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Installation
4 Installation
4.1 Noise Consideration
The preamplifier components associated with the detector bias (HV) have been scientifically cleaned.
This process removes all residues and fingerprints which could cause excessive noise and possible
failure of the preamplifier when high voltage is applied. It is strongly recommended that causion be
exercised never to touch these components nor have them exposed to the atmosphere without the
preamplifier case, for any long duration.
Any capacitance added to the input of the preamplifier will increase the noise contribution and degrade
the rise time performance of the Model CSPA10...13. The capacitance should be minimized by using the
shortest possible interconnecting cable between the detector and the preamplifier.
The detector load resistance R is normally 100 megaohms. If silicon surface barrier detectors are used
whose leakage current is greater than 1 microamp, the voltage drop across the resistor must be allowed
for, or alternatively, the value of R reduced to provide a voltage drop. The latter will cause the 0 pF noise
of the preamplifier to increase, but this will usually be insignificant compared to the noise generated in the
detector by the increased leakage current. Do not reduce R below 10 megaohms without contacting the
factory.
4.2 Detector Bias
The Model CSPA1X-4S Preamplifier HV Input accepts up to ± 4000 VDC from the detector bias supply.
Never connect or disconnect the preamplifier from a detector while the high voltage is on.
Always wait at least one minute after the detector bias has been reduced to zero before disconnecting the
preamplifier from the detector. Maximum stability of the preamplifier is maintained 60-90 seconds after
preamplifier power and high voltage is applied.
The Model CSPA1X-2S has a larger input coupling capacitor (18 nF) for detectors with high capacity . If
the maximum detector bias is below 1000V, the Model CSP1AX-1B is the right choice.
The input connector and the HV bias connector is BNC. It is usually more convenient to use BNC,
because these connectors are much more common.
For Vacuum applications, the feed through connector is in many cases only available as BNC.
ComTec GmbH
11
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