THERMOCOUPLE MODULE WITH WIRE RESISTANCE COMPENSATION

摘要

An interface circuit is provided for an Input/Output (I/O) module in an industrial controller to compensate for voltage generated by a bias current in a thermocouple. During a calibration routine, the interface circuit supplies two known bias currents to a thermocouple and measures a voltage generated across the thermocouple as a result of each bias current. The measured voltages and known current values are used to determine the resistance value of the thermocouple leads. Using two known bias currents provides for an accurate measurement of the resistance value of the thermocouple leads when the thermocouple is generating a voltage corresponding to the measured temperature. Either the I/O module or the industrial controller may determine a voltage resulting from the bias current applied to the thermocouple during operation as a function of the measured resistance and compensate the voltage measured at the thermocouple leads to accurately determine the measured temperature.

主权项

1. An interface circuit for use with an industrial controller and configured to be connected to a temperature sensor, the interface circuit comprising:
a first terminal configured to releasably receive a first lead of the temperature sensor; a second terminal configured to releasably receive a second lead of the temperature sensor, wherein the temperature sensor is of a type to generate a voltage as a function of a measured temperature; and a resistance measuring circuit operatively connected to at least one of the first terminal and the second terminal and configured to measure a resistance value of the first and second leads when the temperature sensor is generating the voltage.