Rapiscan TSA TPM-903B Operation And Service Manual - page 27

TSA TPM903 Operations and Service Manual 

Doc: # 5058 Rev. A 

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4.2.3. FAST COUNT MODE 

Upon occupancy, the system automatically goes into fast count mode. While this mode does not 

take counts any faster, it does update the display more often - every second instead of every five 

seconds - and begins testing for alarm conditions every 0.2 seconds. The controller also stores a 

number of 0.2 second count intervals in RAM, so that it can "anticipate" occupancy and start 

alarm comparisons before the subject actually enters the pillar. 

The system may be forced into the fast count mode by pressing the asterisk(*) key on the keypad. 

Pressing the pound (#) key returns the system to background mode. 

Upon entering the fast count mode, the unit waits for the current interval to go to completion (0.2 

seconds maximum), discards the oldest interval, adds the latest one, tests for alarm conditions, 

and begins another 0.2 second collection interval. This cycle continues during manual FAST 

COUNT, or during occupation and the "occupancy hold-in" period, which starts when the unit 

goes out of occupancy. If an alarm condition occurs, the TPM-903B will hold the alarm on until 

5 seconds after the alarm condition is cleared. 

The radiation alarm level is calculated on the basis of variation from the background. The 

formula for N*Sigma may be found in the Appendix . 

CAUTION 

Do not leave unit in this forced state for normal operation. 

4.2.4. VARIANCE ANALYZER MODE 

In this mode, the unit takes 75 0.2 second background counts and performs a variance calculation 

on the data. A more detailed description of the variance test may be found in the Appendix.