A water conductivity monitoring circuit determines the status of an ion
exchange filter in the water flow to a steam generator. A microprocessor
sends a reference signal to a conductivity sensor circuit that converts
it to an excite signal that is sent to a probe in the water flow. Any
conductivity of the water alters the excite signal, and the modified
signal is compared to the reference signal to establish a value
indicative of the conductivity of the water. The microprocessor compares
the value to at least two thresholds representative of the status of the
filter.