Ludlum Measurements 177 User manual

LUDLUM MODEL 177
ALARM RATEMETER
October 2018
Serial Number 322945 and Succeeding
Serial Numbers

LUDLUM MODEL 177
ALARM RATEMETER
October 2018
Serial Number 322945 and Succeeding
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
Ludlum Measurements, Inc. Page 1-1 October 2018
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.
Section
1
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Model 177 Technical Manual Section 2
Ludlum Measurements, Inc. Page 2-1 October 2018
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.
Section
2
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Model 177 Technical Manual Section 2
Ludlum Measurements, Inc. Page 2-2 October 2018
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.