User Manual - Far West Technology, Inc.
Contents
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3. an oscilloscope at pin 3 of U5 The buffered signal is on pin 1 and an inverted signal is on pin 7 The buffered signal will not go fully positive and the inverted signal will not go fully negative MODEL 6031 INSTRUCTION MANUAL PAGE 5 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS B CONTROLS The only control is the reset button located on one end of the board Pushing it will reset the microprocessor and has the same effect as turning power off and back on IX THEORV OF OPERATION The instrument measures the current from the detector with an integrator The integrator is reset when its output goes pasta threshold Figure 2 shows a simplified schematic of the instrument The ion chamber produces a positive current at the inverting input of the electrometer The electrometer is an integrator with a 1 pF feedback capacitor C3 The output of the electrometer ramps negatively from the ion chamber current When the electrometer output reaches zero volts or ground the output of U2 a comparator changes state This signals the microprocessor to turn on S1 for a few microseconds The voltage from the DAC which is negative is transferred through C2 and D1 to the input of the electrometer and causes the output of the electrometer to swing positively This cycle repeats as long as there is current from the detector After each current pulse the microprocessor looks at the state of the second comparator U3 If the charge pulse was large
4. then directly changes the charge per pulse 0 1 volt with 1 pF feedback capacitor is 0 1 picocoulombs or 0 1 picoamp for a pulse per second The leakage currents are about 1 pulse every minute or about 2 femtoamps and R1 form an RC network to smooth out pulsed radiation X CIRCUITRY Many of the components on the schematic are not used in this model The ion chamber generates a positive current The RC filter R22 and C6 are used to filter out fast peaks and smooth the signal going into the digitizer U2 is a high impedance electrometer op amp that has only a 1 pF feedback capacitor and functions as an integrator The output divider R2 and R14 are not used instead R14 is Shorted The output of the electrometer goes to four comparators 01 The first UL A compares the signal to ground The second U1 B compares it to 1 volt The third U1 C compares it to 5 volt The last one U1 D is not used in this application The output of the comparators are buffered to keep their outputs positive and then they go to the microprocessor U3 This is a single chip RISC micro The program is only about 100 bytes long The microprocessor takes two actions The first is to generate a charge pulse to offset the input current It uses the information from the first comparator U1 A for this When the output of the electrometer goes below ground U1 A goes from high to low and the microprocessor generates a charge pulse by pulsing pin 6 high low high This caus
5. 031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 DRAWING 6031 001 6031 001 MODEL 6031 INSTRUCTION MANUAL PAGE 9 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS R20 00 0K RESISTOR 1 MF 6031 00 R21 49 9 RESISTOR 1 6031 00 22 KM RESISTOR 5 CF 6031 00 R23 OK RESISTOR 5 CF 6031 00 R24 00 0K RESISTOR 1 MF 6031 00 R25 49 9 RESISTOR 1 6031 00 R26 OK RESISTOR 5 CF 6031 00 R27 00 0K RESISTOR 1 MF 6031 00 R28 49 9 RESISTOR 1 6031 00 R29 00 K RESISTOR 5 CF 6031 00 R31 00 0K RESISTOR 1 MF 6031 00 R32 00 0K RESISTOR 1 MF 6031 00 R35 00 0K RESISTOR 1 MF 6031 00 R36 49 9K RESISTOR 1 MF 6031 00 R37 00 K TRIMMER 3 8 SIDE 6031 00 R38 0 RESISTOR 5 CF 6031 00 R39 00 0K RESISTOR 1 MF 6031 00 R40 49 9 RESISTOR 1 6031 00 R41 00 0K RESISTOR 1 MF 6031 00 R42 49 9 RESISTOR 1 6031 00 R44 OK RESISTOR 5 CF 6031 00 R47 00 K RESISTOR 5 CF 6031 00 R48 00 K TRIMMER 3 8 TOP 6031 00 R50 00 K RESISTOR 5 CF 6031 00 RIL OK RESISTOR 5 CF 6031 00 R53 00 K RESISTOR 5 CF 6031 00 R54 0 RESISTOR 5 CF 6031 00 R55 OK RESISTOR 5 CF 6031 00 R56 0 TRIMMER 3 8 TOP 6031 00 R57 OK RESISTOR 5 CF 6031 00 R58 OK RESISTOR 5 CF 6031 00 R59 0 RESISTOR 5 CF 6031 00 R62 00 K TRI
