Thermocouples are without a doubt the most popular type of temperature sensor, and the VTI Instruments EX1000A Precision Voltage Measurement Instrument Series provides 48 voltage channels and supports Type J, K, T, E, S, R, B, and N thermocouples. To help you avoid some common pitfalls when making thermocouple measurements and get the most out of your instrument, we offer the following tips:
- Use the self-calibration feature. In order to deliver high measurement accuracy over a wide ambient operating temperature range, the EX1000A Series includes a self-calibration feature. During self-calibration, the instrument disconnects the input signal conditioning paths from the input jacks and connects them instead to a calibration bus that is driven by an internal calibration source.
Self-calibration should be conducted as often as practical, especially if the ambient environment has changed significantly since the previous calibration. The self-calibration process completes quickly and does not require removal of the actual input connections, making it convenient to run often. If the ambient environmental conditions change quickly, allow the instrument to stabilize before performing a self-calibration. Similarly, allow the instrument to warm up for at least 60 minutes from a cold start before performing a self-calibration.
- Allow the instrument to reach thermal equilibrium with the environment. The accuracy of any thermocouple measurement instrument is largely determined by the stability of the cold junction sensing mechanism. For maximum accuracy and stability, the EX1000A Series has a significant thermal mass that connects the input connectors to the cold junction sensing element. This lowers the sensitivity of the instrument to thermal disturbances, but a significant ambient temperature change over a short period of time may cause transient measurement errors. The reason for this is that the thermal time constants of the thermal mass and the cold junction at the input connector are different. When the ambient temperature changes rapidly these two temperatures will be different resulting in a measurement error. To avoid this error, allow the instrument to reach thermal equilibrium before making measurements after a rapid change in the ambient temperature.
- Allow the instrument to stabilize after inserting a jack or wire connected to a screw terminal. A similar error can occur when you first insert a male thermocouple jack or wire connected to a screw terminal into an EX1000A Series input channel. Because the male thermocouple jack and mating female jack on the EX10xxA are at different temperatures when they first make contact, a transient error will result. If both the unit and male jack are at the same ambient temperature, this error is typically less than 0.1 ºC within 3 minutes. However, a jack at room temperature plugged into a unit that is at a substantially different ambient temperature will cause a significantly larger initial error, as a result it will take a correspondingly longer time for the error to diminish.
For more information on the EX 1000A Series instruments and maximizing thermocouple measurement performance, contact one of our sales representative by visiting powerandtest.com/sales. You can also email us at firstname.lastname@example.org or call 800-733-5427 or 858-450-0085.