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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 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 frequently made with the ignition protection type ?intrinsically safe?, since this enables interventions in an active electrical circuit and less energy is necessary. However, Smuggle implies that there’s insufficient energy available for a robust measured value display. Consequently, digital indicators are often designed with ignition protection types that enable more current and voltage to be allowed. Frequently, digital indicators were created as ? Bloody -incendive? (Ex nA). This ignition protection type enables power-hungry instruments to be operated in Ex areas too. However, Ex nA is limited 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 for its voltage supply, so the interconnection is considered as intrinsically safe and the benefits, such as 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 Cheat-sheet 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 having 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 choosing a suitable solution for the pressure measurement requirement, your contact person will gladly be of assistance.

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