LUDLUM MEASUREMENTS LUDLUM MODEL 3-8 SURVEY METER Instruction Manual

: June 12, 2024
: LUDLUM MEASUREMENTS

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LUDLUM MODEL 3-8 SURVEY METER
Ludlum Model 3-8 Survey Meter
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LUDLUM MODEL 3-8 SURVEY METER

Ludlum Model 3-8 Survey Meter

Section	Page	Content
Introduction	1	Any Geiger-Mueller (G-M) detector offered by Ludlum

Measurements will operate on this unit as well as any scintillation
type detector. The instrument is typically set at 900 volts for G-M
tube operation. For special requirements of G-M or scintillation
detectors, the instrument high voltage may be adjusted from 400 to
1500 volts.
Getting Started| 2| Unpacking and Repacking

Important!
If multiple shipments are received, ensure that the detectors and
instruments are not interchanged. Each instrument is calibrated to
specific detector(s), and therefore not interchangeable.

To return an instrument for repair or calibration, provide
sufficient packing material to prevent damage during shipment. Also
provide appropriate warning labels to ensure careful
handling.

Every returned instrument must be accompanied by an Instrument
Return Form, which can be downloaded from the Ludlum website at
www.ludlums.com. Find the form by clicking the Support tab and
selecting Repair and Calibration from the drop-down menu. Then
choose the appropriate Repair and Calibration division where you
will find alink to the form.

| 2-1| Battery Installation

Ensure the Model 3-8 range selector switch is in the OFF position.
Open the battery lid by pushing down and turning the quarter-turn
thumbscrew

| 2-2| Connecting a Detector to the Instrument

Caution!
The detector operating voltage (HV) is supplied to the detector via
the detector input connector. A mild electric shock may occur if
you make contact with the center pin of the input connector. Switch
the Model 3-8 range selector switch to the OFF position before
connecting or disconnecting the cable or detector.

LUDLUM MODEL 3-8 SURVEY METER
April 2016 Serial Number 234823 and Succeeding
Serial Numbers

Table of Contents

Introduction

1

Getting Started

2

Unpacking and Repacking

2 -1

Battery Installation

2 -1

Connecting a Detector to the Instrument

2 -2

Battery Test

2 -2

Instrument Test

2 -2

Operational Check

2 -3

Specifications

3

Identification of Controls and Functions

4

Safety Considerations

5

Environmental Conditions for Normal Use

5 -1

Warning Markings and Symbols

5 -1

Cleaning and Maintenance Precautions

5 -2

Calibration and Maintenance

6

Calibration

6 -1

Exposure Rate Calibration

6 -1

CPM Calibration

6 -2

Establishing an Operating Point

6 -3

Maintenance

6 -4

Recalibration

6 -5

Batteries

6 -5

Troubleshooting

7

Troubleshooting Electronics w hich utilize a

GM Detector or Scintillator

7 -1

Troubleshooting GM Detectors

7 -3

Troubleshooting Scintillators

7 -4

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Technical Theory of Operation
Low Voltage Supply High Voltage Supply Detector Input Amplifier Discriminator Audio Scale Ranging Meter Drive Meter Reset Fa st /Slow T im e Const a nt
Recycling
Parts List
M ode l 3 -8 Surve y M e t e r Main Board, Draw ing 464 × 204 Wiring Diagram, Draw ing 464 × 212
Draw ings and Diagrams

8
8 -1 8 -1 8 -1 8 -1 8 -2 8 -2 8 -2 8 -2 8 -2 8 -2
9
10
1 0 -1 1 0 -1 1 0 -3
11

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Section
1

Introduction

Section 1

T he Model 3-8 is a portable radiation survey instrument with four linear ranges used in combination with a 0-500 counts per minute meter dial for an overall range of 0-500,000 counts per minute. . The instrument features a regulated high-voltage power supply, unimorph speaker with audio ON-OFF capability, fast-slow meter response, meter reset button and a six-position switch for selecting battery check or scale multiples of ×0.1, ×1, ×10 and ×100. Each range multiplier has its own calibration potentiometer. The unit body and meter housing are made of cast aluminum and the can is 0.090″ thick aluminum.
Any Geiger-Mueller (G-M) detector offered by Ludlum Measurements will operate on this unit as well as any scintillation type detector. The instrument is typically set at 900 volts for G-M tube operation. For special requirements of G-M or scintillation detectors, the instrument high voltage may be adjusted from 400 to 1500 volts.
The unit is operated with two D cell batteries for operation from 4°F (20°C) to 122°F (50°C). For instrument operation below 32°F (0°C) either very fresh alkaline or rechargeable NiCd batteries should be used. The batteries are housed in an externally accessible sealed compartment.

