Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Patent
1990-12-21
1992-03-17
Cuchlinski, Jr., William A.
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
374183, 330260, 330256, G01K 724
Patent
active
050963031
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an electronic circuit arrangement in a type of temperature measurement circuit based on a platinum resistor as a temperature-sensing resistor. In this particular type of measurement circuit, a reference resistor is provided in addition to the platinum resistor, and the measurement circuit is adapted to apply equally large DC currents to both resistors, both resistors having a common return lead. The resulting voltage difference across the resistors is sensed, and by means of at least one operational amplifier this voltage difference is adapted to cause an output DC current from the measurement circuit. This DC current shall be proportional to the voltage difference in order to constitute a measure of the temperature in the temperature-resistance characteristic of the platinum resistor, measurement circuits are which comprise devices for compensating for this non-linearity.
BACKGROUND OF THE INVENTION
A frequently employed and more or less standardized platinum temperature sensor has the type designation PT-100 and this has a primary interest in this connection. Known temperature measurement circuits, for co-operation with such platinum resistors, are available in the form of an integrated circuit or chip, among other things based on a three conductor principle at the input side for connection to the platinum resistor, the reference resistor respectively and with a common return lead as mentioned above. As far as the output of the measurement circuit is concerned, the invention is directed to a situation where the output DC current mentioned appears at two output terminals, for simple and practical adaption to the circuits or the system in which the temperature measurement is to be involved.
More particularly there exist previously known circuits which carry out the necessary linearizing in connection with, for example, the plantinum resistor of type PT-100 mentioned, including solutions based on an increase of the applied current in the sensor when the temperature rises.
U.S. Pat. No. 3,783,692 shows a measurement circuit in which a platinum sensing resistor is incorporated in a bridge configuration. Linearizing of the sensor is obtained by increasing the current therein by means of a specific current source having a negative resistance. Here there is the question of a rather complicated circuit in which it is difficult to calculate the component values for adaption to different temperature ranges to be covered by the measurements.
U.S. Pat. No. 3,754,442 describes a measurement circuit adapted to co-operate with different sensors having different non-linearity. The sensor is connected into a feed-back loop in an operational amplifier. A second operational amplifier controls an indicator and acts to vary the current in the sensor depending upon the output voltage. A rather complicated circuit is also involved there, due to among other things, it is to co-operate with different sensors.
European Patent 0 101 956 relates to a measurement circuit designed with a common differential amplifier in cooperation with a traditional source of current in a four-conductor measurement principle. The output voltage controls the source of current so that the current in the sensor increases with a rising temperature.
U.S. Pat. No. 4,114,446, similarly to some of the patent specifications above, is directed to a relatively complicated measurement circuit comprising a source of current and various amplifiers which by means of several feed-back loops are adapted to linearize the sensing resistor.
SUMMARY OF THE INVENTION
The object of this invention is to provide an arrangement of temperature measurement circuits of the kind described, being based on other and much simpler means than what is previously known, in order to carry out the desired linearizing.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following description the invention will be explained more closely with reference to the drawings, in which:
FIG. 1 shows a simplified diagram of a temperature measurement cir
REFERENCES:
patent: 3139753 (1964-07-01), Brudner
patent: 3754442 (1973-08-01), Arnett
patent: 3783692 (1974-01-01), Hansen
patent: 3857285 (1974-12-01), Athey et al.
patent: 3903743 (1975-09-01), Noller
patent: 4114446 (1978-09-01), Walsh
patent: 4301421 (1981-11-01), Yokoyama
patent: 4516865 (1985-05-01), Hideo
patent: 4699520 (1987-10-01), Wallenfang
Bennett G. Bradley
Cuchlinski Jr. William A.
NORAPP
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