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8. CTION MANUAL PAGE 8 ION CHAMBER AREA MONITOR INSTRUMENTS 6031 PARTS LIST DESIGN QUAN PART NO CAPACITOR TEFLON Q4 R04 RO5 RO6 RO7 RO8 R09 R10 R11 R12 R13 R15 R17 FR107 FR107 1N4004 FR107 2N4117A 2N4117A VN1OKM 2N2222 DESIGN QUAN PART NO R18 R19 0 0 4 0 1 0 0 0 0 4 4 1 3 0 5 5 5 5 5 0 5 0 5 UF 0 UF UF 1 UF 0022 UF 7 UF 01 3KV 01 UF 01 UF 05 UF 3KV 0022 UF 3KV 001 UF 00 PF 001 UF 1 UF 1 UF 1 UF 7 UF 7 UF 0 UF 70 1 UF 1 UF 1 UF 1 UF 1 1 1 UF UF UF 3 UF 00 PF 3KV 047 UF N4148 KV FAST RECOVERX KV FAST RECOVERX N4148 N4148 N4148 N4148 N4148 N4148 KV FAST RECOVERX 0 MH IP IP IP IP IP OWER NPN 4 4 4 OK OK 00 0K 9 9K 00 K 00 0K 9 9K 00 0K 9 9K 00 0K DESCRIPTION CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR CAPACITOR DIODE DIODE DIODE DIODE DIODE DIODE DIODE DIODE DI
9. INSTRUCTION MANUAL MODEL 6031 ION CHAMBER PULSE LINK AREA MONITOR March 1998 Version 2 Health Phvsics Instruments 330 South Kellogg Ave Suite D Goleta CA 93117 805 967 8422 Division of Far West Technologv MODEL 6031 INSTRUCTION MANUAL PAGE 1 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS INTRODUCTION The model 6031 is an ion chamber area monitor Itis designed to be powered bv an HPI Pulse link Receiver The 6031 produces a calibrated pulse output The instrument will operate over a wide range of doserates and a wide range of energies DESCRIPTION AND CONTROLS The model 6031 has all of the controls and connections on one side see Figure 1 These include Digital Counter This is a 6 digit up counter that counts up with every pulse that is transmitted on the Pulse Link Counter Reset Reset for the Digital Counter Pulse Link Connection This is a BNC connector that should be connected to the input to a Pulse Link Receiver through coax Both power and data are transmitted on this connection Accessorv Connector This connector contains signals for testing the instrument The connections are detailed below INSTALLATION The model 6031 is installed by plugging it into a Pulse Link Receiver The BNC on the panel of the 6031 should be mated to the inputon the Pulse Link Receiver through a patch cord with a BNC on each end The counter should be reset after turn on to make it count properly IV OPE
10. MMER 3 8 TOP 6031 00 R63 00 RESISTOR 5 CF 6031 00 R64 RESISTOR 5 CF 6031 00 R65 RESISTOR 5 CF 6031 00 R66 KM RESISTOR 5 CF 6031 00 R67 510 K RESISTOR 5 CF 6031 00 R68 510 K RESISTOR 5 CF 6031 00 R69 2 7 RESISTOR 5 CF 6031 00 R70 K RESISTOR 5 CF 6031 00 R70 0 RESISTOR 5 CF 6031 00 R72 200 M RESISTOR 5 CF 6031 00 R74 499 K RESISTOR 1 MF 6031 00 R75 00 K TRIMMER 3 8 TOP 6031 00 R76 2 K RESISTOR 5 CF 6031 00 R77 2 K RESISTOR 5 CF 6031 00 R79 2 4 RESISTOR 5 CF 6031 00 R80 2 1 RESISTOR 5 CF 6031 00 R81 Zia K RESISTOR 5 CF 6031 00 R82 2307 RESISTOR 5 CF 6031 00 R84 ak RESISTOR 5 CF 6031 00 100 RESISTOR 54 6031 00 RX2 1M RESISTOR 5 CF 6031 00 51 SPST SWITCH PUSHBUTTON 6031 00 52 106 SPDT SEALED SWITCH PUSHBUTTON ALCO 6031 00 T1 BLOCKING TRANSFORMER HPI 6031 00 Ul LP339N QUAD COMPARATOR NATIONAL 6031 00 ULL SUB1000 6 DIGIT COUNTER DISPLAY RED LION C 6031 00 U12 7415221 DUAL MULTIVIBRATOR 6031 00 U13 LM2931 5 0 3 TERMINAL VOLT REGULATOR NATIONAL 6031 00 014 LM2931 5 0 3 TERMINAL VOLT REGULATOR NATIONAL 6031 00 U2 LMC6041A1N SINGLE OP AMP NATIONAL 6031 00 U3 PIC16C55 MICROPROCESSOR MICROCHIP 6031 00 u4 CD4053BE SWITCH CMOS 6031 00 05 TLC27M2 DUAL OP AMP TEXAS INST 6031 00 06 ICL7556 DUAL TIMER 6031 00 U7 TLC27L2 DUAL OP AMP TEXAS INST 6031 00 U8 ICL7660 VOLT CONVERTER 6031 00 8 0 MHZ CRVSTAL 6031 00 MODEL 6031 INSTRUCTION MANUAL PAGE 10 HEALTH PHVSICS ION CHAMBER
