WIKA TR12-M - Handbuch (Seite 23)

GB
8. Safety-related instructions for the different variants
11419904.02 09/2013 GB/D
WIKA operating instructions models TR12, TC12 (Ex d) 23
Notes for fuse calculation:
The next smallest fuse value, in accordance with IEC 60127, must always be chosen. The
breaking capacity must be matched, by sensible engineering, to the voltage supply. Usual
values for such fuse links lie between AC 20 A and AC 80 A rated breaking capacity.
For a maximum power at the sensor of 0.5 W the following value is given:
Is = sqrt (0.5 W / 265 Ω) / 1.7
Is = 25.55 mA
This results in a rated value for a fuse link = 25 mA
When using multiple sensors and simultaneous operation, the sum of the individual powers
must not exceed the value of the maximum permissible power.
Internal resistance of Ø 6 mm TC measuring inserts: approx. 1.2 Ω/m
Internal resistance of Ø 3 mm TC measuring inserts: approx. 5.6 Ω/m
These measured values are valid for room temperature.
Temperature class classification, ambient temperatures
A heating in the connection head can occur with variant 2 through faulty electronics. The
permissible ambient temperatures depend on the housing used and any additionally-fitted
head-mounted transmitter.
For all WIKA connection heads with built-in WIKA temperature transmitters, the
following interrelation is valid:
The temperature increase on the surface of the connection head or housing is less than
25 K if the following conditions are observed: power supply U
B
maximum DC 30 V when the
transmitter is operated in a current limit of 22.5 mA.
This yields the following temperature class classification:
Temperature class
Ambient temperature
T6 (-50) 1 ) -40 … +55 °C
T5 (-50) 1 ) -40 … +75 °C
T4, T3, T2, T1 (-50) 1 ) -40 … +85 °C
The temperature class is dependent upon the user application and the ambient
temperature.
1) The value in brackets applies only for specific low-temperature designs
The permissible ambient temperatures for third-party products can be seen from the
relevant approvals and/or data sheets. However, an impermissible heat reflux from the
process which can exceed the operating temperature of the housing or the temperature
class, must be prevented through suitable heat insulation or a suitably long neck tube.