In Europe plants or machines used in hazardous areas must comply with the ATEX directive 94/9/EC. Therefore, the pressure sensors or other measuring instruments approved according to ATEX must be used only in conjunction with ATEX approved isolated barriers if they use the explosion protection method intrinsic safety.
How to find a suitable isolated barrier for the pressure sensor in your application? First, you need to ensure that the isolated barrier complies with the “proof of intrinsic safety”. This prerequisite allows for the safe operation of the selected combination of pressure sensor and isolated barrier. Apart from the safe operation, the function of the selected combination is also important. Yet, this fact is not considered by the ATEX directive. Basically, you can select a suitable isolated barrier for your pressure sensor by answering five questions:
- What input signal should be processed by the isolated barrier? (output signal of the pressure sensor) (see blog post series “Analogue output signals“)
- What output signal should be provided by the isolated barrier? (input signal of your PLC)
- What supply voltage is provided for the isolated barrier? (24 VDC, 115 VAC, 230 VAC, …)
- Should the input and output of the isolated barrier be active or passive? (see blog post “electrical ciruitry for pressure sensors“)
- Is the “proof of intrinsic safety” fulfilled?