Wika TR12-M Bedienungsanleitung PDF herunterladen (Seite 22)

8. Safety-related instructions for the dierent variants

11419904.02 09/2013 GB/D

WIKA operating instructions models TR12, TC12 (Ex d)22

A heating in the connection head does not occur with variant 1. However, an impermissible

heat reux 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.

8.2 Variant 2:

ATEX/IECEX Ex d housing or connection head with built-in head-mounted transmitter.

The evaluation is made via a current (4 … 20 mA), voltage (2 … 10 V) or eld bus signal,

which is generated from a head-mounted transmitter.

Use in zone 1, marking II 2G Ex d IIC T1-T6 Gb

The ameproof housing or the connection head is in zone 1 (or zone 2). The sensor is in

zone 1. In the case of a separation of Ex-zones, a thermowell (from corrosion-resistant

steel, min. wall thickness 1 mm) must be used.

Use with a thermowell at the partition to zone 0, marking II 1/2G Ex d IIC T1-T6 Ga/Gb

The ameproof housing 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.

max

: 2 W

max:

30 V

A power supply with Ex ia circuitry fullls 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

current loop of the head-mounted transmitter. In the event of a failure, the head-mounted

transmitter will circuit will be interrupted through the fuse tripping.

Example for calculating the fuse for a maximum power at the sensor of 0.8 Watt:

The internal resistance of thermocouples is signicantly lower than the thermal resistance

of a Pt100 sensor, so the much less favourable case for a resistance thermometer has been

calculated.

max

= (1.7 x I

)² x Rw

= Fuse rating

max

= maximum power at sensor = 0.8 W

= Resistance of the sensors (temperature dependant)

at 450 °C = 264.18 Ω in accordance with DIN EN 60751 for Pt100.

The following denes the fuse rating:

= sqrt (P

max

/ R

) / 1.7

= sqrt (0.8 W / 265 Ω) / 1.7

= 32.32 mA

This results in a rated current for a fuse link = 32 mA

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