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Section 2

Section
2

Getting Started
Unpacking and Repacking
Remove the calibration certificate and place it in a secure location. Remove the instrument and accessories (batteries, cable, etc.) and ensure that all of the items listed on the packing list are in the carton. Check individual item serial numbers and ensure calibration certificates match. The Model 3-8 serial number is located on the front panel below the battery compartment. Most Ludlum Measurements, Inc. detectors have a label on the base or body of the detector for model and serial number identification.
Important!
If multiple shipments are received, ensure that the detectors and instruments are not interchanged. Each instrument is calibrated to specific detector(s), and therefore not interchangeable.
To return an instrument for repair or calibration, provide sufficient packing material to prevent damage during shipment. Also provide appropriate warning labels to ensure careful handling.
Every returned instrument must be accompanied by an Instrument Return Form, which can be downloaded from the Ludlum website at www.ludlums.com. Find the form by clicking the “Support” tab and selecting “Repair and Calibration” from the drop-down menu. Then choose the appropriate Repair and Calibration division where you will find alink to the form.
Battery Installation
Ensure the Model 3-8 range selector switch is in the OFF position. Open the battery lid by pushing down and turning the quarter-turn thumbscrew

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Section 2

counterclockwise ¼ turn. Install two D size batteries in the compartment.
Note the (+) and (-) marks inside the battery door. Match the battery polarity to these marks. Close the battery box lid, push down and turn the quarter-turn thumb screw clockwise ¼ turn.
Note:
Center post of a flashlight battery is positive. The batteries are placed in the battery compartment in opposite directions.
Connecting a Detector to the Instrument
Caution!
The detector operating voltage (HV) is supplied to the detector via the detector input connector. A mild electric shock may occur if you make contact with the center pin of the input connector. Switch the Model 3-8 range selector switch to the OFF position before connecting or disconnecting the cable or detector.
Connect one end of a detector cable to the detector by firmly pushing the connectors together while twisting clockwise ¼ turn. Repeat the process in the same manner with the other end of the cable and the instrument.
Battery Test
The batteries should be checked each time the instrument is turned on. Move the range switch to the BAT position. Ensure that the meter needle deflects to the battery check portion on the meter scale. If the meter does not respond, check to see if the batteries have been correctly installed. Replace the batteries if necessary.
Instrument Test
After checking the batteries, turn the instrument range switch to the ×100 position. Place the AUD ON-OFF switch in the ON position. Expose the detector to a check source. The instrument speaker should emit “clicks” relative to the rate of counts detected. The AUD ON/OFF switch will silence the audible clicks if in the OFF position. It is recommended that the

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Section 2

AUD ON/OFF switch be kept in the OFF position when not needed in order to preserve battery life.
Rotate the range switch through the lower scales until a meter reading is indicated. While observing the meter fluctuations, select between the fast and slow response time (F/S) positions to observe variations in the display. The S position should respond approximately 5 times slower than the F position.
Note:
The slow response position is normally used when the instrument is displaying low numbers which require a more stable meter movement. The fast response position is used at high rate levels.
Check the meter reset function by depressing the RES pushbutton switch and ensuring the meter needle drops to 0.
Once this procedure has been completed, the instrument is ready for use.
Operational Check
To assure proper operation of the instrument between calibrations and periods of nonuse, an instrument operational check including battery test and instrument test (as described above) should be performed prior to use. A reference reading with a check source should be obtained at the time of initial calibration or as soon as possible for use in confirming proper instrument operation. In each case, ensure a proper reading on each scale. If the instrument fails to read within ± 20% of a proper reading, it should be sent to a calibration facility for recalibration.

