A Linear Temperature Transmitter Based on Thermocouples Reference Tables

A temperature transmitter is introduced for linear temperature measurement by using thermocouples. It consists of AD590M, standard resistor, amplifier, AD converter, data sampling and processing system, serial output port, digital display, DA converter, 4-20mA.DC output and so on. AD590M is used as current source in addition to cold junction compensation. Under the control of a single chip processor, the amplifier is first calibrated with a standard milli-voltage signal provided from a standard resistor. Then the system samples the value of thermoelectric power of thermocouples. The highly accurate value of thermoelectric power is obtained via computing. Further, the temperature is obtained by looking into the reference table with the value of thermoelectric power. Therefore, high linearity is implemented; and the impact of temperature-drift and non-linearity of amplifier is greatly reduced. The test error is plusmn2degC in -100degC~1372degC without considering the error of thermocouples. In addition, the device implements the temperature measuring of full range of reference table.