Ludlum Measurements 177 User Manual

LUDLUM MODEL 177
ALARM RATEMETER

October 2018

Serial Number 322945 and Succeeding

Serial Numbers

LUDLUM MODEL 177
ALARM RATEMETER

Serial Number 322945 and Succeeding

October 2018

Serial Numbers

Model 177 Technical Manual

STATEMENT OF WARRANTY

Ludlum Measurements, Inc. warrants the products covered in this manual to be free of
defects due to workmanship, material, and design for a period of twelve months from
the date of delivery. The calibration of a product is warranted to be within its
specified accuracy limits at the time of shipment. In the event of instrument failure,
notify Ludlum Measurements to determine if repair, recalibration, or replacement is
required.

This warranty excludes the replacement of photomultiplier tubes, G-M and
proportional tubes, and scintillation crystals which are broken due to excessive
physical abuse or used for purposes other than intended.

There are no warranties, express or implied, including without limitation any implied
warranty of merchantability or fitness, which extend beyond the description of the
face there of. If the product does not perform as warranted herein, purchaser’s sole
remedy shall be repair or replacement, at the option of Ludlum Measurements. In no
event will Ludlum Measurements be liable for damages, lost revenue, lost wages, or
any other incidental or consequential damages, arising from the purchase, use, or
inability to

use product.

RETURN OF GOODS TO MANUFACTURER

If equipment needs to be returned to Ludlum Measurements, Inc. for repair or calibration, please
send to the address below. All shipments should include documentation containing return shipping
address, customer name, telephone number, description of service requested, and all other necessary
information. Your cooperation will expedite the return of your equipment.

LUDLUM MEASUREMENTS, INC.

ATTN: REPAIR DEPARTMENT
501 OAK STREET
SWEETWATER, TX 79556

800-622-0828 325-235-5494

FAX [phone]

Model 177 Technical Manual

Table of Contents

Introduction 1

Getting Started 2

Unpacking and Repacking 2-1

Preparing the Instrument for Use 2-1

Operating the Instrument 2-1

Specifications 3

Description of Controls and Functions 4

Front Panel 4-1

Back Panel 4-2

CAL Control 4-3

Internal Controls (Overhaul Only) 4-4

Safety Considerations 5

Environmental Conditions for Normal Use 5-1

Cleaning Instructions and Precautions 5-1

Warning Markings and Symbols 5-2

Electrical Safety Precautions 5-2

Calibration and Maintenance 6

Calibration 6-1

Establishing an Operating Point 6-2

Maintenance 6-3

Troubleshooting 7

Troubleshooting Electronics that Utilize a GM or Scintillation Detector 7-1

Troubleshooting GM Detectors 7-2

Troubleshooting Scintillators 7-3

Technical Theory of Operation 8

Amplifier 8-1

Model 177 Technical Manual

Discriminator 8-1

Digital Analog Conversion 8-1

Alarm 8-2

Reset 8-2

Audio 8-2

Time Constant 8-2

High Voltage (HV) 8-3

Low Voltage 8-3

Battery Charge 8-3

High Voltage Test 8-3

Alarm Set Voltage 8-3

Battery Test Voltage 8-4

Recycling 9

Parts List 10

Model 177 Alarm Ratemeter 10-1

Main Board, Drawing 347 × 496 10-1

Calibration Board, Drawing 347 × 132 10-4

Wiring Diagram, Drawing 347 × 492 10-5

Drawings and Diagrams 11

Model 177 Technical Manual Section 1

Section

1

T

Introduction

he Ludlum Model 177 Alarm Ratemeter may be used with GM
(Geiger-Mueller) or scintillation detectors for contamination
monitoring, surveying and area monitoring. The unit provides four

ranges (in decades) of the analog meter, enabling measurement from 0
to 500,000 counts per minute (CPM) on the standard meter dial; others are
available. Detector high voltage is adjustable from 400 to 1500 volts.

The unit incorporates an adjustable alarm set point. The alarm setting may be
checked by depressing the front-panel TEST switch. Audible and visual
enunciators are triggered when the meter reading rises above the alarm set
point. Accessory outputs include: Unbuffered Output, Supply Voltage,
Negative Pulse Output, Recorder, and Alarm Sink for Remote Relay. The unit
may be operated from an internal rechargeable battery or by external 9 Vdc
wall transformer.

Ludlum Measurements, Inc. Page 1-1 October 2018

Model 177 Technical Manual Section 2

Section

2

T

Getting Started

he Ludlum Model 177 Alarm Ratemeter is designed for use with

GM (Geiger Mueller) or scintillation detectors, which operate from

400 to 1500 V. Typical applications include contamination

monitoring, surveying, and area monitoring.

