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JOHNSON MODEL GSM-10S
RADIATION MONITOR OPERATIONS & MAINTENANCE MANUAL
SECTION CONTENTS
1----------------------------------------- WARNING HIGH VOLTAGE 2----------------------------------------- SPECIFICATIONS 3---------------------------------------DESCRIPTION
4------------------------------------------------THEORY OF OPERATION
5-------------------------------------------OPERATING CONTROLS 6------------------------------------OPERATING INSTRUCTIONS 7----------------------------------MAINTENANCE 8---------------------------------PARTS LIST 9----------------------------------SCHEMATICS
Wm B. Johnson & Associates Inc.
POBox 472 216 Edgar Ave. Ronceverte. West Virginia 24970
Telephone: 304-645-6568
Fax: 304-645-2182
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1.0
WARNING HIGH VOLTAGE
High voltage is used in the operation of this equipment. Severe shock may result if personnel fail to observe safety precautions. Learn the areas containing HIGH VOLTAGE in each piece of equipment. Be careful not to contact HIGH VOLTAGE when installing or working on this equipment. When servicing, ground points of high potential before touching them.
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FRONT VIEW FIGURE 1 PAGE 2
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SPECIFICATIONS
INPUT SENSITIVITY ----------------------
0.05 V-PP MAXIMUM 5V-PP
MINIMUM - NEGATIVE PULSES RANGES ------------------------------------------------------ 3 RANGES - X100, X10 &X1 METER SCALE IS 0 - 500 CPM EACH RANGE HAS SEPARATE CALIBRATION CONTROLS ± 3% OF FULL SCALE
LINEARITY --------------------------------------
RESPONSE TIME --------------------------
DRIFT --------------------------------------------
4 SECONDS -> 20 SECONDS
LESS THAN 5%
TEMPERATURE COEFFICIENT ------------
LESS THAN 5%
HIGH VOLTAGE --------------------------------------ADJUSTABLE FROM 500-1500 VDC REGULATED ± 1%
LOW VOLTAGE ------------------------------------
+8.5 VDC REGULATION ± 0.5 %
BATTERIES ------------------------------------------------2 -1.5 VDC "D" CELL ALKALINE BATTERY OPERATION -------------------------- 200 HRS NOMIAL
2.5" SCALE - RUGGIZIDED METER MOVEMENT CALIBRATED 0500 CPM - LINEARITY ± 3%
METER -----------------------------------------------------
RANGE ~~~~----------------------------------------------- 5 DEC CENT. TO 60 DEG CENT. HUMIDITY RANGE ------------------------------- 5 - 95% NON CONDENSING WEIGHT ------------------------------------------ 3 1/4 POUNDS INCLUDING BATTERY HOUSING -------------------------------------- 16 Ga. ALUMINUM WITH HEAVY DUTY CARRYING HANDLE HOUSING FINISH -------------------------------- BLUE CATALYZED POLYURETHANE WASH PRIMER UNDERCOAT
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3.0 DESCRIPTION
The Johnson Model GSM-10S is a ruggedized, portable rate meter designed to provide years of dependable service under lab and field conditions. A durable panel meter displays the detector signal in counts per minute and condition of the internal "D" size batteries. The 3 linear ranges are calibrated in 0-500, 0-5,000 & 0-50,000 counts per minute. The circuitry has very low drift over a wide range of environmental conditions due to conservative design, low temperature coefficient components and tight regulation of the 8.5 vdc & high voltage power supplies. Over range meter readings can be "zeroed" instantly by a push button switch on the front panel. Response time is variable from 4 -2 0 seconds for 90% of full scale. A high efficiency speaker is provided to indicate the relative strength of the radiation field at the detector and can be switched on or off from the front panel. The heavy duty cast aluminum top and bottom housings are secured together by heavy duty stainless steel latches with a "O" ring seal.
