LUDLUM 375-20 User manual

LUDLUM MODELS 375-20, 375-30,
375-32 AND 375-34
DIGITAL WALL-MOUNT AREA MONITORS
September 2020
Serial Number 278020 and Succeeding
Serial Numbers

LUDLUM MODELS 375-20, 375-30,
375-32 AND 375-34
DIGITAL WALL-MOUNT AREA MONITORS
September 2020
Serial Number 278020 and Succeeding
Serial Numbers

Ludlum Measurements, Inc. September 2020
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. September 2020
Table of Contents
Introduction 1
Getting Started 2
Power Up 2-1
Radiation Units 2-2
Checking Parameters 2-2
Setting Alarm Points 2-2
Operational Check 2-3
Specifications 3
Operator Controls and Setup 4
Calibration Controls 4-1
Dipswitch (under calibration cover) 4-2
RS-232 Output 4-3
9-Pin Remote Data Connector 4-3
9-Pin Relays Connector 4-4
Detector Setups 4-4
Common Options and Modifications 5
Relay Options 5-1
Ethernet Interface Option 5-5
Time and Date Stamp Option 5-5
Printer DIP Switch Settings 5-6
Sigma Alarm Modification Option 5-7
4 to 20 mA Isolated Output Driver Option 5-8
Safety Considerations 6
Environmental Conditions for Normal Use 6-1
Cleaning Instructions and Precautions 6-1
Warning Markings and Symbols 6-2
Replacement of Main Fuse 6-3
Detector Connector 6-3

MODELS375-20,375-30,375-32&375-34
Ludlum Measurements, Inc. September 2020
Electrical Safety Precautions 6-3
Calibration 7
High Voltage 7-1
Calibration Parameters 7-1
Analog Output 7-2
Discriminator 7-2
Battery Charge 7-2
Recycling 8
Receiving and Installation 9
Unpacking and Repacking 9-1
Installation 9-2
Models 375-20 & 375-30 9-2
Models 375-32 & 375-34 9-3
Parts List 10
Model 375-20 Digital Wall-Mount Area Monitor 10-1
Model 375-30 Digital Wall-Mount Area Monitor 10-1
Model 375-32 Digital Wall-Mount Area Monitor 10-1
Model 375-34 Digital Wall-Mount Area Monitor 10-1
Main Board, Drawing 558 x 1 10-1
Wiring Diagram, Drawing 558 x 136 10-6
Drawings and Diagrams 11

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Introduction
he Model 375 Digital Wall-Mount Area Monitor is designed to
monitor for nuclear radiation. Featuring a wall-mount chassis, the
Model 375 has a four-digit LED display that is readable from 9 m (30
ft) away. Backlit indicators warn of low radiation alarm (yellow), high
radiation alarm (red), instrument failure (red) and low battery (yellow). A green
status light is a positive indication of instrument operation.
Parameters are protected under a calibration cover. Calibration is easily
accomplished by moving the CAL dipswitch to the right, and using the push
buttons to increment or decrement the calibration constant, dead time
correction, and alarm point parameters. Parameters are stored in non-volatile
memory (retained even with power disconnected).
A five-decade logarithmic analog output is provided. A battery backup provides
48 hours of additional use after the primary power is removed.
Note:
The detector does not contain any consumable materials.
Note:
If the detector is used in a manner not intended by the
manufacturer, the detector may not function properly.
Section
1
T

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The information contained in this manual is pertinent to the following Model
375 systems:
The Model 375-20 includes two Model 44-137 scintillation detectors and
custom length cables. Detectors may be supplied with or without
environmental enclosures.
The Model 375-30 includes two Model 44-99 scintillation detectors, each
with internal lead shield to reduce background radiation. Detectors may be
supplied with or without environmental enclosures.
The Model 375-32 features an instrument chassis that mounts in one of
two freestanding towers; furnished with two Model 44-99 scintillation
detectors (one in each tower), each with internal lead shield to reduce
background radiation.
The Model 375-34 features two chassis mounted into two freestanding
towers including two displays (one in each tower); furnished with four
Model 44-99 scintillation detectors, each with an internal lead shield to
reduce background radiation.
The Model 44-137 scintillation detectors are intended to detect low levels of
waste radiation. Examples of environments these detectors may be used
include scrap yards and hospitals. The Model 44-137 contains lead shields
around the crystal, which allow specific coverage areas for radiation detection.
These detectors are included with the Ludlum Model 375-20 Waste Monitor.
Model 44-137:
Detector: two each 5.1 x 5.1 cm ( 2 x 2 in.) diameter thick shielded NaI(Tl)
scintillation detectors with weathertight housings
Size(each): 8.9 x 22.4 cm (3.5 x 8.8 in.) (Dia x L)
Weight (each): 5.8 kg (12.7 lb)
Electronics size: 18.7 x 24.6 x 6.4 cm (7.5 x 9.7 x 2.5 in.) (H x W x L)
Electronics weight: 2.9 kg (6.5 lb)

