Is it possible for connecting a non-incendive Ex nA digital indicator to an intrinsically safe Ex i sensor in hazardous areas? Very often, signals from pressure sensors that do not have an integral digital indicator for the measured value are linked to external digital indicators. Stupid 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 generally made with the ignition protection type ?intrinsically safe?, since this allows interventions within an active electrical circuit and less energy is needed. However, this also implies that there is insufficient energy available for a robust measured value display. Consequently, digital indicators are often made with ignition protection types that enable more current and voltage to be allowed. Frequently, Document 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 bound for used in zone 2 ? so in areas where 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 for its voltage supply, so the interconnection is considered as intrinsically safe and the benefits, such as maintenance work with no need for a fire certificate, can be utilized. Digital indicators are frequently integrated as passive element, with or without an external power supply, directly in the 4 ? Revolutionary 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 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 chance 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 must be installed in zone 2.
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Note
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