Ludlum Measurements 78 User manual

LUDLUM MODEL 78 AND 78-1
DIGITAL ANALOG STRETCH SCOPE
March 2021
Serial Number 299335 and Succeeding
Serial Numbers

LUDLUM MODEL 78 AND 78-1
DIGITAL ANALOG STRETCH SCOPE
March 2021
Serial Number 299335 and Succeeding
Serial Numbers

Ludlum Measurements, Inc. March 2021
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]

Ludlum Measurements, Inc. March 2021
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Battery Installation 2-1
Operational Check 2-2
Specifications 3
Identification of Controls and Functions 4
Display 4-1
Display Status Definitions 4-1
Front Panel Controls 4-2
Main Board Controls 4-2
Cal/Switch Board Controls 4-3
Safety Considerations 5
Environmental Conditions for Normal Use 5-1
Warning Markings and Symbols 5-1
Cleaning and Maintenance Precautions 5-2
Maintenance 6
Recalibration 6-1
Batteries 6-2
Technical Theory of Operation 7
Detector Input/Amplifier 7-1
Discriminator 7-1
Low Voltage Supply 7-1
High Voltage Supply 7-2
Detector Overload 7-2
Microprocessor 7-2
Audio 7-2
S1 (Function) 7-3
S2-S4 7-3

Model78 TechnicalManual
Ludlum Measurements, Inc. March 2021
LCD Drive 7-3
Backlight Drive 7-3
Instrument Setup 8
Entering or Changing Switch Board Parameters 8-1
The Function Switch 8-1
Function Switch Position Descriptions and Variables 8-2
Loading Default Parameters 8-4
Calibration 8-4
General Detector Setup Information 8-5
Exposure Rate Calibration 8-5
Detector Overload (OVL) Calibration 8-6
Recycling 9
Parts List 10
Model 78 Digital Analog Stretch Scope 10-1
Main Circuit Board, Drawing 272 x 591 10-1
Cal/Switch Board, Drawing 272 × 352 10-3
Display Board, Drawing 408 × 259 10-4
Chassis Wiring Diagram, Drawing 272 × 596 10-5
Drawings and Diagrams 11

Model78and78-1 TechnicalManual Section1
Ludlum Measurements, Inc. Page 1-1 March 2021
Introduction
he Ludlum Model 78 and 78-1 Digital/Analog Stretch Scope features two radiation
radiation detectors mounted on a 3.7 m (12 ft) extendable pole. The two energy-
compensated, Geiger-Mueller (GM) detectors measure gamma radiation from 0.1 mR/hr
mR/hr to 1000 R/hr (1µSv/h –10,000mSv/h). The Model 78 measures in R (Roentgen)
(Roentgen) units while the 78-1 measures in Sieverts.
Both an analog meter and a backlit 4-digit LCD (liquid crystal display) are utilized for display. The
4-decade logarithmic meter face spans from 0.1 to 1000. The digital readout displays the level of
radiation in either mR/hr or R/hr (µSv/h), depending upon the detector selected. The LCD also
has indicators for low battery, alert, alarm, overflow, and detector overload.
Other instrument features include Dead Time Correction (DTC) to compensate for detector dead
time; audible click-per-event with programmable 1, 10, 100, and 1000 divide-by; LCD backlight
with programmable "on" time; programmable fixed or variable response time; and a count
overflow visual alarm.
Warning
There is a reduced response in pulsed fields due to the detector dead time.
The Model 78 incorporates independent adjustable alarms for both detectors. There are two alarm
indications. The first-level alarm is indicated by display of ALERT on the LCD. The second-level
alarm is indicated by display of ALARM and a continuous audible tone. The audible alarm can be
silenced (acknowledged) by depressing the RESET switch.
The electronics front panel is equipped with switches for control of detector selection, audio
on/off, fast or slow response times, LCD backlight, display reset, and power on/off. A headphone
jack is also available. Two “D” cells located in the handle provide power to the electronics. Battery
life is approximately 250 hours.
The stretch scope is made of stainless steel tubing that retracts to an overall length of 105.9 cm
(41.7 in.). The handle can be removed for storage, reducing the length to 92 cm (36.2 in.). The
electronics are housed in an aluminum body with a beige powder-coat finish and subsurface-
printed Lexan front panel. Front-panel switches are sealed with rubber “boots” for resistance to
moisture.
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