Split Range DP Orifice Flow Meter - What Ranges

[Instrument1352]

Hi,

Here is the application as follows:

Existing orifice plate, 500mbar DP @ full scale gas flow of 900scfm (I know it is high DP!). I am going to use two DP transmitters in a split range arrangement.
Which of these would you suggest?

1- Transmitter A: 0-50mbar (284scfm)

​

Transmitter B: 50-500mbar (900scfm) – TD of 3.1:1

2- Transmitter A: 0-25mbar (201scfm)
Transmitter B: 25-500mbar (900scfm) – TD of 4.5:1

3- Transmitter A: 0-10mbar (127scfm)
Transmitter B: 10-500mbar (900scfm) – TD of 7:1

4- Other?

Thank you!

 

[danw2]

500mbar (200 inches wc) doesn't seem to be an excessively high DP to me. I see that quite often. Higher permanent loss than 100 inwc, but if it works . . . .

Traditionally 3:1 has been an acceptable tunrdown, some work with 4:1. Option 3 at 7:1 pushes traditional OP turndown with the issue being noise and uncertainty at the low end of turndown, not from the transmitter, but from the flow through the flow element itself.

But I have no personal experience with turndown above 4:1. Maybe Roy Matson (or others) will show up and provide an opinion.