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The Model 44-99 scintillation detectors are intended to detect low levels of
waste radiation. Examples of environments these detectors may be used
include scrap yards and hospitals. The Model 44-99 contains lead shields
around the crystal, which allow specific coverage areas for radiation detection.
These detectors are included with the Ludlum Model 375-30 Waste Monitor.
Model 44-99:
Detector: 2 ea. 7.6 cm (3 in.) diameter x 2.5 cm (1 in.) thick shielded NaI(Tl)
scintillation detectors with up to 61 m (200 ft) cables
Size(each): 33 x 43.2 x 21.6 cm (13 x 17 x 8.5 in.) (H x W x L)
Weight (each): 14.5 kg (32 lb)
Model 375:
Electronics Size: 18.7 x 24.6 x 6.4 (7.4 x 9.7 x 2.5 in.) (H x W x L)
Electronics Weight: 2.9 kg (6.5 lb)

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Getting Started
he Model 375 Digital Wall-Mount Area Monitor is designed for
ease of use. This section of the manual is designed to help the first-
time user get started. Initial power-up and basic features of the
Model 375 will be discussed in this section. Other sections of the
manual provide more detailed information.
Power Up
Plug the wall-mount 9 Vdc power supply into a suitable wall (mains) outlet.
If the RS-232 feature is used, plug in a suitably wired 9-pin
connector cable. (See Pages 4-3 and 4-4 for the pin assignments
of the 9-pin connectors.) Turn power ON with the left side panel
switch. Do not turn power OFF unless the unit is to be removed
from service.
Read and then remove the sticker (illustrated to the left) from the
instrument calibration cover. Checking and setting of the alarm-
point(s) is discussed in detail below and on pages 2-2 and 7-1 of
this manual.
Initial power-up (by way of the power switch on the left-side panel) will
momentarily activate the internal front-panel lights, sound the audio, and
display "8888" on the 4-digit LED display. The firmware version number
(39665Nyy) is then displayed as "396" and "65yy"(where “yy”represents the
current version number).
Section
2
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When the instrument has finished measuring background, it will display the
current radiation reading and begin checking for an alarm condition.
Radiation Units
The Model 375 may be calibrated for almost any desired radiation units of
measure. Common units of measure include mR/hr, µR/hr, R/hr, mSv/h,
µSv/h, cps, cpm, and kcpm. In each case, the unit of measure is indicated
underneath the four-digit display. Throughout the rest of this manual, the
notation <units> will be used as a substitute.
Checking Parameters
Check the low alarm point setting by pressing the LOW ALARM button. The
low alarm point will be displayed as long as the button is pressed. The low
alarm point is in units of <units>. The low alarm point can be set from 0.1
<units> to 9999 <units>.
Check the high alarm point setting by pressing the HIGH ALARM button. The
high alarm point will be displayed as long as the button is pressed. The high
alarm point is in units of <units>. The high alarm point can be set from 0.1
<units> to 9999 <units>.
Check the calibration constant by pressing the CAL CONST button. The
calibration constant will be displayed as long as the button is pressed. The
calibration constant is in units of cpm (counts per minute) per <units>. The
calibration constant can be set from 0.1 cpm/<units> to 9999
cpm/<units>.
Check the detector dead time correction by pressing down on the DEAD
TIME button. The dead time correction will be displayed as long as the
button is pressed. The dead time correction is in units of microseconds. The
dead time correction can be set from 0.1 microseconds to 9999 micro-
seconds.
Setting Alarm Points
The LOW ALARM and HIGH ALARM points can only be changed while the
instrument is in calibration mode. Switch the top dipswitch CAL MODE
(behind the calibration cover) to the right to place the instrument into
calibration mode.

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Changing alarm points is done by holding down the corresponding
parameter key and pressing the up or down arrow buttons. Alarm points can
be set in the range of 0.1 to 9999. When an alarm point is changed, the
instrument will sound an audible beep to confirm the saving of the
parameter, and will then return to displaying the current radiation level.
Note:
Once the alarm point(s) is set, it is important to remember to
switch the CAL MODE switch back to the left. This action
protects the parameters from inadvertent changes.
Operational Check (optional)
The operational check is an important assurance that the radiation detector
and electronics are working correctly.
Note:
Ludlum Measurements suggests that an operational check be
performed on a regular basis. Local procedures may
supersede this suggestion.
For an operational check, it is necessary to use a radiation check source (not
included, but available). When not being used, store the check source in a
secure area.
Note:
LMI check sources present very minimal risks and are
therefore unlicensed (Exempt Quantity Sources reference:
10 CFR 30.71 Schedule B). The radioactive element is sealed
(permanently bonded or fixed inside a capsule) so you need
not wash your hands after handling. Radiation exposure
while handling this source is very minimal with no identified
long or short-term risks. Although the amount of radiation
given off by exempt sources is so low that it presents no
significant hazard, they should be handled with care and
respect. Time, distance and shielding are the best ways to
control exposure.

