Models 375-31H Area Monitor with Neutron Detector
Section 7
Ludlum Measurements, Inc.
Page 7-2
January 2021
The dead time correction (
DEAD TIME
) is set when the detector is exposed to a
"high" radiation field. A "high" radiation field in this case is defined as a field
where dead time losses exceed 30%. The dead time correction will elevate the
ratemeter reading to account for counts arriving at the detector during the
detector's dead time. GM tubes typically have long dead times from 50-150
microseconds. Neutron and scintillation detectors generally have short dead times
of 1-5 microseconds.
Note:
Once parameters are set, it is important to remember to
switch the
CAL MODE
switch back to the left. This action
protects the parameters from inadvertent changes.
Analog Output
The analog output is a five-decade logarithmic voltage-out. The maximum
voltage-out while under primary power is 6 volts. The maximum voltage-out
while under battery backup power is 4.5 volts. The five decades are:
0.1 <units> - 1.0 <units>*
1 <units> - 10 <units>*
10 <units> - 100 <units>*
100 <units> - 1000 <units>*
1000 <units> - 10000 <units>*
When the
CAL MODE
dip switch is switched to the right, the analog output
goes to full scale. The analog output goes to full scale during a
DET FAIL
condition.
Note:
For the Model 375 Series One (that displays values to two decimal
places), the analog output starts a decade lower, from 0.01 to 0.1 units, with
the highest decade being 100 to 1000 units. The highest displayed range of
1000 to 10,000 units then has a constant full-scale output.
Discriminator
The
DISC
potentiometer located under the calibration cover is used to set the
threshold for pulses coming from the detector. The desired pulse threshold
depends on the type of detector used. It is adjustable from 2.0 mVdc to 100
mVdc.
