WIKA TR21 Mode D'emploi page 5

2. Design and function
2.2 Description
The model TR21 miniature resistance thermometers consist of a temperature sensor and a
protection tube with a hygienic process connection.
EN
Any change in the temperature causes a change in the resistance of the sensor in the
temperature sensor. This change can be measured directly or can, optionally, be converted
into a 4 ... 20 mA signal proportional to the temperature.
The protection tube is used to adapt the thermometer to the process and protects the
sensor against harsh process conditions. Furthermore, the detachable connection from the
protection tube in the TR21-A and TR21-B variants enables the removal of the temperature
sensor without having to open the process. In this way, any hygienic risk is minimised
and it is possible to calibrate the entire measuring chain (sensor, transmitter if required,
connection cable) on site, without having to disconnect the electrical connections.
This document describes standard versions of instruments. For applications in hazardous
areas special instrument designs are required.
For further information for operation in hazardous areas, see the additional information for
the corresponding ignition protection type (separate document).
2.3 Overview of the process connections, protection tube variants
Miniature resistance thermometer, model TR21-A with protection tube model TW22
■
+ Clamp BioControl DIN 11851/DIN 11864
VARINLINE ®
®
Union nut SMS Welding ball
Process connection, Ball-/Collar-type
Ingold
straight compression fitting
connection
WIKA operating instructions model TR21 5