Model 12-4 Technical Manual Section 6
Ludlum Measurements, Inc. Page 6-1 May 2016
Calibration and Maintenance
Calibration
Calibration controls are located on the front of the instrument under the
calibration cover. The controls may be adjusted with a 1/8-inch blade
screwdriver.
Note:
Local procedures may supersede the following.
Establishing an Operating Point
The operating point for the instrument and detector is established by setting
the detector voltage and instrument sensitivity (HV and DIS). The proper
selection of this point is the key to instrument performance. Efficiency,
background sensitivity, and noise are fixed by the physical makeup of the
given detector and rarely vary from unit to unit. However, the selection of
the operating point makes a marked difference in the apparent contribution
of these three sources of count.
In setting the operating point, the final result of the adjustment is to establish
the system gain so that the desirable signal pulses (including background) are
above the discrimination level and the unwanted pulses from noise are
below the discrimination level and are therefore, not counted.
Adjusting either the instrument gain or the HV controls the total system
gain. Voltage affects control in the detector; DIS (Discriminator) controls the
amplifier gain.
Equipment Required for Calibration
All instruments used in calibrating the Model 12-4 must be calibrated by
standards traceable to the National Institute of Standards and Technology
and must have a current calibration label attached.
Sectio
6
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