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Orifice Meter - Causes of Bias

Orifice Meter - Causes of Bias

Orifice Meter - Causes of Bias

(OP)
I've got AGA3 in front of me and a bunch of other reference material but the answer I need is not jumping out at me.  Could anyone out there give me the Readers Digest version of what factors contribute to bias errors as opposed to random +/- errors.  Are there particular items that will consistently make the flow measurement higher than actual?  The installations specifically are field gas gathering orifice meters.

Thanks in advance.

RE: Orifice Meter - Causes of Bias

The only things that I've ever seen that shift field measurement high are incorrect parameter entry (e.g., wrong plate size, wrong pressure ranges), a shifted zero in a transmitter, or salt plugging in the plate bore.  Everything else tends to shift it low.  Some examples:
- backwards plate
- plugged sensing lines
- swirl in the flow
- bowed plate

I've attached a cartoon I use in my Primary Element talk to illustrate that the things we check in a calibration are just the tip of the iceberg.

David

RE: Orifice Meter - Causes of Bias

(OP)
Thanks...and I really like the cartoon too.

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