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1. Taking the source in hand, place it so that it is located on or near
the center (same location each time) of one of the detectors.
Hold it there for approximately five seconds or until the reading
stabilizes. Take note of the displayed level of radiation.
2. Verify that the reading is within 20% of the last reading
obtained. Remove the source from the detector.
3. If an alarm is activated, ensure that all visual and audible devices
(if applicable) work correctly.
4. Repeat the procedure for the other detector(s) if it was not
triggered by the first test.

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Specifications
Display: four-digit LED display with 2 cm (0.8 inch) character height
Display Range: 000.0-9999
Display Units: can be made to display in µR/hr, mR/hr, R/hr, µSv/h,
mSv/h, Sv/h, µrem/hr, mrem/hr, rem/hr, cpm, cps, and others
Linearity: readings within 10% of true value with detectors connected
Operating Range: depends upon the type of detectors used and the units
of measure
Response: typically 3 seconds from 10% to 90% of final reading
Status (green light): indicates the instrument is functioning properly
LOW ALARM: indicated by a yellow light and slow-beeping (1 per second)
audible tone (can be set at any point from 0.0-9999)
HIGH ALARM: indicated by a red light and a fast-beeping (4 per second)
audible tone (can be set at any point from 0.0-9999)
Note:
Audible indicators can be configured as a single beep if
desired. Audio intensity is controlled by rotating the baffle
on the audio device. Audio intensity may also be adjusted by
moving an internal connector.
DET FAIL: indicated by a red light and an audible tone greater than 68 dB
at 61 cm (2 ft) for conditions of detector overload, no count from
detectors or instrument failure
LOW BAT: indicated by a yellow light, when two hours of battery life
remain
Section
3

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Connector: dependent upon the system
Ethernet (optional): 10 Base-T connection for use with Ludlum software
Calibration Controls: accessible from the front of the instrument
(protective cover provided)
High Voltage: adjustable from 450 to 2500 V
Dead Time: adjustable to compensate for dead time of the detector and
electronics (can be read on the display)
Overload: a display reading of ˝-OL-˝and audible FAIL alarm indicates
detector saturation, usually set to initiate just above the highest range of
the detector
Over-range: A display reading of ˝----˝ and activated low and high alarms
indicate that the radiation field being measured has exceeded the counting
range of the instrument (or when dead time correction accounts for more
than 75% of the displayed reading).
Data Output: a 9-pin connector providing 5-decade log output, RS-232
output, signal ground connection, FAIL and HIGH ALARM signals (current
sink), and direct connection to battery and ground
RS-232 Output: a two-second dump for computer data logging
Remote (optional): Ludlum Model 271 or 272 remote units
Audio: Intensity can vary from approximately 68 dB to 100 dB through
operation of the external rotary baffle and the internal voltage
connection. Frequency is approximately 3 kHz.
Power: 9 Vdc wall-mount adapter, handles any mains voltage in the
world, supplied with four sets of prongs for almost any style wall
receptacle
Battery Life: typically 48 hours in non-alarm condition; 12 hours in alarm
condition
Battery Charger: Battery is continuously trickle charged when the
instrument is connected to line power and turned on.
Instrument Construction: aluminum housing with ivory powder-coat
finish
Instrument Size: 18.7 x 24.6 x 6.4 cm (7.4 x 9.7 x 2.5 in.) (W x H x D)
Instrument Weight (each): 2.9 kg (6.5 lb)

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Operator Controls and Setup
Calibration Controls
Remove the calibration cover to expose the calibration controls. The
calibration controls include the up/down buttons, five calibration
potentiometers, and the option dipswitch (detailed in the following
subsection). The five potentiometers are detailed below.
ANALOG: Used to adjust the logarithmic analog voltage output. It is
adjusted in calibration mode to the full-scale voltage reading or adjusted
to a known point at some given reading.
HV: Used to set the high voltage required for detector operation.
Adjustable from 450-2500 Vdc. The high voltage required will depend
on the type of detector used. Internal GM detectors typically require 550
Vdc. Be sure to check the high voltage with a high-impedance (1000-
Mohm impedance) voltmeter only. A high-voltage checkpoint is located
next to the HV potentiometer.
DISC: Internal discriminator used to set pulse threshold for counting
pulses from the detector. The pad allows direct measurement of
threshold voltage. Utilize a Ludlum Model 500 pulser or equivalent to
inject pulses of the desired threshold size. The pulse height threshold is
adjustable from 2.0 mVdc to 100 mVdc.
BAT CHARGE: Used to set the backup battery, trickle charging voltage.
It is set to 6.9 Vdc while the battery is disconnected.
OVERLOAD: Used to set the detector current overload point. When
excessive radiation causes the detector to overload, this set point will
cause the FAIL light to engage, and the display will be forced to -OL-.
Section
4

