Is it possible to connect a non-incendive Ex nA digital indicator to an intrinsically safe Ex i sensor in hazardous areas? Frequently, signals from pressure sensors that do not have a built-in digital indicator for the measured value are connected 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 instance, the level in storage vessels.
Pressure sensors for hazardous areas are frequently designed with the ignition protection type ?intrinsically safe?, since this enables interventions in an active electrical circuit and less energy is necessary. However, this also means that there is insufficient energy designed for a powerful measured value display. Because of pressure gauge octa , 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). This ignition protection type 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 proper 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 because of its voltage supply, in order that the interconnection is considered as intrinsically safe and the huge benefits, such as for example maintenance work without the need for a fire certificate, can be utilized. ไดอะแฟรม 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 used in a ?Proof of intrinsic safety?. Therefore, an Ex nA indicator can’t be connected in 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 a digital indicator having an Ex i pressure sensor in zone 2. The prerequisite is that the intrinsically safe isolated barrier also possesses an Ex nA approval and must be installed in zone 2.
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