Flowmeter Calibration

In this experiment, the orifice plate flowmeter and Venturi flowmeter were calibrated, with their flow coefficients obtained as functions of the flow rate. The outputs from both flowmeters were compared to the flow rate obtained from the weight time method.

In this experiment, a differential manometer, orifice plate flowmeter, Venturi flowmeter, paddlewheel flowmeter, weight scale, and calibration valve were used.

First, the pressure transducer was calibrated. The transducer should output a voltage that is proportional to the pressure differential in the manometer. In order to calibrate this, the bleed valve of the manometer was opened to various levels in order to create a pressure difference in the manometer without having any flow in the valve, since the flows should be kept constant while calibrating the transducer during this initial step. The pressure was set to five different values, from 0 to 69.2 cm height difference in the manometer, which corresponds to 0 to 10 volts in the transducer. For each interval, the heights and output voltages were measured and then graphed. A least-squares analysis was done on the resulting graph of deflection and voltage.

Next, the weight time method was executed with five different flow rates. For each trial, the flow rate was adjusted to be 0.81, 0.64, 0.49, 0.36, 0.25, 0.16, 0.09, and 0.04 times the maximum height difference of the manometer. Then, the valve was opened until the scale indicated that the amount of water was equal to the initial weight. When this happens, the second weight was added to the scale and three timers were started. When the weight of the water reached the second weight value, the timers were stopped. The averages of the three obtained times was recorded, along with the voltage from both the transducer and the paddlewheel flowmeter.

After obtaining the data from the weight time method in addition to the voltages from the orifice plate flowmeter, the velocity values from each method were compared against each other. The two methods were compared to each other by plotting the manometer deflection, which was calculated using the transducer output on the orifice plate flowmeter, and the calculated flow rate from the weight time tests. If the orifice plate was calibrated correctly, the calibration curve should have a power rule relation (the same relation as manometer deflection and flow rate calculated only from the weight time method), which is indicated by a linear relationship between the two variables when the plot is set to a linear log scale.

For the paddlewheel flowmeter, the paddlewheel voltage was plotted against the flow rate calculated using the weight time method. If calibrated correctly, the resulting curve should resemble a linear relationship, since the voltage output is proportional to the velocity of the paddlewheel, which is in turn proportional to the flow rate of the fluid (since that is what causes the wheel to turn). The linear relationship of the graph indicates that the voltage output of the paddlewheel is correlating well to the actual velocity and flow rate of the fluid.