COMPOSITE THERMISTOR TEMPERATURE SENSOR HAVING STEP-FUNCTION RESPONSE

• US 3,673,538 A
• Filed: 12/05/1969
• Issued: 06/27/1972
• Est. Priority Date: 12/05/1969
• Status: Expired due to Term

• Current Assignee: Robert C. Faxon
• Original Assignee: Robert C. Faxon
• Inventors: Faxon, Robert C.
• Primary Examiner(s): Bennett, Jr., Rodney D.
• Assistant Examiner(s): Kinberg, R.
• Application Number:
  US04/882,799
• Time in Patent Office: 935 Days
• Field of Search: 338/22,23,25 317/41 323/68,69
• US Class Current: 338/25
• CPC Class Codes: G05D 23/1927 using a plurality of sensors G05D23/1902, G05D23/1917, and G05D23/1919 take precedence
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor
• CPC Class Codes: H01C 7/022 mainly consisting of non-metallic substances H01C7/021 takes precedence

Abstract

A temperature sensor including first and second PTC thermistor elements each having a well-defined transition temperature above which the resistance of the element rises relatively abruptly and below which it changes relatively little, the transition temperature of the second element being substantially greater than that of the first element. The thermistor elements are substantially identically thermally responsive to a body whose temperature is sensed by the sensor. The elements are electrically interconnected to cause the sensor resistance to be an equivalent resistance which varies as a function of the resistance of the elements and changes relatively abruptly at temperatures determined by the transition temperatures of the elements thereby providing the sensor with a step-function R vs. T characteristic.

Claims

1. A temperature sensor for use in a control circuit adapted to perform first and second control functions in response to changes in the resistance of said sensor at respective first and second control temperatures determined by said sensor, said sensor comprising a first thermistor element having a positive temperature coefficient and a well-defined transition temperature above which the resistance thereof rises relatively abruptly and below which the resistance thereof changes relatively little;

and a second thermistor element having a positive temperature coefficient and a well-defined transition temperature, substantially greater than that of said first element, above which the resistance of said second element rises relatively abruptly and below which the resistance thereof changes relatively little;

the resistance of said second element at the transition temperature thereof being substantially greater than the resistance of said first element at the transition temperature thereof;

said first and second elements being substantially identically thermally respoNsive to a source of heat and being electrically interconnected in parallel-circuit relationship whereby the sensor resistance is a parallelequivalent resistance which varies as a function of the resistances of said elements and changes relatively abruptly at said control temperatures, said control temperatures being determined by the transition temperatures of said elements.

2. A temperature sensor as set forth in claim 1 further comprising a substantially temperature-insensitive resistance which does not vary substantially with respect to changes in the temperature sensed by said sensor, said temperature-insensitive resistance being series-connected with one of said elements, the other of said elements being connected across the series-connected one element and temperature-insensitive resistance.

3. A temperature sensor as set forth in claim 2, wherein said temperature-insensitive resistance is series-connected with said second element.

4. A temperature sensor comprising first and second thermistor elements each constituted by thermistor material having a well-defined transition temperature above which the resistance thereof changes relatively abruptly and below which the resistance thereof changes relatively little, the transition temperature of said second element being substantially greater than that of said first element, the resistance of said second element at the transition temperature thereof being substantially greater than the resistance of said first element at the transition temperature thereof, each of said elements having opposite ends and having respective surfaces, said elements being secured together in face-to-face relationship at said surfaces, and electrical contact means at the opposite ends of said elements adapted to be interconnected in an electrical circuit.

5. A temperature sensor comprising first and second thermistor elements each constituted by thermistor material having a well-defined transition temperature above which the resistance thereof changes relatively abruptly and below which the resistance thereof changes relatively little, the transition temperatures of the first and second elements being substantially different from one another, the resistance of said second element at the transition temperature thereof being substantially greater than the resistance of said first element at the transition temperature thereof, each of said elements having opposite ends and having respective surfaces, said elements being secured together in face-to-face relationship at said surfaces, electrical contact means at the opposite ends of said elements, said elements electrically connected in parallel by metallic areas bridging respective opposite end portions of said elements and adapted to be interconnected in an electrical circuit.

6. A temperature sensor comprising first and second thermistor elements each constituted by thermistor material having a well-defined transition temperature above which the resistance thereof changes relatively abruptly and below which the resistance thereof changes relatively little, the transition temperatures of the first and second elements being substantially different from one another, each of said elements having opposite ends and having respective surfaces, said elements being secured together in face-to-face relationship at said surfaces, each element being of semicylindrical form thus having a flat axial face in a diametrical plane with said first and second ends being of semicircular form and normal to said axial face, said elements being joined together over the said axial faces thereof and electrical contact means at the opposite ends of said elements adapted to be interconnected in an electrical circuit.

7. A temperature sensor comprising first and second thermistor elements each constituted by thermistor material having a well-defined transition temperature above which the resistance thereof changes relatively abruptly and below which the resistance thereof changes relatively little, The transition temperatures of the first and second elements being substantially different from one another, each of said elements having opposite ends and having respective surfaces, said elements being secured together in face-to-face relationship at said surfaces, the first element is of tubular form thus having an axial bore, and the second element fills the bore and electrical contact means at the opposite ends of said elements adapted to be interconnected in an electrical circuit.