9200 User`s Manual
Contents
1. SPARE Fuse NUS eM ACTIVE FUSE LINE CORD Lc ACCESS DOOR RECEPTACLE in open position FIGURE 1 0 POWER RECEPTACLE MODULE UN 01 217 Rev LN 359201 Page 2 of 3 9200CE Manual Supplement dd 9200 dpoaficalions ac ACCURACY and ANALOG OUTPUT 1 EMC In an RF field of 3V m Additional Uncertainty ac and dc Displayed and Analog Output dd to 9200 inst 0 5 Gauss 1x Probes 5 0 Gauss 10x Probes 0 5 mG x100 Probes HUMIDITY RANGE 0 C TO 35 0 RH maximum 35 C to 50 C 50 RH maximum ALTITUDE RANGE 6562 ft 2000m maximum Chango 9200 ipecificalions page 1 POWER ac Volts 105 125 210 250 Frequency 50 60 Hz 50 60 Hz Current 250mA 125 mA Chago 9200 spocificalioms paga 2 INTERNAL BATTERY Sealed lead acid Power sonic PSI220 or F W Bell I N 335635 UN 01 217 Rev I N 359201 Page 3 of 3 MODEL 9200 2000 TABLE OF CONTENTS SECTION MODEL 9200 GAUSSMETER DESCRIPTION l A 00 000000000 l B FUNCTIONAL SECTION MODEL 9200 GAUSSMETER PREPARATION I A POWER RECEPTACLE Il B PROBE INSTALLATION POWER UP IHD PROBE ZERO SECTION FI2. 9200CE Manual Supplement International Electrical Svmbols rwol im front of page 1 of the 9200 Manual AN Caution Refer to this manual before using the meter Caution Risk of electric shock SAFETY INSTRUCTIONS A GENERAL For safe and correct use of this gaussmeter it is necessary that both operating and servicing personnel follow generally accepted safety procedures plus the safety cautions and warnings specified If it is determined that safety protection has been impaired the gaussmeter must be made inoperative and be secured against any unintended operation For example safety may be impaired if the gaussmeter fails to perform or shows visible damage A A WARNING The opening of covers or removal of parts might expose live parts and accessible terminals which can be dangerous AA WARNING Any interruption of protective earth conductors or disconnection of the protective earth terminals inside or outside of the gaussmeter can create a dangerous condition ZAwarnic The hall probe is a non contact measuring device The probe is not to contact a surface which exceeds a voltage of 30V r m s 42 4V peak or 60V d c AN WARNING Replace the battery only with a Powersonic 1220 or F W Bell I N 335635 Installing the wrong type battery could cause damage fire or an explosion AN All input and output voltage except line mains are less than 20 volts A CAUTION For continued protection replace the fuse wi
3. 3 kohms 3 V to 15 V 3 3 k ohms 15 ft 4 5 meters Utilization of the serial port permits the gaussmeter to control a remote terminal or printer device This is particularly useful if the the user and gaussmeter must be physically separated by some distance or if the user wishes to have a hard copy of all gaussmeter activity The terminal printer may be connected directly to the gaussmeter or indirectly through a modem following the electrical connections described above The RS 232 characteristics of both devices must match in order for successful communication to take place Since the characteristics of the gaussmeter are fixed at the factory the terminal printer must be capable of having its characteristics adjusted to match 10 MODEL 9200 9000 m SERIES GAUSSMETERS SECTION ill continued Field Measurement Operations Whenever field measurements are taking place the gaussmeter will transmit a continuous listing of field measurements and status in a formatted ASCII character stream as shown in Figure III B Initially a FORMFEED FF control character is transmitted If a printer is connected this should cause the paper feeder to advance to the top of the next page l a terminal is connected this usually clears the screen The FF is followed by CARRIAGE RETURN CR and a LINEFEED LF Then a three line header is printed Each line is followed by a CR and LF A second LF provides the blank line between data
