RELAY CONTROL SYSTEM FOR PREVENTION OF CONTACT EROSION

• Main Author: WILLIAM R. LANDIS
• Format: Patent
• Language: English
• Published: 02.02.1971
• Subjects: BASIC ELECTRIC ELEMENTS; BASIC ELECTRONIC CIRCUITRY; ELECTRIC SWITCHES; ELECTRICITY; EMERGENCY PROTECTIVE DEVICES; PULSE TECHNIQUE; RELAYS; SELECTORS

1320358 Arc rupturing in switches HONEYWELL Inc 2 Nov 1970 [11 Dec 1969] 52067/70 Heading H1N [Also in Division H3] To prevent erosion of the contacts of a relay having its contacts 42, 43 in an A.C. circuit and its coil 41 energized by a solid state circuit connected by a rectifier to the A.C. source 10, means, e.g. a resistor 26, are provided in the rectifier 22...25 to unbalance the ripple voltage to cause the solid-state circuit to energize the relay to close its contacts at a particular point in the A.C. cycle, so that should contact bounce occur, the arc drawn has the appropriate polarity to avoid transfer of contact material from one contact to the other, the contacts being of dissimilar materials. In the arrangement shown, a capacitor 38 is charged until its voltage exceeds the voltage across the relay coil 41 and interbase resistance of a unijunction transistor 33, the latter voltage being that of an instantaneous low peak voltage as determined by the unbalance of the ripple. As a result, the capacitor can only discharge through the transistor 33 at a point on a given half cycle of the A.C. supply to energize the relay coil so that, for example, if the relay contacts are of tungsten and silver cadmium oxide, the tungsten contact is always the anode when arcing occurs due to contact bounce. The relay may have holding contacts 48, 49.