Specification notes

The following tables with the TC specification apply only when using the internal cold junction. In the ELM334x/ ELM370x, each channel has its own cold junction sensor.

The terminal can also be used with an external cold junction if required. The uncertainties must then be determined for the external cold junction on the application side. The temperature value of the external cold junction must then be communicated to the terminal via the process data for its own calculation. The effect on the TC measurement must then be calculated on the system side.

Thermal stabilization

The specification values for the measurement of the cold junction given here apply only if the following times are adhered to for thermal stabilization at constant ambient temperature

• after switching on: 60 min
• after changing wiring/connectors: 15 min

Ambient air in motion

For a constant TC measurement, thermally stable environmental conditions around the ELM terminal are important. Air movements around the terminal with a possibly varying air temperature must be avoided. If these are unavoidable, the separately available ZS9100‑0003 shielding hood should be used for thermal shielding. The following specification was created without a shielding hood in a quiet environment.

Wire cross-section on push-in connector

Depending on the temperature gradient, the TC wire supplies heat to the ELM connector or removes heat from it. Even under thermally constant conditions, this leads to an offset deviation. If very accurate measurement is required, this can have a disruptive effect. The above values apply to a wire thickness of 0.2 mm (0.0314 mm²). For thicker wires an offset deviation occurs due to the temperature gradient according to the following diagram:

So the terminal is measuring "too warm" and the specified amount must be subtracted from the measured value accordingly.

The diagram was determined at room temperature (23 °C) and corresponding terminal operational temperature. A deviated room temperature has no appreciable influence, because the terminal temperature adjusts itself accordingly again and the heat gradient remains the same.

Note: Additional measurement deviations related to the TC wire cross-section/diameter are negligibly small for Lemo and Mini-TC connector types.

Specification of the internal cold junction measurement