Flowmeter Calibration Manual

To calibrate the flowmeters, first, data needs to be collected. Start by collecting data from the flowmeter while performing weight-time measurements at varying flow rates. Once the data has been collected, see steps below corresponding to flowmeter type.

For Venturi and Orifice-Plate Flowmeters: To begin the calibration process, first the calibration curve must be created. Plot the measured flow rate as a function of the measured manometer deflection. To create the calibration curve, plot a trendline for the data.

Use a trendline approximation function in a spreadsheet program to create this curve. Because the manometer deflection is proportional to the square of the flow rate, the data should appear linear when plotted on a logarithmic scale. For this same reason, the trendline of the data should be of form Q = k*∆h^m, where m is between 1 and 0.

This curve and its corresponding equation can then be used to determine the flow rate provided the manometer deflection can be measured accurately.

For Venturi and Orifice Plate Flowmeters: Using values from the calibration curve created in the previous step, plot the discharge coefficient as a function of Reynold's number on Linear-Log scales. See attached picture for example. Reynolds Number: Re = V1*D/v where V1 is the fluid velocity, D is the full pipe diameter, and v is the viscosity. You may notice that the discharge coefficient may appear to be relatively constant or have an unexpected variation over the range of Reynold's numbers tested. This is because flow separation occurs as the fluid passes through the reduced diameter section of the flowmeter, which is not accounted for in the theoretical derivation of the Discharge Coefficient, which causes deviation from the theoretical value of 1.

For Paddlewheel flow meters: Plot the flow rates measured using the weight-time method as a function of the flow meter's output voltage. Take note of any flow rates under which the paddlewheel is motionless, or any flow rates where increasing the flow rate does not increase the velocity of the paddlewheel. Note these "cutoff" velocities, and note that the flowmeter being tested is unsuitable for measuring these flows in pipes of this size. Paddlewheel flowmeters are accurate, however as they are a mechanical device the correct paddlewheel flowmeter for each application needs to be appropriately sized.