LUDLUM 177-56 User manual

LUDLUM MODEL 177-56
RATEMETER
January 2019
Serial Number 322945 and Succeeding
Serial Numbers

LUDLUM MODEL 177-56
RATEMETER
January 2019
Serial Number 322945 and Succeeding
Serial Numbers

Model 177-56 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 177-56 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 2-2
Specifications 3
Description of Controls and Functions 4
Front Panel 4-1
Back Panel 4-2
CAL Control - Alpha 4-3
Internal Controls (Overhaul Only) 4-4
CAL Control – Beta 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

Model 177-56 Technical Manual
Amplifier 8-1
Discriminator 8-1
Digital Analog Conversion 8-1
Time Constant 8-2
Reset 8-2
High Voltage (HV) 8-2
Low Voltage 8-2
Battery Charge 8-3
High Voltage Test 8-3
Battery Test Voltage 8-3
Recycling 9
Parts List 10
Model 177-56 Ratemeter 10-1
Main Board, Drawing 347 × 603 10-1
Calibration Board, Drawing 347 × 132 10-4
Power/Data Board, Drawing 347 x 489 10-5
Pancake Slave Board, Drawing 347 x 595 10-5
Wiring Diagram, Drawing 347 × 613 10-6
Drawings and Diagrams 11

Model 177-56 Technical Manual Section 1
Ludlum Measurements, Inc. Page 1-1 January 2019
Introduction
he Ludlum Model 177-56 is a dual-detector (scintillator/GM) system,
allowing selection of either alpha or beta readings, functioning as an
alpha/beta frisking station.
Note:
There is no ALARM audio on this system.
It provides both aural and visual indication of the count rate of the detector
selected.
The ratemeter has four multiplier scales of 1, 10, 100 and 1K, which result in a
range of 0-500,000 counts per minute.
The regulated high-voltage power supply for the primary detector
(scintillator/alpha) is externally adjustable and the secondary detector
(GM/beta) by an internal trimmer.
The unit features preset calibration for GM or scintillation detectors. Other
features include fast or slow time constant, adjustable audio volume, recorder
output, and TTL compatible pulse output.
Internal tests include high voltage test (HV).
Section
1
T

Model 177-56 Technical Manual Section 2
Ludlum Measurements, Inc. Page 2-1 January 2019
Getting Started
he Ludlum Model 177-56 Ratemeter is designed for use with GM
(Geiger Mueller) or scintillation detectors. Typical applications
include contamination monitoring, surveying, area monitoring, and
frisking station.
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 177-56 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
For scintillation detectors, the most stable part of the plateau will have to be
determined to select the correct operating point. For GM tubes, the voltage
is set to 900 volts, unless otherwise indicated.
For scintillator detectors, the high-voltage supply will normally require
adjustment each time the detector or source of energy is changed. The gain
spectrum of the photomultiplier tubes is very wide (1000 to 1 typically at a
Section
2
T

Model 177-56 Technical Manual Section 2
Ludlum Measurements, Inc. Page 2-2 January 2019
single operating point). Expose the detector to a source and increase the
voltage until a stable reading is obtained from the source.
Connect the instrument to line power, and then turn the power switch to
ON. Select the operating point and connect a scintillation or GM detector
to the instrument. Expose the detector to a source and run a count-versus-
HV plateau by adjusting the HV potentiometer located on the back panel.
Finally, select an operating point when a stable reading (small change in
count with change in high voltage) is achieved.
Note:
Most GM detectors will operate at 900 volts. However, some
smaller GM tubes operate at lower voltages.
Operating the Instrument
The high voltage should be adjusted as determined in the procedure above.
Response and volume will be as desired.
The range selector should be set at an appropriate range and the detector
connected.
Increase the meter count and listen for audio circuit sound.
Reset button, when depressed, should drive the meter to zero.
Proceed with use.

