Ronan X96S MASS FLOW GAUGE - Manual (Page 66)

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ION Chamber
Detector/Amplifier Ronan’s ion chamber detector is filled with an inert
Assembly high-pressure gas. It uses low-voltage (-15VDC) bias
and generates a low-level current proportional to the gamma
radiation incident on the detector. The current
(DET-7471-XXX) generated is on the order of 10 ρA, so an electrometer amplifier is
required to convert the current to a low-impedance, high level
voltage signal. The signal is then measured by the X96S
Microprocessor, which converts the voltage signal to a output of
4-20mA for a specified measuring range.
Circuit Description The current, generated by the ion chamber, is fed into an inverting
amplifier. The amplifier output is filtered by a resistance
capacitance low-pass filter, and fed into another amplifier. The
output from that amplifier is proportionally fed back to the input
amplifier after going through a gain resistance potentionmeter on
the X96S input board.
The detector’s gain is adjusted through the X96S gain resistance
potentionmeter whenever the signal output of the detector is too
high or too low. The output must be less than 3.0VDC with an
empty vessel.
An offset zero control on the amplifier board is factory adjusted
and Glyptal coated.
The most important components of the amplifier are the
operational amplifier , feedback resistor and feedback capacitor. If
these components are substituted, the performance of the system
will be adversely affected.
Servicing the Detector The ion-chamber detector contains pressurized inert gas. The ion
chamber itself is not serviceable and must be returned to the
factory for service. Instructions follow for “Detector
Removal/Replacement.”
However, a qualified technician can troubleshoot and service the
detector’s amplifier assembly. Some precautions are needed
when handling the detector/amplifier assembly.
It is important to keep the interior of the detector/amplifier dry.
Moisture on the high-impedance components will cause leakage
currents. If the amplifier lid is opened, it is important to see that
warm, dry air is introduced into the amplifier before replacing
the gasket lid.