Unpacking and Repacking

Remove the calibration certificate and place it in a secure location. Remove
the instrument 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 between instruments and detectors (if applicable). The
Model 177 serial number is located on the back panel of the instrument.

To return an instrument for repair or calibration, provide sufficient packing
material to prevent damage during shipment.

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 a link to
the form.

Preparing the Instrument for Use

Turn the power switch to the ON position. Depress the BAT TEST button.
Check that the meter reads above the BAT TEST indication. If the battery
does not check, the instrument will operate on 9 Vdc wall transformer only.
The battery may be trickle charged from 9 Vdc wall transformer.

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Model 177 Technical Manual Section 2

Select the operating voltage. This voltage is set by the manufacturer for the
detector shipped with the instrument and recorded on the Certificate of
Calibration. For other detector/instrument setups, consult the detector manual
or manufacturer. Then adjust the HV potentiometer accordingly.

Note:

Most GM detectors will operate at 900 volts. However, some
smaller GM tubes operate at lower voltages.

Operating the Instrument

Connect a detector to the instrument. Obtain a meter reading from a check
source or calibrated source, if available. Remove the source.

Set the instrument to the appropriate range with the RANGE selector switch.

If the alarm point is not already set, press the ALARM TEST switch and adjust

ALARM SET for the desired alarm point.

Note:

The meter displays the alarm set point when the ALARM TEST
switch is depressed. Recheck the set point after locking the

ALARM SET control.

Increase the meter count to exceed the alarm threshold. Both the alarm lamp
and audible alarm signal should activate.

Depress the RESET button. The meter needle should drive to zero and the
alarm circuit should de-energize, shutting off both the visual and audible
alarms.

Depress the HV TEST button and ensure that the high voltage is properly set.

Proceed with use.

Ludlum Measurements, Inc. Page 2-2 October 2018

Model 177 Technical Manual Section 3

Section

3

Specifications

0

Power: 95-250 Vac wall transformer and 6 volt gell-cell (sealed lead-acid)

battery; typical battery life of approximately 50 hours in a non-alarming
condition with a fully charged battery.

Fuse: internal resettable

Response Time: toggle switch control selects FAST (2.2 seconds) or

SLOW (22 seconds) response, for 90% of full-scale reading

Linearity: within 5% of full scale; typically ±2% of full scale reading when

measured with an electronic pulse generator

Battery Dependence: Meter readings vary less than 3% within battery

check limits.

High Voltage: variable from 400 to 1500 V

Input Sensitivity: adjustable from -10 through -100 mV

Connector: Series "C"

Audio: unimorph speaker with volume control located on the front panel

Meter: 1 mA, size 6.4 x 6.4 cm (2.5 x 2.5 in.), DC movement

Meter Scale: 0-500 CPM; 0-1.5 kV; BAT TEST

Ranges: four ranges of X1 through X1K

Recorder Output: adjustable from 0 to 1.25 V at 1 mA

Alarm Output: current sink to 200 mA DC, open circuit voltage not to

exceed 50 Vdc

Unbuffered Output: may be used to externally add to or subtract from the

meter reading

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Model 177 Technical Manual Section 3

Alarm Range: adjustable from 0 through 150% of full scale

Alarm Output: visual indicator (lamp), audible tone and remote current

sink

Alarm Control: factory set to latching, non-latching alarm available

through the removal of main board resistor R116

Finish: powder coat paint

Size: 12.7 x 20.3 x 15.2 cm (5 x 8 x 6 in.) (H x W x D), excluding handle

Weight: 1.9 kg (4.2 lb) with battery

Ludlum Measurements, Inc. Page 3-2 October 2018

Model 177 Technical Manual Section 4

Section

4

Description of Controls and
Functions

Front Panel

Power ON-OFF Switch: provides 9 Vdc through a wall transformer to the

instrument and trickle-charges the standby battery. In case of line power
failure, the battery automatically comes on-line to power the instrument.
The battery will provide up to 50 hours of operation.

Note:

To recharge the battery, the ON-OFF switch must be in the ON
position.

Power-on Lamp: a red lamp that comes on when power is supplied to the

instrument.

VOLUME Control: varies the volume of the audio output through the

unimorph speaker. This control has minimal effect on the audio when the
alarm is activated.

Audio Speaker: a unimorph speaker, located behind the front panel.

ALARM Lamp: a red lamp that comes on when the alarm threshold has

been exceeded. The lamp will remain on (unless the alarm is configured to
“non-latching”) until the reset button is depressed, driving the meter
needle below the alarm threshold.

Ludlum Measurements, Inc. Page 4-1 October 2018

RANGE Selector Switch: a four-position switch providing range

multipliers of X1K, X100, X10, and X1. With a scale (meter face) of 0-500
CPM, the full range of the instrument is 0 to 500,000 CPM .

