Which ignition protection type is suitable for battery-operated pressure measuring instruments, which are increasingly being used in combination with a radio unit? WIKA has clearly answered this question for its portfolio: “Ex i”, i.e. intrinsic safety. This article explains why.
In the course of the digitalisation of processes, the topic of “ignition protection type for battery-operated pressure measuring instruments” is coming up more and more frequently. This is because, among other things, companies are increasingly replacing purely mechanical measuring instruments with electrical combination models with an on-site indication and a radio unit for data transmission. These instruments usually have long-life batteries as a power source. The measuring locations fitted with these instruments, in turn, are often located in potentially explosive environments, for example in the chemical industry.
Plant operators generally prefer two ignition protection types for pressure measuring instruments in explosive atmospheres: Ex i (intrinsically safe) and Ex d (explosionproof enclosure). Both are standardised types of protection and are therefore classified as equally safe within a category. In the case of pressure and other measuring instruments, this is electrical equipment, suitable for gas or gas-and-dust atmospheres depending on the approval.
Pressure measuring instruments with battery operation and “Ex i” will not trigger ignition
Why WIKA uses the Ex i ignition protection type for pressure measuring instruments with battery operation can be explained by looking at its definition: An intrinsically safe design prevents the instrument from igniting an explosive atmosphere at all. Its values for power, current and voltage are correspondingly low. This is the case with pressure and other measuring instruments with battery operation.
With ignition protection type Ex d, the possible values for current and voltage are significantly higher than with Ex i. In addition, ignition sources can also be present in the instruments themselves. For this reason, their housings must be encapsulated in an explosionproof manner so that any possible explosion cannot escape to the outside.
Galvanic isolation of measuring instrument and PLC is not necessary
It is true that the Ex i ignition protection type is linked to more regulations than just the values for power, current and voltage. In the case of battery operation, however, these alone remain the decisive criteria. This is because instruments with such a power supply are not electrically connected to any PLC outside the Ex zone, for example. They transmit the measured values via a radio unit and/or display them on site. This eliminates the otherwise necessary galvanic isolation of the measuring instrument and the PLC through the installation of an Ex-certified power supply, as well as the additional documentation effort – one certificate for each Ex i circuit.
Despite the unambiguous Ex i ignition protection type for pressure measuring instruments with battery operation and radio unit, there are always requests for such instruments with Ex d design. Such a variant might not be a problem from a technical point of view, however it would not be advisable from an economic point of view. Firstly, because the purchase costs are generally higher than for an Ex i instrument due to the explosionproof enclosure, and secondly, because a special antenna would also be required for reliable radio transmission.
WIKA’s pressure measuring instruments with battery operation and ignition protection type Ex i: the precision digital pressure gauge model CPG1500 and the Bourdon tube pressure gauge model PGU with radio unit model NETRIS®3
Note
On the WIKA website, you can find out more about our pressure measuring instruments with battery operation and ignition protection type Ex i for applications in the process industry: the precision digital pressure gauge model CPG1500 and the Bourdon tube pressure gauge model PGU with radio unit model NETRIS®3. If you have any questions, your contact will gladly help you.
Also read our posts
Flame arrester protects sewage vacuum truck tanks
Switch with “CCC Ex” for the Chinese market
Natural gas: On-site calibration optimised at the metering skid