LUDLUM MEASUREMENTS LUDLUM MODEL 3-8 SURVEY METER Instruction Manual
- June 12, 2024
- LUDLUM MEASUREMENTS
Table of Contents
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
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
Ludlum Measurements, Inc.
April 2016
Model 3-8 Survey Meter
Technical Manual
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
Ludlum Measurements, Inc.
April 2016
Model 3-8 Survey Meter
Technical Manual
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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Technical Manual
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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Technical Manual
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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Technical Manual
Section 5
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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Technical Manual
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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Technical Manual
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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Section 7
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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Section 7
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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Technical Manual
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.
Ludlum Measurements, Inc.
Page 8-1
April 2016
Model 3-8 Survey Meter
Technical Manual
Section 8
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.
Ludlum Measurements, Inc.
Page 8-2
April 2016
Model 3-8 Survey Meter
Technical Manual
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.
Page 10-2
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
Ludlum Measurements, Inc.
Page 10-3
April 2016
Model 3-8 Survey Meter
Technical Manual
Section 10
AUDIO BATTERIES MISCELLANEOUS
Reference
DS1
B1-B2
-
-
-
-
-
- M1
-
-
-
-
-
Description
Part Number
UNIMORPH TEC3526-PU
21-9251
D DURACELL BATTERY 21-9313
PORTABLE BATTERY NEGATIVE
CONTACT ASSEMBLY
2001-065
PORTABLE BATTERY POSITIVE
CONTACT ASSEMBLY
2001-066
MODEL 3 CASTING
7464-219
MODEL 3 MAIN HOUSING 8464-035
PORTABLE CAN
ASSEMBLY (MTA)
4363-441
PORTABLE KNOB
08-6613
METER ASSEMBLY METER
BEZEL W/GLASS
W/O SCREWS
4364-188
METER MOVEMENT (1mA) 15-8030
PORTABLE METER FACE 7363-136
HARNESS-PORT CAN WIRES 8363-462
PORTABLE BATTERY LID WITH
STAINLESS CONTACT
2009-036
PORTABLE LATCH KIT W/O
BATTERY LID
4363-349
PORTABLE HANDLE(GRIP)
W/SCREWS
4363-139
PORTHANDLE FOR CLIP
W/SCREWS
4363-203
REPLACEMENT CABLE
(STD 39inch)
40-1004
CLIP (44-3 TYPE) W/SCREWS 4002-026-01
CLIP (44-6 TYPE) W/SCREWS 4010-007-01
Ludlum Measurements, Inc.
Page 10-4
April 2016
Model 3-8 Survey Meter
Technical Manual
Section
11
Draw ings
Section 11
MAIN CIRCUIT BOARD, Drawing 464 × 204 (3 sheets) MAIN CIRCUIT BOARD LAYOUT,
Drawing 464 × 205 (2 sheets)
CHASSIS WIRING DIAGRAM, Drawing 464 × 212
Ludlum Measurements, Inc.
Page 11-1
April 2016