Rapiscan TSA TPM-903B Operation And Service Manual - page 15

TSA TPM903 Operations and Service Manual 

Doc: # 5058 Rev. A 

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3.4.1.5. BKG TIME 

Sets the background counting time for the system. Press <1> to increment the time by 5 seconds, 

<7> to decrement the time by 5 seconds. Press <#> to accept the setting. Range is 20 - 120 

seconds. 

* If you have an area with large background fluctuations, you can increase the BKG Time to help 

average out those bkg spikes over a longer period of time (say ~1 minute). 

3.4.1.6. SHOW VERSION 

Displays the software version number, press any key to return to the setup menu. 

3.4.1.7. KEYPAD RESET 

When enabled, requires any alarm to be silenced by using the keypad. 

3.4.1.8. ADJ. DISCRIM 

Opens the menu to adjust the LLD and ULD. The discriminators set the energy levels at which 

the system will be accept counts. If the isotopes are unknown, leaving the discriminators set at 

the factory defaults of 0.068 and 5.040 volts is normally acceptable. When the system is shipped 

from the factory, the discriminators are set to accept energy in the approximate range of 22 keV 

to 1650 keV. The settings are necessarily site specific, and may require adjustment to meet local 

requirements. The relationship of discriminator voltage to energy level, in keV, is approximately 

1 volt of discriminator level equals 330 keV. Using this formula, the factory settings equal: 

LLD 0.068 volts = 22.4 keV 

ULD 5.040 volts = 1,650 keV 

This relationship is an approximation. In practice, the actual values will vary slightly. Always 

test the system with the isotope(s) of interest to ensure maximum sensitivity. Refer to the formula 

for signal to background ratio in Appendix A for details on optimizing the discriminator settings 

for specific isotopes. 

NOTE: After changing the discriminator settings, always run a variance test to ensure that 

system noise is not affecting the count data. 

Two methods of adjustment are provided: 

1. Direct entry: Press the zero key from the "ADJUST ULD/LLD" menu. The operator will be 

prompted for a new LLD setting. Press the pound (#) key to accept the current setting. Three 

digits must be entered to change the value: volts, tenths of a volt and hundredths of a volt; press 

the pound (#) key to complete the operation. 

NOTE: Since the Digital to Analog Converters (DACs) have limited resolution, manual entries 

will be rounded to nearest value the DACs can output.