The leading ignition protection type is critical for the electrical connection of a pressure sensor with explosion protection. It does not necessarily have to be the one with the stricter requirements. This applies, for example, for the UHP pressure transducers of the WU series from WIKA. They have been designed for use in semiconductor production.
Explosion protection is an indispensable safety precaution there. This is because the substances required for manufacturing include highly flammable gases. Consequently, there is a risk of an explosive atmosphere forming.
Explosion protection concept
UHP pressure transducers for such processes must be designed with the corresponding safety. In addition to their small design and specific process connections, the models WUC-1x and WU-2x have a comprehensive explosion protection concept. The marking of the instruments provides information on this:
- II 3G Ex ec ic IIC T6/T5/T4 Gc X
The abbreviations listed in them mean, in greater detail:
|II 3G:||Equipment group 2 (all areas except mining), can be used in zone 2 (rare and short-term Ex atmosphere).|
|Ex ec ic:||Ignition protection types “ec” (increased safety) and “ic” (intrinsically safe; zone 2).
“Ex ec” has replaced the ignition protection type “Ex nA” (non-sparking) since the start of 2022. However, this does not affect the Ex concept of the instruments.
|IIC:||Explosion group (here: gases, resistive ignition energy of 40 µJ, suitable for hydrogen/acetylene).|
|T6/T5/T4:||Temperature classes. T6 as the highest requirement stands for a maximum permissible surface temperature in the Ex environment < 85 °C (max. surface temperature of the WUC-1x and WU-2x: 40 °C).|
|Gc:||“Equipment Protection Level” (EPL) for zone 2 per IEC 60079-0|
|X:||Specific requirements which are listed in the operating instructions (for example, the suitable mating connector).|
“ec” is the leading ignition protection type
It is noticeable that the marking contains two ignition protection types. However, only one is relevant for the electrical connection: the leading ignition protection type. In the case of the pressure transducers from the WU series, this is the Ex ec (Ex nA up to 2022) mentioned first and not the stricter Ex ic. This can also be seen in the connection values in the data sheet and operating instructions. Only the specification of the maximum supply voltage UN = 30 V, which is also stated in the IECEx certificate, is relevant here.
What does the classification “Ex ic” stand for? It only applies to the potentiometer of the transducer. The resistive component has an intrinsically safe circuit and can therefore be adjusted to correct zero drift during operation. In their overall form, the WU models do not require an intrinsically safe circuit. However, they must never be disconnected from the circuit during operation or when an Ex atmosphere is present.