Hot Primary Air flow is not proportional to Hot Air Damper Opening

Instrumentation Flow
1

In Any Mill - Hot Primary Air flow is not proportional to Hot Air Damper Opening.
After opening of 40 % of Hot Air Damper the Flow is not at all proportional to the opening percentage.

2

It is a Differential Pressure type Flow meter, installed by SEPCO 3, at 660 MW Power plant. I am looking for a solution.

3

Make sure you have the correctly calibrated DP transmitter installed.

Try a simple test.

Gradually vary the damper from 0% to 100%, note down the DP flow transmitters readings.

Create a table with 0%, 25%, 50%, 75%, 100% and make a graph with respect to flow.

You can use more sample points if required.

Then it will be easy to analyze the problem. Repeat the above steps to confirm that the readings are accurate and precise.