Small-signal cutoff problem
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I saw that recently someone asked about small-signal rejection, and I realized that our engineering work hardly involves this aspect. Finding that strange, I asked some senior employees, and they said that our small-signal rejection is handled by the safety gate. However, when I checked the documentation related to the safety gate, it didn’t mention any function for small-signal rejection, nor was there any information on how much of the signal is rejected. It’s strange. Has anyone encountered a safety gate with such a function? Or is small-signal rejection handled elsewhere?
Our low-flow cut-offs are all set in the header; I’ve never heard of a function called safety barrier
This can also be achieved with software
There are those that can be cut at the header, and then there are those that require using a computer software via a data cable for processing; the latter method yields better results. We have done this before – not sure if it would work well for you
Many smart meters have built-in functionality for filtering out low-level signals; therefore, in less stringent applications, there is no need to add an additional filtering mechanism.
It’s usually done by removing it from the header; I’ve never heard of it being done within the safety barrier
When using an orifice plate for flow measurement, small-signal rejection is performed. But it’s all done within DCS, using software.
Reply 1# zhuirvine: Small-signal rejection can often be achieved right in the header; if the signal enters the DCS, it can be removed through the configuration parameters.
They are generally removed from the on-site form to ensure consistency and prevent confusion.
Modern mainstream intelligent differential pressure flow transmitters all have a low-signal rejection function, which safety barriers are unable to provide. Based on practical maintenance experience, it is recommended to implement a small-signal rejection function in the DCS. Advantages: 1. It can accurately reflect the actual operating condition of the instrument. 2. It is possible to easily change the resection range in DCS. 3. It facilitates fault diagnosis.
Only when the flow rate is proportional to the square root of the pressure difference. Only then does it make sense to remove the small signal.