Thermocouple-failure warning circuit

Claim 2

A thermocouple-failure warning circuit for use with a thermocouple-controlled operational amplifier, said warning circuit comprising, in combination, first and second voltage supply leads for connection to a source of DC electrical potential; a thermocouple having first and second leads coupled to input terminals of said operational amplifier, said thermocouple first lead being coupled to said first voltage supply lead; a resistor, said thermocouple second lead being coupled through said resistor to said second voltage supply lead; a warning device; a transistor Having an output circuit and a control electrode, the output circuit of said transistor being connected with said warning device to control the actuation of said warning device; first circuit means for coupling said warning device and transistor output circuit across a source of electrical potential; and second circuit means for changing the state of conduction of the output circuit of said transistor if either said thermocouple is open-circuited between its first and second leads or if said thermocouple is short-circuited to the electrical potential of said second voltage supply lead, said circuit means being connected to said transistor control electrode and having an input electrical lead connected to said thermocouple second lead, whereby, said warning device may be actuated by a change in the state of conduction of aid transistor output circuit if said thermocouple is open-circuited or short circuited.

Claim 3

A thermocouple-failure warning circuit in accordance with claim 1, wherein said second circuit means comprises a second transistor having an output circuit and a control electrode, said input electrical lead being coupled to said second transistor control electrode, said output circuit of said second transistor being coupled to said control electrode of said first-mentioned transistor, said second transistor output circuit being conductive in its output circuit in the absence of said thermocouple being open-circuited between said thermocouple first and second leads and in the absence of said thermocouple being short-circuited to the electrical potential of said second voltage supply lead.

Claim 4

A thermocouple-failure warning circuit in accordance with claim 2, wherein said second circuit means further comprises a third transistor having an output circuit coupled to said control electrode of said first-mentioned transistor, said third transistor having a control electrode coupled to said output circuit of said second transitor, the output circuits of said first-mentioned transistor and said third transistor being nonconductive when the output circuit of said second transistor is conductive, and the output circuits of said first-mentioned transistor and third transistor being conductive when the output circuit of said second transistor is conductive.

Claim 5

A thermocouple-failure warning circuit for use with a first thermocouple-controlled operational amplifier and a second thermocouple-controlled operational amplifier, said warning circuit comprising, in combination, first and second voltage supply leads for connection to a source of DC electrical potential; a first thermocouple having first and second leads coupled to input terminals of said first operational amplifier, said first terminals of said first and second thermocouples being coupled to said first voltage supply lead; a first resistor, said second lead of said first thermocouple being coupled through said first resistor to said second voltage supply lead; a second resistor, said second lead of said second thermocouple being coupled through said second resistor to said second voltage supply lead; a warning device; a transistor having an output circuit connected to said warning device to control actuation of said warning device, said transistor having a control electrode; circuit means for coupling said warning device and transistor output circuit across a source of electrical potential; and gate circuits means for changing the state of conduction of the output circuit of said transistor if either of said first and second thermocouples is either open-circuited or short-circuited to the electrical potential of said second voltage supply lead, said gate circuit means having a first input electrical lead connected to said second lead of said first thermocouple and having a second input electrical lead connected to said second lead of said second thermocouple; whereby, said warning device may be actuated by a change in the state of conduction of said transistor output circuit if either of said first and second tHermocouples is either open-circuited or short-circuited.

Claim 6

A thermocouple-failure warning circuit for use with a first thermocouple-controlled operational amplifier and a second thermocouple-controlled operational amplifier, said warning circuit comprising, in combination, first and second voltage supply leads for connection to a source of DC electrical potential; a first thermocouple having first and second leads coupled to input terminals of said first operational amplifier, said first terminals of said first and second thermocouples being coupled to said first voltage supply lead; a first resistor, said second lead of said first thermocouple being coupled through said first resistor to said second voltage supply lead; a second resistor, said second lead of said second thermocouple being coupled through said second resistor to said second voltage supply lead; a warning device; a transistor having an output circuit connected to said warning device to control actuation of said warning device, said transistor having a control electrode; circuit means for coupling said warning device and transistor output circuit across a source of electrical potential; and gate circuits means for changing the state of conduction of the output circuit of said transistor if either of said first and second thermocouples is either open-circuited or short-circuited to the electrical potential of said second voltage supply lead, said gate circuit means having a first input electrical lead connected to said second lead of said first thermocouple and having a second input electrical lead connected to said second lead of said second thermocouple; whereby, said warning device may be actuated by a change in the state of conduction of said transistor output circuit if either of said first and second tHermocouples is either open-circuited or short-circuited.

Claim 7

A thermocouple-failure warning circuit in accordance with claim 4 wherein said gate circuit means comprises a plurality of interconnected solid-state switching devices coupled between said control electrode of said transistor and said first and second input electrical leads, said plurality of solid-state switching devices collectively causing an electrical potential to be applied to said control electrode of said transistor to maintain the output circuit of said transistor in a conductive state when either of said thermocouple is open-circuited or short-circuited to said second voltage supply lead.

Claim 8

A thermocouple-failure warning circuit in accordance with claim 5 wherein said plurality of solid-state switching devices comprises: a third resistor; a second transistor having its base coupled through said third resistor to said first input electrical lead and having its emitter connected to said second voltage supply lead; a fourth resistor; a third transistor having its base coupled through said fourth resistor to said second input electrical lead and having its emitter connected to said second voltage supply lead; a fourth transistor having its emitter connected to said control electrode of said first-mentioned transistor; circuit means for coupling the collectors of said second, third and fourth transistors to a source of electrical potential; a first diode having its anode connected to said collector of said second transistor and having its cathode connected to the base of said fourth transistor; and a second diode having its anode connected to the collector of said third transistor and having its cathode connected to the base of said fourth transistor.