Resistance bulb compensation circuits

Claim 2

An improved temperature detecting device of the type normally having; a bridge circuit containing a temperature sensing element, having three sensor leads, with a known temperature coefficient of resistance for developing a voltage related to temperature, wherein the improvement comprises: means to detect the voltage drop across the sensing element connected to two of the sensor leads; and compensation means for supplying an additional component of current through the sensing element in response to the detecting means to compensate for non-linearities of the temperature coefficient.

Claim 3

The improved temperature detecting device of claim 1 wherein the bridge circuit further contains source resistors for supplying a nearly constant current to the sensing element, wherein the improvement further comprises: second compensation means for supplying a second additional component of current to the sensing element to compensate for the non-constant source current.

Claim 4

The improved temperature detecting device of claim 1 wherein the improvement further comprises: balancing means for supplying a balance current to the bridge equal to the components of current supplied to the sensing element for compensation.

Claim 5

A linear temperature measuring circuit comprising: a temperature sensing element; a first lead connected to a first end of the element; a second lead connected to a second end of the element; a third lead connected to a second end of the element; a zeroing resistance in series with the second lead forming one half of a bridge circuit, the ends of the series combination being the output of the bridge; a first fixed resistance; a second fixed resistance in series with the first, this fixed resistance series combination being connected across the output to form the second half of the bridge; a source of excitation voltage connected from the third lead to the common point between the first and second fixed resistances; and a compensation network for detecting the voltage drop across the sensing element and supplying additional current to the first lead to compensate for any non-linearity between voltage drop and temperature in the temperature sensing element.

Claim 6

A linear temperature measuring circuit comprising: a temperature sensing element; a first lead connected to a first end of the element; a second lead connected to a second end of the element; a third lead connected to a second end of the element; a zeroing resistance in series with the second lead forming one half of a bridge circuit, the ends of the series combination being the output of the bridge; a first fixed resistance; a second fixed resistance in series with the first, this fixed resistance series combination being connected across the output to form the second half of the bridge; a source of excitation voltage connected from the third lead to the common point between the first and second fixed resistances; and a compensation network for detecting the voltage drop across the sensing element and supplying additional current to the first lead to compensate for any non-linearity between voltage drop and temperature in the temperature sensing element.

Claim 7

The temperature measuring circuit of claim 4 wherein the compensation network comprises: an operational amplifier having its positive input connected to the first lead; a firSt input resistor connected between the negative input of the amplifier and the second lead; a negative feedback resistor connected between the negative input of the amplifier and the output thereof; and a positive feedback resistor connected between the output of the amplifier and the first lead to supply a compensating current to the temperature sensing element.

Claim 8

The temperature measuring circuit of claim 5 wherein the compensation network further comprises: a second positive feedback resistor connected between the output of the amplifier and the end of the zeroing resistance connected to the bridge output, equal in value to the first positive feedback resistor in order to supply a second compensating current to the bridge to prevent unbalance.

Claim 9

The temperature measuring circuit of claim 6 wherein the compensation network further comprises: a second input resistor connected between the negative input of the amplifier and the third lead to compensate for source impedance.

Claim 10

The temperature measuring circuit of claim 7 wherein the compensation network further comprises: a first biasing resistor connected from the negative input of the amplifier to the common point between the fixed resistances; a second biasing resistor connected between the positive input of the amplifier and the common point between the fixed resistances; and a third biasing resistor inserted between the positive input and the first lead, whereby the amplifier may be powered by the source of excitation voltage.

Claim 11

The temperature measuring circuit of claim 7 wherein the temperature sensing element is a platinum resistance bulb.