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Section 3

Section
3

Specifications
0
Pow er: Two D cell batteries housed in a sealed externally accessible compartment.
Battery Life: Typically greater than 2000 hours with alkaline batteries and with the AUD ON-OFF switch in the OFF position.
End-of-Battery Life Warning: At 2.1 Vdc the meter needle will drop to the edge of the BAT TEST or BAT OK area when the meter selector switch is moved to the BAT position. At 2.0 Vdc a steady audible tone will be emitted to warn the user of the low battery condition.
High Voltage: Adjustable from 400 to 1500 volts.
Threshold: Fixed at 40 mV ± 10 mV.
Meter: 2.5″ (6.4 cm) arc; 1 mA; pivot-and-jewel suspension.
Meter Dial: 0-500 cpm, BAT TEST (others available).
Meter Compensation: Temperature compensation is provided by thermistors on the main circuit board.
Multipliers: ×1, ×10, ×100, ×1K.
Range: Typically 0-500,000 counts/minute (cpm).
Linearity: Reading within 10% of true value with detector connected.
Battery Dependence: Less than 3% change in readings to battery failure indication.
Calibration Controls: Individual potentiometers for each range; accessible from front of instrument (protective cover provided).
Audio: Built-in unimorph speaker with ON-OFF switch (greater than 60 dB at 2 feet).

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Section 3

Response: Toggle switch for fast (4 seconds) or slow (22 seconds) from 10% to 90% of final reading. Reset: Push button to zero the meter. Connector: Series BNC right angle. Cable: 39-inch with BNC connector. Construction: Cast and drawn aluminum with beige powder-coat finish. Size: 6.5″ (16.5 cm) H × 3.5″ (8.9 cm) W × 8.5″ (21.6 cm) L. Weight: 3.5 lbs. (1.6 kg) including batteries.

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Section 4

Section
4

Identification of Controls and Functions

Range Selector Sw itch: A six-position switch marked OFF, BAT, ×1K, ×100, ×10, ×1. Turning the range selector switch from OFF to BAT provides the operator with a battery check of the instrument. A BAT check scale on the meter provides a visual means of checking the battery-charge status. Moving the range selector switch to one of the range multiplier positions (×1K, ×100, ×10, ×1) provides the operator with an overall range of 0 to 500,000 cpm. Multiply the scale reading by the multiplier to determine the actual scale reading.
Calibration Controls: Recessed potentiometers which are used to calibrate the individual range selections and allow for high voltage adjustment from 400 to 1500 volts. A protective cover is provided to prevent tampering.
Battery Compartment: Sealed compartment to house two D cell batteries.
RESET Button: When depressed, this switch provides a rapid means to drive the meter to zero.
AUD ON-OFF Sw itch: In the ON position, operates the unimorph speaker, located on the left side of the instrument. The frequency of the clicks is relative to the rate of the incoming pulses. The higher the rate, the higher the audio frequency. The audio should be turned OFF when not required to reduce battery drain.
F-S Toggle Sw itch: Provides meter response. Selecting the fast, F position of the toggle switch provides 90% of full scale meter deflection in four seconds. In the slow, S position, 90% of full scale meter deflection takes 22 seconds. In F position there is fast response and large meter deviation. The S position should be used for slow response and damped, meter deviation.

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Section 5

Section
5

Safety Considerations
Environmental Conditions for Normal Use
Indoor or outdoor use
No maximum altitude
Temperature range of 20°C to 50°C (4°F to 122°F). May be certified for operation from 40°C to 65°C (40°F to 150°F).
Maximum relative humidity of less then 95% (non-condensing)
Pollution Degree 1 (as defined by IEC 664).
Warning Markings and Symbols
Caution!
The operator or responsible body is cautioned that the protection provided by the equipment may be impaired if the equipment is used in a manner not specified by Ludlum Measurements, Inc.

Caution!
Verify instrument voltage input rating before connecting to a power converter. If the wrong power converter is used, the instrument and/or power converter could be damaged.