4. 2 Remove the two screws holding the rear RS 232 filler panel 3 Install the 25 position female D connector from the inside of the rear panel Secure the connector with two screwiocks and two 4 40 X 1 4 KEPS nuts KEPS nuts should be mounted on the inside 4 Connect the 3 position connector to J4 connector located at the rear of the base board next to the power transformer 5 Replace the top cover then the two shrouds Secure the shrouds with the eight screws 14 WARRANTV FW BELL warrants each instrument of its manufacture to be free from defects in material and workmanship Our obligation under this warranty is limited to servicing or adjusting any instrument returned to our factory for that purpose and to replac ing any defective parts thereof This warranty covers instruments which within one year after delivery to the original purchaser shall be returned with transportation charges prepaid by the original purchaser and which upon examination shall disclose to our satisfaction to be defective If it is determined that the defect has been caused by misuse or abnormal conditions of operation repairs will be billed at cost after submitting an estimate to the purchaser reserves the right to make changes in design at any time without incurring any obligation to install same on units previously purchased This warranty is expressly in lieu of all other obligations or liabilities on the part of
5. lines The users should be aware that the serial transmission rate is much slower than the rate at which the display is updated with new readings In other words the gaussmeter does not wait for a transmission to be completed before taking another reading Readings taken curing a transmission Sequence may not appear in the next transmission F W BELL MODEL 9200 GAUSSMETER VERSION 1 0 Reading Relative 1 667 kG 55 33 G 1 547 kG 445 28 G 245 6 G Range Auto Peak Probe Type Batt 2kG OFF ON BULK 1X OK 2kG OFF ON BULK 1X OK 200 G ON OFF BULK 1X OK F W BELL MODEL 9200 GAUSSMETER VERSION 1 0 Heading Relative 4 244 8 G 245 9 G 245 6 G Range Auto Peak Probe Type Batt 200 G ON OFF BULK 1X OK 200 G ON OFF BULK 1X OK 200 G ON OFF BULK 1X LOW Figure lil B Sample Terminal Display or Printer Output 11 MODEL 9200 7009 SECTION IV IV A INTRODUCTION The MODEL 9200 Gaussmeter is a microprocessor controlled dc coupled gaussmeter designed to accurately measure magnetic fields in the 10 MODEL 9200 milligauss to 20 kilogauss range at frequencies up to 10 kHz The following E THEORY OF sections and Figure IV A describe and illustrate the theory of operation of the OPERATION MODEL 9200 To 200 kilogauss with a 10X probe IV B POWER SUPPLV The power supplv section of the MODEL 9200 consists of a balanced full wave rectified filtered power supply followed b
6. ELD MEASUREMENT OPERATIONS DISPLAY INDICATORS SECTION IV MODEL 9200 THEORV OF OPERATION IV B Iv D Iv E IV F BLOCK DIAGRAMS WARRANTV MODEL 7 9200 9000 SERIES GAUSSMETERS MODEL 9200 SPECIFICATIONS RANGES RESOLUTION RANGES RESOLUTION PROBES GAUSS TESLA GAUSS TESLA 2 200 1 mG 1 ul DIX 20 G 2 10 m 1 gf 01X 1X 200 G 20 mM 100 mG 10 uT 01X 1X 10X 2 200 1 6 100 uT 1X 10X 20 KG 2 T 10 G 1 1X 10X 200 kG 20 T 1006 10 mM 10X dc ACCURACY Displayed dc ACCURACY Analog Output ac ACCURACY For all displayed ranges and analog output Sine Wave Input gt 10 of Full Scale ANALOG OUTPUT OUTPUT NOISE 20G 0 5 of Reading 16 Counts 2006 200kG 0 5 of Readina 2 Counts of of Ranges Reading Full Scale 2G 20G 0 5 0 5 200 G 200 kG 0 5 0 3 of Full Scale dc 9 analog output only 1 10 49 1 50 99 2 100 499 2 3 4 Frequency Hz 500 999 1k 10k Accuracies specified for 23 C 5 C WARM UP TIME 30 MINUTES Accuracies do not include probe errors Recommended calibration cycle is one year Output Voltage 2 0 V Full Scale Response Time 50 5 approximately F S Step Input Source Impedance lt 100 Q Termination Standard BNC Connector 35 dB below Full Scale rms on 20G Range 55 dB below Full Scale rms on 200G to 20 kG Range TEMPERATURE 20 3
7. FW BELLy ING and F W BELL TNS neither assumes authorizes any other person to assume for them any other liability in connection with the sales of FW BELL ING instruments DAMAGE IN SHIPMENT The instrument should be examined and tested as soon as it is received if it does not operate properly or is damaged in any way immediately file a claim with the carrier The claim agent will provide report forms A copy of the completed form should be forwarded to us We will then make the necessary arrangements for repair or replacement All correspondence concerning this instrument should include model and serial numbers SHIPPING INSTRUCTIONS Contact the factory for Return Material Authori zation number prior to shipping All returns must be shipped to the factory with an RMA st Use the original shipping carton and inserts if possible or pack the instrument in a sturdy con tainer and surround the entire instrument with two to three inches of shock absorbing material Ship to division ef Bee Veedneloaies F W BELL INE Repair Department 6120 Hanging Moss Road Orlando FL 32807 Phone 407 678 6900
