Method for determining pump flow rates using motor torque measurements

A system for determining an actual fluid flow rate through a motor driven pump controlled by a variable speed drive at a determined motor torque, comprising:

• a measuring means coupled to said motor to determine said motor torque;
• a measuring means coupled to said motor to determine a speed value;
• a memory retaining a plurality of known characterizing flow rate values corresponding to a plurality of known characterizing torque values for each of a plurality of known characterizing speed values;
• a processor, in communication with said memory, operative to:
• receive said determined torque value and said determined speed value;
• determine a flow rate value from said plurality of characterizing flow values at each of two known speed values selected from said plurality of known characterizing speed values, wherein a first one of said two known speed values is selected greater than said measured speed and a second one of said two known speed values is selected less than said measured speed;
• and
• determine said actual fluid flow rate proportional to said determined flow rate value at each of said selected known speeds, said selected known speed values and said measured speed.