Determining Thermocouple Accuracy on a dataTaker Data Logger

The spec sheets for any of the dataTaker DT8X series of loggers do not contain direct accuracy information on temperature measurements by thermocouple.  Instead it offers a voltage accuracy based on the full scale of the voltage being measured. The Applications Specialists at CAS DataLoggers have assembled this brief tech article to show you how to use the voltage output to determine thermocouple accuracy using these flexible data logging systems.

A thermocouple uses 2 different metals to create a small electrical charge.  The measurement of this charge can then be scaled to a temperature.  The DT8X series of loggers is calibrated to ITS-90 standards when it comes to reading thermocouples.  You can use this standard to determine the accuracy in degrees of the thermocouple.

Using the tables contained at:, the voltage output from a thermocouple can be determined for a certain temperature.  This is done by selecting a temperature range for the correct type of thermocouple, then cross-referencing the resulting table.

For instance, a K-type thermocouple at 1200° Celsius will output 48.838 millivolts.  If we check the accuracy of a DT8X logger on the spec sheet, we will see that the accuracy for DC voltage at normal operating temperatures (5°-40° C) is 0.1%, meaning that there may be a +- 0.048 mV variance.  Looking at the table at 1200° Celsius, the difference between 1200 and 1201 is .037 mV, putting the accuracy of the dataTaker at that temperature range, just over +- 1° C.

The new Series 3 dataTaker monitoring solutions from CAS DataLoggers feature universal input channels for use with a wide range of input signal types to measure almost any signal including Temperature, Current, Voltage, 4-20mA Loops, Resistance, Strain Gauges, Bridges, Frequency, Digital, Serial and Calculated Measurements. These intelligent devices also offer powerful alarm and programming capabilities enabling them to process measurements and initiate actions on their own.

Boasting a rugged design and construction, dataTaker products are world-renowned for surviving rough handling and environments, built to last over years of constant operation. Their extensive communications arrays include RS232 with modem support, USB, Ethernet and USB memory stick ports so you can choose to connect to the device locally, remotely or over the Internet. This versatility is increased with the logger’s multiple SDI-12 sensor networks, Modbus for SCADA systems, FTP and Web interface, so dataTakers are ready to be rolled out in any number of industrial machine monitoring projects.