolar for all measurement inputs R40 is switched in by IC17 D under control of signal CTRL2A for Ohms measurements only Q10 limits the output of IC40 for open circuit Ohms measurements R67 is necessary to ensure that under that same condition even if F4 turns off completely there is always current to keep IC17 A biased correctly Without this precaution the converter would lock up IC10 Q13 and C29 form the converter s integrator The mea
49. ngs which comprise the complete resistance measurement IC40 has a gain of ten when measuring HI SENSE and LO SENSE across the unknown and a gain of one when measuring REF HI and REF LO Accuracy in this range is therefore dependent on the ratio stability of R30 and R31 For all other resistance ranges the gain of IC40 remains fixed at one Continuity detection is performed by IC11 A and associated components IC11 A compares the incoming unknown HI sense line with the 50mV reference voltage generated by R29 and R28 If the HI sense voltage is less than 50mV IC11 A turns on Q16 via RP4 D which raises the CONT DET line The CONT DET line is polled by the CPU under interrupt and the buzzer is sounded if the instrument is in the Ohms function and the continuity buzzer is programmed as active 11 Because the CPU input pin used by CONT DET can also be used as the processor HALT bar input it is necessary to ensure at power up that the CONT DET signal is held high until the power up routine has time to change the function from HALT bar to input port For this reason RES bar hold Q16 turned on at power up via R102 and C61 ensures that CONT DET does not fall before the software has had time to set up the input port Reference Generator refer to main circuit diagram sheet 1 The meter uses a temperature stabilised Zener IC16 as the central reference generator Note that IC16 maintains a junction temperature of 85 C so it can be expected to be hot IC1
50. nnected to AG by F5 The LO voltage is sensed at the drain of F5 via IC6 C IC7 B and IC4 B IC11 B and associated components form an active filter which is switched in on critical ranges via IC5 E The ranges where the filter is switched in are indicated in fig 6 where CTRL11A is shown to be high Input Signal Conditioning DC Current refer to main circuit diagram sheet 1 DC current readings require only one sub reading per complete reading This is the sense reading from the hi end of the current shunt The lo end of the current shunts is connected to and sensed via AG This sub reading is made when the reference readings are made at regular intervals of a few seconds The DC current shunt sense voltage is connected to the A D converter buffer input via IC4 D RL1 IC8 A and IC6 B pin 2 of IC6 selecting the sense voltage up to 200mA and pin 1 selecting the 10A sense The 200uA to 200mA current shunts are contained in RP2 and R74 is the 10A shunt The current is switched into the appropriate shunt in RP2 by MOSFETs F6 F1 F2 or F3 The 10A shunt is fed from a separate input socket and so is not switched The MOSFETs are turned on by high going signals on their gates The 10A input is fuse protected by FS2 and lower current ranges are protected by FS1 V4 and V5 prevent high voltage transients from occurring if the current is fed from an inductive source when the fuse blows these could otherwise prevent the arc from extinguishing within th
51. of the earth bonding screw on the rear panel Ensure that there is no breakdown between the two points Note that there may be AC leakage current up to 100uA which is permissible 23 PCB ASSY MAIN 44812 0540 Part Number 20030 0263 20037 0301 20210 0101 20234 0027 22010 0610 22247 9604 22312 0242 22315 0242 22454 0010 22573 0041 22573 0203 22573 0205 22574 0400 22575 0065 22575 0103 23185 0047 23185 1100 23185 1220 23185 1390 23185 1560 23185 2100 23185 2150 23185 2180 23185 2220 23185 2270 23185 2330 23185 2390 23185 2470 23185 2560 23185 3100 23185 3220 23185 3470 23185 4100 23185 4330 23185 4470 24 Description WASHER M3 ZPST WASHER M3 SHK PROOF ZPST NUT M3 ZPST SCREW M3 X 6 PNHDPZ ZPST BATTERY 3V LITH 20MM BUTTON RELAY 1P C O MIN LATCHING FUSE CLIPS PCB MOUNTING FUSE 10A F HBC 20 x 5mm RECEPTACLE RED 187 5 HEADER2 WAY STRAIGHT HEADER3 WAY STRAIGHT 156P HEADER5 WAY STRAIGHT 156P SKT9W R A D TYPE RS232 HEADER 20 WAY 2X10 STR SKELN HEADER 16 WAY 2X8 STR SKELN RES4 R7J W25CF RD25S RES 100RJ W25CF RD25S B R RES 220RJ W25CF RD25S B R RES 390RJ W25CF RD25S B R RES 560RJ W25CF RD25S B R RES 1KOJ W25CF RD25S B R RES 1K5J W25CF RD25S B R RES 1K8J W25CF RD25S B R RES 2K2J W25CF RD25S B R RES 2K7J W25CF RD25S B R RES 3K3J W25CF RD25S B R RES 3 K9J W25CF RD25S B R RES 4K7J W25CF RD25S B R RES 5KGJ W25CF RD25S B R RES 10KJ W25CF RD25S B R RES22KJ W25CF RD25S B R RES47KJ W25CF RD25S B R