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The Model 3-8 Survey Meter is marked w ith the follow ing symbols:
CAUTION, RISK OF ELECTRIC SHOCK (per ISO 3864, No. B.3.6) designates a terminal (connector) that allows connection to a voltage exceeding 1 kV. Contact with the subject connector while the instrument is on or shortly after turning off may result in electric shock. This symbol appears on the front panel.
CAUTION (per ISO 3864, No. B.3.1) designates hazardous live voltage and risk of electric shock. During normal use, internal components are hazardous live. This instrument must be isolated or disconnected from the hazardous live voltage before accessing the internal components. This symbol appears on the front panel. Note the following precautions:
Warning!
The operator is strongly cautioned to take the following precautions to avoid contact with internal hazardous live parts that are accessible using a tool:
1. Turn the instrument power OFF and remove the batteries. 2. Allow the instrument to sit for 1 minute before accessing
internal components.
The “crossed-out wheelie bin” symbol notifies the consumer that the product is not to be mixed with unsorted municipal waste when discarding; each material must be separated. The symbol is placed on the battery compartment lid. See section 9, “Recycling” for further information.
Cleaning and Maintenance Precautions
The Model 3-8 may be cleaned externally with a damp cloth, using only water as the wetting agent. Do not immerse the instrument in any liquid. Observe the following precautions when cleaning or performing maintenance on the instrument:
1. Turn the instrument OFF and remove the batteries.
2. Allow the instrument to sit for 1 minute before cleaning the exterior or accessing any internal components for maintenance.

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Section 6

Section
6

Calibration and Maintenance
Calibration
Calibration controls are located on the front of the instrument under the calibration cover. The controls may be adjusted with a 1/8-inch blade screwdriver.
Note:
Local procedures may supersede the following

The instrument may be calibrated using Exposure Rate Calibration or CPM Calibration. Both methods are described below. Unless otherwise specified, the instrument is calibrated to Exposure Rate at the factory.
Note:
Measure High Voltage with a Model 500 Pulser or a High Impedance voltmeter with a high meg probe. If one of these instruments is not available use a voltmeter with a minimum of 1000 megohm input resistance.
Exposure Rate Calibration
Connect the input of the instrument to a negative pulse generator, such as a Ludlum Model 500 Pulser.
Caution!
The instrument input operates at a high potential. Connect the pulse generator through a 0.01µF, 3,000-volt capacitor, unless the pulse generator is already protected.

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Section 6

Adjust the HV control for the proper operation voltage of the detector to be used. Disconnect the Pulser and connect the detector to the instrument.
Turn the range selector switch to the ×1K position. Expose the detector to a calibrated gamma field which corresponds to approximately 80% of fullscale meter deflection. Adjust the ×1K calibration control for the proper reading.
Reposition the detector so the field corresponds to approximately 20% of full- scale meter deflection. Confirm that the meter reading is within ± 10% of the field.
Repeat this process for the ×100, ×10, and ×1 ranges.
CPM Calibration
Connect the input of the instrument to a negative pulse generator, such as a Ludlum Model 500 Pulser.
Caution!
The instrument input operates at a high potential. Connect the pulse generator through a 0.01µF, 3,000-volt capacitor, unless the pulse generator is already protected
Adjust the HV control for the proper operating voltage of the detector to be used. Adjust the Pulser negative pulse frequency to provide a meter deflection of approximately 80% of full-scale on the ×1K range. Adjust the ×1K calibration control for the proper reading.
Check the 20% scale indication of the Model 3-8 by reducing the Pulser count rate by a factor of 4. The Model 3-8 should read within ± 10% of the actual pulse rate. Decrease the pulse rate of the Model 500 by one decade and turn the Model 3-8 range selector to the next lower range. Repeat the above procedure for the remaining lower ranges.

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Section 6

Note:
In the event that any reading is not within ± 10% of the true value on any scale after any of the above calibration methods is performed, a reading within ± 20% of true value shall be acceptable- if a calibration graph or chart is provided with the instrument. Instruments that cannot meet these criteria are defective and require repair.
Establishing an Operating Point
The operating point for the instrument and detector is established by setting the instrument high voltage (HV). The proper selection of this point is the key to instrument performance. Efficiency, background sensitivity and noise are fixed by the physical makeup of the given detector and rarely vary from unit to unit. However, the selection of the operating point makes a marked difference in the apparent contribution of these three sources of count.
In setting the operating point, the final result of the adjustment is to establish the system gain so that the desirable signal pulses (including background) are above the discrimination level and the unwanted pulses from noise are below the discrimination level and are therefore not counted. The system gain is controlled by adjusting the high voltage.
Note:
Measure the high voltage with a Ludlum Model 500 Pulser. If the Pulser does not have a high voltage readout, use a high impedance voltmeter with at least 1000 megohm input resistance to measure the high voltage.
Calibration shall include response evaluations and adjustment for two points of each scale of the instrument. The points shall be separated by at least 40% of the full-scale value and should be represented by points of approximately equal distance from the mid-point of the scale. For example, 25% and 75%, or 20% and 80% could be used.
G-M Detectors: In the special case of G-M detectors, a minimum voltage must be applied to establish the Geiger-Mueller characteristic. The output pulse height of the G-M Detector is not proportional to the energy of the detected radiation. Most G-M detectors operate at 900 volts, although