11. ODE DIODE DIODE CHOKE HEADER HEADER HEADER HEADER HEADER FET FET CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM MONO MONO MONO MONO MONO MONO MONO MONO MONO MONO TANTALUM CERAM CERAM CERAM MONO MONO DISC TANTALUM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM DISC DISC DISC DISC DISC MONO MONO MONO MONO MONO MONO TANTALUM TANTALUM TANTALUM CERAM CERAM CERAM CERAM CERAM CERAM CERAM CERAM MONO MONO MONO MONO MONO MONO MONO MONO ELECTRO TANTALUM TANTALUM CERAM CERAM FET N CHAN TRANSISTO RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR DESCRIPTI RESISTOR RESISTOR R 5 CF 5 CF ou 99 ON 1 5 DISC MONO HEALTH PHVSICS MOLES MOLES MOLEX MOLEX MOLEX SILICONIX SUPPLIER SUPPLIER DRAWING 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6031 00 6
12. RATION The instrument will produce a pulse rate proportional to the radiation level 1 mR h equals 25 Hz and 1 R h equals 250 Hz The instrument will need about 1 minute after turn on to be operational Right after turn on there is about a 10 second delay Then the instrument produces many pulses per second tapering off to the radiation field This is the high voltage stabilizing It gives you an indication that the instrument is functioning MODEL 6031 INSTRUCTION MANUAL PAGE 2 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS The outer equilibrium wall can be removed for low energv operation The inner wall is made of stvrofoam and is easilv damaged The sticker on the front indicates the front of the wall CALIBRATION ACCESSORY CONNECTOR 4 Oe e DIGITAL COUNTER PULSE LINK CONNECTION A COUNTER RESET Figure 1 Location of Controls V ACCESSORY CONNECTION The accessory connection allows the instrument to be operated without the Pulse Link Some of the signals are available from this connector The pin definitions are PIN DESCRIPTION K Output pulse L Ground M External power N 5 VDC output Connector type Cannon 15 pin Part Number 06 14 15P PIN FUNCTIONS AND DESCRIPTIONS Output pulse This is an LSTTL positive going output pulse for each discriminated event This is nota buffered signal however it will drive 1 LSTTL load Ground
13. Signal and power ground This is the negative input for external power MODEL 6031 INSTRUCTION MANUAL PAGE 3 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS External Power This is the positive input for external power It can power the instrument instead of or with the Pulse Link The external power should be above 9 volts The instrument can be powered continuously by connecting external power to this input before removing the Pulse Link connection 5 VDC Output This is an output of 5 volts This is the positive connection The ground pin is the negative connection VI CONSTRUCTION The electronics is all housed inside the cast aluminum case The case is gasketed and sealed To gain access to the circuit boards remove the four screws on the bottom of the case These screws are captive The large circuit board is held in place with 4 screws around the edge To remove the board it is necessarv to unsolder the high voltage lead and unscrew the electrometer connection The high voltage lead is located in the high voltage section near the electrometer cover The electrometer cover is located in the center of the circuit board Remove the four screws holding the cover Remove the 4 40 nut spacer that holds the lug to the center electrode Disconnect the cables from the board and the board is free to be lifted from the box Before removing the circuit board itis a good idea to short the high voltage to ground to keep from destroving anv