4.0 THEORY OF OPERATION
The GSM-10S utilizes field proven Circuitry, conservative design and heavy duty components to assure reliability and dependable senvice. The electronic circuitry is located on a industrial grade printed circuit board for good accessibility and reliability. Interconnections have been minimized and carefully routed to increase the reliability of the instrument. Separate non-interacting controls are provided to calibrate each range, low voltage power supply and high voltage supply. Low coefficient, well regulated internal power supplies provides clean, well regulated DC power to all of the components and assures stable operation over a wide range of conditions. The detector signal is amplified to a useable level through part of Ul. The remaining part of Ul and part of U2 are a Schmitt trigger that provides a constant amplitude pulse to part of U3. U3 converts the signal pulse to a constant area pulse for integration into a precision analog signal that is proportional to the incoming signal. Calibration of each range is controlled by potentiometers P3 P5. These potentiometers control the calibration of each range by adjusting the width of the constant area pulse from U3. The constant area pulses from U3 are integrated by U4 and the associated circuitry into a precision analog signal that is proportional to the detector signal. The precision analog signal is current amplified by U5 to operate the 1 made full scale panel meter. The constant amplitude pulse from U1/U2 is also routed to the other half of 113. This part of U3 generates a wider pulse that is processed through Q8 (audio amplifier) to the high efficiency speaker to produce an audible "click" for each pulse from the detector. The highly regulated LOW VOLTAGE supplied to all of the circuitry is generated by a high efficiency oscillating power supply. The major components of the 8.5 vdc power supply are part of U6, Q4 and T2. PI is utilized to adjust the voltage of this power supply. The HIGH VOLTAGE is also generated by a oscillating power supply. The major components of the high voltage supply are by part of U6, Q7 and Tl. P2 is utilized to adjust the voltage of the high voltage supply. Both power supplies utilize low temperature components and feedback to assure tight regulation and low temperature coefficient. The BAT test position of the front panel connects the battery voltage through R41 to the panel meter to indicate the battery condition.
5.0 OPERATING CONTROLS & INDICATORS - FRONT PANEL
5.1 CONTROLS - MAIN FUNCTION SWITCH CONTROL SETTING FUNCTION
INSTRUMENT
OFF --------------------------------------- ALL POWER DISCONNECTED TO THE
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5.1 CONTROLS - MAIN FUNCTION SWITCH - CONTINUED
BAT ----------------------------PANEL METER CALIBRATED bat ok INDICATES IS BATTERY VOLTGE IS SATISFACTORY FOR NORMAL OPERATION. METER SCALE IS CALIBRATED 0 - 500 CPM IN 50 DIVISIONS. METER READING IS MULTIPLIED XI FOR ACTUAL READING IN CPM. FULL SCALE IS 500 CPM METER SCALE IS CALIBRATED 0 - 500 CPM IN 50 DIVISIONS. METER READING IS MULTIPLIED X10 FOR ACTUAL READING IN CPM. FULL SCALE IS 5,000 CPM METER SCALE IS CALIBRATED 0 - 500 CPM IN 50 DIVISIONS. METER READING IS MULTIPLIED X100 FOR ACTUAL READING IN CPM. FULL SCALE IS 50,000 CPM
X 1 --------------------------------------
X 10 --------------------------------------
X 100 ------------------------------------
5.2 CONTROLS - RESET SWITCH
INSTANEOUSLY RESETS THE RATEMETER PANEL METER TO ZERO
5.3 CONTROLS - RESPONSE
ADJUSTS THE TIME CONSTANT (SPEED OF RESPONSE) OF THE METER FROM 4 - 20 SECONDS FOR 90% OF FULL SCALE.
5.4 CONTROLS - AUDIO SWITCH
TURNS THE AUDIBLE SIGNAL INDICATING THE RADIATION STRENGTH AT THE DETECTOR ON OR OFF.
5.5 CONNECTORS FRONT PANEL
5.5.1 PROBE - BNC FEMALE - INPUT TO THE RATEMETER FROM THE PROBE 5.5.1 PHONE - BNC FEMALE - OUTPUT PULSES TO OPERATE HEADPHONES
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CALIBRATION CONTROLS AND MAJOR COMPONENTS FIGURE 2
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7.0 MAINTENANCE
A. GENERAL - Preventive and corrective maintenance procedures are presented in the section. Maintenance must be performed by personnel qualified to service radiation monitoring equipment, not only to assure the maintenance is performed safely, but that the instrument is correctly calibrated.
