Ludlum Measurements 336641, Manual

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Model 3A Survey Meter
page 3
rate-plot on semi-log paper. Set the operating
voltage at the flattest position of the curve near
the knee of the curve.

For GM detectors, adjust the HV to 900 volts.
For special applications, the power supply may
be adjusted from 400 to 1500 volts.
Note: Measure high voltage with a Model 500 pulser
or a high-impedance voltmeter with a high-meg
probe. If one of these instruments is not available,
use a voltmeter with a minimum of 1000 megohm
input resistance. Do not use a vacuum tube type
voltmeter for this adjustment unless an external,
high-voltage multiplier probe is used.
5.3 Alarm Circuit
After HV and range controls are set, the alarm set
control may be adjusted to the desired alarm
threshold. Minimum setting is 10% of the meter
scale; maximum setting is full-scale deflection.
When the alarm circuit is energized, both the audio
and visual indications should occur. Pushing the
reset button resets the meter and alarm circuit.
6. MAINTENANCE
Instrument maintenance consists of keeping the
instrument clean and periodically checking the
batteries and the calibration.
To assure proper operation of the instrument
between calibrations, the instrument should be
tested with a check source prior to each use. A
reference reading should be obtained when exposed
to the check source in a constant and reproducible
manner at the time of calibration. If the instrument
response differs from the reference reading by more
than ±20%, the instrument should be returned to a
calibration facility for maintenance, repair, or
recalibration as required.
Recalibration should be accomplished after any
maintenance or adjustment of any kind has been
performed on the instrument. Battery replacements are not considered to be maintenance, and do not
normally require the instrument to be recalibrated.
Ludlum Measurements recommends recalibration at
intervals no greater than one year. Check the
appropriate regulatory agency’s regulations to
determine required recalibration intervals.
The batteries should be removed and the battery
contacts cleaned of any corrosion at least every
three months. If the instrument has been exposed to
a very dusty or corrosive atmosphere, service
batteries more frequently.
Use a spanner wrench to unscrew the battery
contact insulators, exposing the internal contacts
and battery springs. Removing the handle will
facilitate access to these contacts.
Note: Never store the instrument over
30 days without removing batteries.
Although this instrument will operate at
very high ambient temperatures,
battery seal failure can occur at
temperatures as low as 38
˚C (100 ˚F).