Electronic temperature sensing system

• US 3,880,006 A
• Filed: 08/07/1972
• Issued: 04/29/1975
• Est. Priority Date: 08/07/1972
• Status: Expired due to Term

• Current Assignee: Noel Poduje
• Original Assignee: Noel Poduje
• Inventors: Poduje, Noel
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Shoon, Frederick
• Application Number:
  US05/278,557
• Time in Patent Office: 995 Days
• Field of Search: 73/362AR
• US Class Current: 374/173
• CPC Class Codes: G01K 7/21 for modifying the output characteristic, e.g. linearising

Abstract

An electronic system for providing an output voltage linearly representative of sensed temperature and in which different sensor modules are interchangeable with different processing circuitry modules without the need for recalibration. The sensor modules include a resistance temperature dependent sensor and associated compensating resistors. Predetermined voltages in this sensor module are sensed by the processing circuitry through a multiconductor cable and compensation and excitation currents are applied to the sensor module from the processing circuitry through the cable. Cable losses are of negligible effect on system accuracy. The processing circuitry provides a temperature indicating output signal from the sensed voltages and employs feedback control of the excitation current from this output signal to linearize the sensor response. Circuit adjustments of the processing circuitry permit standardization of all circuits for interchangeability of different circuitry modules. Also, the compensating resistors of the sensor module are adjusted during manufacture to provide the same variation in output signal with sensed temperature, irrespective of sensor characteristics, thereby permitting the interchange of different sensor modules without recalibration. As a result, different sensor and circuit modules may be interconnected by cables of different length without the need for recalibration to maintain system accuracy.

Claims

1. A system for sensing temperature comprising:

a temperature dependent resistance element;

a first calibration resistor of a preselected value;

a second calibration resistor of a preselected value;

said first resistor, said element and said second resistor being serially connected in that order to define a sensor module;

a cable having five conductors connected to said sensor module, a first conductor connected to said first resistor at the free end, second and third conductors connected to the junction between said first resistor and said element and fourth and fifth conductors connected to the free end of said second resistor;

a reference level source connected to said first conductor;

a controllable current source operative to apply a current to said second conductor representative of said reference level and a control signal in response thereto;

said controllable current source including a current pump circuit;

an amplifier having an inverting input connected to said third conductor and an output connected to said fourth conductor whereby said third conductor and the junction between said first resistor and said element are substantially maintained at a predetermined virtual potential and the current through said element and second resistor from said current and reference level sources are conducted over said fourth conductor;

a buffer amplifier having a feedback path therearound coupled to said fifth conductor;

an output amplifier;

a switch having a selector arm applied to an input of said output amplifier;

first and second variable resistors responsive to said buffer amplifier output to conduct to first and second selectable terminals of said switch for selective application to the input of said output amplifier;

said first and second variable resistors being adjusted to provide said output amplifier with respective gains to indicate temperature at its output in Centigrade and Fahrenheit scales; and

means for combining variable degrees of current from said reference level source with the signal at saiD first and second selectable terminals to provide predetermined signal offsets of said Centigrade and Fahrenheit scales and to compensate for system to system variations.

2. A temperature sensing system comprising:

a circuit including means for providing first and second currents along respective paths for application to a sensor module; and

means operative in response to a signal voltage from said sensor module to provide an output indication of sensed temperature;

a sensor module including a resistance temperature dependent element;

means for applying said first current from said circuit along a first path to one terminal of said element;

means for applying said second current from said circuit along a second path to said one terminal of said element;

means in said sensor module for producing a predetermined adjustment in said second current;

means for providing a signal voltage for said circuit representative of the voltage response of said element to said first and second currents and representative of temperature sensed by said element; and

means for providing a predetermined adjustment in the slope and offset of said signal voltage by an amount producing a predetermined correspondence between said signal voltage and the temperature sensed by said element throughout the operating temperature range whereby different sensor modules can be interchanged with said circuit without system recalibration.