14. asures the high voltage through the voltage divider consisting of R72 and R74 If the high voltage is too low the comparator will turn on the one shot The output of the one shot turns on Q3 and generates a pulse on T1 The output of T1 which is a step up transformer is stepped up through the trippler consisting of 09 10 amp 11 and 16 23 amp 19 C26 provide feed forward to speed up the turn off of the comparator U7 B is a buffer The filter R65 R66 C20 C21 and C22 reduce the high voltage ripple The low voltage power supply consists of U13 and U14 both 3 terminal 5 volt voltage regulators The negative voltage is generated by U8 The references U10 and U9 are not used The Pulse Link signal is generated by the microprocessor U3 pin 14 whenever it generates a charge pulse This signal is shortened by the one shot U12 A and fed to Q4 where is creates the current pulse on the Pulse Link line L1 isolates the power supplies from the Pulse Link signal The counter U11 counts the pulses for direct viewing MODEL 6031 INSTRUCTION MANUAL PAGE 7 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS JUMPER SETTINGS The jumpers are set as follows Ti 1 1 Meg 1 resistor from pin 2 to pin 1 of U12 Mounted on bottom of PCB 2 Jumper pin 1 and 2 3 Jumper pin 1 and 2 4 Jumper 1 and 2 No jumper umper pin 1 and 2 umper pin 1 and 2 umper pin 1 and 2 umper pin 1 and 2 1 No jumper e O ON MODEL 6031 INSTRU
15. enough to trip U3 then the microprocessor through the DAC reduces the size of the charge pulse If the comparator did not trip then the microprocessor increases the output of the DAC Thus the output of the DAC is constantly changing up and down by 1 bit to keep the reset pulse at the 0 1 volt reference level If the ion chamber has no input and the leakage currents make the output of the electrometer go positive rather than negative then eventually U4 would trip when the output of the electrometer reached 0 5 volt At this point the microprocessor pulses S2 This injects current into the electrometer causing the output to go negative The microprocessor stops the pulses when U3 trips indicating the output of U1 has dropped to the 0 1 volt level 1 ION CHAMBER 1 COMPARATOR ELECTROMETER Pa WV gt MICROPROCESSOR DAC A AVREF l COMPARATOR 1V REF 1 COMPARATOR Figure 2 Block Diagram MODEL 6031 INSTRUCTION MANUAL PAGE 6 ION CHAMBER AREA MONITOR HEALTH PHYSICS INSTRUMENTS When the instrument is first turned on the system ramps up and down using S1 and S2 to set the DAC so that the current pulse is of the correct magnitude The Calibration control changes the level of the 0 1 volt reference and
16. es the switch U4 B to turn on and off generating the pulse through Q2 The size of the current pulse is set by the DAC The height of the current pulse is determined by the voltage at the output of the DAC buffer U5 and by the DAC ladder network R6 to R42 The microprocessor looks at the height of the pulse by way of the second comparator U1 B If U1 has tripped then it adjusts the DAC up If U1 has not tripped the DAC is decreased In this way the system oscillates around the voltage set by R37 which is around 1 volts The adjustment U48 is also modified by the output pulse from pin 14 of the microprocessor This decreases the voltage across R37 to make up for losses at high counting rates If Comparator U1 C trips it indicates that the input is leaking and the output of the electrometer is going positive The microprocessor takes action to keep the integrator from going too positive by pulsing the switch U4 A TP9 This signal injects a current into the input through Q1 that causes the electrometer to go negative When it reaches the level of the second comparator U 1 B of 1 volt it stops The Buffer U5 inverts the output of the ladder network R6 to R42 to go negative The High voltage is generated by the high voltage power supply The high voltage is set at 700 Volts U6 A is a square wave oscillator It continually generates a square wave on pin 5 The other half of U6 is a one shot that is resetable through comparator U7 The comparator me