52. orted at any time by pressing any function key When calibration of a function is started the meter is automatically switched to the range for the first calibration step and the user is prompted for the first input required A c is displayed in the right most character which indicates calibration mode The calibration prompt can be replaced at each step by default calculated readings by pressing the AUTO key When the meter reading is stable the c flashes The pre programmed stability criteria are different for each function and range When the c is flashing pressing the RANGE UP key causes the meter to automatically calculate the step s calibration constant If the calculated constant is within about 596 of the expected value it is accepted and the meter moves onto the next step If the calculated value is unacceptable then F is displayed in the right most character the meter bleeps and the input reading calculated using default calibration values is displayed One more press of RANGE UP is required to step onto the next calibration step The step will also fail to calibrate if the RANGE UP key is pressed when c is not flashing A failure at any calibration step will make the calibration for this function unsuccessful and inhibit storage of calibration constants for this function until it is successfully calibrated When the last step in the function has been successfully calibrated the c changes to P At this point the STORE key m
53. ote sense facility Two low thermal EMF zero Ohm links are necessary to short across the meter s input terminals for certain calibration steps Default Calibration For non calibrated operation it is possible to load default calibration constants into the EEPROM from the ROM This is necessary when the instrument is switched on for the very first time and if an error is detected in the EEPROM at power up To perform a default calibration the instrument must first be put into calibrate mode with the instrument switched off This is done by depressing the recessed CAL switch located at the top 19 left hand corner of the front panel using a suitable narrow tool The switch should be made to latch in The instrument is then switched on and the display shows DeF cAL Pressing the STORE key stores the default calibration constants in EEPROM overwriting any that may already have been there Depress the CAL switch to unlatch it and release the instrument from calibrate mode Manual Calibration Switch on the instrument and enter calibrate mode by depressing and latching in the CAL switch The CAL LED will light Start the calibration of the required function by pressing the appropriate function key Except for Ohms pressing the AC or DC key will change the selected function and or start the calibration too Calibration of a function can be restarted at any time by pressing the same function key again Calibration of a function will be ab
54. put signal lo ref hi ref lo DC voltage readings require two sub readings one where the input attenuator s output is fed to the A D converter and one where the bottom of the attenuator is fed to the converter As in all voltage and current measurements reference hi and reference lo sub readings are performed at timed intervals once the meter function has been established The AC voltage and all current functions require only one sub reading per displayed reading the reference lo sub reading also being used as the signal lo sub reading This has the advantage of speeding up the reading rate For AC voltage and current measurements the signal hi sub reading is taken from the AC DC converter output For DC current measurements the signal HI sub reading is taken directly from the input current shunt Resistance measurements require four sub readings The details of the signal paths used for the sub readings of each meter function are given in the sections describing detailed circuit operation The buffer amplifier IC40 which drives the A D converter is switched between gains of x1 and x10 according to the meter function and range The A D converter is of the charge balance type controlled directly by the CPU The counters for the A D converter reside within the CPU The dividing line between A D and CPU sections is therefore more blurred than the diagram suggests The basic remote interface is an opto isolated RS232 which is incorporated in eac
