3
3. INSTALLATION
3.1. CONNECTION TO PROPORTIONAL
COUNTER
A direct connection with shielded cable should be
made between the proportional counter and the
Input SHV connector on the preamplifier. The
performance of the 142PC Preamplifier, like that of
all other such low-noise preamplifiers, is degraded
as the capacity at the input increases. Therefore it
is important that the length of coaxial cable used
between the proportional counter and the
preamplifier be kept at the minimum length that is
necessary. Also it is preferable to use 93
S
or 100
S
characteristic impedance cable rather than 75
S
or
50
S
cable because the capacity per foot is less for
the cable with the higher characteristic impedance.
Type RG-62/U cable is recommended; this has a
93
S
impedance and a capacitance of 13.5 pF/ft
(40.1 pF/m). An AMP 51426-2 connector mates
with the SHV connector on the 142PC Preamplifier.
Once the input cable installation has been made,
the electronic noise performance of the 142PC can
be predicted by calculating the cable capacity from
the above information and adding the capacity
expected from the proportional counter.
3.2. CONNECTION TO AMPLIFIERS
Either or both the E and T outputs of the 142PC can
be connected to an amplifier input for further
processing. The output impedance through either of
these connectors is 93
S
providing series
termination for 93
S
cable so that long unterminated
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 spectrometer 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 142PC, 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 142PC 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
operating. 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 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 142PC 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
:
s). 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 142PC.
The Test Pulse input may be used for the output of
a pulser such as the ORTEC 419 or 448 to calibrate
the preamplifier E output amplitude in terms of
energy for multichannel analyzer calibration.
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 proportional counter 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
142PC can be accepted through a charge
terminator and into the Input connector on the
142PC. If external capacitance is to be included for
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