8. ON H continued Gaussmeter Preparation KEYWAY PROBE CONNECTOR INSTRUMENT RECEPTACLE T Figure Il B Probe Connector and Receptacle Il C POWER UP Locate the power switch on the front panel and depress the side marked 1 During power on all display segments are momentarily flashed on then off Then the display will seek a number between 1 052 and 1 817 This is an internal calibration number determined by the probe attached Then CAL and a flashing ZERO PROBE annunciator will appear on the display H D ZERO PROBE Insert the probe into the zero gauss chamber in the front panel of the gaussmeter This protects the probe from the effects of stray fields and permits any probe offsets to be zeroed out Depress and release the ZERO pushbutton When the zeroing process is complete the MODEL 9200 will display approximately 0 00 The instrument will return to the previously selected settings Atthis point the instrument control can be accomplished via the front panel pushbuttons MODEL 9200 9000 SERIES GAUSSMETERS SECTION 111 FIELD MEASUREMENT OPERATIONS DISPLAY INDICATORS The display in the MODEL 9200 provides the following information 1 POLARITY The area immediately to the left of the numerical reading indicates the polarity of the reading No sign indicates that the North magnetic field flux lines are entering a transverse probe on the side of the probe on which the F W Bell logo appears o
9. hich connects either the probe signal or a reference signal to the amplifier stages which follow The availability of the reference signal permits the microprocessor to generate a correction factor to compensate for any offsets which may be generated by the probe or amplifiers initial amplification is provided by a preamplifier stage with a gain of approximately forty Also present in this section is a digitally controlled offset adjusting circuit which is used to correct any probe dc offset which may have been detected during the PROBE ZERO operation Following the preamplifier are the digitally controlled range switch the remainder of the amplification and the digitally controlled calibration circuit This latter circuit is used to fine tune the gain in the signal channel to provide the calibrated 2V full scale output The output of the calibration control drives another digital Switch which directs the signal to the true rms detector and then to the A D converter in the ac mode or directly to the A D converter in the dc mode 12 MODEL 9200 7008 SECTION IV continued IV D DIGITAL SECTION Theorv of Operation Communication between the analog and digital sections of the MODEL 9200 is accomplished via the O bus On the digital side of the bus are onnected the kevboard its buffer and the 10 MHz 80C31 microprocessor with its Support circuitry Inputs from the front panel pushbuttons are directed to the microprocessor via the bus Also c
10. ivated or deactivated by momentarily pressing and releasing the PEAK pushbutton The peak reading is held indetinitely and is reset only when the feature is deactivated 9 AUTORANGE Indicates that the instrument is in the AUTORANGE mode 10 GAUSS or K GAUSS Indicates either k gauss or gauss depending on range 11 mTESLA or TESLA Indicates either m tesla or tesla depending on range MODEL 9200 9000 SERIES GAUSSMETERS SECTION continued Field Measurement Operations o Tij PROBE AC DC PEAK HOLO l E E eee GAUSS l LA m psa zr ZERO PROBE READING Figure III A MODEL 9200 Display II B ANALOG OUTPUT A BNC connector on the rear panel provides a means for the user to display the actual magnetic field waveform On a scope the output level for a dc field is 2 volts de for a full scale input For a full scale ac sinusoidal field the output waveform will be 5 657 volts peak to peak RS 232 OUTPUT OPERATION As an option the MODEL 9200 can be equipped with an RS 232 output port Specifications for this port are as follows Baud Rate 1200 Stop Bits 1 Parity None Character Length 8 Bits Connector Type Typical TX Output Voltage Minimum TX Output Load RX Input Voltage Range Typical RX Input impedance Maximum Cable Length Standard 25 pin D Pin2 RX receive data Pin3 TX transmit data 7 Signal ground 3 7 V