55. rd via its own inbuilt serial SIO port Serial communication between the two processors is asynchronous The GPIB CPU uses internal RAM and the external ROM IC7 IC1 and IC2 are GPIB buffers The remote processor s power on reset signal is generated by IC5 A and IC4 B The reset period is determined by the time constant of C9 and R2 Note that this time constant is required to be less than that of the main board s reset time for correct operation at power up The state of the RS232 GPIB switch is read by the main CPU at power up only The interface between the switch and the main CPU is optically isolated by IC8 on the GPIB board 17 9 10 11 12 13 14 15 16 17 18 19 8 7 1 CTRL No VOLTS DC A A O x x x 10 0 1 0 LL dc O 0 3 x O 1i x ab 200mV LOZ AA i 9 A A O O O 0 0 1 1 200mV HIZ 2V LOZ 2v HIZ 20V A A O DO O 1L x 1 0O 9 a x 1 2 x x 1 L 100000 0 A O O A D O x O A O O A 1 0 0 O02 OO 2 3 o 200V ikv A O A x VOLTS AC 200mV 2V A 1 1 A A A o x 1 0 00 Q 1 x x 0 0 D O x Yd 4 1 1 0 0 0 A A I 1 1 20V 0 A O0 0 A O 1 1 0 0 200V 750V x 0 AMPS DC 1 1 1 x 1 0 x A A x 2 X A A x A A O A A O A A O x x
56. rence resistor REF HI and REF LO and at each end of the unknown resistance X HI and X LO The complete reading is calculated from these four sub readings X resistance REF resistor X HI X LO REF HI REF LO The measurement current is generated by biasing the HI end of the reference resistor with the Ohms reference voltage OHMS REF of approximately 4V OHMS REF is generated in resistive attenuator R35 and R23 IC7 A selects the OHMS REF as the bias for IC51 which forms a unity gain buffer to drive the reference resistor via R117 and F7 The REF HI voltage is passed to the A D buffer via IC6 C and IC7 B Because R117 has significant resistance the actual bias on the reference resistor varies with selected reference resistor and the unknown resistance In the 200Ohms and 2kOhms ranges RP1 D 1kOhm is selected by IC2 IC1 D and IC1 B to form the reference resistor Measurement current flows from RP1 D to the unknown resistor via IC1 D and RL2 and the REF LO voltage is sensed via IC1 B and IC5 A Similarly in the 20kOhm and 200kOhm ranges RP1 D and RP1 C are selected and sensed RP1 C forms the 2MOhm range reference resistor Measurement current flows via IC1 A and the REF LO voltage is sensed via IC1 C Similarly R78 forms the reference resistor for the 20MOhm range in conjunction with IC8 B and IC8 D The measurement current passes through the positive temperature coefficient resistor PTC1 and R11 These provide protection against o
57. se mounted on the rear panel The 10A range is protected by a 10A 20mm HRC fuse mounted on the main board To change this fuse first remove the top cover of the instrument The 10A fuse is designated FS2 and is located near the input sockets SUPPLIES TO REMOTE INTERFACES POWER DISPLAY Fig 1 Block Diagram General Overview amp Principles Operation refer to the block diagram fig 1 The input signal conditioning includes the input attenuator current shunts and analogue switches required for range switching All analogue switches are either CMOS gates or MOSFETs By software calibrating every meter range high precision components are avoided the only requirement is stability The reference for voltage and current measurements consists of a reference diode with dividers connected to analogue ground Resistance measurements use a separate Ohms reference voltage and are made using a ratiometric method so that the reference actually becomes the voltage across the reference resistor The input multiplexer consists of analogue gates which feed the A D converter with the signals necessary to perform a complete meter reading Each complete meter reading requires up to four sub readings each with a different signal fed to the A D converter for the duration of one 20ms or 100ms conversion period The complete reading is calculated from the sub readings using the following generalised formula reading input signal hi in
