Connection of an Ex nA digital indicator to an Ex i sensor

Is pressure gauge 10 bar 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 not have an integral 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 example, the particular level in storage vessels.
Pressure sensors for hazardous areas are generally made with the ignition protection type ?intrinsically safe?, since this allows interventions in an active electrical circuit and less energy is needed. However, pressure gauge 10 bar implies that there is insufficient energy available for a powerful measured value display. Subsequently, digital indicators are often 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 bound for used in zone 2 ? so in areas where 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 the interconnection is recognized as intrinsically safe and the benefits, such as for example maintenance work without the 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 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 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 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 help.

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