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

Is it possible to connect 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 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 example, the level in storage vessels.
Pressure sensors for hazardous areas are generally designed with the ignition protection type ?intrinsically safe?, since this enables interventions within an active electrical circuit and less energy is necessary. However, this also implies that there’s insufficient energy available for a powerful measured value display. Therefore, 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). Blunder enables power-hungry instruments to be operated in Ex areas too. However, Ex nA is bound for use 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 because of its voltage supply, so the interconnection is recognized 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 has no 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 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 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 must be installed in zone 2.
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Ex barrier and intrinsically safe pressure sensors ? an inseparable pair
Proof of intrinsic safety for an ATEX-approved pressure sensor
Should you need any help with choosing a suitable solution for your pressure measurement requirement, your contact person will gladly be of assistance.

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