Models 375 (Including Series One), 375/1, 375/2 & 375/4 Section 4
Ludlum Measurements, Inc. Page 4-1 May 2017
Operator Controls and Setup
Calibration Controls
Remove the calibration cover to expose the calibration controls.
Warning!
Do not touch the circuit board in the calibration window
due to potential for electric shock.
The calibration controls include the up/down buttons, five calibration
potentiometers, and the option dipswitch (detailed in the following
subsection). The five potentiometers are detailed below.
ANALOG: used to adjust the logarithmic analog voltage output. Adjusted
in calibration mode to the full-scale voltage reading or adjusted to a
known point at some given reading.
HV: used to set the high voltage required for detector operation.
Adjustable from 450-2500 Vdc. The high voltage required will depend
on the type of detector used. Internal GM detectors typically require 550
Vdc. Be sure to check the high voltage with a high impedance (1000-
Mohm impedance) voltmeter only. A high-voltage checkpoint is located
next to the
HV potentiometer.
DISC: internal discriminator used to set negative pulse threshold for
counting pulses from the detector. Pad allows direct measurement of
threshold voltage. Utilize a Ludlum Model 500 Pulser or equivalent to
inject pulses of the desired threshold size. The pulse height threshold is
adjustable from 2.0 mVdc to 100 mVdc.
BAT CHARGE: used to set the backup battery trickle charging voltage. It
is set to 6.9 Vdc while the battery is disconnected.
Sectio
4
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