Model 177-56 Technical Manual Section 3
Ludlum Measurements, Inc. Page 3-1 January 2019
Specifications
0
Power: 95-250 VAC wall transformer and 6-volt gel-cell (sealed lead-acid)
battery; typical battery life of approximately 50 hours with a fully charged
battery.
Fuse:1 amp 3AG fuse
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 1 (Alpha):variable from 400 to 1500 V (rear-panel
adjustment)
High Voltage 2 (Beta):900 V (internal adjustment on the pancake board)
Input Sensitivity 1 (Alpha):adjustable from -10 through -100 mV
Input Sensitivity 1 (Beta):-10 to -20 mV (fixed)
Connectors: for the beta GM detector, it is a series “C” connector. For
the alpha scintillator, it is an MHV connector.
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
Section
3

Model 177-56 Technical Manual Section 3
Ludlum Measurements, Inc. Page 3-2 January 2019
Unbuffered Output:may be used to externally add to or subtract from the
meter reading
Finish: powder coat paint
Size:16 x 20.3 x 17.5 cm (6.3 x 8 x 6.9 in.) (H x W x D), excluding handle
Weight: 1.9 kg (4.2 lb) with battery

Model 177-56 Technical Manual Section 4
Ludlum Measurements, Inc. Page 4-1 January 2019
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 online 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.
Audio Speaker: a unimorph speaker, located behind the front panel.
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.
Section
4

Model 177-56 Technical Manual Section 4
Ludlum Measurements, Inc. Page 4-2 January 2019
Connectors: The beta/GM detector is a series C connector. The alpha/
scintillator is an MHV connector.
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 in the BAT OK marking. If the needle is on or below the lower
mark, the battery is dead and should be charged.
HV TEST Button: When this button is depressed, the meter displays the
detector high voltage. (scintillator/Alpha HV 1 only)
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.

Model 177-56 Technical Manual Section 4
Ludlum Measurements, Inc. Page 4-3 January 2019
PIN 3: instrument common (ground).
PIN 4: N/A was alarm sink in m177.
PIN 5: Pulse out. A negative pulse connected to the
discriminator output through a 0.001 µF capacitor,
typically -4.0 volts. This output comes from the scintillation
(MHV) side only.
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 – Alpha
Remove the calibration (cal) cover plate to access the following calibration
potentiometers:
DISCR: Discrimination control. Alpha scintillator side, 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: X1000 through X1 calibration controls used to
calibrate each of the ranges.
HV ADJ: used to set detector operating voltage (for alpha/scintillators).
RCDR: used to calibrate the recorder output.

Model 177-56 Technical Manual Section 4
Ludlum Measurements, Inc. Page 4-4 January 2019
Internal Controls (Overhaul Only)
The following controls are located internally, on the main circuit board:
BAT C: used to adjust charge voltage to 6.825 volts.
BAT T: used to adjust meter test voltage reading to 5.97 volts at the BAT
OK line (dead battery line).
HV T: used to adjust the high-voltage test reading to correspond with the
actual high-voltage output (HV Alpha/scintillator only).
CAL Control – Beta
Pancake DISC:The discrimination level on the pancake board (-595) is
fixed at around 10 mV and can be checked with a Ludlum m500 pulser.
Apply an -80mV signal to the C connector on the front panel to test.
Note: Approaching -10 mV, the trip point can cause oscillation
and will yield count errors. Normal pancake inputs over-drive the
-10 mV level and are counted properly.
GM HV: used to adjust the pancake GM detector bias voltage to 900 ±25
VDC. This trimmer is located on the pancake board mounted on the left
rear chassis of the unit (looking from the front). Use care when adjusting
this trimmer. This trimmer is set at the factory and should not need
adjustment.

Model 177-56 Technical Manual Section 5
Ludlum Measurements, Inc. Page 5-1 January 2019
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 177-56 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.
2. Allow the instrument to sit for one minute before cleaning.
Section
5

Model 177-56 Technical Manual Section 5
Ludlum Measurements, Inc. Page 5-2 January 2019
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.

Model 177-56 Technical Manual Section 5
Ludlum Measurements, Inc. Page 5-3 January 2019
•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 177-56 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.

Model 177-56 Technical Manual Section 6
Ludlum Measurements, Inc. Page 6-1 January 2019
Calibration and Maintenance
Calibration
Note:
Local procedures may supersede the following.
In order to calibrate both the ratemeter and HV, the user will need a Ludlum
Model 500 pulser or equivalent and a high–impedance voltmeter with at
least 1000 Megohm meter input resistance to adjust the detector voltage.
Use the MHV (alpha connector) and 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.
Drive the meter to full scale (500x) and adjust RCDR (recorder output) for 1-
volt output.
Alpha scintillators should be set to -35 ±10 mV. To lower the scintillation
detector operating voltage, decrease the input sensitivity to 10 ±2 mV.
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 177-56 to an external voltmeter (using the MHV
connector). 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 rear-panel HV control, vary the high-voltage
output from 500 to 1200 VDC and ensure that the high-voltage meter reads
within 10% of the Model 177-56 meter reading.
Section
6