Thermocouple signal amplifier

Claim 2

Apparatus for amplifying a small DC voltage signal from a thermocouple comprising, in combination, a point of reference potential, means for adding a first voltage signal to the DC voltage signal generated by the thermocouple so as to generate a control signal that is equal to their algebraic sum, said means varying said first voltage signal in response to ambient temperature variations, means for generating a second voltage signal equal to the first voltage signal at a certain ambient temperature, an AC amplifier having input and output terminals, a modulator for alternatively applying the control and second signals to the input terminal of the AC amplifier, the AC amplifier generating an amplified signal on the output terminal that is indicative of the voltage signal on the input terminal, signal separating means coupled to the output terminal of the AC amplifier for blocking the DC component of the amplified signal and passing the AC component thereof, an integrator having input and output terminals, a demodulator for alternately coupling the AC component of the amplified signal from the signal separating means to the point of reference potential and applying the AC component of the amplified signal to the input terminal of the integrator, a feedback impedance connected between the integrator output terminal and the means for generating the second voltage signal for effecting a change in the second voltage signal in response to voltage changes at the integrator output terminal, and an oscillator having first and second output terminals that are each connected to the modulator and demodulator, the oscillator controlling the modulator and demodulator by alternatively generating first and second timing signals on its respective first and second output terminals, the first timing signal causing the modulator to apply the second voltage signal to the AC amplifier input terminal and causing the demodulator to couple the AC component of the amplified signal to the point of reference potential and the second timing signal causing the modulator to apply the control signal to the input terminal of the AC amplifier and causing the demodulator to apply the AC component of the amplified signal to the integrator input terminal, the integrator thereby generating a signal on its output terminal that is indicative of the DC voltage signal and is of an amplitude determined by the feedback impedance magnitude.

Claim 3

Apparatus for amplifying a small DC voltage signal from a thermocouple comprising, in combination, a point of reference potential, means for adding a first voltage signal to the DC voltage signal so as to generate a control signal that is equal to their algebraic sum, said means varying said first voltage signal in response to ambient temperature variations, means for generating a second voltage signal equal to the first voltage signal at a certain ambient temperature, an AC amplifier having input and output terminals, a modulator for alternately applying the control and second signals to the input terminals of the AC amplifier whereby the AC amplifier generates an amplified signal at its output terminal that is indicative of the voltage signal on the input terminal, the modulator including a first controlled switch defining a controlled current path between the means for generating the second voltage signal and the AC amplifier input terminal and a second controlled switch defining a second controlled current path between the thermocouple and the AC amplifier input terminal, the first and second controlled switches having respective first and second control terminals and being effective to close the respective first and second current paths when a certain potential is applied to the control terminal of the corresponding controlled switch, a blocking capacitor having one terminal connected to the output terminal of the AC amplifier for separating the AC and DC components of the amplified signal, an integrator having input and output terminals, a demodulator connected between the other terminal of the capacitor and the integrator input terminal for alternatively discharging the capacitor and applying the AC component of the amplified signal to the input terminal of the integrator, the demodulator including a third controlled switch defining a controlled discharge path from the capacitor to the point of reference potential and a fourth controlled switch defining a current path from the capacitor to the integrator input terminal, the third and fourth controlled switches each having a control terminal and each being effective upon application of a certain potential to the control terminal to complete the respective currents paths, a feedback impedance connected between the integrator output terminal and the means for generating the second voltage signal for effecting a change in the second voltage signal in response to voltage changes at the integrator output terminal, and an oscillator having first and second output terminals on which are alternately generated first and second timing signals of the certain potential, the first output terminal of the oscillator being connected to the control terminal of the first and third controlled switches and the second output terminal of the oscillator being connected to the control terminal of the second and fourth controlled switches so as to effect closure of the first and third controlled current paths during a first time interval and closure of the second and fourth controlled current paths during a second time interval whereby the integrator generates a signal on its output terminal that is indicative of the DC voltage signal and is of an amplitude determined by the magnitude of the feedback impedance.

Claim 4

Apparatus for amplifying a small DC voltage signal from a thermocouple comprising, in combination, a point of reference potential, means for adding a first voltage signal to the DC voltage signal so as to generate a control signal that is equal to their algebraic sum, said means varying said first voltage signal in response to ambient temperature variations, means for generating a second voltage signal equal to the first voltage signal at a certain ambient temperature, an AC amplifier having input and output terminals, a modulator for alternately applying the control and second signals to the input terminals of the AC amplifier whereby the AC amplifier generates an amplified signal at its output terminal that is indicative of the voltage signal on the input terminal, the modulator including a first controlled switch defining a controlled current path between the means for generating the second voltage signal and the AC amplifier input terminal and a second controlled switch defining a second controlled current path between the thermocouple and the AC amplifier input terminal, the first and second controlled switches having respective first and second control terminals and being effective to close the respective first and second current paths when a certain potential is applied to the control terminal of the corresponding controlled switch, a blocking capacitor having one terminal connected to the output terminal of the AC amplifier for separating the AC and DC components of the amplified signal, an integrator having input and output terminals, a demodulator connected between the other terminal of the capacitor and the integrator input terminal for alternatively discharging the capacitor and applying the AC component of the amplified signal to the input terminal of the integrator, the demodulator including a third controlled switch defining a controlled discharge path from the capacitor to the point of reference potential and a fourth controlled switch defining a current path from the capacitor to the integrator input terminal, the third and fourth controlled switches each having a control terminal and each being effective upon application of a certain potential to the control terminal to complete the respective currents paths, a feedback impedance connected between the integrator output terminal and the means for generating the second voltage signal for effecting a change in the second voltage signal in response to voltage changes at the integrator output terminal, and an oscillator having first and second output terminals on which are alternately generated first and second timing signals of the certain potential, the first output terminal of the oscillator being connected to the control terminal of the first and third controlled switches and the second output terminal of the oscillator being connected to the control terminal of the second and fourth controlled switches so as to effect closure of the first and third controlled current paths during a first time interval and closure of the second and fourth controlled current paths during a second time interval whereby the integrator generates a signal on its output terminal that is indicative of the DC voltage signal and is of an amplitude determined by the magnitude of the feedback impedance.