11. lock non magnetic connector that mates with selected F W Bell fourth generation Hall probes This is a multi purpose receptacle that accepts an international instrumentation line cord The middle ground contact is connected to the chassis This receptacle also contains the line fuse storage space for a spare fuse and a line voltage selector mechanism WARNING See SECTION I before applying power to the gaussmeter or damage may result Optional 25 pin D type female connector for RS 232 communications talker only Standard BNC connector which provides a calibrated output signal which is an accurate representation of the input waveform A full scale input signal will be represented by a 2 volt output at this connector Label identifying the model number serial number and line power data MODEL 9200 7000 SECTION continued General Description Figure l A MODEL 9200 Front Panel Figure l B MODEL 9200 Rear Panel MODEL 9200 9000 SERIES GAUSSMETERS SECTION Il MODEL 9200 GAUSS METER PREPARATION Il A POWER RECEPTACLE HEAD THIS CAREFULLY The MODEL 9200 gaussmeter has been factory configured to operate on a line voltage of 115 Vac If operation at 230 Vac is required pertorm the following steps or damage will resuit 1 See Figure Il A This is the power cord receptacle designed to accept an internati
12. o the Zero Gauss Chamber before starting this sequence 5 RANGE PUSHBUTTON Momentarv contact pushbutton switch used to select the desired full scale range of the MODEL 9200 On power up the MODEL 9200 will be in the AUTORANGE mode Other available ranges are 20 G 200 G 2 kG and 20 kG using a 1x probe or 200 G 2 kG 20 kG and 200 kG using a 10x probe MODEL 9200 J000 SERIES GAUSSMETERS SECTION continued General Description 6 MODE PUSHBUTTON 7 PEAK PUSHBUTTON 8 RELATIVE PUSHBUTTON 9 DISPLAY LIGHT PUSHBUTTON 10 PROBE CONNECTOR REAR PANEL 11 POWER RECEPTACLE FUSE HOLDER LINE VOLTAGE SWITCH 12 RS 232 PORT 1 CONNECTOR 13 ANALOG OUTPUT 4 INFORMATION LABEL Momentary contact pushbutton switch used to select the desired operating mode of the MODEL 9200 On power up the MODEL 9200 will be in the DC GAUSS mode The MODE pushbutton can be used to select the AC GAUSS AC TESLA DC GAUSS or DC TESLA mode Momentary contact pushbutton switch used to toggle the PEAK HOLD function on or off When the function is toggled ON the words PEAK HOLD will appear on the display Momentary contact pushbutton switch used to toggle the RELATIVE measurement function on or off When the function is activated the words ZERO READING will appear on the display Momentarv contact pushbutton switch used to turn the display lights on and off Nine pin twist
13. of Reading C From 0 C to 50 C Probe not included EFFECTS FREQUENCY RANGE dc Mode dc Displaved ac Mode 10 Hz to 10 kHz FREQUENCY RANGE dc to 10kHz Analog Output TEMPERATURE RANGE Operating 0 Cto 50 C Storage 20 C to 460 C FRONT PANEL DISPLAY Type 3 1 2 digit LCD Viewing Area 2 1 2 6 35 cm W 0 7 1 78 cm H POWER ac Volts 105 125 or 210 250 Frequency 80 60 Hz 50 60 Hz Current EA 5 MODEL 9200 2000 INTERNAL BATTERV Sealed lead acid Eagle Picher CF 12 V2 YUASA NP 1 9 12 or equivalent Note Recharging circuit built in BATTERY LIFE 8 hours Under normal use after full recharge FRONT PANEL ZERO GAUSS CHAMBER Cavity Size 0 344 in 0 9 cm LD 2 0 in 5 1 cm D Attenuation 80 dB in a 300 G field COMMUNICATION PORT RS 232 Standard 25 pin D connector optional Talker only BAUD RATE 1200 PARITY NONE STOP BITS 1 CHARACTER LENGTH 8 WARM UP TIME 30 minutes SIZE 8 8 22 35 cm W 4 5 11 43 cm H including feet 11 27 94 cm D WEIGHT Net 7 lbs 10 oz 3 46 kg Shipping 15 lbs 2 oz 6 86 kg MODEL 9200 9000 SERIES GAUSSMETERS SIMPLIFIED OPERATING INSTRUCTIONS FOR THE MODEL 9200 GAUSSMETER 1 Check the rear panel power receptacle to insure that the voltage showing is the voltage you will be using 115 volts ac or 230 volts ac If itis necessary to change this setting refer to Section Il A for further information 2 Connect the probe to
14. onal instrumentation line cord This assembly also contains the line fuse and voltage selector Remove the line cord 2 Near the top of the assembly is a slot Insert a narrow screwdriver blade into the slot and gently release the access door the door will not open unless the line cord is removed The door will swing down 3 Remove the voltage selector drum marked 115 VAC by pulling straight out 4 Remove both fuse holders marked with a by pulling straight out The left hand holder is used to hold a spare fuse The right hand fuse holder is the actual in circuit fuse The gaussmeter is shipped with a 230 Vac 1 8 A fuse in the spare location and a 115 Vac 1 4 A fuse in the active location Reverse the positions of the holders and reinstaii making sure that the 7 points to the right 5 Rotate the voltage selector drum to read 230 VAC and reinstall 6 Close access door The 230 VAC legend should be visible through the access door window Reinstall the line cord ACCESS SLOT Figure Il A Rear Panel Power Receptacle Il B PROBE INSTALLATION Install the probe connector so that the molded kevs in the connector bodv line up with the keyways in the front panel mating connector Figure 11 8 Push the connector in until the threaded sieeve makes contact with the receptacle Rotate the sleeve clockwise to secure the connector to the receptacle MODEL 9200 2000 SERIES GAUSSMETERS SECTI
