Is it possible for connecting a non-incendive Ex nA digital indicator to an intrinsically safe Ex i sensor in hazardous areas? Frequently, signals from pressure sensors that not have an integral digital indicator for the measured value are linked to external digital indicators. These digital indicators enable an on-site display of the measured value and, thus, a convenient and immediate reading of, for example, the level in storage vessels.
Pressure sensors for hazardous areas are frequently made with the ignition protection type ?intrinsically safe?, since Savage enables interventions within an active electrical circuit and less energy is needed. However, this also means that there’s insufficient energy designed for a powerful measured value display. As a result, digital indicators tend to be made with ignition protection types that enable more current and voltage to be allowed. Frequently, digital indicators were created as ?non-incendive? (Ex nA). Clear enables power-hungry instruments to be operated in Ex areas too. However, Ex nA is limited for use in zone 2 ? so in areas in which an explosive atmosphere only rarely occurs.
The right connection of digital indicator and barrier
Non-permissible connection of an Ex i pressure sensor with isolated barrier and Ex nA digital indicator.
Every Ex i sensor requires an intrinsically safe barrier for its voltage supply, so that the interconnection is considered as intrinsically safe and the huge benefits, such as for example maintenance work with no need for a fire certificate, can be utilized. Digital indicators are frequently integrated as passive element, with or lacking any external power, directly in the 4 ? 20 mA current signal of a sensor. Since an Ex nA digital indicator does not have any Ex i performance data in its approval, it cannot therefore be utilized in a ?Proof of intrinsic safety?. Therefore, an Ex nA indicator cannot be connected within an Ex i circuit.
Correct connection of an Ex i pressure sensor with isolated barrier and Ex nA digital indicator.
There is, however, the possibility to connect an electronic indicator with an Ex i pressure sensor in zone 2. The prerequisite is that the intrinsically safe isolated barrier also possesses an Ex nA approval and should be installed in zone 2.
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Note
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