Study of a thyristor driven pump as a flow indicator

In the present paper, the load current of a thyristor driven pump has been utilized as a mass flow sensing parameter of a fluid being lifted by the pump. The motor load current has been sensed by an opto-isolator based circuit and the output of this circuit has been displayed in a PC monitor using Labtech Notebook Pro software. A theoretical equation relating the output of opto-isolator circuit with mass flow rate has been derived and experimental study has been carried out to verify this theoretical equation, assuming the volume flow rate of water at constant room temperature to be proportional to mass flow rate. The experimental results are presented in the paper. It has been observed that the opto-isolator output and the on-line display in PC monitor both vary almost linearly with mass flow rate. Percentage deviation of the experimental results from ideal linearity and repeatability in terms of standard deviation are found to be within tolerable limit.