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Section 6

some miniature detectors operate at 400-500 volts. Refer to the detector operating manual for specific recommendations. If a recommended setting is unavailable, plot a HV versus count rate curve to produce a plateau graph similar to the one displayed below. Adjust the HV for 2550 volts above the knee or start of the plateau. For mixed detector use, the high voltage may be tailed for both, as long as the G-M detector is operated within the recommended voltage range.
Scintillators: Scintillation type detectors have a wide gain spectrum, typically 1000:1 at a single operating point. An operating voltage versus count rate curve (plateau) must be established to determine the proper operating voltage. The operating voltage is typically set above the knee of the plateau. Plot the HV versus background and source count to produce a plateau graph similar to the one in the figure below. Adjust the HV to 25-50 volts above the knee or start of the plateau. This provides the most stable operating point for the detector.

Note:
If more than one detector is to be used with the instrument and the operating voltages are different, the HV will have to be readjusted for each detector substitution.
Maintenance
Instrument maintenance consists of keeping the instrument clean and periodically checking the batteries and the calibration. The Model 3-8 instrument may be cleaned with a damp cloth (using only water as the wetting agent). Do not immerse instrument in any liquid. Observe the following precautions when cleaning:
1. Turn the instrument OFF and remove the batteries.
2. Allow the instrument to sit for 1 minute before accessing internal components.

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Section 6

Recalibration Recalibration should be accomplished after maintenance or adjustments have been performed on the instrument. Recalibration is not normally required following instrument cleaning, battery replacement, or detector cable replacement.
Note:
Ludlum Measurements, Inc. recommends recalibration at intervals no greater than one year. Check the appropriate regulations to determine required recalibration intervals.
Ludlum Measurements offers a full service repair and calibration department. We not only repair and calibrate our own instruments but most other manufacturer’s instruments. Calibration procedures are available upon request for customers who choose to calibrate their own instruments.
Batteries The batteries should be removed any time the instrument is placed into storage. Battery leakage may cause corrosion on the battery contacts, which must be scraped off and/or washed using a paste solution made from baking soda and water. Use a spanner wrench to unscrew the battery contact insulators, exposing the internal contacts and battery springs. Removal of the handle will facilitate access to these contacts.
Note:
Never store the instrument over 30 days without removing the batteries. Although this instrument will operate at very high ambient temperatures, battery seal failure may occur at temperatures as low as 100°F.

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Section
7

Troubleshooting

Section 7

O ccasionally, you may encounter problems with your LMI instrument or detector that may be repaired or resolved in the field, saving turnaround time and expense in returning the instrument to us for repair. Toward that end, LMI electronics technicians offer the following tips for troubleshooting the most common problems. Where several steps are given, perform them in order until the problem is corrected. Keep in mind that with this instrument, the most common problems encountered are: (1) detector cables, (2) sticky meters, (3) battery contacts.
Note that the first troubleshooting tip is for determining whether the problem is with the electronics or with the detector. A Ludlum Model 500 Pulser is invaluable at this point, because of its ability to simultaneously check high voltage, input sensitivity or threshold, and the electronics for proper counting.
We hope these tips will prove to be helpful. As always, please call if you encounter difficulty in resolving a problem or if you have any questions.
Troubleshooting Electronics w hich utilize a
GM Detector or Scintillator

SYMPTOM
No power (or meter does not reach BAT TEST or BAT OK mark)

POSSIBLE SOLUTION
1. Check batteries and replace if weak.
2. Check polarity (See marks inside batter lid). Are the batteries installed backwards?

