Model 3 Technical Manual Section 6
Ludlum Measurements, Inc. Page 6-2 April 2016
Exposure Rate Calibration
Connect the input of the instrument to a negative pulse generator, such
as a Ludlum Model 500 Pulser.
Caution!
The instrument input operates at a high potential.
Connect the pulse generator through a 0.01 µF, 3000-volt
capacitor, unless the pulse generator is already protected.
Adjust the HV control for the proper operation voltage of the detector to be
used. Disconnect the pulser, and connect the detector to the instrument.
Turn the range selector switch to the ×100 position. Expose the detector to
a calibrated gamma field, which corresponds to approximately 80% of full-
scale meter deflection. Adjust the ×100 calibration control for the proper
reading.
Reposition the detector so the field corresponds to approximately 20% of
full-scale meter deflection. Confirm that the meter reading is within 10% of
the field.
Repeat this process for the ×10, ×1, and ×0.1 ranges.
If your gamma exposure range cannot calibrate two positions on each scale,
the pulser may be used to “electronically calibrate” the remaining points.
Reconnect the pulser to the instrument and determine the count rate
conversion at a previous range calibration point. Then use that conversion
rate to calibrate other points or scales.
If, for example, you can exposure rate calibrate the 400 µR/hr point, first
use the pulser to get the count rate equivalent to the calibrated 400 µR/hr
point. Then switch the pulser multiplier switch to the next lower setting, and
adjust the appropriate calibration control on the Model 3 for the meter to
read 40 µR/hr.
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