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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 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 made with the ignition protection type ?intrinsically safe?, since this allows interventions in an active electrical circuit and less energy is needed. However, this also implies that there’s insufficient energy designed for a robust 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 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 limited 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 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. Digital indicators are frequently integrated as passive element, with or lacking any external power supply, 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 utilized in a ?Proof 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 an electronic indicator with an Ex i pressure sensor in zone 2. Conclusive 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
Note
In the event you need any help with choosing a suitable solution for the pressure measurement requirement, your contact person will gladly be of assistance.

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