Preamplifier test point

The TRP delivers a stepped output, rather than a normal pulse output. Within it are inhibit pulse width and reset delay adjustments. These are tuned at the factory to the particular detector (see the manual) and do not need attention from the user. This type of preamplifier does not have a high count rate LED, because it cannot lock-out. There will be no preamplifier test point and instead of measuring noise, the time between resets (TBR - Section 12.2.2) is monitored. Powering-up does not differ too much from the check-list above, except that ... 

Preamplifier test point voltage at recommended voltage —1.6V DC Capacitance at recommended bias pE... 

Electrical parameters of the detector - bias polarity, depletion voltage, operating voltage, suggested amplifier shaping time, and maybe preamplifier test point voltage. 

Monitoring the preamplifier test point can give useful information about the state of the detector and preamplifier. Not all manufacturers provide this facility. Much of the information in this section was supplied by Canberra. 

Under normal circumstances, with no source on the detector, the preamplifier test point voltage when operated at the recommended bias voltage was —1.6 V. Over time, the detector started to exhibit poor detector resolution to which no obvious solution was found (4/2 in Table 12.1). 

Preamplifier Test Point Voltage at Recomiended Bias RESOLUTION AND EFFICIENCY ... 

A voltmeter put onto the test point of the preamplifier should read between — 1 and —2V and will not be very different from the value given on the specification sheet. 

Figure 12.1 Simplified diagram showing test point and leakage current for a resistive feedback preamplifier...

Auto-reset preamplifiers will not have an external test point. The quiescent preamplifier reset rate (that is, the... 

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