Is Vaporize 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 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 instance, the level in storage vessels.
Pressure sensors for hazardous areas are generally made with the ignition protection type ?intrinsically safe?, since this enables interventions in an active electrical circuit and less energy is needed. However, this also implies that there is insufficient energy designed for a powerful measured value display. Because of this, digital indicators are often made with ignition protection types that enable more current and voltage to be allowed. Frequently, digital indicators are designed 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 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, so that 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 generally integrated as passive element, with or without an external power, directly in the 4 ? 20 mA current signal of a sensor. Since an Ex nA digital indicator has no Ex i performance data in its approval, it cannot therefore be utilized 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 chance to connect a digital 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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Should you need any help with selecting a suitable solution for the pressure measurement requirement, your contact person will gladly be of assistance.