Ronan X96S LEVEL GAGE - Manual (Page 42)

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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 level (or
density) output of
4-20mA for a specified measuring range.
Refer to drawing B-6409-K. The current (I), generated
Circuit Description by the ion chamber, is fed into the inverting input
terminal of the electrometer amplifieer, (IC1). The electrometer
amplifier output is filtered by R2C4 (a microphonic, low-pass
filter) and fed into a follower amplifier. The output of IC2 is
proportionally fed back to the inverting terminal to provide a
closed-loop gain based on the value of the gain resistance
potentionmeter (R2) on the X96S input board. (B-9742-K).
The detector’s gain is adjusted whenever the signal output of the
detector is too high and may saturate the input of the X96S, which
is approximately 3.5VDC. The output must be less than 3.0VDC
with an empty vessel.
An offset zero control (R6), used to null the offset voltage of the
electrometer amplifier, is factory adjusted and glyptal coated. R6
is adjusted to make the output, (TP1), zero with Rf shorted. (TP2
is circuit common.)
The most important components of the amplifier are the
operational amplifier (IC1), feedback resistor (Rf), and feedback
capacitor (Cf). If these components are substituted, the
performance of the system will be adversely affected.
Reference:
B-6409-K
B-9742-K