Ratemeter: a four-decade linear meter with ranges of 0-500, 0-5000,

0-50,000, 0-500,000 CPM. Other meter faces are available depending on
the application. Readout is on a 6.4 cm (2.5 in.) scale panel meter. A
separate scale is provided for battery check and high voltage readout.

Model 177 Technical Manual Section 4

Connector: Series "C" connector (Series BNC and MHV connectors are

also available). The connector is provided on the front of the instrument
for connection to a detector.

RESET Button: This button, when depressed, provides a rapid means of

driving the meter needle to zero.

FAST-SLOW RESPONSE Toggle Switch: When in the FAST position, this

switch provides 90% of full-scale meter deflection in 2.2 seconds. With
this switch in the SLOW position, 90% of full-scale meter deflection takes
22 seconds. If quick needle response and maximum deviation are desired,
the FAST position should be used. For slow response and damped meter
movement, the SLOW position should be used.

BAT TEST Button: When this button is depressed, the meter displays the

battery status. A sufficiently charged battery is indicated when the meter
needle is on or within the BAT TEST range.

HV TEST Button: When this button is depressed, the meter displays the

detector high voltage.

ALARM TEST Button: When this button is depressed, the meter displays

the alarm calibration set point.

ALARM SET: used to adjust the alarm calibration set point. Note the

locking knob below the control.

Back Panel

9 VDC INPUT: Input for external 9 Vdc.

Data: a 9-pin type “D” data plug with connections as follows:

PIN 1: Battery terminal. This is a direct connection and does

not go through the front panel ON-OFF switch. Use to parallel
the battery.

PIN 2: Unregulated supply from approximately 6 volts, battery

only at 8.7 volts with wall transformer plugged in. Limit
current drain to 50 milliamperes.

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Model 177 Technical Manual Section 4

PIN 3: instrument common (ground).

PIN 4: alarm sink. The open collector of a 2N7002L. Limits

sink current to 200 milliamperes with open circuit voltage
limited to a range of 0 to +50 volts. Unit conducts when in
alarm.

PIN 5: Pulse out. A negative pulse connected to the

discriminator output through a 0.001 µF capacitor,
typically -4.0 volts.

PIN 6: Unbuffered output ties directly to the meter drive

circuit. (R124/C122). Approximately 1.3 volts at full scale.
Using an external constant current sink will allow background
subtract. At full scale, draws out approximately 3.3
microamperes to zero the meter.

PIN 7: Recorder output, adjustable from 0 to 1.0 volts at

1 milliamperes.

PIN 8 and PIN 9: Spares

CAL Control

Remove the calibration (cal) cover plate to access the following calibration
potentiometers:

DISCR: Discrimination Control. For pancake-type GM detectors (i.e.

Model 44-9), adjust DISCR for 80 ±10 millivolts. All other GM detectors
and scintillators should be set to 35 ±10 millivolts. If a lower operating
voltage for a scintillator is desired, adjust the discriminator to 10 ± 2
millivolts. This control has an adjustable range of 10 to 100 millivolts. A
Ludlum Model 500 Pulser may be used to determine the discrimination
level.

Calibration Controls: X1K through X1 calibration controls used to

calibrate ranges.

HV ADJ: used to set detector operating voltage.

RCDR: used to calibrate the recorder output.

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Model 177 Technical Manual Section 4

Internal Controls (Overhaul Only)

The following controls are located internally, on the main circuit board:

BAT C:

BAT T: used to adjust meter test voltage reading to 5.97 volts at the BAT

OK

HV T: used to adjust the high-voltage test reading to correspond with the

used to adjust charge voltage to 6.825 volts.

line.

actual high-voltage output.

Ludlum Measurements, Inc. Page 4-4 October 2018

Model 177 Technical Manual Section 5

Section

5

Safety Considerations

Environmental Conditions for Normal Use

Indoor use only

No maximum altitude

Temperature range of -20 to 50 °C (-4 to 122 °F)

Maximum relative humidity of less then 95% (non-condensing)

Wall transformer supply voltage range of 95-250 Vac, 50/60 Hz single
phase (less than 100 mA)

Maximum transient voltage of 1500 Vac

Installation Category II (Overvoltage Category as defined by IEC 1010-1)

Pollution Degree 2 (as defined by IEC 664) (Normally only
nonconductive pollution occurs. Temporary conductivity caused by
condensation is to be expected.)

Cleaning Instructions and Precautions

The Model 177 Alarm Ratemeter 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:

1. Turn the instrument OFF and disconnect the instrument power

cord.

Ludlum Measurements, Inc. Page 5-1 October 2018

2. Allow the instrument to sit for one minute before cleaning.

Model 177 Technical Manual Section 5

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.

Electrical Safety Precautions

Warning!

