National Instruments Corporation

Al Becker

Michel G Haddad

Bakul Damle

Bakul V Damle

A circuit that protects a current shunt or any analog measuring circuit without the implementation of fuses. In a particular embodiment, a circuit comprises a current shunt and a plurality of transistors that may be configured to function as a fuse. One of the transistors may be deactivated once the input voltage exceeds a negative threshold voltage. The other transistor may be deactivated once the input voltage exceeds a positive threshold voltage. By deactivating the transistors once the input voltage exceeds a negative or a positive threshold voltage, the transistors are configured to function as a fuse and provide input protection for a current shunt or for any analog measuring circuit. In another particular embodiment, a circuit provides protection for a first and second current shunt where the second current shunt is less in resistance than the first current shunt. The circuit further comprises a plurality of transistors that may be configured to function as a fuse. The circuit further comprises a current limiter to protect the second current shunt at a second range and a voltage limiter to protect the current limiter at a first range, where the second range is smaller than the first range. The voltage limiter operates to deactivate the transistors once the input voltage exceeds a negative or positive voltage threshold of the first range. The current limiter operates to limit the current flowing through the transistors once the input voltage exceeds a negative or positive voltage threshold of the second range.

Input protection circuit implementing a voltage limiter

A method and apparatus for reducing the effects of ground loops in a thermocouple measurement device employing a differential amplifier for signal amplification. A resistor is coupled at the input of the differential amplifier to provide a DC ground reference. A capacitor is coupled in parallel to the resistor to compensate for AC noise and prevent the inputs from floating out of common mode range.

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Austin, TX, United States of America

Al Becker