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SYMPTOM No power (or meter does not reach BAT TEST or BAT OK mark) (continued) Nonlinear Readings
Meter goes full-scale or “Pegs Out”

POSSIBLE SOLUTION
3. Check battery contacts. Clean them with rough sandpaper or use an engraver to clean the tips.
4. Remove the can and check for loose or broken wires.
1. Check the high voltage (HV) using a Ludlum Model 500 Pulser (or equivalent). If a Multimeter is used to check the HV, ensure that one with high impedance is used, as a standard Multimeter could be damaged in this process.
2. Check for noise in the detector cable by disconnecting the detector, placing the instrument on the lowest range setting, and wiggling the cable while observing the meter face for significant changes in readings.
3. Check for “sticky” meter movement. Does the reading change when you tap the meter? Does the meter needle “stick” at any spot?
4. Check the “meter zero.” Turn the power OFF. The meter should come to rest on “0”.
1. Replace the detector cable to determine whether or not the cable has failed- causing excessive noise.
2. Check the HV and, if possible, the input threshold for proper setting.

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SYMPTOM
Meter goes full-scale or “Pegs Out” (continued)

POSSIBLE SOLUTION
3. Remove the can and check for loose or broken wires.
4. Ensure that the instrument’s “can” is properly attached. When attached properly, the speaker will be located on the left side of the instrument. If the can is on backwards, interference between the speaker and the input preamplifier may cause noise.

No Response to Radiation
No Audio

1. Substitute a “known good” detector and/or cable.
2. Has the correct operating voltage been set? Refer to the calibration certificate or detector instruction manual for correct operating voltage. If the instrument uses multiple detectors, confirm that the high voltage is matched to the current detector being used.
1. Ensure that the AUD ON-OFF switch is in the ON position.
2. Remove the instrument housing and check the connection between the circuit board and the speaker. Plug in the 2-pin connector if necessary.

Troubleshooting GM Detectors
1. If the tube has a thin mica window, check for window breakage. If damage is evident, the tube must be replaced.
2. Check the HV. For most G-M tubes, the voltage is normally 900 Vdc, or 460-550 Vdc for “peanut” tubes (Ludlum Model 133 series).

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Section 7

3. If the input sensitivity is too low, the user could see some double- pulsing.
4. Wires to the tube may be broken or the crimped connector could have a loose wire.
Troubleshooting Scintillators
1. Alpha or Alpha/Beta scintillators are prone to light leaks. They can be tested for this problem in a dark room or with a bright light. If a light leak is determined, changing the Mylar window assembly will usually fix the problem.
Note:
When replacing the window, make sure to use a window made with the same thickness Mylar and the same number of layers as the original window.
2. Verify that the HV and input sensitivity are correct. Alpha and gamma scintillators typically operate from 10-35 mV. High voltage varies with the photomultiplier tubes (PMT) from as low as 600 Vdc, to as high as 1400 Vdc.
3. On a gamma scintillator, visually inspect the crystal for breakage or humidity leakage. Water inside the crystal will turn it yellow and gradually degrade performance.
4. Check the PMT to see if the photocathode still exists. If the end of the PMT is clear (not brownish), this indicates a loss of vacuum which will render the PMT useless.

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Section 8

Section
8

Technical Theory of Operation

Low Voltage Supply
Battery voltage is coupled to U11 and associated components (a switching regulator) to provide 5 volts at pin 8 to power all logic circuits. A voltage divider (R27 and R32) located at pin 1 of U11 sets the end-of-batterylife squeal at 2.0 Vdc. Components R12 and C30 provide filtering to create +5 VA used by the amplifier and discriminator circuits.
High Voltage Supply
High voltage is developed by pulses from the switching regulator U13 to transformer T1. High voltage is multiplied by the ladder network of diodes CR3 through CR7 and capacitors C18 through C27. High voltage is coupled back through R39 to pin 8 of U13. High voltage output is set by front panel potentiometer R42, which sets the voltage feedback of 1.31 Vdc to pin 8 of U13. R38 and C28 provide filtering.
Detector Input
Detector pulses are coupled from the detector through C6 to amplifier input pin 2 of U4. CR1 protects U4 from input shorts. R37 couples the detector to the high voltage supply.
Amplifier
A self-biased amplifier provides gain in proportion to R15 divided by R14, with some gain loss due to feedback capacitor C4. A transistor (pin 3 of U4) provides amplification. U6 is configures as a constant current source to pin 3 of U4. The output self-biases to 2 Vbe (approximately 1.4 volts) at the emitter of Q1. This provides just enough bias current through pin 3 of U4 to conduct all of the current from the current source. Positive pulses from the emitter of Q1 are coupled to the discriminator.