17. negative or positive excursions Reset Pulse Height Method 2 This method should be used as a last resort It is much touchier and not as easy to set as method 1 Connect a clip lead from TP 15 to one side of a 1K ohm resistor With the other side of the resistor touch pin 18 of U3 the 24 pin IC Push the reset button and wait 2 seconds then remove the resistor This puts the instrument in a special mode where it will continually reset itself Connect an oscilloscope between ground and the testpoint TP3 Set the oscilloscope on 0 2 V cm and 10 ms sweep speed You should see a negative ramp Adjust R62 until the period of the ramp is 50 ms The instrument will also ramp at turn on This allows you to check the reset pulse height setting without connecting the clip lead ust turn the instrument on and look at If you do it by turning on the power you will also have a rising high voltage and this will effect the reading If however you wait a minute or so for high voltage to stabilize then push the reset button on the circuit board S1 then the microprocessor will initiate a turn on and ramp the system You only have a few seconds to watch the signal but you can reset it as many times as you need Incidentally there is a delay of a few seconds from the time you push the reset button until the ramp begins CHECKING THE RANGE OF THE DAC You can also check the DAC at turn on It ramps up from ground The signal can be found by looking with
18. part of the instrument bv getting vour hand between high voltage and anv component The desiccant is mounted in the lid Make sure that it is replaced or baked out for 3 hours at 300 F if it is pink Itcan also be put in a vacuum oven to remove the moisture All controls screws and openings are treated with RTV silicone sealant to keep the box from breathing with atmospheric pressure changes VII CALIBRATION If the instrument is new perform all the adjustments described in the adjustment section Expose the instrument to about 100 mR h Adjust R37 until the output frequency reads 25 0 Hz To adjust R37 itis necessary to remove the screw on the outside of the case and use a long screwdriver to adjust the control Replace the screw and nylon washer to maintain the integrity of the case It may be necessary to remove the cover the first time the control is adjusted to learn where to move the screwdriver The instrument can be calibrated with the cover removed It is a good idea when calibrating the instrument to check the desiccant The desiccant is mounted in the lid Make sure that it is replaced or baked out for 3 hours at 300 F if itis pink Itcan also be putin a vacuum oven to remove the moisture Vill INTERNAL ADJ USTMENTS AND CONTROLS USTMENTS The calibration high voltage lower threshold upper threshold and reset pulse height all located on the circuit board Thev are adjusted as follows NOTE There is a te
19. stpoint for ground TPGND located near the 3 terminal regulators MODEL 6031 INSTRUCTION MANUAL 4 ION CHAMBER AREA MONITOR HEALTH PHVSICS INSTRUMENTS High Voltage Connect a high voltage voltmeter probe gt 10000 Meg between 10 lead and ground lead Adjust R75 until the voltmeter reads 700 volts Lower Threshold Connect a voltmeter between ground lead and 7 of U1 an LP339 lead Adjust R37 until the voltmeter reads 0 1 volts To adjust R37 itis necessary to remove the screw on the outside of the case and use a long screwdriver to reach the control Replace the screw and nylon washer to maintain the integrity of the case Upper Threshold Connect a voltmeter between ground lead and 9 of U1 an LP339 lead Adjust R48 until the voltmeter reads 0 5 volts Reset Pulse Height Method 1 Connect the positive lead of a 0 05 volt negative power supply to the chassis of the 6031 Hook the negative lead to the center terminal of the ion chamber inside of the small electrometer box on the circuit board Connect an oscilloscope between ground and the testpoint TP3 Set the oscilloscope on 0 2 V cm and 10 ms sweep speed Turn R62 20 turns counter clockwise or until it clicks Slowly turn it clockwise Atsome point you should see ramp Adjust R62 until the negative portion of the ramp is at 1 volt The ramp should start at 1 volts and go to 5 volts If you turn it too far there will be large
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