TST310
2
Hauser
Function and system design
Measuring principle
These resistance thermometers use a Pt100 temperature sensor according to IEC 60751. This temperature
sensor is a temperature-sensitive platinum resistor with a resistance of 100
Ω
at 0 °C (32 °F) and a temperature
coefficient
α
= 0.003851 °C
-1
.
There are generally two different kinds of platinum resistance thermometers:
•
Wire wound (WW)
: Here, a double coil of fine, high-purity platinum wire is located in a ceramic support.
This is then sealed top and bottom with a ceramic protective layer. Such resistance thermometers not only
facilitate very reproducible measurements but also offer good long-term stability of the resistance/
temperature characteristic within temperature ranges up to 600 °C (1112 °F). This type of sensor is relatively
large in size and it is comparatively sensitive to vibrations.
•
Thin film platinum resistance thermometers (TF):
A very thin, ultrapure platinum layer, approx. 1
μ
m
thick, is vaporized in a vacuum on a ceramic substrate and then structured photolithographically. The
platinum conductor paths formed in this way create the measuring resistance. Additional covering and
passivation layers are applied and reliably protect the thin platinum layer from contamination and oxidation
even at high temperatures.
The primary advantages of thin-film temperature sensors over wire wound versions are their smaller sizes and
better vibration resistance. A relatively low principle-based deviation of the resistance/temperature
characteristic from the standard characteristic of IEC 60751 can frequently be observed among TF sensors at
high temperatures. As a result, the tight limit values of tolerance category A as per IEC 60751 can only be
observed with TF sensors at temperatures up to approx. 300 °C (572 °F). For this reason, thin-film sensors are
generally only used for temperature measurements in ranges below 400 °C (932 °F).
Measuring system
a0012727
Example of an application
A
Built-in RTD thermometer TST310
B
Temperature transmitter iTEMP
®
DIN rail TMT12x. The two-wire transmitter detects the measurement signals of the
resistance thermometer in a 2, 3, or 4-wire connection and converts them into an analog 4 to 20 mA measurement
signal.
C
RIA16 field display unit
– The display unit measures the analog signal from the transmitter and shows this on the display. The LC display shows
the current measured value in digital form and as a bar graph indicating a limit value violation. The display unit is
looped into the 4 to 20 mA circuit and gets the required energy from there. More information on this can be found
in the Technical Information (see "Documentation").
D
Active barrier RN221N
– The RN221N active barrier (24 V DC, 30 mA) has an galvanically isolated output for supplying voltage to loop
powered transmitters. The universal power supply works with an input supply voltage of 20 to 250 V DC/AC, 50/
60 Hz, which means that it can be used in all international power grids. More information on this can be found in
the Technical Information (see "Documentation").