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Discriminator
Comparator U8 provides discrimination. The discriminator is set by a voltage divider (R21 and R23), coupled to pin 3 of U8. As the amplified pulses at pin 4 of U8 increase above the discriminator voltage, 5 volt negative pulses are produced at pin 1 of U8. These pulses are coupled to pin 5 of U9 for meter drive and pin 12 of U9 for audio.
Audio
Discriminator pulses are coupled to univibrator pin 12 of U9. The front panel audio ON-OFF selector controls the reset at pin 13 of U9. When ON, pulses from pin 10 of U9 turn on oscillator U12, which drives the housingmounted unimorph speaker. Speaker tone is set by R31 and C14. Tone duration is controlled by R22 and C7.
Scale Ranging
Detector pulses from the discriminator are coupled to univibrator pin 5 of U9. For each scale, the pulse width of pin 6 of U9 is changed by a factor of 10 with the actual pulse width being controlled by the front panel switch, the analog switches U1 and U2, and the related potentiometers. This arrangement allows the same current to be delivered to C9 by 1 count on the ×0.1 range as 1000 counts on the ×100 range.
Meter Drive
Pulses from pin 6 of U9 charge capacitor C9. A constant current driver (opamp U10 and transistor Q2) delivers proportional current to the meter. For battery test (BAT TEST), the meter is directly coupled by the analog switch U3 to the batteries through resistor R8.
Meter Reset
Ratemeter reset is initiated by changing the voltage differential at C9 to zero when the RESET button is depressed.
Fast/Slow Time Constant
For the slow time constant, C17 is switched from the output of the meter drive to parallel C9.

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Section
9

Recycling

Section 9

L udlum Measurements, Inc. supports the recycling of the electronics products it produces for the purpose of protecting the environment and to comply with all regional, national and international agencies that promote economically and environmentally sustainable recycling systems. To this end, Ludlum Measurements, Inc. strives to supply the consumer of its goods with information regarding reuse and recycling of the many different types of materials used in its products. With many different agencies, public and private, involved in this pursuit it becomes evident that a myriad of methods can be used in the process of recycling. Therefore, Ludlum Measurements, Inc. does not suggest one particular method over another, but simply desires to inform its consumers of the range of recyclable materials present in its products, so that the user will have flexibility in following all local and federal laws.

The following types of recyclable materials are present in Ludlum Measurements, Inc. electronics products, and should be recycled separately. The list is not all-inclusive, nor does it suggest that all materials are present in each piece of equipment:

Batteries

Glass

Aluminum and Stainless Steel

Circuit Boards

Plastics

Liquid Crystal Display (LCD)

Ludlum Measurements, Inc. products which have been placed on the market after August 13, 2005 have been labeled with a symbol recognized internationally as the “crossed-out wheelie bin” which notifies the consumer that the product is not to be mixed with unsorted municipal waste when discarding; each material must be separated. The symbol will be placed near the AC receptacle, except for portable equipment where it will be placed on the battery lid.

The symbol appears as such:

Ludlum Measurements, Inc.

Page 9-1

April 2016

Model 3-8 Survey Meter

Technical Manual

Section
10

Parts List

Model 3-8 Survey Meter Main Board, Draw ing 464 × 204
CAPACITORS
TRANSISTORS

Reference
UNIT
BOARD
C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C14 C15 C16 C17 C18-C27 C28 C29 C30-C31 C32
Q1 Q2

Description
Completely Assembled Model 3-8 Survey Meter
Completely Assembled Main Circuit Board
47pF, 100V 0.1uF, 35V 0.0047uF, 100V 10pF, 100V 0.01uF, 50V 100pF, 3KV 0.022uF, 50V 1uF, 16V 10uF, 25V 100pF, 100V 68uF, 10V 10uF, 25V 470pF, 100V 220pF, 100V 68uF, 10V 47uF, 10V 0.01uF, 500V 0.001uF, 2KV 10uF, 25V 1uF, 16V 470pF, 100V
MMBT3904LT1 MMBT4403LT1

Ludlum Measurements, Inc.

