System for accurate measurement of temperature

• US 4,122,719 A
• Filed: 07/08/1977
• Issued: 10/31/1978
• Est. Priority Date: 07/08/1977
• Status: Expired due to Term

• Current Assignee: Environmental Systems Products
• Original Assignee: Environmental Systems Products
• Inventors: Kreikebaum, Gerhard, Carlson, Thomas B.
• Primary Examiner(s): Ciarlante, Anthony V.
• Application Number:
  US05/813,951
• Time in Patent Office: 480 Days
• Field of Search: 73/342, 73/362 AR, 73/362 SC
• US Class Current: 374/167
• CPC Class Codes: G01K 1/026 arrangements for monitoring a plurality of temperatures, e.g. by multiplexing
• CPC Class Codes: G01K 1/028 arrangements for numerical indication
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers

Abstract

An improved system for accurately measuring temperature. The system is microprocessor based and automatically compensates for errors from such elements as cable resistance, drift and aging of the signal conditioning electronics. The system converts a non-linear electrical signal from a probe directly to a temperature indication in degrees Celcius. In the preferred embodiment, there is employed a multiplicity of probes and the system provides for automatically scanning of the probes and computation of the temperature for each.

Claims

1. A system for accurately measuring the temperature at a plurality of spaced apart locations comprising a plurality of platinum resistance probes one of which is located at each situs of temperature measurement, a source of constant current of a predetermined value, means connecting said current source in electrical communication with each of said probes, amplifier means, multiplexor means interposed in electrical communication between said probes and said amplifier means whereby each of said probes is selectively connected in electrical communication with said amplifier means, analog to digital convertor means, means connecting said amplifier means in electrical communication with said analog to digital connector means, microprocessor means, means connecting said analog to digital convertor means in electrical communication with said microprocessor means, display means, means connecting said display means in electrical communication with said microprocessor means, means for selectively developing a digital representation of a variable probe parameter and introducing the same to said microprocessor, means monitoring said source of constant current and developing an electrical signal representative of the variance of said current source from its predetermined value and feeding said signal to said microprocessor, means monitoring the drift of said analog to digital convertor from its zero and full scale bases and developing electrical signals representative of such variances and feeding said signals to said microprocessor, whereby the electrical resistance of each of said probes is selectively monitored, converted to its corresponding temperature equivalent and displayed.

2. The system of claim 1 including first and second fixed known standard resistances, means connecting said resistances in electrical communication with said multiplexor means whereby each of said fixed resistances is selectively connectable into said system in lieu of one of said probes.

3. The system of claim 1 including means monitoring the drift of said analog to digital convertor means from its zero and full scale bases and developing an electrical signal representative of such variance, and means communicating said signal to said microprocessor as an input signal thereto for compensating for such drift.

4. The system of claim 1 including a plurality of dip switches individual ones of which when introduced into said system provide to said microprocessor a digital representation of a variable probe parameter.

5. A system for accurate temperature measurement comprising in combination a platinum resistance whose electrical resistance varies with its temperature, a source of relatively constant current of a predetermined known value, at least two electrical leads connecting said platinum resistance in series with said current source, amplifier means, at least two electrical leads connecting said platinum resistance in electrical communication with said amplifier means whereby when said constant current is impressed through said platinum resistance an electrical signal is developed that has a voltage value proportional to the value of said constant current times the then existing resistance value of said platinum resistance and said altered electrical signal is fed to said amplifier and amplified to develop an output signal in analog form, an analog to digital convertor means, means connecting said amplifier in electrical communication with said analog to digital convertor means, microprocessor means, means connecting said analog to digital convertor means in electrical communication with said microprocessor means in electrical communication with said display means, means electrically connecting said source of constant current to said microprocessor means whereby the value of said current source becomes an input signal to said microprocessor means and said microprocessor monitors said current value and compensates for any variance of said current from its predetermined value in any processing within said microprocessor of said signal from said analog to digital convertor, means monitoring the drift of said analog to digital converter from its zero base and providing to said microprocessor an input signal representative of such drift, means monitoring the drift of said analog to digital convertor from its full scale base and providing to said microprocessor an input signal representative of such drift, means for selectively developing a digital representation of a variable probe parameter and introducing the same to said microprocessor.