How to allocate on-site instrument signals
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A steam flow meter with temperature and pressure compensation; the client requires that the flow meter, pressure transducer, and thermistor signals all be fed into an on-site accumulator (secondary meter). At the same time, the pressure signal, temperature signal, and compensated flow signal also need to be sent to the DCS. The site is the explosion area. In this case, both the pressure signal and the temperature signal need to be fed into the signal distributor, where they are then split into two. I would like to ask everyone: is the signal distributor intrinsically safe? Can it be placed at the explosion site? Is it still necessary to install an explosion-proof instrument box on-site, with a signal distributor placed inside it?
To determine whether a signal distributor is intrinsically safe, it is necessary to check the specifications and certifications of the specific product. Intrinsically safe equipment is suitable for explosive hazard areas and can be used directly on-site. If the signal distributor is not intrinsically safe, it must indeed be installed within an explosion-proof instrument box to ensure the safety of the entire system. It is recommended to verify with the product supplier its safety certifications and suitable operating environments to ensure compliance and safety. At the same time, attention should also be paid to signal wiring and shielding to avoid signal interference. .
Normally, your integrator should have a signal output, and it’s possible to connect to that signal output. The integrator itself is located inside an explosion-proof box, right? Of course, a signal distributor can also be used, so it is not affected by whether the integrator is faulty or not. It depends on whether your instrument itself is intrinsically safe or explosion-proof; if it’s explosion-proof, there’s no need to worry about the impact of the signal distributor.
Several methods can be employed: (1) Use a 1-to-2 intrinsically safe barrier to distribute temperature and pressure signals, with one route going to the calculation instrument and the other to the DCS; the AO output from the flow totalizer provides the flow rate after temperature and pressure compensation, which is sent to the DCS. (2) Without using a safety barrier, the RS485 communication from the flow totalizer is used to send temperature, pressure, instantaneous flow rate, and cumulative flow rate data to the DCS for display (communication is not recommended when temperature, pressure, flow rate, etc., are involved in important control or interlock functions).
It’s better to use a small explosion-proof box; the temperature and pressure signals are divided into two streams – one is sent to the flow meter and the other to the DCS. The calibrated flow signal is also sent to the DCS. If the DCS has a 485 module and the flow meter also has one, then there is no need for division; the temperature, pressure, and corrected flow values can be sent back to the DCS directly through it. Basically, no one includes the steam flow rate and pressure/temperature in the interlocks.
The integrator itself can be made intrinsically safe or explosion-proof, and it can be used directly. The integrator can also output flow, temperature, and pressure signals