Model 12-4 Technical Manual Section 6
Ludlum Measurements, Inc. Page 6-3 May 2016
Warning!
Avoid electrical shock! Do not allow any conductive material
to come in contact with internal parts.
Depress the Model 12-4 HV pushbutton. The Model 12-4 meter pointer
should be over the 1.5 mark on the kV dial scale. If it is not, remove the
Model 12-4 from the can and adjust the HV potentiometer (R49) on the
main board until the pointer is over the 1.5 kV mark. Place the Model
12-4 back in the can, with the unimorph speaker on the left side.
Depress the Model 12-4 HV button and adjust the Model 12-4 HV CAL
potentiometer (front panel) until the Model 12-4 meter indicates 0.5 kV.
The pulser voltmeter should read 0.5 kV ± 10%.
Depress the Model 12-4 HV button and adjust the Model 12-4 HV CAL
potentiometer (front panel) until the Model 12-4 meter indicates 2.0 kV.
The pulser voltmeter should read 2.0 ±10% kV.
Reset the Model 12-4 HV to 1100 volts.
Set the pulser for -2 mV.
Adjust DIS for a stable meter reading, and then back off the control until
the meter reading declines 10%.
Detector Plateau
Secure a Model 2200 (or equivalent instrument) with input
discrimination adjusted to -2 mV.
Connect the Model 12-4 detector to the Model 2200. Background count
should be less than 1 cpm (counts per minute).
Place the Model 12-4 detector assembly in a neutron field. Expose the
detector to a 20 mrem/hr neutron field. Run a plateau of cpm versus
detector high voltage, within a suggested range of 1000-1250 volts.
Use 25-volt steps.
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