TECHNICAL DATA
7
39
OPTITEMP TT 53 C/R
www.krohne.com
06/2018 - 4006523501 - MA OPTITEMP TT 53 R01 en
7.1 Measuring principles
The kind of the measuring principle depends on the measuring insert that you combine with the
transmitter. In matters of the thermometer type the manufacturer offers two different
measuring inserts, either with a resistance thermometer or with a thermocouple. This
transmitter supports both types.
7.1.1 Resistance temperature sensor
The measuring insert with a temperature-sensitive sensor made from a platinum(Pt) RTD,
whose value at 0
°
C / +32
°
F is 100
Ω
. That is where the name "Pt100" comes from.
It is generally valid that the electric resistance of metals increases according to a mathematical
function as the temperature rises. This effect is taken advantage of by resistance temperature
sensors to measure temperature. The "Pt100" temperature sensors features a measuring
resistance with defined characteristics, standardised in IEC 60751. The same is true for the
tolerances. The average temperature coefficient of a Pt100 is 3.85 x 10
-3
K
-1
in the range from
0...+100
°
C / +32...+212
°
F.
During operation, a constant current I (
≤
1 mA) flows through the Pt100 RTD, which brings about
a voltage drop U. The resistance R is calculated using Ohm's Law (R=U/I). As the voltage drop U
at 0
°
C / +32
°
F is 100 mV, the resulting resistance of the Pt100 temperature assembly is
100
Ω
(100 mV / 1 mA = 100
Ω
).
Figure 7-1: Pt100 resistance temperature sensor in 4-wire connection at 0
°
C / +32
°
F, schematic.
1
Pt100 RTD
2
Voltage meter
3
Current source
