Thermocouple circuit detector for simultaneous analog trend recording and analog to digital conversion

A thermocouple circuit condition detector for use at the input circuit of a thermocouple amplifier having an input filter network and having one terminal of a thermocouple circuit connected to a first input terminal of said thermocouple amplifier and the other terminal of said thermocouple circuit connected to circuit common and to the second input terminal of said thermocouple amplifier comprising:

• an A.C. source of test pulses for producing a voltage pulse of short duration relative to the response time of said input filter,
• a first coupling circuit connected from said source of test pulses to said first input terminal of said thermocouple amplifier,
• an A.C. differential comparator amplifier having first and second input terminals and an output terminal,
• a second coupling circuit connected from said first input terminal of said thermocouple amplifier to said first input terminal of said comparator amplifier,
• a voltage divider network connected between said source of test pulses and said second input terminal of said comparator amplifier to apply thereto a voltage signal of magnitude at all times during the duration of said test pulse, greater than the potential developed at said first terminal of said comparator amplifier, when said thermocouple is normal and through at least part of the duration of said test pulse less than the potential developed at said first terminal of said comparator amplifier, when said thermocouple is open circuited, and
• a circuit condition indicator connected to the output of said comparator amplifier to provide an indication of an output circuit condition of said thermocouple when the potential applied to said first input terminal exceeds the potential applied to said second input terminal of said comparator amplifier.

A thermocouple circuit condition detector for use at the input circuit of a thermocouple amplifier having an input filter network and having one terminal of a thermocouple circuit connected to a first input terminal of said thermocouple amplifier input filter network and the other terminal of said thermocouple circuit connected to circuit common and to the second input terminal of said thermocouple amplifier input filter network comprising:

• a source of test pulses for producing a voltage pulse of short duration relative to the response time of said input filter,
• an A.C. coupling circuit connected from said source of test pulses to said first input terminal of said thermocouple amplifier input filter network to produce during the application of each of said test pulses a circuit condition voltage at said terminal that increases exponentially to a first value if said thermocouple circuit is open and to a second value that is smaller than said first value if said thermocouple circuit is normal,
• a voltage divider network having its input connected to said source of test pulses to produce an output voltage less than said first value and greater than said second value, and
• means for comparing said circuit condition voltage and the output of said voltage divider network and producing an open circuit signal when said circuit condition voltage exceeds said output voltage from said voltage divider network.