KROHNE OPTITEMP TT 10 C-R EN - Manual (Page 41)

TECHNICAL DATA
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OPTITEMP TT 10 C/R
www.krohne.com 02/2013 - 4000752703 - MA OPTITEMP TT 10 C/R R03 en
Technical data
7.1 Measuring principle
7.1.1 Resistance thermometer
The transmitter works together with a measuring insert that has a Pt100 RTD. This kind of
measuring inserts features a temperature-sensitive sensor made from a platinum 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 thermometers
to measure temperature. The "Pt100" thermometer 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 thermometer is 100 Ω (100 mV /
1 mA = 100 Ω).
Figure 7-1: Pt100 resistance thermometer in 3-wire connection at 0°C / +32°F, schematic.
1 Pt100 RTD
2 Voltage meter
3 Current source
.book Page 41 Tuesday, February 26, 2013 1:43 PM