Browse Prior Art Database

MOLTEN SALT ELECTROCHEMICAL SYSTEM FOR TEMPERATURE SENSING

IP.com Disclosure Number: IPCOM000008912D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-23
Document File: 4 page(s) / 191K

Publishing Venue

Motorola

Related People

Gretchen E. Fougere Han Wu: AUTHOR [+2]

Abstract

Temperature sensing is an important technique in many technologies. In the automation and con- trol of manufacturing equipment, temperature sens- ing and control is especially critical. Conventional temperature sensing technologies rely on mecha- nisms which change with temperature: 1) Resistance of the sensor changes as the tem- perature changes. Thermistors are the most common example of this type of sensor.

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MO7VROLA Technical Developments

MOLTEN SALT ELECTROCHEMICAL SYSTEM FOR TEMPERATURE SENSING

by Gretchen E. Fougere Han Wu and Shekhar L. Pendalwar

PROBLEM(S) SOLVED BY THE INVENTION

  Temperature sensing is an important technique in many technologies. In the automation and con- trol of manufacturing equipment, temperature sens- ing and control is especially critical. Conventional temperature sensing technologies rely on mecha- nisms which change with temperature:

  1) Resistance of the sensor changes as the tem- perature changes. Thermistors are the most common example of this type of sensor.

  2) Contact changes in the element of a mechan- ical switch occur with temperature changes. Thermal cut-offs (TCOs) belong to this category.

  3) Potential difference between wires is propor- tional to the temperature. Thermocouples employ this difference to detect temperature.

  The above existing technologies are limited in several ways. They require additional circuitry to measure the change in resistance, contact, or poten- tial and are therefore not active elements. Also, mechanical switches are for one-time use only. The following was devised to address those limitations.

  This invention proposes another temperature sensing technique utilizing electrochemically active electrodes and a molten salt electrolyte. The molten salt electrolyte is insulative when in the solid form but becomes conductive as the temperature increas- es above its melting point. By using this type of sensor, the need for another sensing/control element in the circuit is eliminated; the sensor can act as a voltage/current source when the temperature reach- es the critical point at which the molten salt

becomes conductive. This temperature sensing device can be used in conjunction with any electron- ic equipment which requires protection from extreme temperature conditions. The molten salt device is small in size and lightweight allowing for its direct incorporation onto a circuit board.

SOLUTION TO THE PROBLEM(S)

  The proposed sensor has voltage as an output; therefore, this temperature sensor could be used as an active element. A small amount of molten salts could be placed between plates or encapsulated with electrode wires and placed with the circuitry to be protected. The output voltage could be used to short the circuit and protect a battery, for example. Alternative electrolyte materials that could be used are glasses or polymers with salts. Any material with a negligible open circuit voltage at ambient conditions could be used if it transforms to a con- ductive material at a critical temperature. The tran- sition from non-conductive to conductive can be a step function for a monolithic material or can occur over a temperature range for a two-phase mixture. The transition could occur in reverse for liquid molten salts which freeze and become insulative at

cold temperatures.

  Under certain temperature conditions, molten salt materials transform from insulative to conduc...