Failure to comply with the following instructions could result
in a hazardous situation, which, if mishandled, could result in
death or serious personal injury.

When installing the unit:

• Do not expose the unit to rain or an environment where it may be

splashed by water or other liquids, as doing so may result in fire or
electric shock.

• Use the unit only with the voltage specified on the unit. Using a

voltage higher than that which is specified may result in fire or
electric shock.

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Model 177 Technical Manual Section 5

• Do not cut, kink, otherwise damager nor modify the power supply

cord. In addition, avoid using the power cord in close proximity to
heaters, and never place heavy objects – including the unit itself –
on the power cord, as doing so may result in fire or electric shock.

• Avoid installing or mounting the unit or its power supply in

unstable locations, such as a rickety table or slanted surface. Doing
so may result in the unit falling down and causing personal injury
and/or property damage.

The Model 177 Alarm Ratemeter is marked with the following symbols:

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 disconnect the power
cord.

2. Allow the instrument to sit for one minute before accessing
internal components.

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.

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 back panel.
See section 9, “Recycling,” for further information.

The “CE” mark is used to identify this instrument as being acceptable for
use within the European Union.

Ludlum Measurements, Inc. Page 5-3 October 2018

Model 177 Technical Manual Section 6

Section

6

Calibration and Maintenance

Calibration

Note:

Local procedures may supersede the following.

Connect the instrument to a Ludlum Model 500 Pulser (Pulse Generator) or
equivalent.

The ratemeter may be calibrated by adjusting the calibration controls labeled
1, 10, 100, and 1K. Starting with the 1000 range, apply 400,000 CPM from
the pulser. Adjust the 1K calibration control for a meter reading of 400.
Drop the pulse rate to 100,000 CPM and ensure a meter reading of 100 ±10.

Repeat this procedure for the lower scales with scaled pulse rates.

For pancake-type GM detectors (i.e. Model 44-9), adjust DISCR for 80 ±10
millivolts. All other GM detectors and scintillators should be set to 35 ±10
millivolts. To lower the scintillation detector operating voltage, decrease the
input sensitivity to 10 ±2 millivolts. Adjustment is made by setting the pulse
generator amplitude to the desired pulse height. Adjust DISCR until the meter
reaches 75% of the generated incoming count rate.

Connect the Model 177 to an external voltmeter. Adjust the rear panel HV
control for a reading of 1000 Vdc on the voltmeter. Depress HV TEST. On
the main board, adjust HV for a meter reading of 1.0 kV. Using the rear­panel HV control, vary the high-voltage output from 500 to 1500 Vdc and
ensure that the high-voltage meter reads within 10% of the Model 177
meter reading.

Adjust RCDR (recorder output) for 1 volt output (equivalent to full scale).

Ludlum Measurements, Inc. Page 6-1 October 2018

Adjust ALARM SET to the desired set point.

Model 177 Technical Manual Section 6

Establishing an Operating Point

The operating point for the instrument and detectors is established by
setting the detector voltage and instrument sensitivity (HV and DIS). 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 significant difference in the
contribution of these three sources of count.

The purpose of setting the operating point 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. The pulses above the discrimination level are counted
by the instrument, while those below are not.

The total system gain is controlled by adjusting the instrument gain or the
high voltage. Voltage affects the output of the detector. Amplifier gain is
controlled by the DIS (discriminator) control.

In special cases of GM detectors, a minimum voltage must be applied to
establish the Geiger-Mueller characteristic. Further changes in gain will not
affect this type of detector.

The operating point for each detector is set at a compromise point between
sensitivity, stability, and background contribution. These operating points are
best for general monitoring. In application, these arbitrarily selected points
may not be a better operating point. The following guidelines are presented:

GM Detectors: The output pulse height of the GM detector is not

proportional to the energy of the detected radiation. Adjusting DIS will
have minimal effect on the observed count rate unless the setting is so
low that the instrument double pulses.

For most GM detectors, set DIS for 30-40 millivolts and adjust HV to the
GM tube recommended high voltage. Most GM detectors operate at
900 volts; however, some miniature detectors operate at 400-600 volts.
If a recommended setting is unavailable, run a plateau of HV setting vs.
count rate. Then set the high voltage on the low side of “center.”

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Model 177 Technical Manual Section 6

Scintillators: Set DIS for 10 millivolts. Carefully increase HV until the

instrument plateaus on the background count. This provides the most
stable operating point for the detector.

Maintenance

Instrument maintenance consists of keeping the instrument clean and
periodically checking the battery and calibration.

An instrument operational check should be performed prior to each use by
exposing the detector to a known source and confirming the proper reading
on each scale.

Recalibration should be accomplished after any maintenance or adjustment
has been performed on the instrument. Ludlum Measurements recommends
recalibration at intervals no greater than one year. Local regulations may
have precedence over this recommendation.

