Fluke Biomedical 942A-200L-M4 - Manual (Page 48)

942A-200L-M4 & 942A-200L-M5 UDR
Operator Manual
3-8
Check Source Mode
The LED check source verifies operation of the photomultiplier tube, detector preamplifier, and the UDR
electronic circuits. The integrity of the crystal is verified through the No CPM FAIL logic in the UDR. The
LED check source option requires the use of a Model 9420-200L UDR, a Model 844-211L Junction Box
and a 943-25TL or 943-36L series scintillation detector. To operate the check source, press the CHECK
SOURCE pushbutton and hold it down. Pressing the CHECK SOURCE pushbutton will energize the
CHECK SOURCE relay to provide + 15v DC to the pulser circuit board located in the Model 844-211L
Junction Box, illuminate the green check source indicator and force the display to 0.00E0. The pulser
circuit will provide a fixed pulse output to drive a LED mounted in the photomultiplier (PMT) tube base of
the 943-25TL or 943-36L series scintillation detectors. The pulsed light output of the LED will be seen by
the PMT, converted to an output pulse, and displayed as an increased radiation value on the UDR digital
display. Releasing the CHECK SOURCE pushbutton will turn off the +15v DC to the pulser circuit board,
extinguish the check source indicator, de-energize the check source relay, clear the 60 second count
buffer, and return the UDR to normal operation. The UDR will then display 0.00E0 and begin counting
the detector pulses. Within approximately 10 seconds, an estimate of the current radiation value will be
displayed and the displayed value will begin to increase, indicating the normal background radiation level
within 60 seconds. An internal configuration jumper allows the alarms to be activated or muted if the
alarm limits are exceeded by the check source reading.
The bargraph operates the same way as it does during normal operation.
The analog outputs are at low scale during check source operation.
Refer to Manual 844-211L-1 for further information.
The normally OPEN (NO) contact on check source relay, K2 (P2, Pins 13 and 14), closes when the check
source function is active and opens when the check source function is inactive.
3.5 Calibration (Scaler) Mode Operation
Calibrate mode for the UDR is entered by turning the rotary set point switch to position 8 and pressing the
ENTER button.
The current calibration time set point is displayed in seconds, with the first digit flashing to indicate the
edit mode. The bargraph will turn off, any high and warn conditions will clear, the fail-safe, warn and high
alarm relays will de-energize, and the radiation unit light (backlights) will turn off. The calibration set point
may be edited, but will reset to 60 seconds whenever the unit is turned off or the functional switch is
moved from position 8.
Once the desired calibration time is set, pressing the ENTER button will start the calibration. The display
will go to zero and the backlights will begin to flash. The UDR will count the pulses received for the
entered calibration time, displaying the current summation of counts received each second. When the
calibration is completed, the final summation of counts for the calibration time is displayed and the
backlights will be steady on.
Another calibration can then be executed by pressing the ENTER button, and the system will again
display the calibration time for editing. Pressing the enter button again starts the calibration cycle. A
calibration in process can be stopped by pressing the ENTER key. Calibrate mode can be aborted at any
time by moving the rotary switch to a position other than position 8. If this is done while the calibration
time is being displayed for editing, press the ENTER key to exit the setpoint edit mode, then rotate the
rotary function switch out of position 8 to exit the calibration mode. Once the calibration mode is exited,
the UDR will do a reset and continue normal operation.