Sprague Electric Company

George H Rodriguez

John P Maher

James E Crews

A self regulating ceramic PTCR (positive temperature coefficient of resistance) heater has a pair of spaced interdigitated electrodes on one major surface of a ceramic PTCR plate. A heat transfer means is provided for extracting heat from the opposite major surface of the PTCR plate. Best heating efficiency is obtained when the thickness of the PTCR plate is about the same or is less than the average spacing between the electrodes.

Self regulating PTCR heater

A ceramic PTCR slug has glass-bonded-aluminum layers bonded to the major opposite surfaces. Patches of silver film are bonded to selected regions of the glass-aluminum layers and stainless steel contacts are spring loaded against the silver patches. The stainless steel contacts provide good thermal isolation to the slug. The low cost contacts are complemented by the minumum use of silver in the electrode. The package provides long life under relatively heavy duty service.

PTCR Package

A PTCR ceramic slug having glass bonded aluminum electrodes is held firmly sandwiched between opposing inner walls in the cavity of a plastic housing by two identical resilient base-metal pieces on either major face of the slug. Each metal piece has metal fingers making spring loaded contact with the adjacent electroded face of the slug to effect the above noted holding and to form base-metal to base-metal electrical contacts. Each metal piece has at least one portion extending through a hole in the housing to provide electrical access to the PTCR slug.

A PTCR thermistor has a doped barium titanate body, and two base metal lead wires being bonded to and ohmically connected to two separate surface regions of the body by means of two conductive electrodes, respectively. The electrodes are comprised of aluminum particles being bound within a matrix of a lead borate glass. The glass amounts to from 20 to 60% by weight. The simple method of making the thermistor may include the selective application of heat to the electrode regions to avoid oxidizing the base metal leads. These thermistors are capable of undergoing many self-heating switching operations in service without deterioration of the lead to body connections.

Growing community of inventors

Williamstown, MA, United States of America

George H Rodriguez