15. onnected to the processor are the 24K bytes of system memory the display controller and display combination and the RS 232 port The digital portion of the MODEL 9200 also includes a circuit to detect the presence or absence of a probe and to signal the processor accordingly 5 85 232 LIHE INPUT Figure IV A MODEL 9200 Block Diagram GND IV E 4TH GENERATION HALL GENERATOR PROBE The F W Bell 4th generation Hall generator probes are derived from their proven 3rd generation counterparts Each probe is terminated in a 9 pin circular non magnetic connector The connector houses a 512 byte non volatile EEPROM device programmed with the probe s calibration factor mode number information and serial number This information is used by the gaussmeter during its calibration routine Also included in the connector is a provision for the installation of a linearizing resistor Four of the connector pins interface to the Hall device itself Another four pins interface to the EEPROM The remaining pin is used by the processor to sense whether or not a probe is connected 13 MODEL 9200 9000 SERIES GAUSSMETERS SECTION IV continued Theorv of Operation IV F INSTALLATION OF RS 232 OPTION CAUTION Disconnect cord from power before servicing Do not short out internal battery terminals 1 Remove the front and rear plastic shrouds by removing the eight screws Carefully lift off the top cover
16. r are entering the tip of an axial probe parallel to the probe s axis The minus sign appears for an opposite field condition 2 READING The numerical reading indicates the actual value of the dc field the true rms value of an ac field or in the PEAK HOLD mode the largest value of a dc field or the maximum rms value of an ac field depending on the operating mode 3 OVER The OVER block is illuminated when the field being measured is greater than the instrument range setting The readout will also display 1999 To obtain a useable reading change the range to a higher range or to AUTORANGE 4 BATTERY LOW INDICATOR The BATT block illuminates when the internal battery voltage is insufficient tor accurate measurements 5 PROBE When a probe is not plugged into the instrument the word PROBE will blink and the phrase ERR will appear 6 ZERO PROBE This indicator ZERO PROBE will flash when the probe is ready to be zeroed upon power up or whenever a probe zero operation is in progress 7 ZERO READING This feature offers the ability to suppress a large field reading so that small variations in the field can be observed It is activated or deactivated by momentarily depressing and releasing the RELATIVE pushbutton 8 AC DC PEAK HOLD In the dc peak hold mode the display indicates the largest peak field measured by the probe In the ac peak mode the MODEL 9200 displays the maximum rms field present This feature is act
17. s as low as 0 010 gauss 1 p tesla or as high as 199 9 Kilogauss 19 99 tesla at frequencies up to 10 kHz can be measured simply accurately and reliably Primary features of the MODEL 9200 include PEAK HOLD AUTORANGING and RELATIVE operation as well as GAUSS or TESLA readout and an optional RS 232 communications port talker only All information is displayed on a custom formatted 3 1 2 digit liquid crystal display LCD Unit power is derived from an internal rechargeable battery pack Front panel pushbuttons allow easy control of all gaussmeter functions I B FUNCTIONAL DESCRIPTION Figures l A and I B depict the MODEL 9200 s front and rear panels respectively The gaussmeter is housed in a 4 5 11 43 cm high x 8 8 22 35 cm wide x 11 0 27 94 cm deep case featuring an adjustable carrying handle which can also be used to support the MODEL 9200 at a variety of convenient viewing angles FRONT PANEL 1 DISPLAY 2 5 6 35 cm W x 0 7 1 78 cm H custom formatted display with 0 4 1 02 cm numerals and user activated lighting 2 POWER SWITCH Rocker type power switch with international legends O OFF 1 ON 3 ZERO GAUSS CHAMBER Recessed double wall mu metal chamber used to shield the probe from stray magnetic fields during the PROBE ZERO operation Attenuation is 80 dB in a 300 G field 4 ZERO PUSHBUTTON Momentary contact pushbutton switch used to initiate the PROBE ZERO sequence Probe should be inserted int
