| 摘要 |
<p>The "Pole-Zero Adviser" for the Pole-Zero Cancellation in Spectroscopy Amplifiers (amplifiers for ionizing radiation pulse spectometry) is a device that makes it possible to achieve a very accurate setting of the control of the Pole-Zero Cancellation adjustment simply by observing a visual indicator on the amplifier, without using any other instrument. It consist essentially of a sampler device for sampling the baseline after every pulse processed in the amplifier, associated to an averager device for averaging the samples, and to a display device, which gives a visual indication of the value and sign of the averager output signal, that is, of the mean value of the baseline sample. The device samples preferably the amplifier output; suitable commands are provided for its operation. In practice, the circuit has a linear gate controlled by a suitable command and followed by a low-pass filter circuit, whose output is connected to the visual indicator. The preferred type of sampling and averaging circuit is the so-called "boxcar integrator". This is essentially an RC low-pass filter having a switch in series to the resistor; the switch, when open, interrupts not only the arrival of the input signal, but also the discharge of the capacitor; the low-pass filter is thus modified by making its time constant RC tend to infinity. In comparation to implementations employing low-pass filters with constant parameters, not modified when the gate device is switched, the boxcar integrator has the advantage of giving an output signal whose value does not depend on the repetition rate of the amplifier pulses. In fact, the output signal of the boxcar integrator is the average over a predetermined number of samples, which is constant for any repetition rate of the random-time pulses generated in the radiation detector. The preferred type of visual indicator device is made by two LEDs (light-emitting-diodes) connected to the averager output, which indicate positive and negative output levels respectively.</p> |
