Ludlum Measurements 194 Series User manual

LUDLUM MODEL 194 SERIES
DOSE EQUIVALENT RATE METER
June 2021
Serial Number 350220
and Succeeding Serial Numbers

LUDLUM MODEL 194 SERIES
DOSE EQUIVALENT RATE METER
June 2021
Serial Number 350220
and Succeeding Serial Numbers

Model194Series User’s 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]

Model194Series User’s Manual
Table of Contents
Introduction 1
Getting Started 2
Unpacking and Repacking 2-1
Description of Controls and Functions 2-1
Specifications 3
Operating Procedures 4
Calibration 5
Non-Radiation Adjustment 5-1
Calibration Equipment Required 5-1
Initial Calibration Procedures 5-2
Cs-137 Gamma Range Calibration 5-3
Cs-137 Gamma Range –Overload Check 5-3
Safety Considerations 6
Environmental Conditions for Normal Use 6-1
Warning Markings and Symbols 6-1
Cleaning and Maintenance Precautions 6-2
Spare Parts List 7
Recycling 8
Drawings and Diagrams 9

Model194Series User’s Manual Section1
Ludlum Measurements, Inc. Page 1-1 October 2020
Introduction
he Ludlum Model 194 DOSE EQUIVALENT RATE
METER is designed to accurately measure gamma radiation
doses. It utilizes a special plastic scintillator that converts the radiation to
visible light, which is then measured and displayed. It is very sensitive and
can measure background levels of radiation as well as higher levels.
The Model 194 is similar to a Micro R meter in sensitivity, but has a flat
energy response and measures ambient dose equivalent, not exposure.
Most Micro R meters utilize sodium iodide (NaI), which over-responds
to many common gamma ray energies, causing incorrect high readings.
The Model 194 measures dose, specifically ambient dose equivalent, and
has a response that is relatively flat over the most common gamma ray
energies. See Figure 1.
Figure 1. Energy Response Comparison
T
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Ludlum Measurements, Inc. Page 1-2 October 2020
The Model 194 is built for rugged use, featuring a well-built aluminum
body and splash-proof seals on all switches. It is also simple to use, with
no firmware or software built into the instrument.
The Model 194 can measure in units of µrem/hr (mrem/hr in the high
range) or in the SI units of µSv/h. It features a 3 ½ digit digital liquid
crystal display (LCD) with large, easy-to-read digits. A backlight toggle
switch illuminates the display under low lighting conditions.
The Model 194 detector is located inside the aluminum “can” and well
protected against shock and possible damage. The “/E”variant is built
for extremely low levels of energy. The detector extends from the
aluminum can and has a low-energy metallized polyester window to
enhance sensitivity for gamma rays in the 10-60 keV range. A vinyl cap
covers and protects the thin window when not being used.
The Model 194 is powered by two AA alkaline batteries, located in a
sealed compartment on the front panel. Battery life will depend on
many factors but is typically 200 hours under typical conditions.
There are options available to add to this instrument’s versatility,
including a headphone modification (part # 4475-118) and a shoulder
strap (part # 4475-120).
This manual encompasses the Model 194 Series, which includes the
Model 194 (µrem/hr display and internal detector), the Model 194/E
(µrem/hr display and extended detector), the Model 194/S (µSv/h
display and internal detector), and the Model 194/SE (µSv/h display
and extended detector).

Model194Series User’s Manual Section1
Ludlum Measurements, Inc. Page 2-1 October 2020
Getting Started
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. The Model 194 serial number is located on the side of the
unit.
To return an instrument for repair or calibration, provide sufficient packing
material to prevent damage during shipment. Be aware that the thin mica
window of the detector may be damaged (imploded) because of pressure
differentials if the unit is shipped by air. Protect the unit by putting it inside a
sealed can or other protective enclosure.
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 “Service Department” from the drop-down menu. Then choose
the appropriate Repair and Calibration division where you will find a link to
the form.
Note:
Ludlum Measurements, Inc. recommends recalibration at
intervals no greater than one year, assuming that regular
operational checks are performed. Check the appropriate local,
state, and federal regulations to determine required
recalibration intervals.
Description of Controls and Functions
Range Selector Switch: A four-position rotary switch marked OFF, BAT,
LO, and HI. Turning the range selector switch from OFF to BAT position
provides the operator with a battery check of the instrument (see BAT OK
lamp function below). Moving the range selector switch to the LO range
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position provides the operator with a full-scale reading of 1999 µrem/hr (or
19.99 µSv/h). Moving the range selector switch to the HI range position
provides the operator with a full-scale reading of 199.9 mrem/hr (or 1999
µSv/h).
BAT OK lamp: illuminates when the main rotary switch is in the BAT
position and when the battery voltage is above 2.1 volts. NOTE: Batteries
should be replaced if the lamp becomes dim or does not illuminate.
Range Calibration Adjustments: Recessed potentiometers located under
the calibration cover (CAL), on the left side of the front panel.
AUD: controls starting point of audio frequency. When completely
counter-clockwise, audio is quiet until approximately 100 µrem/hr
(1 µSv/h). When completely clockwise, frequency is approximately 3
kHz at background levels of radiation. Typically adjusted to get a
few clicks at background levels of radiation.
L-HV: controls detector voltage for low range, typically set to
calibrate the high point (~80%) of full-scale reading
LZERO: controls linearity for low range, set at background or at a
low point (~10%) of full-scale reading
H-HV: controls detector voltage for high range, typically set to
calibrate the high point (~80%) of full-scale reading
HZERO: controls linearity for high range, set at background or at a
low point (~10%) of full-scale reading
AUDIO: At low readings, the audio clicks. At higher readings, a continuous
tone with increasing frequency as meter reading increases.
AUDIO ON/OFF: Switches audio on or off.
F-S toggle switch: Selecting the fast, "F," position of the toggle switch
provides 90% of full-scale meter deflection in 3 seconds. In the slow, "S,"
position, 90% of full-scale meter deflection takes 15 seconds. The "S"
position should be used for slow response and more accurate measurements.
LAMP ON/OFF: turns display backlight on or off.
Center of Detector: The center of the internal detector is indicated by
shallow dimples in the instrument’s “can,”located under the display. The
center of the extended detector for the /E or /SE version is on the
centerline of the extended cylinder and at the point where the cylinder meets
the can.

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Ludlum Measurements, Inc. Page 3-1 October 2020
Specifications
0
Detector: 3.2 x 3.2 cm (1.25 × 1.25 in.) lead-loaded plastic scintillator
Linearity: ±10%
Energy Response (Model 194 and 194/S only): energy-flat within 30%
ambient dose equivalent from 50 to 1300 keV, relative to 137Cs response
Detector Voltage: adjustable from front panel calibration controls during
calibration, variable from approximately 250 to 1200 Vdc
Operating Voltage: two ranges, LO and HI
LO: 0 to 1999 µrem/hr or 0.00 to 19.99 µSv/h
HI: 0.0 to 199.9 mrem/hr or 0 to 1999 µSv/h
Response Time: in the F (fast) position, response time is 3 seconds, and 15
seconds in the S (slow) position; both measurements made for a response
from 10% to 90% of the final reading
LCD Display: 3 ½ digit LCD, digit height 10.2 mm (0.4 in.), 0-2 V input, with
over-range indication (leftmost “1” and no other digits)
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