18. th the same type 5 X 20mm slow blow 125mA at 250V for 230 volt operation or 250mA at 250V for 115 volt operation EMC APPLICATION NOTE Use only a high quality double shielded cable for the RS 232 connection Keep the cable length less than 3 meters Long cables gt 3m with insufficient EMI shielding can cause excessive emissions or may be susceptible to external interference UN 01 217 Rev A I N 359201 Page 1 of 3 9200CE Manual Supplement INSTRUMENT PREPARATION place behind Safely A WARNING FOLLOW THESE INSTRUCTIONS OR DAMAGE AC POWER CONNECTION MAY RESULT Figure 1 0 depicts the rear panel power module containing the line cord receptacle line fuse and the voltage programming drum You can select operation from either 115 or 230 Vac service The selected voltage will appear through the window in the module If this does not match your service do the following 1 Turn the power switch to the OFF o position and remove the line cord 2 Insert a narrow flat screwdriver behind the access slot and gently pry open the access door Flip the door down 3 Grasp the voltage programming drum and pull it straight out of the module 4 Rotate the drum to show the correct voltage then insert the drum into the module 5 Reverse the position of the fuses 6 Close the access door and insert the line cord MT us SLOT ACCESS DOOR TE VOLTAGE PROGRAMMING in closed position 115 Vac 115 Vac
19. the connector on the front panel of the gaussmeter 3 Connect power to the MODEL 9200 and turn the instrument on by locating the power switch on the front panel and depressing the side marked 1 4 The Gaussmeter will initiate a self calibration of internal circuitry This takes about 20 seconds Following this the phrase CAL will appear accompanied by a flashing Probe Zero Annunciator 5 insert the probe into the ZERO GAUSS CHAMBER on the front panel 6 Prior to taking readings it is necessary to zero the gaussmeter This is done by depressing the ZERO pushbutton The word CAL will disappear and after the instrument zero s on each range the PROBE ZERO annunciator will disappear 7 Now the Model 9200 is ready to measure magnetic fields Allow the Gaussmeter to warm up for 30 minutes to obtain tne greatest accuracy For complete details on any of the above procedures consult appropriate sections within the manual Also for information on other features consult the table of contents to locate the proper sections MODEL 9200 9000 SERIES GAUSSMETERS SECTION GAUSSMETER DESCHIPTION l A INTRODUCTION The MODEL 9200 gaussmeter is a microprocessor based instrument designed to facilitate the measurement of magnetic fields in a wide variety of applications Either steady state dc or alternating ac fields can be measured When matched with the appropriate F W Bell fourth generation probe field
20. y a 5 volt regulator and a 15 volt converter Also powered from the raw supply is the charging circuit for the built in rechargeable battery The charging circuit is designed so that as long as the unit is connected to line voltage the battery is being trickle charged Operation from 115 Vac or 230 Vac line voltage is selected by programming the line voltage input receptacle on the rear panel of the gaussmeter This reconfigures the electrical connection of the transformer to be compatible with the available line voltage This receptacle also contains the line fuse The center terminal of the receptacle is tied to the metal frame of the chassis IV C ANALOG SECTION The analog section of the MODEL 9200 consists of circuitry to provide a bias current for the probe control the source of the input signal correct probe generated offset errors amplifv the signal switch ranges calibrate the signal channel accomplish the rms conversion of ac signals and convert the processed analog signal to digital form The bias current section provides under processor control either 10 mA or 100 mA of dc bias current to the probe Which tevel is provided is determined by information obtained by the processor directly from the probe itself When a properly biased probe is exposed to a magnetic field a signal voltage is generated and delivered to the gaussmeter via the probe connector This signal then enters a solid state switching circuit w
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