Problem with taking the square root of differential pressure measurement?
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Is the square root calculation for differential pressure measurement performed in the transmitter or in the DCS? What are their respective advantages and disadvantages? If taking the square root of a transmitter, are transmitters that can have their square root taken a special type? Or can all transmitters be freely chosen to take the square root or not?
It doesn’t matter where the square root is taken; only intelligent (digital) transmitters are capable of performing this operation, as ordinary transmitters cannot carry out square root calculations.
The square root function of differential pressure transmitters is intended solely for flow measurement; it can be applied either at the DCS end or at the transmitter end, and there are no inherent advantages or disadvantages associated with it. Generally, transmitters come equipped with this square root function, but in some cases the manufacturer has set restrictions on making changes, in which case the modifications must be done at the DCS end
Personally, I think it’s better to use DCS for taking square roots; this way, there’s no need to do it again when performing maintenance or replacing the gauge, solving the problem once and for all!
From the perspective of fault diagnosis, it’s better to use the transmitter’s square root value.
Differential pressure transmitters, whose output signal has been squared, have certain limitations in terms of their application range. It's more flexible for taking square roots in DCS.
This post was last edited by qugd on 2015-11-23 at 22:17. Nowadays, they are all smart transmitters, and the computing power of DCS systems is also very high; it makes no difference whether the square root is taken on the differential pressure side or the flow rate side. There is no essential difference. But I recommend deciding whether to apply the square root on the transmitter based on the meaning of the digit code. At a certain flow measurement point, the designer may choose different signal modes based on the on-site conditions. If it is PDT-12345, it indicates that this is a differential pressure signal; the transmitter does not apply any square root operation, and the DCS performs the conversion based on the actual conditions ； If it is FT-54321, it indicates that this is a flow signal; the transmitter performs a square root operation, which facilitates judgment by those on site. The DCS can simply receive the signal directly.
I personally recommend taking the square root in DCS. Taking the square root at the instrument side makes it easy to take another square root at the DCS side ； Additionally, when the instrument does not have square root functionality, it can be used in other applications; once square root functionality is enabled, it cannot be changed on-site if a 475 device is not available. Even in cases where a 475 device is present, changes cannot be made if the user does not know how to operate it