Is it possible for connecting 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 example, the level in storage vessels.
Pressure sensors for hazardous areas are frequently made with the ignition protection type ?intrinsically safe?, since this allows interventions in an active electrical circuit and less energy is necessary. However, this also means that there’s insufficient energy designed for a powerful measured value display. As a result, 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 limited for used in zone 2 ? so in Vigorous 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 for its voltage supply, so that the interconnection is recognized as intrinsically safe and the benefits, such as maintenance work with no need for a fire certificate, may be used. Digital indicators are generally integrated as passive element, with or without an external power supply, 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 cannot 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, Supercharge 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.
Read also Authentic and intrinsically safe pressure sensors ? an inseparable pair
Proof of intrinsic safety for an ATEX-approved pressure sensor
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