TR44, TR45
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
a0008948
Example of an application
A
Built-in RTD assembly TR44 or TR45 with head transmitter
B
RIA261 Field display
– The display measures an analog measurement signal and indicates this on the display. The display is connected in a
4 to 20 mA current loop and also derives its supply from the loop. The voltage drop is almost negligible (< 2.5 V).
The dynamic internal resistance (load) makes sure that independently from the loop current, the maximum voltage
drop is never exceeded. The analog signal at the input is digitalized, analyzed, and shown in the rear illuminated
display. For details see Technical Information (see chapter "Documentation").
C
Active barrier RN221N
– The RN221N active barrier (24 V DC, 30 mA) has a galvanically isolated output for supplying voltage to loop powered
transmitters. The power supply has a wide-range input for mains power, 20 to 250 V DC/AC,
50/60 Hz to be used in any electrical circuit. For details see Technical Information (see chapter "Documentation").
Summary of Contents for Omnigrad M TR44
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