58. surement current is gated into the integrator for the duration of the main conversion period by pulling IC 17 pin 2 low IC17 is a 13 14 transistor array and IC17 A is a common emitter pair wired to form a diode switch At the end of the conversion period pin 2 is pulled high to divert the measurement current from the integrator The main conversion period is determined by the CPU control signal CB ENABLE whose state is changed within the CPU s NMI routine which is initiated by the low going edge of the 600Hz signal generated in IC14 CB ENABLE is accurately timed at IC13 B by the rising edge of the 600Hz clock CB ENABLE is held high for the duration of the main conversion period For 572 digit operation the conversion period is 100ms and for 475 digit operation it is 20ms IC20 C Q11 and Q12 form two constant current sources in the ratio of 1 64 determined by R36 R37 and R38 IC20 C is biased at about 5V below the 10V rail by R18 R34 and R17 Note that this resistor chain also provides the feedback for the 10V regulator compromised of IC46 A and Q7 During the main conversion period Q11 current is diverted away from the integrator by holding IC17 B on and IC17 C off This is achieved by alow DISCHARGE ENABLE signal from the CPU forcing gate IC12 C output low At the start of the main conversion period D19 is turned on by the output of IC13 A This ensures that Q4 is turned off so that the only current into the integrator at the start
59. t Diagrams Circuit Diagram Main Board Input Signal Conditioning and A D Converter Circuit Diagram Main Board CPU Section Keyboard and Display Circuit Diagram GPIB Interface Board 33 155 12
60. time the software was revised to V1 18 the easiest way to identify instruments built in this way is to check that the software revision shown briefly at power up is V1 18 or later Main Pcb Refer to schematics Issue 4 onwards The true RMS converter IC15 was changed from an AD737 to an AD636 which has a faster conversion rate and wider bandwidth some associated components changed see below Analogue gate IC9 C was added to switch the guard track driver IC20 D this allows the guard track which surrounds the input signal conditioning tracks to follow the DC input signals more closely by switching in the RC filter for AC function only Input protection resistors R1 and R93 were changed to a different type with improved thermal EMF characteristics this required the addition of R122 in series with R1 to maintain the protection The opto coupler providing isolation between the main board and the RS232 IEEE interface was moved from the interface board was IC8 on that board to the main board now IC31 this simplifies the isolation requirements of the connecting flat cable which also changed A link must be fitted between pins 6 amp 7 of PJ4 on the main board when no interface board is fitted Pcb mounted fuses FS3 4 5 6 7 were fitted to ensure that the instrument fully complied with the LVD directive by remaining safe under any Single Fault condition Main component changes were as follows IC15 AD737JN 27165 0400 AD636KH 27165 0411
61. used To allow a remote controller to know when the reading is stable the READ command may be used When in calibrate mode the response to this command is inhibited until the meter reading is stable and the c is flashing AC Voltage Input Attenuator Frequency Checks and Adjustment After calibration of the AC Volts function the following checks should be carried out and if necessary adjustments made VC1 VC2 and VC3 are accessed through holes in the upper aluminium screen VC1 is adjusted through the rear most hole and VC3 through the hole closest to the front of the meter 200mV AC Switch the meter to 200mV AC and check that with an input signal of 200mV at 20kHz the meter reads 195 000 50 digits If necessary adjust VC1 2V AC Switch the meter to 2V AC and check that with an input signal of 2 00000V at 10kHz the meter reads 2 00000 x 50 digits If necessary adjust VC2 20V AC Switch the meter to 20V AC and check that with an input signal of 20 0000V at 50kHz the meter reads 20 4000 x 50 digits If necessary adjust VC3 21 DC Volts Calibration Step No 1 coo NO O R ON Input Value 000 000mV 0 00000V 00 0000V 200 000mV 2 00000V 2 00000V 20 0000V 200 000V 1000 00V AC Volts Calibration Step No 1 O R N 7 Input Value 200 000mV500Hz 40 000mV500Hz 2 00000V500Hz 0 40000V500Hz 20 0000V500Hz 200 000V500Hz 750 00V500Hz DC Amps Calibration Step No 1 2 3 4 5 Input Value
