Temperature indicating device

• US 3,927,571 A
• Filed: 01/18/1974
• Issued: 12/23/1975
• Est. Priority Date: 01/18/1974
• Status: Expired due to Term

• Current Assignee: Premark FEG LLC (Illinois Tool Works Inc.)
• Original Assignee: Stuart E. Athey
• Inventors: Athey, Stuart E.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Shoon, Frederick
• Application Number:
  US05/434,557
• Time in Patent Office: 704 Days
• Field of Search: 73/362R,362AR 315/122 324/96,99D,13P,13R 340/227R,172,228
• US Class Current: 374/111
• CPC Class Codes: G01K 3/005 Circuits arrangements for indicating a predetermined temperature fire detection G08B17/00
• CPC Class Codes: G01K 7/24 in a specially-adapted circuit, e.g. bridge circuit

Abstract

A digital type temperature indicator employs a thermistor temperature sensor and first and second comparator circuits, each having two inputs, one connected to the thermistor and the other connected to an adjustable reference representing a reference temperature level. A first indicator lamp indicates when the temperature is below a first reference level, a second lamp indicates when the temperature is in the range between the first and a second reference temperature levels, and the third lamp indicates when the temperature exceeds the second reference temperature level.

Claims

1. A temperature indicating apparatus for indicating whether a temperature under observation is under, over, or within a predetermined range of temperatures, said apparatus including a single temperature responsive means providing an electrical output which varies in response to the temperature sensed thereby, first and second comparator circuits, each having an input connected to the output of said temperature responsive means, and an input connected respectively to a first and a second adjustable electrical reference source representing first and second reference temperature levels, each of said comparator circuits providing an output which is either a source of current or ground depending upon the magnitude of the input from said temperature responsive means relative to its respective reference source, first, second and third indicator elements connected in series between a source of current and ground, the outputs from said first and second comparator circuits being connected to the junction between said first and second and said second and third indicator lamps, respectively, whereby only said first element is illuminated when the temperature being observed is below the first reference level, only said second lamp is illuminated when the temperature being observed is in the range between the first and second reference levels, and only said third element is illuminated when the temperature being observed exceeds the second reference level.

2. The apparatus of claim 1 wherein said temperature responsive element is a thermistor element.

3. The apparatus of claim 2 wherein said thermistor element is connected in a voltage divider circuit to provide a voltage output correlating positively with the temperature of said thermistor element.

4. The apparatus of claim 1 wherein said comparator circuits are operational amplifiers.

5. The apparatus of claim 4 wherein said operational amplifiers each have has an adjustable source of reference signal connected to one input terminal.

6. The apparatus of claim 1 wherein said indicator elements are energy emitting lamps.

7. The apparatus of claim 6 wherein said energy emitting lamps are light emitting elements.

8. The apparatus of claim 7 wherein said indicator elements are solid state light emitting devices.