Chapter 5 Web-Based Operations
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Lynx DSA User's Manual - 9240227J
D. Methods of Detector Matching
This appendix discusses detector matching using pole/zero, manual fast discriminator
adjustment and baseline restorer adjustments.
Pole/Zero Compensation
Pole/zero compensation is extremely critical for achieving good performance at high
count rates when using detectors with RC preamps. It is equally important for good
overload recovery due to high energy and cosmic events. The Pole/Zero adjustment
range accommodates RC preamp fall times of 40
µ
s to 1.7 ms. When a reset preamp
is used, Pole/Zero compensation is not required and the Pole/Zero value must be set
to zero (0). If the Lynx is connected to a detector with a reset preamp such as the
Mirion Model 2101 or 2008, use the Genie Gamma Acquisition and Analysis to
change the preamp type from RC to TRP.
With TRP selected, the pole/zero compensation is automatically set to a value of
zero, representing the matching required for a fall time of infinite duration, which
requires no compensation. If the preamplifier type selected is RC and the Lynx is
connected to a reset preamp, the P/Z setting must be manually set to a value of zero
(0).
Note: Once the Pole/Zero is optimized for the intended detector, the digital filter
shaping parameters (Rise Time and Flat Top) can be changed as required
without the need to make further Pole/Zero adjustments. However the
Pole/Zero compensation must be readjusted if the detector is changed.
Manual Fast Discriminator Threshold
In some cases, you may want to set the Fast Discriminator threshold manually. For
best performance, set the threshold just above the system noise level.
1.
Set the Amplifier Gain and shaping as required.
2.
Set the FDisc Mode in the Gain Device Adjust screen to “Manual”.
3.
Remove all excitation sources from the vicinity of the detector.
4.
Use the FDisc setting slider bar in the Gain Device Adjust screen to set the
fast discriminator threshold just above the system noise as indicated in step 5.
5.
The following steps optimize the discriminator sensitivity to insure the
threshold is at its lowest setting, just above the noise level:
•
Adjust the FDisc Setting to 0%. The ICR LED indicator continuously
glows green.
