Temperature measuring apparatus

Claim 2

Apparatus for measuring the average temperature at any two or more sensing points comprising, at each sensing point, a fourterminal temperature responsive resistance element having first and second current leads and first and second voltage leads, said first voltage lead in each instance being connected between one end of the element and the first current lead and the second voltage lead in each instance being connected between the other end of the element and the second current lead, current feeding means for feeding a constant current through each element via the current leads of the elements, said current feeding means including first and second common terminals and for each element, a first resistor in series with the element and connected at one end to the first current lead of the element and a second resistor in series with the element and connected at one end to the second current lead, the other ends of said first resistors being connected to said first common terminal and the other ends of said second resistors being connected to said second common terminal, the current feeding means being arranged so that, if the elements are all at the same temperature, the potentials at the connections of the first voltage leads of all the elements are the same and the potentials at the connections of the second voltage leads are all the same, circuit means for each element including a high impedance connecting the first voltage lead to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage leads of all the elements, and means responsive to a potential related to the potential between the first and second output terminals wherein the values of said first resistors are sufficiently large that current flow through each of said responsive elements is substantially constant, wherein the values of said second resistors are large compared with changes in the lead resistances and the values of the leAd resistances are substantially equal for each of said responsive elements, and wherein the values of said impedances are sufficiently large that currents therethrough do not effectively disturb the potentials of said voltage leads.

Claim 3

Apparatus as claimed in claim 1 and having a switch in series with each of said high impedances whereby the output of any chosen sensing element may be selected for averaging.

Claim 4

Apparatus as claimed in claim 1 and having a potential divider connected between said common terminals, said potential divider having at least two taps, and wherein said second output terminal is connected to one tap on the divider and wherein said means responsive to the potential related to the potential between the first and second output terminals comprises means for measuring the potential between said first output terminal and another tap on the divider.

Claim 5

Apparatus for measuring the average temperature at any two or more points selectable out of a number of sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current leads and first and second voltage leads, said first voltage lead in each instance being connected between one end of the element and the first current lead and the second voltage lead in each instance being connected between the other end of the element and the second current lead, a voltage supply source having first and second terminals, a separate series resistance connected between the first current lead of each temperature responsive element and the first terminal of the supply source, circuit means including further series resistances connecting between the second current lead of each temperature responsive element to a return current path to the supply source, the aforesaid series resistances being of such magnitude that, if the temperature responsive elements are all at the same temperature, the potential drops across the temperature responsive elements are equal, circuit means for each element including a switch and a high impedance connected to the first voltage lead of each responsive element to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage leads of all the temperature responsive elements, a potential divider having at least two taps connected between said first and second terminals of the voltage supply source, means connecting said second output terminal to one tap on said divider, and means responsive to the potential between said first output terminal and a second tap on said divider wherein the values of each said first mentioned separate series resistance is sufficiently large that current flow through each of said responsive elements is substantially constant, wherein the values of said further series resistances are larger compared with the changes of lead resistances and the values of the lead resistances are substantially equal for each of said responsive elements, and wherein the values of said impedances are sufficiently large that currents therethrough do not effectively disturb the potentials of said voltage leads.

Claim 6

Apparatus for measuring the average temperature at any two or more points selectable out of a number of sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current leads and first and second voltage leads, said first voltage lead in each instance being connected between one end of the element and the first current lead and the second voltage lead in each instance being connected between the other end of the element and the second current lead, a voltage supply source having first and second terminals, a separate series resistance connected between the first current lead of each temperature responsive element and the first terminal of the supply source, circuit means including further series resistances connecting between the second current lead of each temperature responsive element to a return current path to the supply source, the aforesaid series resistances being of such magnitude that, if the temperature responsive elements are all at the same temperature, the potential drops across the temperature responsive elements are equal, circuit means for each element including a switch and a high impedance connected to the first voltage lead of each responsive element to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage leads of all the temperature responsive elements, a potential divider having at least two taps connected between said first and second terminals of the voltage supply source, means connecting said second output terminal to one tap on said divider, and means responsive to the potential between said first output terminal and a second tap on said divider wherein the values of each said first mentioned separate series resistance is sufficiently large that current flow through each of said responsive elements is substantially constant, wherein the values of said further series resistances are larger compared with the changes of lead resistances and the values of the lead resistances are substantially equal for each of said responsive elements, and wherein the values of said impedances are sufficiently large that currents therethrough do not effectively disturb the potentials of said voltage leads.