To maintain the life of the battery, it is recommended that the instrument be
constantly connected to external power with the power switch in the ON
position, even when the instrument is not in use. This will keep the internal
battery fully charged.

When the instrument is used without external power, adequate charge time
must be allowed for the internal battery to recharge. If possible, leave the
instrument on with line power applied overnight and weekends. At a
minimum, allow one hour of charge time for each hour of use. If the battery
is inadvertently allowed to fully discharge, and is left in that state, constant
charging for 500 hours (3 weeks) may be required for battery recovery.

Note:

The ON-OFF switch must be in the ON position to charge the
batteries. If the unit is out of service for extended periods of
time, charge the battery every six months.

It is recommended that the internal GEL-CELL battery be replaced every
four years.

Ludlum Measurements, Inc. Page 6-3 October 2018

Model 177 Technical Manual Section 7

Section

7

O

Troubleshooting

ccasionally, you may encounter problems with your LMI
instrument or detector that may be repaired or resolved in the
field, saving turn-around 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 detector cables and sticky meters.

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 that Utilize a GM or Scintillation Detector

SYMPTOM

No power (or meter
does not reach BAT

TEST

or BAT OK

mark)

POSSIBLE SOLUTION

1. Check battery and charge if necessary.

2. Check for loose or broken wires,

especially between the main board
and the calibration board.

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Model 177 Technical Manual Section 7

SYMPTOM

Non-linear Readings

Meter goes full-scale
or “pegs out”

POSSIBLE SOLUTION

1. Check the high voltage (HV) by

pressing the HV TEST button. 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 and
placing the instrument on the lowest
range setting. Wiggle the cable and
observe the reading for significant
changes.

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 see if it

has failed, causing excess noise.

2. Check the HV and, if possible, the

input threshold for proper setting.

3. Check for loose wires, especially

between the main board and the
calibration board.

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.

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Model 177 Technical Manual Section 7

2. Check the HV. For most GM tubes, the voltage is normally 900
Vdc, or 460-550 Vdc for “peanut” tubes (Ludlum Model 133
series).

3. If the input sensitivity is too low, the user could see some
double-pulsing. See Page 4-3, “DISCR” for further information
on sensitivity/discrimination control.

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 aluminized
polyester window assembly will usually fix the problem.

Note:

When replacing the window, make sure to use a window made
with the same thickness of aluminized polyester 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 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.

Ludlum Measurements, Inc. Page 7-3 October 2018

Model 177 Technical Manual Section 8

Section

8

Technical Theory of Operation

Amplifier

Negative detector pulses are coupled through C124 to emitter follower Pin
U121. R127 protects the input from inadvertent high-voltage shorts. R129
couples the detector to the high-voltage supply.

Negative pulses from emitter, Pin 2 of U121, are coupled through C121 to
amplifier Pin 5 through Pin 7 of U121. This amplifier is self-biased and
provides gain in proportion to R029 divided by R0210. Transistor (pins 4, 5,
6, U121) provides amplification. Pins 12 and 15 of U121 are coupled as a
current mirror to provide a load for Pin 6 of U121. The output self-biases to
2 Vbe (approximately 1.4 volts) at Pin 7 of U121. This provides just enough
bias current through Pin 6 of U121 to conduct all of the current from the
current mirror.

Positive pulses from Pin 7 of U121 are coupled to the discriminator.

Discriminator

Comparator U021 provides discrimination. The discriminator is set by the
DIS (Discriminator) control located on the rear panel, coupled to Pin 5 of
U021. Negative pulses (approximately 5 volts) at Pin 7 of U021 are coupled
to Pin 5 of U011 for meter drive and Pin 11 of U011 for audio.

Digital Analog Conversion

Pin 7 of U021 is connected to the dual univibrator, U011. For each low
pulse for Pin 7 of U021, Pin 6 of U011 goes high. The pulse of Pin 6 of
U011 is typically 5.0 volts for 6 milliseconds on X1 to 6 microseconds on
X1K. This pulse is connected to the constant current drive U012. The pulse
width control (R3-C2 on calibration board) is utilized for calibration
adjustment. Controls R4 through R6 allow calibration on other scales.

For each positive pulse connected to Pin 8 of U012, a constant current pulse
is sourced at Pin 15 of U012. This current pulse charges C122, which is

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Model 177 Technical Manual Section 8

discharged by R124. The average voltage on C122 is coupled through HV,

BAT, and ALARM TEST switch to voltage-follower Pin 5 of U311. Pin 7 of

U311 drives the meter and recorder output.

Time Constant

The meter time constant is determined by R124 and C122. For a slower time
constant, C122 is paralleled by C101. When C101 is not used, it is connected
to Pin 7 of U311 (voltage follower), maintaining the same voltage level as
C122. This allows C101 to be switched in or out of the circuit without
transients.

