Measurement Of Thermocouples (With Measurement Uncertainties) - Beckhoff ELX3312 Operating Manual

4.4 Measurement of thermocouples (with measurement
uncertainties)
In the measuring range of a given thermocouple type, a measured voltage is converted internally into a
temperature according to the set transformation. Since the channel internally measures a voltage, the
corresponding measurement error in the voltage measurement range must be taken as a basis.
The following tables with the specification of the thermocouple measurement are only valid when using the
internal cold junction.
The ELX331x can also be used with an external cold junction if required. The uncertainties must then be
determined for the external cold junction by the application. The temperature value of the external cold
junction must then be communicated to the ELX331x via the process data for its own calculation.
The effect on the measurement of the thermocouples must then be calculated on the plant side.
The specifications of the internal cold junction and the measuring ranges given here are only valid if the
following times for thermal stabilization at constant ambient temperature are observed:
• after power on: 60 minutes
• after changing wiring/plugs: 15 minutes
Specification of the internal cold junction measurement
Measuring mode
Basic accuracy: Measuring error at 23°C, with averaging
Temperature coefficient
ELX3312 and ELX3314
Tc
Version: 1.3.0
Basic function principles
Cold junction
< ±2.5°C
< 25 mK/K
43