Calibration of a Flowmeter

The idea of calibration is to get a single equation that gives valid values. The equation doesn’t always have to be linear, but its use is essential when trying to obtain the most accurate measurements from a device. In this lab, flowmeters were calibrated.

Flowmeters are an instrument that measures bulk fluid movements of a liquid or gas. This Instructable will guide you calibration of these flowmeters

Specifically we will calibrate the measuring devices of the Venturi meters, orifice plate meters, and paddlewheel flowmeters. The Venturi and orifice plate meters measure differences of pressure change so they are calibrated once the flow coefficient as a function of the flow rate is determined.

The experiment consisted of a hydraulic and paddlewheel flowmeter connected to separate pipes and a weighing tank. For the hydraulic flowmeter a mercury manometer was also connected to quantify the pressure differences. For the paddlewheel flowmeter a transmitter that gave an output current was sent through a resister produces a voltage output. This transmitter read the revolutions from the paddlewheel device.

The output voltage from the pressure transducer that measures pressure differences from the hydraulic flowmeter was calibrated. Started the calibration off by zeroing the transducer output and then, closed the discharge valve while opening the manometer valve to reduce the pressure. Then 5 voltage values were taken and the heights from the manometers. It is important to note the maximum output voltage did not go over 10 V. To receive data from the paddlewheel and hydraulic flowmeters check the Gain Adjust control of the paddlewheel flowmeter is set at 6.25 turns (P1 and P4) and 3 turns for P3. Then use the Zero Adjust control to zero the output of the paddlewheel. Next, the discharge valve was opened and both differential pressure voltage and paddlewheel voltage were measured. At max flow rate the manometer, time weight, and paddlewheel values were taken. The max manometer deflection was taken as well. This procedure was repeated 10 times whilst decreasing the flow rate each time.

Plotting the Q and manometer deflection gives the orifice plate flowmeter graph presented above. As the manometer deflection increases the flow rate increases. With the orifice meter we were able to artificially increase or decrease area with the plates shown in the second picture. The third picture is the discharge coefficient (Cd) versus the Reynolds number (Re). This reflects the equation Re*D = V* D/v where D=diameter, v=viscosity, V=velocity. The graph shows the Cd decreases exponentially when Re is increased. This means Cd is low for slow moving fluids. The Cd for the orifice is quite low because the orifice has turbulence that is created. For more accurate results one should use the Venturi meter which has a higher Cd because it doesn't cause turbulence. For our results we got Cd for the Venturi meter to be .9 and .6 for the orifice.

For the paddlewheel the flow entered in the perpendicular direction which rotated the wheel which gave the voltage from the rotation of the device. This meant the flow rate was accurate when the flow rate was high. This is because when the flow rate is very small It wouldn't necessarily rotate the device. The max velocity found was 5.427 m/s and the low was .590 m/s.

Good luck with your calibrations and welcome to the company! If any questions please feel free to contact me.