Model 194 Series
User’s Manual
Section 5
Ludlum Measurements, Inc.
Page 5-3
October 2020
Cs-137 Gamma Range Calibration
1.
Switch the instrument to LO range.
2.
Ensure that the center of the detector is correctly placed and expose the
instrument to a calibrated field of 1500 µrem/hr (15 µSv/h). Adjust the
front-panel potentiometer marked L-HV until the instrument LCD
shows 1500 µrem/hr (15.00 µSv/h) within 10%.
3.
Change the calibrated field to 150 µrem/hr, expose the detector and
adjust the front-panel control marked LZERO until the LCD shows
150 µrem/hr (1.50 µSv/h) within 10%. For a less “jumpy” reading,
toggle the F/S switch to S (slow).
4.
Switch the instrument to HI range.
5.
Ensure that the center of the detector is correctly placed and expose the
instrument to a calibrated field of 150 mrem/hr (1500 µSv/h). Adjust
the front-panel potentiometer marked H-HV until the instrument LCD
shows 150.0 mrem/hr (1500 µSv/h) within 10%.
6.
Change the calibrated field to 15.0 mrem/hr, expose the detector and
confirm that the LCD shows 15.0 mrem/hr (150 µSv/h) within 10%.
IF necessary, adjust the potentiometer marked HZERO in order to
correct the reading. For a less “jumpy” reading, toggle the F/S switch to
S (slow).
7.
Document all four readings above on an appropriate calibration
certificate.
8.
Open the can of the instrument and use the voltmeter or multimeter to
measure the DC voltages at the test points marked HVL and HVH, and
document these voltages on the appropriate calibration certificate.
Cs-137 Gamma Range – Overload Check
1.
If desired, place the instrument in a high radiation field equal to 10
times the highest measurable value. For the Model 194, this field would
be 2000 mrem/hr or 20 mSv/h.
2.
Confirm that the instrument, in either LO or HI range, displays the
overload symbol on the display (a leftmost single digit “1”). Document on
the calibration certificate that this test was performed.