WARNING
Up to 1500 vdc can be present on center contact of the front panel DETECTOR CONNECTOR, Although the voltage is current limited, physical contact will result in a very uncomfortable electric shock. The front panel FUNCTION switch must be in the OFF position for at least 30 seconds before connecting or disconnecting the external radiation detector cable.
7.1 TEST INSTRUMENTS REQUIRED
* VTVM capable of accurately reading 0 - 10 vdc to 0.010 vdc with input impedance of at least 20 meg Q . * High Voltage voltmeter capable of reading 1500 vdc with input impedance of at least 100 meg £2.
* Oscilloscope with at least 20 Mhz band pass and 0.10 v-pp input sensitivity.
* Pulse Generator with variable pulse amplitude control. Range 0 - 50,000 pulses per minute (833.33 pps) variable from 0.250 v-pp to 5 v-pp. Accuracy 1% or better of indicated output. Pulse generator must be capable of operation with 1500 vdc present at the output of the generator. 3-4 foot length of coaxial cable (Rg 58) with male BNC connectors on each end. Refer to FIGURES 1& 2 and controls.
* *
7.2 TEST PROCEDURES
7.2.1 ADJUST HIGH VOLTAGE POWER SUPPLY 7.2.1.1 Remove TOP housing of the GSM-10S by removing the latches located on each end of the housing..
7.2.1.2 Connect the HIGH VOLTAGE voltmeter to the PROBE INPUT BNC receptacle
7.2.1.3 Adjust the MAIN SELECTOR switch to the X100 range. 7.2.1.4 Adjust potentiometer P2 until the HIGH VOLTAGE reads 900 vdc ±20 vdc 7.2.1.5 This completes adjustment of the High Voltage power supply.
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7.2.2 RATEMETER ADJUSTMENT & CALIBRATION
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7.2.2.1 Remove TOP housing of the GSM-10S by removing latches located on the end of the housing. 7.2.2.2 Connect the PULSE GENERATOR to the INPUT BNC receptacle. 7.2.2.3 Adjust the MAIN SELECTOR switch to the X100 position. 7.2.2.4 Adjust the PULSE GENERATOR output to 50,000 cpm with an amplitude of 0.50 vpp. Increase the amplitude of the output pulse to 5.0 v-pp. Meter reading should remain constant. 7.2.2.5 Adjust potentiometer P5 until the panel meter reads 50,000 cpm. 7.2.2.6 Adjust the MAIN SELECTOR switch to the X10 position. 7.2.2.7 Adjust the PULSE GENERATOR output to 5,000 cpm with an amplitude of 0.50 v-pp. 7.2.2.8 Adjust potentiometer P4 until the panel meter reads 5,000 cpm. Increase the amplitude of the output pulse to 5.0 v-pp. Meter reading should remain constant. 7.2.2.9 Adjust the MAIN SELECTOR switch to the XI position. 7.2.2.10 Adjust the PULSE GENERATOR output to 500 cpm with an amplitude of 0.50 v-pp.
7.2.2.11 Adjust potentiometer P3 until the panel meter reads 500 cpm. Increase the amplitude of the output pulse to 5.0 v-pp. Meter reading should remain constant. 7.2.2.12 This completes calibration of the rate meter.
7.2.3 RAPID TROUBLE SHOOTING GUIDE GENERAL: The RAPID TROUBLE SHOOTING GUIDE is designed to provide a quick method of determining the overall problems that exist in the major sections of this instrument. The guide is not all inclusive and is best utilized as a diagnostic aid prior to undertaking the repair of the instrument. The sections covered by the RTS are: 7.2.3.1 8.5 VOLT POSITIVE POWER SUPPLY 7.2.3.2 HIGH VOLTAGE POWER SUPPLY 7.2.3.3 PANEL METER MOVEMENT 7.2.3.4 AUDIO OUTPUT
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