Variable sensitivity monitor circuit

Claim 1

In a process or equipment of the type wherein process or equipment conditions are monitored to detect an abnormal condition and wherein when said process or equipment is first started up or turned on, a transient having a magnitude substantially larger than the steady-state monitored condition limits is normally produced, the improvement comprising: a gain switched device adapted to be connected between a monitored device a monitor circuit for detecting said abnormal condition of the monitored device, and means actuated at start-up or turn-on of the monitored device for controlling said gain switched device to decrease the gain thereof during said transient and thereafter increase the gain of said gain switched device to a normal steady-state level thereby changing the sensitivity of the monitor circuit during the transient period from that during normal steady-state operation, said gain being decreased at start-up or turn-on by an amount sufficient to prevent expected transients normally encountered at start-up or turn-on from falsely indicating an abnormal condition, while allowing abnormal transients to be recognized during turn-on or start-up.