Ronan X96S DENSITY GAGE - Manual (Page 57)

Density Gage Manual 012407 53
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 A, 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 amplifier, (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 potentiometer
(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