Hardware Options
Lynx DSA User's Manual - 9240227J
107
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
µ
s or greater. The long tail (pole) is normally
removed prior to 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 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
range from 0 to 4095 units. The values 1 to 4095 represent cancellation of
preamplifier time constants from 1.7 ms to 40
µ
s respectively; a value of zero sets the
pole/zero compensation off (time constant of infinity).
The Lynx'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 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 Stop button is pressed. In case of timeout, an error will be reported that
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 in order to successfully complete
within a three-minute time period.
In order 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
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.
