ICR Threshold Adjustment
Though the ICR threshold defaults to the automatic mode, in some cases you may
want to set the ICR threshold manually. The ICR threshold must be set just above the
system noise level to achieve optimum PUR performance. The ICR Auto Threshold
Mode is enabled/disabled through a 2016 software switch.
1. Using the 2016 software, disable the PUR Auto Threshold setting.
2. Set the amplifier Gain and Shaping as required.
3. Remove all excitation sources from the vicinity of the Detector.
Optimizing the Discriminator
This procedure optimizes the discriminator sensitivity to insure the threshold is at its
lowest setting, just above the noise level.
1. Adjust the 2016 ICR THRESH control fully clockwise. The ICR RATE LED
indicator is off.
2. Adjust the ICR RATE control counterclockwise until the ICR RATE LED
indicator glows green continuously if the PUR is off, or red if the PUR is on.
3. Adjust the control clockwise until the indicator blinks occasionally.
4. The PUR threshold is now properly set.
Note With PUR Auto Threshold disabled, the PUR Threshold must be rechecked
and adjusted if the Detector/Preamplifier or Amplifier’s GAIN or SHAPING
are changed.
ADC Peak Detect Adjustment
Normally, the ADC will start its conversion when the peak of the input signal is de
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tected. With the Delayed Peak Detect feature found in all Canberra ADCs, SCA cali
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bration is greatly simplified because the peak value is held by the ADC’s stretcher
circuit until the end of the Delayed Peak period and allows the SCA’s output to be
used as a GATE input to the ADC. At high count rates, however, this extended ADC
window will allow later and larger pulses to be partially captured; this can dull the ap
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parent sharpness of the SCA’s ULD cutoff. This is strictly an artifact of the ADC peak
capture and is minimized by reducing the width of the Delayed Peak period.
To adjust the Delayed Peak period:
44
Performance Adjustments
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