What is the turn down of an orifice plate? Is it 3:1?

Firstly, lets bust a myth pedaled by many alternative technology manufacturers. A 3:1 turndown would have been a typical turndown ratio of a single orifice plate some 30-40 years ago based on the differential pressure transmitters of that time. Modern DP transmitters can allow a 8:1 sometimes 10:1 turndown with excellent accuracy over a single plate or fixed beta.

If a client was to consider changing the orifice plate to a different beta or 1 of 5 potential betas stored within the roto-boss, this can provide a vast turndown capability upwards of 2000:1. Consider also with this the potential use of stacked DP transmitters (scaled to suit low flow and high flow) the range of turndown per plate can then be significantly increased!

So, what is the turndown of an orifice plate? Ultimately it all depends on whether you have a plate changer like a Senior Orifice meter or a Roto-boss and also what your real need for flow ranges is. One thing is for sure, with modern DP transmitters you can expect 8:1 as a minimum.

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