Alarm

An alarm is provided by U021, Pins 1, 2, and 3. The alarm set control biases
the op-amp U021 for a low output. When the meter signal at Pin 3 exceeds
the bias of Pin 2, the output at Pin 1 goes high. Q102 and Q103 saturate,
allowing supply voltage to be coupled to:

Lamp voltage through R004.

Audio oscillator U16 through CR112.

R116 couples back to base of Q102, locking up the Alarm On.

Through CR113 to audio transformer T211, allowing full voltage for full
volume.

Through R111 to saturating current sink Q101 for external use.

Reset

Reset is provided by coupling a voltage to the base of transistors U012 pins
1, 2, 3, and 4, 5, 6. Both transistors saturate. One discharges C122, causing
the meter to zero. Pin 3 U012 turns Q102 off, allowing the alarm to reset.

Audio

A high on Pin 4 U111 turns the oscillator on, saturating Q111 with each
positive swing of the oscillator. T211 couples the pulses to the unimorph.
Audio volume is controlled by voltage, applied to Pin 2 of T211. This is
either 4.3 volts from the alarm circuit or 0 to 4.3 volts from external volume
control through emitter follower Q104.

Ludlum Measurements, Inc. Page 8-2 October 2018

Model 177 Technical Manual Section 8

For counting, audio pulse width is set by R113/C111 of U011 with one
pulse per count. For an alarm condition, Pin 4 U111 is held high through
CR112 until alarm is reset. Alarm audio tone is controlled by R117 and
C112.

High Voltage (HV)

The high-voltage power supply is a blocking oscillator utilizing Q401-T411
and quadrupler CR123, CR421, CR422, and through CR423. The HV
output is controlled by conduction to ground through Q302. With Q302
saturated, the HV output is maximum.

The op amp, U311 Pins 1, 2, 3, is used as a comparator to compare the
voltage reference at Pin 3 to the feedback voltage at Pin 2 through R322 for
voltage control and regulation. High voltage is adjusted by HV control R311
changing bias on Pin 2 U311. With the HV control wiper at ground, high­voltage output is maximum.

Low Voltage

Low voltage is supplied by internal battery B1 (wiring diagram, 347 × 126)
or external power T1. Unregulated power at C125 is coupled to voltage
regulator VR211 and battery charger U201-Q301.

Regulated low voltage is supplied to the balance of the circuit through
VR131 at 5.0 volts and U301 at 1.2 volts.

Battery Charge

Battery charge is provided by voltage regulator U201 and power transistor
Q301. R402 limits charge current for discharged battery. A negative voltage
coefficient of -0.0063 volts per degree F is provided by ratio of R013/R201.
R013 sets output voltage to 6.825 volts.

High Voltage Test

High voltage test is supplied by R001 through HV TEST switch, BAT TEST
switch, ALARM TEST, Pin 5 of U311, and then the meter. The HV readout is
calibrated by R001.

Alarm Set Voltage

Alarm set voltage is coupled from ALARM SET control through the ALARM

TEST

switch, voltage follower Pin 5 of U311, and to the meter.

Ludlum Measurements, Inc. Page 8-3 October 2018

Model 177 Technical Manual Section 8

Battery Test Voltage

Battery test voltage is controlled by R002 through BAT TEST switch, ALARM

switch, then voltage follower Pin 5 of U311 to the meter.

TEST

Ludlum Measurements, Inc. Page 8-4 October 2018

Model 177 Technical Manual Section 9

Section

9

L

Recycling

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 that 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 on
the back panel, except for portable equipment where it will be placed on the
battery lid.

The symbol appears as such:

Ludlum Measurements, Inc. Page 9-1 October 2018

Model 177 Technical Manual Section 10

Section

10

Model
Ratemeter

Main Board
347

CAPACITORS

Parts List

Reference Description Part Number

177 Alarm

, Drawing

× 496

UNIT Completely Assembled Model 177 Alarm Ratemeter 48-1632

BOARD Completely Assembled
Circuit Board 5347-502

C001 10µF, 25V, 04-5655
C011 47PF, 100V 04-5660
C012 68µF, 10V 04-5654
C021 0.1µF, 50V 04-5663
C022 0.001µF, 100V 04-5659
C023-C024 0.1µF, 50V 04-5663
C025 10PF, 100V 04-5673
C101 22µF, 20V 04-5672
C111 0.022µF, 50V 04-5667
C112 470PF, 100V 04-5668
C121 0.001µF, 100V 04-5659
C122 2.2µF, 20V 04-5671
C123 1µF, 35V 04-5656
C124 100PF, 3KV 04-5532
C125 3300µF, 35V 04-5675
C211 47µF, 10V 04-5666
C221 0.0056µF, 3KV 04-5522
C301-C302 47µF, 10V 04-5666
C311-C312 0.01µF, 50V 04-5664
C321 100PF, 3KV 04-5532
C322 0.0056µF, 3KV 04-5522
C323 0.0047µF, 3KV 04-5547

