WIKA TR12 Serie Manual De Instrucciones página 11

3. Commissioning, operation
3.4.2 Variant 2
The thermometer is fitted to a certified enclosure with "flameproof enclosure" ignition
protection type, which has electronics built into it. If the thermometer is marked with
II 2G Ex db IIC T1 ... T6 Gb, then it is designed for use in zone 1. If the thermometer is
marked with II 1/2G Ex ia IIC T1 ... T6 Ga/Gb, then it is designed for use with a thermowell
at the partition to zone 0.
▶
ATEX/IECEx Ex d case or connection head with built-in head-mounted transmitter
The evaluation is made via a current (4 ... 20 mA), voltage (0 ... 10 V) or fieldbus signal,
which is generated from a head-mounted transmitter.
Use in zone 1, marking II 2G Ex db IIC T1 ... T6 Gb
The flameproof case or the connection head is in zone 1 (or zone 2). The sensor is in
zone 1.
Use at the partition to zone 0, marking II 1/2G Ex db IIC T1 ... T6 Ga/Gb
The flameproof case or the connection head is in zone 1 (or zone 2). The sensor is within a
thermowell (min. wall thickness 1 mm) which extends into zone 0 via a process connection.
The thermometer should be operated with a power-limiting circuit.
P : 2 W
max
U : 30 V
max
A power supply with Ex ia circuitry fulfils these conditions, but is not required if the limits
can be achieved through other measures. The responsibility rests with the operator.
WIKA recommends realising the power limitation through a suitable fuse in the 4 ... 20 mA
circuit of the head-mounted transmitter. In the event of a failure of the head-mounted
transmitter, the circuit will be interrupted through the fuse tripping.
Example for calculating the fuse for a maximum power at the sensor of 0.8 W:
The internal resistance of thermocouples is significantly lower than the thermal resistance
of a Pt100 sensor, so the much less favourable case for a resistance thermometer has
been calculated.
P = (1.7 x I )² x Rw
max s
I = Fuse rating
s
P = maximum power at sensor = 0.8 W
max
R = Resistance of the sensor (temperature-dependent)
w
at 450 °C = 264.18 Ω in accordance with DIN EN 60751 for Pt100
WIKA additional information TR12/TC12, flameproof enclosure (Ex d)
EN
11