3. A system for sensing temperature comprising:

a resistance temperature dependent element;

a first calibration resistor of preselected value;

a second calibration resistor of preselected value;

said element and said second resistor being serially interconnected and the series combination thereof being connected in series with said first resistor to define a sensor module;

a cable having five conductors connected to said sensor module, a first conductor being connected to said first resistor at the free end thereof, second and third conductors being connected to the junction between said first resistor and said series combination, and fourth and fifth conductors being connected to the free end of said series combination;

circuit means connected to the said sensor module by said cable and including means operative to apply first and second currents to said first and second conductors respectively;

means coupled to said third and fourth conductors and operative to substantially maintain the junction between said first resistor and said series combination at a virtual potential thereby to provide a reference potential at said junction;

means coupled to said fifth conductor and operative in response to a voltage across said series combination to provide an output signal representative of sensed temperature.

4. The temperature sensing system of claim 3 wherein said circuit means includes means for varying at least said second current in response to said output signal to linearize the variation of said output signal with temperature.

5. The temperature sensing system of claim 3 wherein said circuit means further includes means for scaling said output signal to provide temperature representations in a predetermined temperature scale.

6. The temperature sensing system of claim 3 wherein said circuit means further includes:

means for scaling said output signal to represent temperature in a plurality of scales; and

means for selecting one of said scales for output indication.

7. A temperature sensing system comprising:

a sensor module including means for applying a first current to a point of virtual potential within said module;

means for applying a second current along a separate path to said point of virtual potential within said module;

a resistance temperature dependent element having a predetermined resistance versus temperature characteristic and connected within said module to said point of virtual potential;

a circuit conNected to said sensor module and including means for establishing said virtual potential;

means for producing said first current for application to said module;

means responsive to a signal across said resistance temperature dependent element for controlling the magnitude of said first current in response thereto;

means responsive to said signal across said resistance temperature dependent element for indicating temperature sensed thereby.

8. A temperature sensing sytem comprising:

a sensor module including a resistance temperature dependent element;

first and second compensation resistors each of predetermined value;

said element and said second resistor being serially interconnected and the series combination thereof being connected in series with said first resistor;

a plurality of terminals, a first terminal being connected to the free end of said first resistor, a second terminal being connected to the junction between said first resistor and said series combination, and a third terminal being connected to the free end of said series combination;

a circuit connected to the terminals of said sensor module and including means for applying an excitation signal to said module terminal to cause excitation current flow through said series combination;

means for applying a compensating current to said first module terminal to cause compensating current flow through said first resistor and said series combination;

means coupled to said third terminal for sensing a signal across said series combination;

means responsive to said sensed signal for controlling said excitation current; and

means operative in response to said sensed signal for indicating temperature sensed by said element.

9. The temperature sensing system of claim 2 further including means responsive to said signal voltage from said sensor module for providing a variation in at least said first current applied to said sensor module to linearize the variation in detected signal voltage with temperature sensed by said element.

10. A system for sensing temperature comprising:

a temperature dependent resistance element;

a first calibration resistor of a preselected value;

a second calibration resistor of a preselected value;

said first resistor, said element and said second resistor being serially connected in that order to define a sensor module;

a cable having five conductors connected to said sensor module, a first conductor connected to said first resistor at the free end, second and third conductors connected to the junction between said first resistor and said element and fourth and fifth conductors connected to the free end of said second resistor;

a reference level source connected to said first conductor;

a controllable current source operative to apply a current to said second conductor representative of said reference level and a control signal in response thereto;

said controllable current source including a current pump circuit;

an amplifier having an inverting input connected to said third conductor and an output connected to said fourth conductor whereby said third conductor and the junction between said first resistor and said element are substantially maintained at a predetermined virtual potential and the current through said element and second resistor from said current and reference level sources are conducted over said fourth conductor;

a buffer amplifier having a feedback path therearound coupled to said fifth conductor;

an output amplifier operative to provide an output signal representative of temperature; and

circuit means coupling the output of said buffer amplifier to the input of said output amplifier.