62. vervoltage on the HI input in conjunction with Q2 and Q3 not shown on simplified schematic A high voltage on the HI input will cause either Q2 or Q3 to clamp the REF LO sense line at 3 5V The initial surge current into these transistors is limited by the 1KOhm cold resistance of PTC1 and R11 However very quickly PTC1 heats up to reduce the current to a safe low level Resistance measurements may be made in two terminal or four terminal mode Four terminal mode requires that the HI and LO SENSE terminals are connected externally to the resistance being measured In this way the voltage across the unknown resistance can be sensed without the measurement leads resistance causing inaccuracies The instrument defaults to two terminal measurements if the and LO SENSE terminal are left unconnected the sensing being performed internally at the Hl and LO measurement terminals The HI voltage on the unknown resistance is sensed via R1 RL1 R44 and via R93 in two terminal mode or via the HI SENSE terminal in four terminal mode The LO voltage on the unknown is sensed via IC7 B IC7 C R95 and via R94 in two terminal mode or via the LO SENSE terminal in four terminal mode R95 and Q1 provide protection from overvoltage on the LO SENSE terminal In the 200Ohms range the reference resistor used is 1k contained in RP1 To scale the measured resistance correctly the gain of the A D buffer IC40 is switched between x1 and x10 during the four sub readi
63. ws anode driven from IC37 and the columns driven by the digit driver IC39 The keyboard is scanned using the digit multiplex drive signals from IC38 The keyboard columns are read into the CPU via input port lines COLO COL1 COL2 and COL3 Memory and port decoding are provided by IC32 IC19 and IC29 D20 isolates IC32 B pin 6 from IC29 B so that current does not flow from out of IC32 into the main 5V supply via the input protection diodes of IC29 when the instrument is switched off IC49 is the EEPROM used for storing calibration constants It is controlled and accessed via IC48 which is decoded as PORT 2 at address 0401H The EPROM is written to serially via DO of ICA8 and read from via the CPU input port line P52 Note that because P52 doubles as the processor s Memory Ready input is necessary to ensure that this line is held high at power up To this end the output enable of IC48 is held high by the RES signal which tri states the latch output allowing R97 to pull the chip select pin of the EEPROM low The deselected EEPROM has tri stated outputs which allows R98 to hold the Memory Ready input high The EEPROM contents are protected from accidental overwriting by two methods The main overwrite protection is the CAL ENABLE signal driven directly from the recessed CAL switch on the front panel This signal has to be high to allow the EEPROM to be programmed Similarly pin 7 of the EEPROM the PRE input must be high to en
64. y range Max input 750V rms 1kV peak any range AMPS Range Accuracy Voltage Burden Max Input 200uA 0 08 12D 1A 300V 2mA 0 08 12D 300mV max fuse protected 20mA 0 08 12D 200mA 0 08 12D 10A up to 2000mA 0 06 10D 650mV max 10A 300V above 2000mA 0 12 10 fuse protected TRMS AC AMPS Range Accuracy 45Hz 1kHz Voltage Burden Max Input 200uA 0 37 100D 1A 300V 2mA 0 37 100D 300mV max fuse protected 20mA 0 37 100D 200mA 0 37 100D 10A up to 2000mA 0 3496 100D 10A 300V above 2000mA 0 4 Yo 100D 650mV max fuse protected Additional error at crest factor 3 typically 0 7 DISPLAY Display Type Scale Length Reading Rate Overange Indication Overflow Indication Annunciators Input Characteristics Input Current DC NMR 1k Unbalanced CMR Hi Z Null Digital Filter T HOLD Touch amp Hold DEV 13mm LED 8 digit Selectable 5 digit or 475 digit 3 readings sec 57 digit 10 readings sec 477 digit Displays OL if input too great for range Displays OFLO if calculated result too large for display LED annunciators for range function and program modes lt 100pA gt 60dB at 50 60Hz gt 120dB at DC 50Hz 60Hz DC ranges gt 60dB at DC 50Hz 60Hz AC ranges Switchable high impedance gt 1GOhm on 200mV and 2V DC ranges COMPUTING FUNCTIONS Operates over full range values can be stored

1906 Multimeter Service Manual

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