SIGMA BM-286A - Manual (Page 39)

5. MAINTENANCE page 36
Model BM-286A
5.3. DISCRIMINATOR ADJUSTMENT
The Upper and Lower Level Discriminators (ULD & LLD) set the maximum and minimum
energy levels at which the system accepts counts. The LLD must be set high enough to prevent
system noise from being amplified and counted.
The DOS machine sets the levels on the RCS-120 discriminator card but gets its values from the
NT machine.
The upper and lower level discriminators’ adjustment range is 0 keV to approximately 1.5 MeV.
These levels are controlled by entering the Utilities Menu and pressing the Detectors, Scale and
Disc. button.
The Set Discriminator box and detector counts will appear with the previous upper and lower
settings. Using the up and down arrows the values for upper and lower can be changed but are
not sent to the DOS machine until the send button is pressed. Observe the counts in the detector
boxes to insure you have not reached the lower level noise threshold.
The approximate energy level in keV can be obtained by multiplying the settings by 150. The
exact value may vary slightly due to variations in the detectors and electronics. For initial set-up,
a good starting point is:
NOTE:
If either level is changed you must always
recalculate all waste stream efficiencies.
The unit will also acquire a new background when leaving the Utilities Menu.
Always run a variance after adjusting the levels.
SETTINGS FOR PLASTIC DETECTORS
LLD = 0.3 volts = 45 keV
ULD = 10.0 turns = 1.5 MeV