Fluke Biomedical 956A-201-M2 - Manual (Page 28)

3-2
Should a very high intensity radioactive source be detected, the G-M tube may become saturated (i.e.
pulses are separated by a period less than the dead time of the tube). This would have the effect of
holding the preamplifier output at a relatively constant output voltage, resulting in count loss at the readout.
Anti-Jam circuitry in the preamplifier produces a full-scale output square wave signal, providing a full-scale
indication at the readout.
G-M Detector Response Time
The response time of the system to a step change in radiation value is 60 seconds, due to the operation of
the pulse counting algorithms. The detector radiation value displayed is the result of a rolling average of
the latest 60, one-second values, and is updated once per second. An alarm will be initiated within one
second after the current one-minute average exceeds the alarm setpoint.
Check Source
A manual check source may be initiated from the UDR by the operator to check detector operation. The
Check Source push-button is a momentary contact switch, and is active as long as the pushbutton is
depressed. Upon initiation and removal of the check source request, the internal counting registers are
cleared and the display value will be based on the number of new values received. After 60 seconds, the
display value will reflect the average of the past 60 values. During check source activation, analog outputs
are muted (forced to zero). The High and Warn alarms are normally inhibited during check source
operation, but may be enabled by removing Jumper JP3-5, on the UDR main printed circuit board (see
Table 2-12). The counters are cleared upon exiting Check Source mode, resulting in a display of 0.00.
After one minute, the current radiation value will be displayed.
3.3 UDR OPERATION, MODEL 956A-201-M2
Operation of the 956A-201-M2 UDR consists of operator functions and configuration functions. All
operator functions are performed using the front panel. Configuration functions are performed using
internal switches and/or jumpers that are accessible via partial removal of the UDR from the mounting
enclosure.
Normal Operation
If the measured radiation field is within the range of the detector during power-up, the mR/h value will be
displayed as a three digit number: N.NN, where N = 0 to 9. A backlit insert will display engineering units in
mR/h, R/h, or kR/h. The bargraph will display the value on the fixed mR/h scale and any indicator lights
that are on should be green, providing the operator with a visual indication of normal operation. The
analog outputs will track the displayed value, and the alarm outputs will be active. The Warn, High, and
Fail relays operate in the Fail Safe Mode.
WARN/HIGH Alarms
If the measured radiation field increases above the WARN alarm limit, the WARN alarm indicator will turn
on flashing (amber color), the bargraph will change color to amber, and the warn alarm relay will de-
activate. If the measured radiation field increases above the HIGH alarm limit, the HIGH alarm indicator
will turn on flashing (red color), the bargraph will change color to red, and the high alarm relay will de-
activate.
Non-fail-safe relay operation for the HIGH and WARN alarms is
available as a firmware option at time of purchase.
NOTE