Model 194 Series
User’s Manual
Section 5
Ludlum Measurements, Inc.
Page 5-2
October 2020
Initial Calibration Procedures
1.
If any calibration procedure cannot be completed satisfactorily, the
instrument should be tagged and removed for proper disposition.
2.
A “low” gamma background radiation area is needed, defined as an area
away from known radiation sources, measuring 15 uR/hr (0.15 µSv/h)
or less.
3.
Ensure that the AA batteries measure at least 2.4 Vdc (turn rotary
switch to BAT and battery voltage is shown on LCD). Verify green
LED labelled BAT OK illuminates.
4.
Check to see if the instrument is marked for international units of
µSv/h, and if so, ensure that the internal dipswitch SW5 is set for
position 1 ON and position 2 OFF. Otherwise, internal dipswitch SW5
is set for position 1 OFF and position 2 ON.
5.
Remove the CAL cover on the front panel to access the calibration
potentiometers. Open the instrument to access the test points on the
main board. Each test point is labelled.
For first time calibration only:
In a low-background area with the detector
connected, use the voltmeter to measure the following points, and adjust the
appropriate calibration potentiometer to the target voltage, in this order:
CAL POT
TESTPT
TARGET
L-HV
HVL
0.750 Vdc
H-HV
HVH
0.500 Vdc
Switch the rotary RANGE switch to LO to adjust LZERO until
display shows approximately 5 µrem/hr (or 0.05 µSv/h).
Switch the rotary RANGE switch to HI to adjust HZERO until
display reads zero.
