Engee documentation

Thermocouple

Thermocouple.

thermocouple

Description

The Thermocouple block represents a thermocouple model using the standard polynomial parameterization defined in the NIST ITS-90 thermocouple database [1].

For thermocouple types B, E, J, K (t≤0 °C), N, R, S, or T, the electromotive force (thermo-EMF) E on the device is (in mV):

Where:

  • - i-th element of the parameter value Coefficients [c0 c1 …​ cn].

  • - is the temperature difference in degrees Celsius between the temperature at the thermal port A and the cold junction temperature (the value of the Reference temperature parameter).

In the equation, the voltage across the device as a function of the temperature difference is calculated in millivolts. The voltage at the unit output is measured in volts.

For type K thermocouples (t≥0 °C), the equation contains an additional exponential term:

where:

and are additional coefficients required only for the type K thermocouple and determined by the value of the parameter Coefficients [a0 a1 a2].

The following equation describes the thermal behaviour of the block:

where:

  • - heat flux into the A port.

  • - value of Dissipation factor parameter, dissipation factor.

  • - value of Thermal time constant parameter, time constant.

  • - is the rate of temperature change.

Assumptions and limitations

  • The high-order polynomials used in this block are very sensitive to the number of significant digits used for calculations. When specifying the Coefficients [c0 c1 …​ cn] parameter, use all available significant digits.

  • The values of Coefficients [c0 c1 …​ cn] are defined for use within the specified temperature range.

Ports

Non-directional

A - hot junction temperature
heat

Thermal port that defines the hot junction temperature of the thermocouple.

+ - positive
electricity

Electrical port, represents the positive terminal of the thermocouple.

- is the negative
electricity

Electrical port, represents the negative terminal of the thermocouple.

Parameters

Electrical

Thermocouple type - thermocouple type
Type B, E, J, K (t≤0 °C), N, R, S or T (By default) | Type K (t≥0 °C)

Select one of the modelling options:

  • Type B, E, J, K (t≤0 °C), N, R, S or T - standard polynomial parameterization is used.

  • Type K (t≥0 °C) - an exponential term is added to the equations when the value of the temperature difference is greater than 0 °C.

*Coefficients [c0 c1 …​ cn]` - coefficients c0, c1, …​ cn
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] (by default)

The vector of coefficients in the equation describing voltage as a function of temperature.

Coefficients [a0 a1 a1 a2] are the coefficients a0, a1, and a2
[0, 0, 0] (By default)

Vector of additional coefficients , and , required only for type K thermocouple.

Dependencies

To use this parameter, set the Thermocouple model parameter to Type K (t≤0 °C).

Thermal

Reference temperature - nominal cold junction temperature
0 °C (By default) | Positive scalar

The temperature that the unit subtracts from the temperature at the thermal port when calculating the device output voltage.

Thermal time constant - time constant for the thermal equation
1 s (By default) | `positive scalar'.

The time for the thermocouple temperature to reach 63% of the final temperature change for a jump in ambient temperature.

Dissipation factor - dissipation factor for the thermal equation
0.001 W/K (by default) | `positive scalar'.

Thermal power required to raise the temperature of the thermocouple by 1 К .

Initial temperature - initial temperature value t
`25 °C (By default)

Initial value of hot junction temperature .

Bibliography

  1. Dean C. Ripple, NIST ITS-90 Thermocouple Database, December 21, 1999 (https://srdata.nist.gov/its90/main/)