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There has been some confusion in correlating the 10-turn counting dials, found on some of our Ludlum Scaler/Ratemeters, to their purpose. For example, the HV controls used on the Model 2000, 2200, 2929, and M2500's are used to vary the detector operating voltage (HV). The vernier scale on the dial has no correlation to the actual HV output (unless noted what the dial reading is for a specific HV output). The HV output is read on the analog meter kV (kilovolt) scale or an external HV meter at the detector connector. The 10-turn dial is simply used to vary the HV output and to utilize the locking feature incorporated on the dial.

Ten-turn dials are also used to control the THRESHOLD and WINDOW parameters on Scaler/Ratemeters. When used for this application, the vernier scale does correlate to the use of the control(s). Using the Model 2200 as an example: The THRESHOLD (THR) dial is adjusted to 1.00 (1 in the dial window, vernier scale positioned at 0), then 10 millivolt (mV) pulses are applied to the detector input and the DISCR (discriminator) control is adjusted until the M2200 just starts to count. The WINDOW (WIN) control is adjusted to 1.00 and an internal adjustment is set to where the M2200 stops counting with 20 mV applied to the detector input. This calibration sequence matches the WIN and THR counting threshold levels to their vernier dial readings so that they can be used in determining the "counting window" used for Single Channel Analyzation (refer to LMI Newsletter Volume I Number 3 and Volume IX Number 1).

By David Wyatt, June 1994

PDF: June 1994 Newsletter