Claim 7

Apparatus as claimed in claim 4 wherein the potential divider is adjustable and wherein the voltage responsive means is a null balance detector.

Claim 8

Apparatus for measuring the average temperature at any two or more sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, current feeding means for feeding a constant current through each element via the current terminals of the elements, said current feeding means including first and second common terminals and for each element, a first resistor in series with the element and connected at one end to the first current terminal of the element and a second resistor in series with the element and connected at one end to the second current terminal, the other eNds of said first resistors being connected to said first common terminal and the other ends of said second resistors being connected to said second common terminal, the current feeding means being arranged so that, if the elements are all at the same temperature, the potentials at the first voltage terminals of all the elements are the same and the potentials at the second voltage terminals are all the same, circuit means for each element including a high impedance connecting the first voltage terminal to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage terminals of all the elements, means responsive to a potential related to the potential between the first and second output terminals, an operational amplifier having an input and an output, a constant voltage source, a resistive input connecting said constant voltage source to said amplifier and means connecting the first said common output terminal to the amplifier input and the second common terminal to the amplifier output.

Claim 9

Apparatus for measuring the average temperature at any two or more sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, current feeding means for feeding a constant current through each element via the current terminals of the elements, said current feeding means including first and second common terminals and for each element, a first resistor in series with the element and connected at one end to the first current terminal of the element and a second resistor in series with the element and connected at one end to the second current terminal, the other eNds of said first resistors being connected to said first common terminal and the other ends of said second resistors being connected to said second common terminal, the current feeding means being arranged so that, if the elements are all at the same temperature, the potentials at the first voltage terminals of all the elements are the same and the potentials at the second voltage terminals are all the same, circuit means for each element including a high impedance connecting the first voltage terminal to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage terminals of all the elements, means responsive to a potential related to the potential between the first and second output terminals, an operational amplifier having an input and an output, a constant voltage source, a resistive input connecting said constant voltage source to said amplifier and means connecting the first said common output terminal to the amplifier input and the second common terminal to the amplifier output.

Claim 10

Apparatus as claimed in claim 6 wherein the means responsive to the potential between the two output terminals is connected between the common second voltage terminals of the temperature responsive elements and a datum potential source for the input of the operational amplifier.

Claim 11

Apparatus as claimed in claim 7 wherein the current input terminal of the operational amplifier is connected to a tap on a potential divider connected across the supply source.

Claim 12

Apparatus as claimed in claim 8 wherein said means responsive to the potential between the two output terminals is connected between the second voltage terminals of the temperature responsive elements and the supply source terminal which is not connected to the first current input terminals of the temperature sensing elements.

Claim 13

Apparatus as claimed in claim 6 wherein the sensor elements have a resistance R Rt(1+At+Bt2) where Rt is the resistance at datum temperature T is the temperature above the datum and A and B are coefficients and where A has a positive value and B has a negative value and wherein there is provided a phase inverting feedback circuit across said operational amplifier to give a separate feedback current dependent on the voltage at the common second voltage terminals of the temperature sensing element and feeding back the currents separately to the current input terminals of the respective sensing elements, the feedback circuits having resistors for the various feedbacks proportioned to compensate for the non-linearity between the resistance of each sensing element and temperature.

Claim 14

Apparatus as claimed in claim 6 and for measuring the average temperature at any two or more points wherein, for each sensing point, said circuit means including a high impedance also includes a switch whereby the outputs of any one or more of the sensing elements may be selectively connected to the input of said operational amplifier.

Claim 15

Apparatus as claimed in claim 11 wherein the switches are float-operated switches each of which closes when the associated temperature responsive element is immersed in a liquid.

Claim 16

Apparatus for measuring the average temperature at any two or more points selectable out of a number of sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, current feeding means for feeding a constant current through each element via the current terminals of the elements, the current feeding means including, for each element and in series therewith a resistor connected to the first current terminal and a resistor connected to the second current terminal, the current feeding means feeding the elements being arranged so that, if the elements are all at the same temperature, the potentials at the first voltage terminals oF all the elements are the same and the potentials at the second voltage terminals are all the same, circuit means for each element including a switch and a high impedance connecting the first voltage terminal to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage terminals of all the temperature responsive elements and means responsive to the potential between the first and second output terminals, said switches being float-operated switches each of which closes when the associated temperature responsive element is immersed in a liquid.

