Importance of Calibrating Flowmeters

Introduction: Importance of Calibrating Flowmeters

My job is very important, and if I am to be replaced, then it is vital that you understand how to calibrate flowmeters, as well as why I do it. If a flowmeter is reading incorrectly, it will lead to spillages or an underfill, as the flow being greater or lesser means there will be a disparity between the expected and actual drainage. An excessive flow could also damage pipes, and a rusty paddle flowmeter could lead to low flow rates not being accounted for at all.

Step 1: (Linear) Flow Rate As a Function of the Orifice-plate Meter

The line of best fit is the calibration curve.

Step 2: (Logarithmic) Flow Rate As a Function of the Orifice-plate Meter

Alternate calibration, data appears to be a straight line, meaning a power law can be applied.

Step 3: Reynolds Graph, Linear Scale

Step 4: Reynolds Graph, Logarithmic Scale

Step 5: Output Voltage Vs Flow Rate

Step 6: FAQs

Is the discharge coefficient Cd essentially constant over the range of Reynolds numbers tested? Are the experimentally measured values for Cd close to the ideal value of unity derived theoretically? What corrections might need to be made to the theory to obtain more realistic values for Cd?

- The Reynolds number is proportional to velocity and velocity is proportional is to flow rate. If the velocity increases then so will the discharge coefficient. Therefore the coefficient is not constant with the Reynolds number. The discharge coefficient only reaches to about .6, the error is caused by assuming inviscid flow.

How reliable is the paddlewheel flowmeter? Was the reading more accurate at high or low flow rates?

- Linear relation with high R^2 value, seemingly no inconsistency at higher or lower flow rates. A low enough flow rate could cause the friction to cancel the movement at lower flow rates.

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