4
Once the input cable installation has been made,
the electronic noise performance of the 142IH can
be predicted by calculating the cable capacity from
the above information and adding the capacity
expected from the detector.
3.2. CONNECTION TO AMPLIFIERS
Either or both the E and T outputs of the 142IH can
be connected to an amplifier input for further
processing. The output impedance through either of
these connectors is 93
S
, providing a series
termination for 93
S
cable so that long cable lengths
can be driven easily. Although the outputs are
marked E (for Energy) and T (for Timing), the pulse
characteristics are identical and the circuits are
interchangeable.
In an energy spectroscopy system, the preamplifier
output is furnished into a shaping main amplifier. In
a timing spectrometer system, the preamplifier
output is furnished into a timing filter amplifier. With
the dual output connections on the 142IH, the
signals can be furnished simultaneously to both
types of spectrometer systems. If either the E or T
output connector is not being used, it should simply
be left open-circuited (unterminated).
3.3. INPUT POWER
Power for the 142IH is supplied through the Power
Cable that is captive through the rear panel of the
unit. The normal connection for this power cable is
included on the rear panel of the mating ORTEC
amplifier, furnishing ±12 V and ±24 V from the bin
and power supply in which the amplifier is operated.
If this facility is not available or if such a connection
would increase the loading on the bin and power
supply beyond its maximum rated capacity, use an
ORTEC 114 Preamplifier Power Supply to furnish
the operating power requirements through the
captive cable. The ORTEC 114 can furnish power
for two ORTEC preamplifiers simultaneously if
desired.
3.4. TEST PULSE
A voltage test pulse for energy calibration can be
accepted through the Test Pulse input connector on
the 142IH without the use of an external charge
terminator. The test input of the preamplifier has an
input impedance of 93
S
and its circuitry provides
charge injection to the preamplifier input. The
shape of this pulse should be a fast risetime (less
than 40 ns) followed by a slow exponential decay
back to the baseline (200 to 400 µs). While the test
pulses are being furnished, connect either the
detector (with bias applied) or the equivalent
capacitance (without bias applied) to the Input
connector on the 142IH.
The Test Pulse input may be used in conjunction
with the output of a pulser such as the ORTEC 419
or 448 to calibrate the preamplifier E output
amplitude in terms of energy for calibration of a
multichannel analyzer. However, due to stray
coupling between the test circuit and other portions
of the preamplifier circuitry, the transient
performance of the preamplifier is best determined
by connecting the actual detector signal through the
Input connector instead of using the pulse generator
output signals for this calibration.
A voltage test pulse for transient response in the
142IH can be accepted through a charge terminator
and into the Input connector on the 142IH. If
external capacitance is to be included for these
tests, an SHV tee can be inserted between the Input
connector and the charge terminator, and this will
then accommodate the test capacitances. Do not
furnish any bias during these tests.
3.5. DETECTOR BIAS INPUT
Operating bias for the detector is supplied to the
Bias connector on the 142IH and, through a filter
and a large bias resistance, to the Input signal
connector. From there it is furnished out through the
signal input cable to the detector.
Connect a cable from the detector bias supply
(ORTEC 428 or 459 is typical) to the Bias connector
on the 142IH. Type SHV connectors are used in this
high-voltage circuit and the mating cable should be
furnished with the bias supply module.
Содержание 142IH
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