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3.3. SIGNAL PROCESSING AMPLIFIER
A single printed circuit board attached directly to the front face of the instrument contains all power
supply and signal processing electronics.
Proprietary circuitry is used for the recognition and elimination of transient signals due to radon or
high-energy cosmic ray pulses. The RS400 instruments, with digital display, use a dedicated
internal circuit to disable the pulse rejection circuit when the measured signal reaches
approximately 80-100
μ
Sv/hr.
An OFFSET control is furnished in order to adjust the reading to zero in case of offsets caused by
tritium contamination of the chambers or otherwise.
A front panel control has been provided for adjustment of the set point (level) at which the acoustic
alarm is desired to sound. The acoustic signaler has the second function of alerting the user that
sample gas flow is impeded.
All power supplies are regulated. A warning LED on the front panel will illuminate red when the
battery terminal voltage has dropped to about 2.2 V. This signals that the batteries should be
replaced – WITHIN 1 HOUR AFTER THE WARNING LED ILLUMINATES. It will also illuminate
when the high voltage power supply (HVPS) operates outside of specified voltage range.
Two plug and jack connections are found on the sides of the instrument. One is for an external
power, and the other is the RS-232 cable connection to a personal computer.
