Manual Inhibit Mode
Lynx II DSA User's Manual – 7096089 177
Manual Inhibit Mode
The Inhibit time can also be set manually, by changing either the Lynx II Inhibit Setting
adjustment or the inhibit pulse width adjustment on the preamp. For certain detector
characteristics and applications, it may be necessary to set the Inhibit time interval longer
than provided by the Automatic mode. Manual adjustment may be necessary if the preamp
signal contains extra time constants resulting in abnormal behavior which extends the
overload recovery time beyond the norm. The effect often becomes more noticeable at
high gains.
To use the Lynx II manual inhibit adjustment, set the TRP Inhibit Mode to Manual. This
setting can be changed on the fourth page of the MCA | Adjust | Gain dialog. Before
adjusting the Inhibit Setting, the Preamp Type must have been previously set to TRP using
the MCA | Adjust | Filter dialog. If this is not first done, the inhibit controls are not
available in the MCA | Adjust | Gain dialog. The Inhibit Setting slider bar can adjust the
inhibit duration between 0 and 160 µs and becomes active in the Manual Inhibit Mode.
The optimum Inhibit time is determined using the Lynx II Digital Oscilloscope. Launch
the Digital Oscilloscope and set the trigger source to Inhibit. When using this trigger
source, make sure that the TRP INH output of the reset preamp has been connected to the
Lynx II Reset input. Otherwise, the oscilloscope will not be triggered and an error
message may be displayed.
The overload recovery time of the trapezoid signal is measured to set the required inhibit
time. The overload period is marked by the duration of the large negative overload
excursion in the oscilloscope waveform. Measure the duration of the overload signal in
microseconds; the overload signal begins with the large negative excursion and ends upon
return to the baseline (see Figure 108). Set the Inhibit Setting equal to the measured
overload time period.
Adjustment Tips
When viewing and measuring the overload recovery characteristics it's best to set the ICR
to a low rate; between 1 and 5 kcps. Otherwise, pile up will make it difficult to view the
recovery characteristic. On some reset preamps, the Inhibit signal pulse width is
adjustable. For preamps with this provision, the preamp inhibit time can also be set to
inhibit pulse processing during the reset period. Consult the Detector/Preamp Operator’s
manual for this adjustment. Note that when the Lynx II Inhibit Mode is set to “Manual”,
the system inhibit duration will be the time interval set by the Lynx II Inhibit Setting slider
bar “OR” the external (preamp) inhibit duration, whichever lasts longer.
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