Beckhoff ELX3312 Operating Manual page 42

Basic function principles
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 + U
k m r
T = f(U )
out k
Overview of suitable thermocouples
The following thermocouples are suitable for temperature measurement:
Type
(according to
EN60584-1)
B
1
C
E
J
K
2
L
N
R
S
T
2
U
1
) not standardized according to EN60584-1
2
) 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 meters. For longer cable lengths, suitable surge protection should be pro-
vided.
42
Element Implemented
temperature range
Pt30%Rh-Pt6Rh 600°C to 1820°C
W5%Re-W25%Re -18°C to 2316°C
NiCr-CuNi -100°C to 1000°C
Fe-CuNi -100°C to 1200°C
NiCr-Ni -200°C to 1370°C
Fe-CuNi -200°C to 900°C
NiCrSi-NiSi -100°C to 1300°C
Pt13%Rh-Pt 0°C to 1767°C
Pt10%Rh-Pt 0°C to 1760°C
Cu-CuNi -200°C to 400°C
Cu-CuNi -200°C to 600°C
Version: 1.3.0
Color coding
(sheath - plus pole - minus pole)
gray - gray - white
not defined
violet - violet - white
black - black - white
green - green - white
blue - red - blue
pink - pink - white
orange - orange - white
orange - orange - white
brown - brown - white
brown - red - brown
ELX3312 and ELX3314