Cables - Pyramid CR10 User Manual

PSI System Controls and Diagnostics
collected). Since the final shaped pulse output is generally required to be positive polarity to suit
multichannel analysers or pulse counting circuits, and must be positive if the -BR baseline
restoration option is fitted, the CR10 should have the -N polarity configuration. Inside the CR10
the pre-amplifier stage is inverting, so the -N configuration means that no further inverting stages
are used, and the output pulses will be positive.
Proportional counter tube
Figure 5. Schematic CR10 installation for readout of a proportional chamber

9.3.3 Cables

Try to locate the CR10 as close to the detector as possible, as far as space and radiation levels
permit. Screened cable between the CR10 and the detector loads the input with capacitance,
which affects both the noise level and the risetime of the input stage. Using a lower capacitance
coaxial cable such as RG-59 or RG-62 will allow longer cable to be used. Anti-triboelectric
cable is recommended to avoid interference from cable movement.
The following figure shows the measured wideband noise as a function of input capacitance for
two input conversion gain options (-G0 1400 mV C-1, -G1 130 mV C-1), and two shaping time
constants (-T2 250 nsec, -T4 1 µsec). The capacitive load was applied by connecting increasing
lengths of RG-58 coaxial cable, with nominal capacitance 0.95 pF cm-1. The measured voltage
noise at the output was converted to input charge based on measured pulse height of a known
detector charge signal.
The plots show that increased shaping time constant gives lower noise across the load curve, and
that the most sensitive input amplifier configuration is the least tolerant of capacitive loading.
CR10 User Manual
CR10
CR10_UM_180115
Test pulse
generator
+/- 12 VDC
PSU
MCA or
counter
HV bias
PSU
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