Patent US 3,993,166

An electrical alarm system, which responds to improper and/or unsafe loading of a fork-lift truck or other load-sustaining apparatus equipped with a suitable sensing transducer, is controlled by a high-gain electronic differential switch whose comparisons of reference and sensing-transducer electrical signals are uniquely improved by a combination of: (a) unidirectionally-positive feedback which produces a dynamic transient hysteresis effect; (b) steady-state feedback or hysteresis which prevents false triggering of the system by ambient noise and vibration; (c) a regulator and electrical interference suppression network; and (d) low-level high-frequency partial filtering of oscillations in the waveform of sensing-transducer output signals. Fail-safe system operation is assured by network connections and output actuations which prevent the handling of loads when system cabling is disabled, as well as when overloading is sensed.