PROBE SYSTEM FOR RELIABLY MONITORING A CONDITION IN A METALLURGICAL PROCESS

摘要

A probe system for reliably monitoring a condition in a metallurgical process is provided which includes a probe having a circuit for generating a low DC voltage signal indicative of a condition in the metallurgical process, and an impedance monitoring circuit electrically connected to the probe circuit for passively and continuously measuring the impedance of the probe circuit to determine its reliability without disturbing its DC signal. The probe may be a slag detector, a thermocouple, a sulfur sensor, or an oxygen sensor of the type used in steel manufacturing processes. The impedance monitoring circuit includes an oscillator assembly and a known impedance that is serially connected to the probe circuit by means of coupling capacitors that prevent the conduction of potentially biasing DC currents through the probe circuit. A band pass filter circuit having an input is connected between the known impedance and the probe circuit for generating a residual voltage which, when compared to the voltage applied by the oscillator circuit, indicates the impedance of the probe circuit. The impedance monitoring circuit advantageously detects a failure condition in such probes even when the failed probe continues to generate a low DC voltage that spuriously indicates a normal operating condition.