Model 12-4 Technical Manual Section 4
Ludlum Measurements, Inc. Page 4-1 May 2016
Identification of Controls and
Functions
Meter
: 6.4 cm (2.5 in.) arc, 1 mA analog type with pivot-and-jewel
suspension. Typical meter dial is 0-10 mrem/hr, 0-2.5 kV and BAT TEST.
Connector: Used to connect the detector to the instrument. Typically
series ˝C,˝ but can be ˝BNC˝, ˝MHV˝, ˝UHF,˝ or others.
Range Selector Switch: a six-position switch marked OFF, BAT, ×1000,
×100, ×10, and ×1. Turning the range selector switch from OFF to BAT
provides the operator with a battery check of the instrument. A BAT
check scale on the meter provides a visual means of checking the
battery-charge status. Moving the range selector switch to one of the
range multiplier positions (×1000, ×100, ×10, ×1) provides the operator
with an overall range of 0 to 10,000 mrem/hr. Multiply the scale reading
by the multiplier to determine the actual scale reading.
Discriminator Adjustment: allows the input sensitivity to be adjusted
from 1 to 100 mV; factory set at -2 mV.
HV Adjustment: provides a means of varying the high voltage from 200
to 2500 V; factory set at 1100 V.
Range Calibration Adjustment: recessed potentiometers located under
the calibration cover on the right side of the front panel. These
adjustment controls allow individual calibration for each range
multiplier.
Battery Compartment: sealed compartment to house two ˝D˝ cell
batteries.
AUD ON-OFF Toggle Switch: In the ON position, it operates the
unimorph speaker located on the left side of the instrument. The
frequency of the clicks is relative to the rate of the incoming pulses. The
higher the rate, the higher the audio frequency. This switch should be
turned
OFF when not required in order to reduce battery drain.
Sectio
4
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