Temperature measuring apparatus and method with resistance amplifier

Claim 2

Apparatus for generating a signal as a function of the resistance change of a resistance temperature detector element comprising: a. a resistance bridge network having its inputs connected to a constant current source; b. a resistance temperature detector element connected in one leg of the bridge; c. a first operational amplifier connected across the outputs of said bridge to generate an output signal; d. a second operational amplifier having one input terminal and its output terminal connected in series with the resistance temperature detector element in said one leg of said bridge, and e. means for applying a feedback signal derived from the output of said first operation amplifier to the other input of said second operational amplifier whereby the second operational amplifier will balance the bridge by adding an incremental potential to said one leg to compensate for any potential change in said leg caused by a change in the resistance of said resistance temperature detector.

Claim 3

The apparatus of claim 1 including a variable resistance connected in another leg of the bridge network operative to balance the bridge network to generate zero potential at the output of said first operational amplifier for a predetermined base temperature condition of the resistance temperature detector.

Claim 4

The apparatus of claim 2 wherein the means for deriving the feedback signal includes a voltage divider having a first resistance portion and a second resistance portion connected between the output of the first operational amplifier and ground, and a voltage intermediate said first and second portions of the voltage divider for extracting the feedback signal.

Claim 5

The apparatus of claim 3 including span adjusting means for varying the total effective resistance of the two resistance portions of the voltage divider.

Claim 6

The apparatus of claim 4 wherein the span adjusting means includes means for varying the effective resistance of one of the resistance portions of said voltage divider.

Claim 7

The apparatus of claim 5 wherein the said feedback signal is applied to the non-inverTing input of said second operational amplifier and wherein a feedback resistor is connected between the output and the inverting input of said second operational amplifier.

Claim 8

The apparatus of claim 1, including means for selectively connecting a particular remotely disposed resistance temperature detector element into said one leg of the bridge network, and for sequentially connecting others of a plurality of remotely disposed resistance temperature detector elements into the bridge network.

Claim 9

The apparatus of claim 1 wherein a three wire lead connection is used to connect a remotely disposed detector element to the bridge network.

Claim 10

Apparatus for generating a signal as a function of the resistance temperature detector element comprising: a. a resistance bridge network having its inputs connected to a constant current source; b. a resistance temperature detector element connected in one leg of the bridge; c. a first operational amplifier having its non-inverting input connected to a first bridge output connected to said one leg containing the resistance temperature detector element and to an amplifier ground and having its inverting input connected to the other output of the bridge, said first operational amplifier being operated in the feed back mode wherein said first operational amplifier assumes an output voltage which drives the potential on the inverting input to virtual ground; d. a voltage divider connected between the output of the operational amplifier and amplifier ground for generating an output signal thereacross; e. a feedback loop for said first operational amplifier including a second operational amplifier connected in series with the resistance temperature detector element in said one leg of the bridge with its inverting input connected to said first bridge output, its non-inverting input connected to a tap of the voltage divider and its output connected to the resistance temperature detector, said second operational amplifier also having a feedback resistor connected between its output terminal and its inverting input, whereby the second operational amplifier will balance the bridge by adding an incremental potential to said one leg to compensate for any potential change in said leg caused by a change in the resistance of said resistance temperature detector.

Claim 11

Apparatus for generating a signal as a function of the resistance temperature detector element comprising: a. a resistance bridge network having its inputs connected to a constant current source; b. a resistance temperature detector element connected in one leg of the bridge; c. a first operational amplifier having its non-inverting input connected to a first bridge output connected to said one leg containing the resistance temperature detector element and to an amplifier ground and having its inverting input connected to the other output of the bridge, said first operational amplifier being operated in the feed back mode wherein said first operational amplifier assumes an output voltage which drives the potential on the inverting input to virtual ground; d. a voltage divider connected between the output of the operational amplifier and amplifier ground for generating an output signal thereacross; e. a feedback loop for said first operational amplifier including a second operational amplifier connected in series with the resistance temperature detector element in said one leg of the bridge with its inverting input connected to said first bridge output, its non-inverting input connected to a tap of the voltage divider and its output connected to the resistance temperature detector, said second operational amplifier also having a feedback resistor connected between its output terminal and its inverting input, whereby the second operational amplifier will balance the bridge by adding an incremental potential to said one leg to compensate for any potential change in said leg caused by a change in the resistance of said resistance temperature detector.

Claim 12

The apparatus of claim 9 including a variable resistance connected in another leg of the bridge network operative to balance the bridge network to generate zero potential at the output of said first operational amplifier for a predetermined base temperature condition of the resistance temperature detector, and means for varying the effective resistance of one portion of said voltage divider to vary the magnitude of the output signal for any given temperature condition of the resistance temperature detector element whereby the bridge network is provided with independent span and suppression controls.

Claim 15

The method of claim 11 including the step of varying the load impedance in a second leg of said bridge network to balance the d-c bridge network to generate zero potEntial at the output of said operational amplifier for a predetermined base temperature condition of the resistance temperature detector.