Claim 17

Apparatus for measuring the average temperature at any two or more points selectable out of a number of sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, current feeding means for feeding a constant current through each element via the current terminals of the elements, the current feeding means including, for each element and in series therewith a resistor connected to the first current terminal and a resistor connected to the second current terminal, the current feeding means feeding the elements being arranged so that, if the elements are all at the same temperature, the potentials at the first voltage terminals oF all the elements are the same and the potentials at the second voltage terminals are all the same, circuit means for each element including a switch and a high impedance connecting the first voltage terminal to a common first output terminal, circuit means connecting in common to a second output terminal the second voltage terminals of all the temperature responsive elements and means responsive to the potential between the first and second output terminals, said switches being float-operated switches each of which closes when the associated temperature responsive element is immersed in a liquid.

Claim 18

Apparatus for measuring the average temperature at any two or more sensing points comprising: a. at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, b. current feeding means for feeding a constant current through each element via the current terminals of the element, said current feeding means comprises an operational amplifier, each element being connected as a separate feedback circuit across the amplifier and each having an associated input resistance, c. a common voltage source feeding said input resistances, d. said input resistances and current feeding means being such that if all the elements are at the same temperature, the potentials at the first voltage terminals of all the elements are the same and the potentials at the second voltage terminals are all the same, e. circuit means for each element including a high impedance connecting the first voltage terminal to a common first output terminal, f. circuit means connecting, in common to a second output terminal the second voltage terminals of all the temperature responsive elements, and g. means responsive to the potential between the first and second output terminals.

Claim 19

Apparatus for measuring the average temperature at any two or more sensing points comprising: a. at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, b. current feeding means for feeding a constant current through each element via the current terminals of the element, said current feeding means comprises an operational amplifier, each element being connected as a separate feedback circuit across the amplifier and each having an associated input resistance, c. a common voltage source feeding said input resistances, d. said input resistances and current feeding means being such that if all the elements are at the same temperature, the potentials at the first voltage terminals of all the elements are the same and the potentials at the second voltage terminals are all the same, e. circuit means for each element including a high impedance connecting the first voltage terminal to a common first output terminal, f. circuit means connecting, in common to a second output terminal the second voltage terminals of all the temperature responsive elements, and g. means responsive to the potential between the first and second output terminals.

Claim 20

Apparatus for measuring the average temperature at any two or more points selectable out of a number of sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, a voltage supply source having first and second terminals, a separate series resistance connected between the first current terminal of each temperature responsive element and the first terminal of the supply source, an operational amplifier for feeding current to said second current terminal of each temperature responsive element, a return current path connecting the first current terminals to the supply source, the aforesaid series resistances being of such magnitudes that, if the temperature responsive elements are all the same temperature, the potential drops across the temperature responsive elements are equal, circuit means for each element including a switch and a high impedance connecting the first voltage terminal of each responsive element to the input of said operational amplifier, circuit means connecting in common to a second output terminal the second voltage terminals of all the temperature responsive elements and means responsive to the potential between the two output terminals.

Claim 21

Apparatus for measuring the average temperature at any two or more points selectable out of a number of sensing points comprising, at each sensing point, a four-terminal temperature responsive resistance element having first and second current terminals and first and second voltage terminals, a voltage supply source having first and second terminals, a separate series resistance connected between the first current terminal of each temperature responsive element and the first terminal of the supply source, an operational amplifier for feeding current to said second current terminal of each temperature responsive element, a return current path connecting the first current terminals to the supply source, the aforesaid series resistances being of such magnitudes that, if the temperature responsive elements are all the same temperature, the potential drops across the temperature responsive elements are equal, circuit means for each element including a switch and a high impedance connecting the first voltage terminal of each responsive element to the input of said operational amplifier, circuit means connecting in common to a second output terminal the second voltage terminals of all the temperature responsive elements and means responsive to the potential between the two output terminals.