Use Of El33Xx In The Twincat System Manager - Beckhoff EL33-00 Series Documentation

Analog thermocouple input terminal (open-circuit recognition, 1, 2, 4 ch.)

page of 204

/ 204
Contents
Table of Contents
Bookmarks

Table of Contents

thermocouple. Based on the difference to the cold junction temperature, the temperature at the

measurement point can be determined to an accuracy of better than one tenth of a Kelvin with the aid of the

above thermocouple equation.

Sensor circuit

A modification of the sensor circuit with additional devices such as change over switches or multi-

plexer decreases the measure accuracy. We strongly advise against such modifications.

Internal conversion of the thermovoltage and the reference voltage

Since the coefficients are determined at a reference temperature of 0°C, it is necessary to compensate for

the effect of the reference temperature. This is done by converting the reference temperature into a

reference voltage that depends on the type of thermocouple, and adding this to the measured

thermovoltage. The temperature is found from the resulting voltage and the corresponding characteristic

curve.

= U

+ U

= f(U

)

out

Overview of suitable thermocouples

The following thermocouples are suitable for temperature measurement:

Type (according

Element

to EN60584-1)

Pt30%Rh-Pt6Rh

C *

W5%Re-W25%Re

NiCr-CuNi

Fe-CuNi

NiCr-Ni

L **

Fe-CuNi

NiCrSi-NiSi

Pt13%Rh-Pt

Pt10%Rh-Pt

Cu-CuNi

U **

Cu-CuNi

* not standardized according to EN60584-1

** according to DIN 43710

Maximum cable length to the thermocouple

Without additional protective measures, the maximum cable length from the EtherCAT Terminal to

the thermocouple is 30 m. For longer cable lengths, suitable surge protection should be provided.

2.7