calculate flow rate @ 13mA

mendonsy said:

I came up with the same answer that you did (actually 3.375) so clearly we don't understand the problem!?!

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mendonsy said:

I came up with the same answer that you did (actually 3.375) so clearly we don't understand the problem!?!

Click to expand...

goodoboy said:

what will the signal be if the flow rate is 4 gpm?

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goodoboy said:

The answer is A.

Use the formula for orifice plate:

F2/F1 = sqroot(dp1/dp2)

F2 = flow 1
F1 = flow 2

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Tom Jenkins said:

The flow rate through an orifice is proportional to the square root of the pressure differential. Flow is not linear! The transmitter is a differential pressure one, so dp is linear with mA. However, you can't forget the 20% (4 mA) zero offset when you calculate the differential pressure.

I use the formula:

Q2 = Q1 x Sqrt(dp2/dp1)

So, 4.5 gpm is the right answer. At 4 gpm you should get 11.11 mA.

Try it again, show your work, and if you can't get it I'll show my work.

At 13 mA

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goodoboy said:

I am doing some studying on Flow Measurements and stuck on this problem?

A dp transmitter is calibrated 0 to 80 inH20 and transmits a 4 to 20 mA dc signal. This transmitter is placed across an orifice plate which is sized to create 80 inH20 differential at 6 gpm.

What is the flow rate when the signal is 13 mA dc?

a. 4.5 gpm
b. 3.9 gpm
c. 3.4 gpm
d. 4.9 gpm

I calculate 3.374 gpm, but answer is 4.5 gpm according to book?

Also, what will the signal be if the flow rate is 4 gpm?

Any help please.

Click to expand...

Tom Jenkins said:

The flow rate through an orifice is proportional to the square root of the pressure differential. Flow is not linear! The transmitter is a differential pressure one, so dp is linear with mA. However, you can't forget the 20% (4 mA) zero offset when you calculate the differential pressure.


I use the formula:
Q2 = Q1 x Sqrt(dp2/dp1)


So, at 13 mA 4.5 gpm is the right answer. At 4 gpm you should get 11.11 mA.


Try it again, show your work, and if you can't get it I'll show my work.

Click to expand...