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Dipswitch (under calibration cover)
When the calibration cover is removed, a four-pole dipswitch is accessible
that can activate or deactivate options. These four options are CAL MODE,
LATCH, ALARM, RANGE, and SINGLE BEEP.
Dipswitch 1: Switching the top CAL MODE switch to the right, places
the instrument into calibration mode. Parameters can only be changed
while the instrument is in calibration mode. Calibration mode also
changes the analog output to full-scale so that the full-scale voltage may
be set by the ANALOG potentiometer. Calibration mode also slows the
response time of the display and increases the accuracy. If the display
seems too erratic, leaving this switch in the calibration mode during
operation will help. Moving the CAL MODE switch back to the left locks
the parameters and disables any further changes.
Dipswitch 2: The second switch, LATCH ALARM, changes the high
alarm to a latching alarm. This switch does not affect the low alarm,
which is always non-latching. When switched to the left, the high alarm
is non-latching; the alarm automatically turns off when the radiation
level drops below the alarm point. When switched to the right, the high-
alarm light and audio signals are latched until either the LOW ALARM or
HIGH ALARM button is pressed.
Dipswitch 3: The third switch, RANGE, selects the range of the
instrument. To select the 0.1 <units> - 999.9 <units> range, switch the
RANGE switch to the left. To select the 1 <units> - 9999 <units> range,
switch the RANGE switch to the right.
Dipswitch 4: Switching the fourth switch to the right, places the
instrument into SINGLE-BEEP mode. This option limits the audio
output to a single half-second beep on LOW ALARM and HIGH ALARM.
DET FAIL audio output (steady tone) is not limited.

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BYTE1 0 x
BYTE2 x x
BYTE3 x OR x
BYTE4 x x
BYTE5 . .
BYTE6 x 0
BYTE7 Audio Status =1=on
BYTE8 High Alarm Status=1=on
BYTE9 Low Alarm Status =1=on
BYTE10 Over Range Status=1=on
BYTE11 Monitor Status =1=on
BYTE12 Error Code
BYTE13 Carriage Return (ODH)
BYTE14 Line Feed (0AH)
The RS-232 data includes the
current radiation readings and the
current condition of the status
lights. The data is presented in the
following format:
RS-232 Output
With the CAL MODE dipswitch in the left position, the Model 375 dumps RS-
232 data onto pin 4 of the 9-pin connector every two seconds.
9-Pin Remote Data Connector
(female sockets)
The 9-pin connector provides output signals from the instrument and
input voltage to the instrument. The pin assignments are:
pin1- +BATTERY
pin2- GND IN
pin3- FAIL_L
pin4- RS232 DUMP
pin5- ANALOG OUT
pin6- NA
pin7- HIGH ALARM_L
pin8- EXT RESET_L
pin9- +5VDC OUT
The FAIL and HIGH ALARM digital signal outputs are open drain 2N7002
outputs, able to sink about 50 mA each.

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9-pin Relays Connector (male pins)
The 9-pin relay connector provides a Form C (common, normally open, and
normally closed) contact for the three fail-safe relays of LOW ALARM
(alert), HIGH ALARM, and FAIL. The pin assignments are:
pin1- FailNO
pin2- FailNC
pin3- AlertCOM
pin4- AlarmNO
pin5- AlarmCOM
pin6- FailCOM
pin7- AlertNO
pin8- AlertNC
pin9- AlarmNC
Detector Setups
Model 375-20
Typical response and set points for the Model 375-20 with Model 44-137
Scintillation Detectors are as follows:
Operating Voltage: 600-1200 Vdc, determined by comparing
plateaus
Threshold: 10 mVdc (using a 0.99 m {39 in.} cable)
Calibration Constant: 1600 cpm/µR/hr
Dead Time Correction: 5 µsec
Linear Range with DTC: 10-1500 µR/hr (0.1-15 µSv/h)
Typical Checkpoints:
100 µR/hr
150 µR/hr - calibration constant set point
200 µR/hr
500 µR/hr
1000 µR/hr - dead time correction set point
1500 µR/hr