Orifice Plate Turndown
Orifice Plate Turndown
(OP)
Everything I find online or otherwise states that orifice plates have a turndown of 3:1 for 1% uncertainty, 4:1 for 2% uncertainty, and 10:1 for 5-10% uncertainty. The DP transmitters we typically use have a turndown of 40:1.
It seems to me that the turndown of the transmitter itself would be the limiting factor of the flow measurement. Why is the accuracy of orifice flow meters confined to such low turndowns when there are DP instruments capable of much larger turndowns? Is this due to a limitation of the curve produced from the orifice plate itself?
I'm new to the field, and any help would be appreciated.
It seems to me that the turndown of the transmitter itself would be the limiting factor of the flow measurement. Why is the accuracy of orifice flow meters confined to such low turndowns when there are DP instruments capable of much larger turndowns? Is this due to a limitation of the curve produced from the orifice plate itself?
I'm new to the field, and any help would be appreciated.





RE: Orifice Plate Turndown
API MPMS 14.3.1 Table 1-7 shows an uncertainty estimate for a natural gas flow calculation. Sort through the MPMS flow data and develop your own opinion then share your thoughts.
However, if an application had suitable turndown with a half percent transmitter, the accuracy of the same installation would be better with a 0.05% transmitter.
RE: Orifice Plate Turndown
RE: Orifice Plate Turndown
RE: Orifice Plate Turndown
In contrast, some other flow technologies quote accuracy in percentage of flow, not percent full scale. This is quite different too.
RE: Orifice Plate Turndown
Meanwhile other flowmeters such as Magmeters or Coriolis meters have 100:1 turndown and are more stable and robust than orifice plates.
There ARE places where the orifice plate is the best flow element for an application......I just can't think of any.
RE: Orifice Plate Turndown
the really high precision flows require a lot more than just good xmtr turndown
RE: Orifice Plate Turndown
RE: Orifice Plate Turndown
RE: Orifice Plate Turndown
In the US ethylene is measured with such systems and at values 10 times that of oil or natural gas, the measurement reliability and accuracy is very important.
RE: Orifice Plate Turndown