Ludlum Measurements, Inc. Page 10-1 October 2018

Model 177 Technical Manual Section 10

TRANSISTORS

VOLTAGE REGULATOR

INTEGRATED CIRCUITS

DIODES

THERMISTOR

POTENTIOMETERS / TRIMMERS

Reference Description Part Number

C401-C402 1µF, 35V 04-5656
C403 0.1µF, 50V 04-5663
C411 47µF, 10V 04-5666
C421-C423 0.0047UF, 3KV 04-5547

Q101 2N7002LT1G 05-5840
Q102 MMBT3904T1G 05-5841
Q103 MJD210 05-5843
Q104 MMBT3904T1G 05-5841
Q111 MMBT3904T1G 05-5841
Q301 MJD200 05-5844
Q302 MMBT3904T1G 05-5841
Q401 MJD210 05-5843

VR211 LM2931AT 5.0 05-5813

U011 CD74HC4538M96 06-6297
U012 HFA3096BZ96 06-6468
U021 TLC372IDR 06-6290
U111 ICM7555CBA 06-6300
U121 HFA3096BZ96 06-6468
U201 ICL7663SCBA 06-6302
U301 LM285DR-1-2 05-5845
U311 TLC27M7IDR 06-6292

CR111-CR114 MMBD914LT1G 07-6353
CR201-CR202 CXSH-4LF 07-6358
CR321 1N4007 07-6274
CR401 MMBD914LT1G 07-6353
CR421-CR423 1N4007 07-6274

RT314 250K, 250mW 07-6366

R001 1M, HV TEST 09-6906
R002 50K, BAT T 09-6920
R013 50K, BAT C 09-6920

Ludlum Measurements, Inc. Page 10-2 October 2018

Model 177 Technical Manual Section 10

RESISTORS

Reference Description Part Number

R003 475K, 1%, 250mW 12-7859
R004 150 ohm, 1%, 250mW 12-7062
R011 4.75K, 1%, 250mW 12-7858
R012 82.5K, 1%, 250mW 12-7849
R014-R015 100K, 1%, 250mW 12 7834
R016 100 ohm, 1%, 250mW 12-7840
R021-R022 10.0K, 1%, 250mW 12-7839
R023 100K, 1%, 250mW 12-7834
R024 1.00K, 1%, 250mW 12-7832
R025 10.0K, 1%, 250mW 12-7839
R026-R027 100K, 1%, 250mW 12-7834
R028 10.0K, 1%, 250mW 12-7839
R029 221K, 1%, 250mW 12-7845
R0210 5.62K, 1%, 250mW 12-7871
R1 10.0K, 1%, 250mW 12-7839
R101 1.00K, 1%, 250mW 12-7832
R102 10.0K, 1%, 250mW 12-7839
R103 100 ohm, 1%, 250mW 12-7840
R111 1.00K, 1%, 250mW 12-7832
R112 100K, 1%, 250mW 12-7834
R113 1.00M, 1%, 250mW 12-7844
R114 35.7K, 1%, 250mW 12-7911
R115 100 ohm, 1%, 250mW 12-7840
R116 56.2K, 1%, 250mW 12-7873
R117 1.00M, 1%, 250mW 12-7844
R118 3.32K, 1%, 250mW 12-7870
R121 3.92K, 1%, 250mW 12-7875
R122 10.0K, 1%, 250mW 12-7839
R123 100, 1%, 250mW 12-7840
R124 392K, 1%, 250mW 12-7841
R125 47.5K, 1%, 250mW 12-7872
R126 100K, 1%, 250mW 12-7834
R127 10.0K, 1%, 250mW 12-7839
R128 221K, 1%, 250mW 12-7845
R129 1M, 5%, 250mW 10-7028
R201 165K, 1%, 250mW 12-7877
R202 1.00K, 1%, 250mW 12-7832
R203 2.2 ohm, 5%, 250mW 12-7932
R221 1M, 5%, 250mW 10-7028
R301 10.0K, 1%, 250mW 12-7839

Ludlum Measurements, Inc. Page 10-3 October 2018

Model 177 Technical Manual Section 10

TRANSFORMERS

MISCELLANEOUS

Calibration Board,
Drawing 347

CAPACITORS

POTENTIOMETERS

Reference Description Part Number

R302 1.00K, 1%, 250mW 12-7832
R303 2.21K, 1%, 250mW 12-7835
R311 750K, 1%, 250mW 12-7882
R312 301 ohm, 1%, 250mW 12-7863
R313 475 ohm, 1%, 250mW 12-7851
R315 22.1K, 1%, 250mW 12-7843
R316 1.00M, 1%, 250mW 12-7844
R321-R322 1G 12-7686
R323 1M, 5%, 250mW 10-7028
R401 200 ohm, 1%, 250mW 12-7846
R402 15 ohm, 5%, 1W 12-7738