Page 10-1

Section 10
Part Number
48-1440
5464-204
04-5660 04-5755 04-5669 04-5673 04-5664 04-5735 04-5667 04-5701 04-5655 04-5661 04-5654 04-5728 04-5668 04-5674 04-5654 04-5666 04-5696 04-5703 04-5655 04-5701 04-5668
05-5841 05-5842
April 2016

Model 3-8 Survey Meter

Technical Manual

Section 10

INTEGRATED CIRCUITS
DIODES SWITCHES POTENTIOMETERS / TRIMMERS
RESISTORS

Reference
U1-U3 U4-U5 U6 U7 U8 U9 U10 U11 U12 U13
CR1 CR2 CR3-CR7 CR9
SW1 SW2 SW3-SW4
R33 R34 R35 R36 R42
R1-R5 R6 R7 R8 R9-R11 R12 R13 R14

Description
MAX4542ESA CMXT3904 CMXT3906 MAX4541ESA MAX985EUK-T CD74HC4538M LMC7111BIM5X LT1304CS8-5 MIC1557BM5 LT1304CS8
CMPD2005S RECTIFIER CMSH1-40M CMPD2005S RECTIFIER CMSH1-40M
D5G0206S-9802 TP11LTCQE 7101SDCQE
250K, 64W254, ×1K 250K, 64W254, ×100 500K, 64W504, ×10 250K, 64W254, ×1 1.2M, 3296W, HV
200K, 1/8W, 1% 8.25K, 1/8W, 1% 10K, 1/8W, 1% 2.37K, 1/8W, 1% 10K, 1/8W, 1% 200 Ohm, 1/8W, 1% 10K, 1/8W, 1% 4.75K, 1/8W, 1%

Part Number
06-6453 05-5888 05-5890 06-6452 06-6459 06-6297 06-6410 06-6434 06-6457 06-6394
07-6468 07-6411 07-6468 07-6411
08-6761 08-6770 08-6781
09-6819 09-6819 09-6850 09-6819 09-6814
12-7992 12-7838 12-7839 12-7861 12-7839 12-7846 12-7839 12-7858

Ludlum Measurements, Inc.

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April 2016

Model 3-8 Survey Meter

Technical Manual

Section 10

CONNECTORS
INDUCTOR TRANSFORMER
Wiring Diagram, Draw ing 464 × 212
CONNECTORS

Reference
R15 R16 R17 R18 R19 R20-R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R37 R38 R39 R40 R44
P1 P2
P3
L1
T1

Description
200K, 1/8W, 1% 10K, 1/8W, 1% 1K, 1/8W, 1% 4.75K, 1/8W, 1% 2K, 1/8W, 1% 100K, 1/8W, 1% 1M, 1/8W, 1% 2.49K, 1/8W, 1% 14.7K, 1/8W, 1% 200K, 1/4W, 1% 100K, 1/4W, 1% 68.1K, 1/8W, 1% 100K, 1/8W, 1% 1K, 1/8W, 1% 100K, 1/8W, 1% 475K, 1/8W, 1% 100K, 1/8W, 1% 100K, 1/8W, 1% 4.75M, 1/8W, 1% 500M, 3KV, 2% 402K, 1/8W, 1% 1K, 1/4W, 1%
640456-5 – MTA100 640456-6 – MTA100 (installed as required) 640456-2 – MTA100
22 uH
31032R

Part Number
12-7992 12-7839 12-7832 12-7858 12-7926 12-7834 12-7844 12-7999 12-7068 12-7992 12-7834 12-7881 12-7834 12-7832 12-7834 12-7859 12-7834 12-7834 12-7995 12-7031 12-7888 12-7832
13-8057
13-8095 13-8073
21-9808
21-9925

J1

MTA100×5, MAIN

BOARD 5464-204

13-8140

J2

OPTIONAL (M3 overload)

MTA100×6, 5464-204

13-8171

J3

MTA100×2, MAIN

BOARD 5464-204

13-8178