When it comes to DP flow measurement all that is really needed is some kind of obstruction in the pipe. The challenge becomes having an obstruction that produces an accurate and repeatable measurement with minimal pressure loss. Over the years manufacturers have come up all types of designs. Orifice plates are by far the most common as they are inexpensive and easy to install. However, there are piping considerations as they require a certain number of up- and downstream pipe diameters.
Conditioning orifice plates have been developed that have many of the advantages of traditional orifice plates (low-cost and easy to install) by only require two (2) pipe diameters on either side. This makes the installation quite flexible as they can be located in short runs of pipe. Moreover, they are not subject to fouling like vane straighteners. These are also available with an integral manifold so a differential pressure transmitter can be mounted directly to it.
As with any good process design there are manufacturers that have started making generic versions of conditioning orifice plates. Although the design is proprietary, that seldom prevents a handful from making it to the market. What has been discovered, however, is the generic designs don’t have the proper location of the taps. This leads to errors in the measurement. Furthermore, the larger the beta-ratio (hole diameter to pipe diameter) the greater the error.
What evolves is a classic case of trying to save money by purchasing generic equipment at a lower cost. However, the accuracy of the flow measurement suffers as the design is not proper. Depending on the nature of the application this could cost a significant amount of money due to measurement error. Good process control starts with a good measurement. It provides the foundation for process efficiency.
Invest in your process and use the proper equipment. That includes orifice plates with proper tap alignment. This leads to good reliability and availability of equipment. And that’s no failure.
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