FCU 500, FCU 505 · Edition 02.17
125
Project planning information
Type S: 90%platinum-10%rhodium/platinum
(Pt10Rh-Pt)
This thermocouple can be used permanently in tempera-
tures up to 1600°C in oxidizing or inert atmospheres.
The thermocouple must be enclosed air-tight to protect
it from gases which contain sulphur or phosphorus. Con-
tinuous operation in temperatures over 1000°C results
in wear since the platinum is contaminated with rhodium
by diffusion. In addition, metal vapours may diffuse into
the device at these temperatures. This contamination
causes a change in the thermo-electric voltage towards
negative values over the course of time. The positive leg
can become unstable due to the effect of neutrons.
Connection
The spatial distance between the thermocouple and
temperature module (STM/STL) may be large depend-
ing on the application. Generally, the two legs of a ther-
mocouple have different thermal coefficients. To avoid
errors at the transition points, the thermocouples are
connected to the temperature module using thermo-
cables or compensating cables.
Thermo-cables
KX have the same chemical composi-
tion as Type K thermocouples. This means they act like
an attached thermocouple.
Compensating cables
KCA, KCB, NC, SCA or SCB are
made of a substitute material which is not identical to
the thermocouple material but has similar properties in
certain temperature ranges.
The resistance of a thermocouple together with the
thermo-cable or compensating cable should be
≤ 1000
Ω
. Select the following thermo-cable or com-
pensating cables for this purpose:
Up to length [m]
Minimum dia. [mm]
Thermo-cable KX (NiCr-Ni) for Type K
7
0.1
30
0.2
100
0.4
Compensating cable KCA (Fe-CuNi) for Type K
10
0.1
50
0.2
150
0.4
Compensating cable KCB, NC, SCA, SCB (Cu-CuNi) for Type K, N, S
12
0.1
60
0.2
200
0.4
Reversing the polarity of the thermocouple may result
in measurement errors. We therefore recommend that
the cables are colour-coded pursuant to EN 60584:
Thermocouple
Colour
+ pole
- pole
Type K
green
white
Type N
pink
white
Type S
orange
white
