Pyroelectric temperature compensated sensing device employing differential amplifier

• US 3,999,069 A
• Filed: 08/08/1975
• Issued: 12/21/1976
• Est. Priority Date: 08/08/1975
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: McFadden, Francis J., Taylor, Allen L.
• Primary Examiner(s): Willis, Davis L.
• Application Number:
  US05/603,176
• Time in Patent Office: 501 Days
• Field of Search: 250/338, 250/340, 250/342, 250/349, 250/353
• US Class Current: 250/338.3
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: H10N 15/10 Thermoelectric devices using thermal change of the dielectric constant, e.g. working above and below the Curie point

Abstract

A temperature compensated sensing device for sensing a particular condition includes first and second conductive layers in surface-to-surface contact with and separated by a layer of poled, pyroelectric material. In a preferred embodiment, the second conductive layer is electrically grounded and the first conductive layer is etched to define two interdigitated, electrically unconnected sets of conductive portions. The sets of conductive portions are heated when exposed to the condition desired to be detected and, in turn, heat areas of the pyroelectric layer. As a result, electrostatic charges are developed on the heated pyroelectric areas and appear as voltage potentials on the heated conductive portions. Electronic circuitry having a differential amplifier is electrically connected to the conductive portions for sensing the voltage potentials thereon and for triggering an alarm when certain voltage potentials exist. In a first modified embodiment, the first conductive layer is electrically grounded and the second conductive layer contains the interdigitated conductive portions, and in a second modified embodiment neither of the conductive layers is grounded.

Claims

1. A temperature compensated sensing device for detecting the presence of a particular condition, which sensor comprises:

first and second conductive layers, at least one of said layers is formed to provide at least two electrically unconnected conductive portions and the other of said layers is electrically grounded, with said first layer having at least one area that is exposed to and heated by said condition;

a layer of poled, pyroelectric material interposed between and in surface-to-surface contact with said conductive layers and having at least one area that is heated by said heated area of said first conductive layer to result in the development of electrostatic charges on said heated pyroelectric area and one of the conductive portions in contact with said heated pyroelectric area; and

a sensing circuit for responding to the development of said electrostatic charges and providing an indication of the presence of said condition, which sensing circuit includes a differential amplifier that is electrically connected to said electrically unconnected conductive portions to prevent actuation of the detector when the voltage potentials of the conductive portions are equal.

2. A sensing device as recited in claim 1 wherein said pyroelectric material is formed from polyvinylidene fluoride.

3. A sensing device as recited in claim 1 wherein said first conductive layer is formed to provide the unconnected conductive portions and said second conductive layer is electrically grounded.

4. A sensing device as recited in claim 1 wherein said second conductive layer is formed to provide the unconnected conductive portions and said first conductive layer is electrically grounded.