T211 4275-083 4275-083
T411 40-0902, 9=GND, 10=GND 40-0902

P1 640445-3 MTA 156x3 13-8125
P2 1-640456-2 MTA 100x12 13-8061
P3 1-640456-0 MTA 100x10 13-8066
10 EA. CLOVERLEAF RECEPT.
011-6809-000-599 18-8771
1 EA. #26 Black Coax Ground 2.5 inch 21-9432

× 132

BOARD Completely Assembled
Calibration Board 5347-189

C1 0.0047µF, 100V 04-5570
C2 0.047µF, 100V 04-5565

R1 10K, RECORDER 09-6787
R2 100K, HV 09-6813
R3 1M, X1 09-6814
R4 1M, X10 09-6814
R5 2M, X100 09-6834
R6 250K, X1000 09-6819
R7 10K, DISCRIMIINATOR 09-6787

Ludlum Measurements, Inc. Page 10-4 October 2018

Model 177 Technical Manual Section 10

RESISTOR

RESISTOR NETWORK

MISCELLANEOUS

Wiring Diagram,
Drawing

SWITCHES

POTENTIOMET ERS

CONNECTORS

Reference Description Part Number

R9 680, 1/3W 12-7885

RN1 10K 12-7720

P6 CONN 1-640457-1 MTA100 13 8397

347 × 492

S1 46206-LR SLIDE 08-6523
S2 PA-1002 08-6543
S3 7101-SYZ-QE 08-6511
S4 HV (#923 SWITCHCRAFT) 08-6518
S5 BAT (#923 SWITCHCRAFT) 08-6518
S6 ALARM (#923 SWITCHCRAFT) 08-6518
S7 RESET (30 1 PB GRAYHILL) 08-6517

R1 10K, VOLUME 09-6753
R2 100K, ALARM SET 09-6795

J1 MAIN BOARD 5347-496,

3 PIN SIP
(CONN 640428-3 MTA 156) 13-8124

J2 MAIN BOARD 5347-496,

12 PIN SIP (CONN 1-640441-2) 13-8431

J3 MAIN BOARD 5347-496,

10 PIN SIP
(CONN 1-640441-0MTA 100) 13-8197

J4 CONNECT BOARD 5347-489 13-7801

5 PIN SIP (CONN-3-640428-5 MTA 156)

J5 CONNECTOR BOARD 5347-489 13-8096

2 PIN SIP (CONN3-643193-2 MTA-156)

J6 CALIBRATION BOARD 13-8161

5347-189, 11 PIN SIP
(CONN 1-640441-1 MTA 100)

J7 FLYING LEAD TO MAIN 4478-011
BOARD 5347-293

(RECPT-UG706)

Ludlum Measurements, Inc. Page 10-5 October 2018

Model 177 Technical Manual Section 10

AUDIO

BATTERY

MISCELLANEOUS

J8 CONNECTOR BOARD 5347-489 13-8041
(used for modifications only)

J9 CONNECTOR BOARD 5347-489 13-8461
8 PIN SIP (CONN 3-640441-8)
MTA-100

Reference Description Part Number

DS2 UNIMORPH (TEC3526PU) 21-9251

B1 6V (PS610 GELL CELL) 21-9385

F1 1 AMP (FUSE #312001 AGC-1) 21-9704
DS1 LAMP-PT 502-OUR-002F-W6 21-9169
DS3 LAMP-PT 502-OUR-002F-W6 21-9169
M1 Model 177 METER 4173-166
* KNOB PKG-50B 08-6601
* KNOB-407D2KI 08-6604
* KNOB-LOCK KL 701 08-6607
* KNOB-70-1-2G 08-6637
* WALL TRANSFORMER 21-8887
PX9025AWPL05
9 VDC 2.5A

Ludlum Measurements, Inc. Page 10-6 October 2018

Model 177 Technical Manual Section 11

Section

11

Drawings

MAIN BOARD, Drawing 347 × 496 (4 sheets)

MAIN BOARD Component Layout, Drawing 347 × 503

CALIBRATION BOARD, Drawing 347 × 132

CALIBRATION BOARD Component Layout, Drawing 347 × 133

CONNECTOR BOARD, Drawing 347 x 489

CONNECTOR BOARD Component Layout, Drawing 347 x 490

WIRING DIAGRAM, Drawing 347 × 492

Ludlum Measurements, Inc. Page 11-1 October 2018