Chapter 5 Web-Based Operations
110 Lynx II DSA User's Manual - 7096089
Manual Pole Zero
When operating with preamplifiers using RC feedback, the signal that is processed is
normally a tail pulse with a fast rise time and longer exponential fall time. The fall time
constant, or pole, is typically 50 µs or greater. The long tail (pole) is normally removed
before digitizing and filtering the signal. Removal of the tail time constant is accomplished
by the insertion of another time constant (zero) which compensates for the pole of the
input signal. This is set using the “Pole Zero” parameter.
The optimum “Pole Zero” parameter in the Lynx II can be set manually through the
Manual Pole Zero adjustment, or automatically through the Auto Pole Zero button.
Note: The information of interest for the spectroscopic measurement is contained within
the rise time of the signal. Removal of the tail pulse, or pole, does not affect the
quality of the pulse-height data.
The filter's Manual Pole Zero control allows you to manually adjust the pole/zero setting.
The up/down spin control offers a variable range from 0 to 4095 units. The values 1 to
4095 represent the cancellation of preamplifier time constants from 1.7 ms to 40 µs
respectively; a value of zero sets the pole/zero compensation off (time constant of
infinity).
The Lynx II's built-in Digital Oscilloscope (DSO) or an external oscilloscope connected to
the MON OUT connector can be used as an aid to verify proper automatic or manual
pole/zero compensation by observing that the energy signal returns to the baseline with no
under or overshoot.
Auto Pole Zero Button
Initiates automatic pole/zero adjustment. The Auto P/Z process can be initiated only when
the acquisition is off. Once started, the Auto P/Z process will terminate either when (a)
convergence is achieved or (b) a timeout of approximately 180 seconds has been reached,
or the Stop button is pressed. In case of timeout, an error will be reported that the
convergence was not successful. If the automatic P/Z does not succeed or if stopped
prematurely the original P/Z value will be retained.
Auto Pole Zero Status
The automatic pole/zero is a manually-started procedure that automatically optimizes the
Pole/zero setting (see Manual Pole Zero). The Automatic Pole/Zero requires a number of
valid nuclear events to be processed to successfully complete within a three-minute
period.
To successfully operate, the Automatic Pole/zero procedure expects the following:
• The Incoming Count Rate should be between 300 cps and 20,000 cps with a limited
number of piled-up events.
• A significant number of the event amplitudes should be from 30% to 100% of the
full scale amplitude of the spectrum.
• Automatic pole/zero adjustment will affect the position of the data within the
spectrum so it is only available when the acquisition is not in progress.
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