Electric motor performance testing has always been a crucial factor for ensuring the life and efficiency of motors in the industrial environment. The initial test techniques of no-load, load test, and signature test were constrained and thereby, reliable only to a certain extent.
However, the efficient use of the Digitorque technique lifted these constraints. This method can complete thousands of torque-speed analysis, power measurement, and other production tests within a few seconds. This method also has the power to reveal the accurate torque-speed graph from the locked rotor to the full-load rotor.
The Principle of Operation
The Digitorque method bases the fundamentals of physics on the statement, “If the mass and inertia of a rotating body are known, the change in speed over a specified period of time can be used to calculate the torque applied.”
The Test Fixture Used and the Process of Operation
The test fixture comprises assessing the circulating shaft mounted over reliable bearings with a flywheel of known mass and inertial properties used. In addition, good-quality digital encoder measures accurate values with the coder mounted over the shaft. The formula used for Torque calculation is as follows:
Torque × Time= Inertial Load × variance in Speed
The flywheel is the inertial load with the time interval in this case as the constant value produced by a crystal oscillator. The digital encoder records the change in speed. All these values when placed in the formula tend to give the value of torque produced.
The Measurements
Torque Ripple and Switch Speed
These ripples are the outcome of some manufacturing defects in motors. These defects range from improper bearings; inappropriate shaft bends, air gap defects, rotor imbalance, rotor hits and open rotor bars. A distortion in the graph produced from the above outcome depicts the ripples.
Torque Friction measurement
Whenever there is an excess of friction torque produced, it indicates incorrectly placed or defective bearings or spoiled shaft. If the measurement exceeds the defined test limits, you can change the speed to make the friction torque fall within the limits.
Coupling to the shaft
The outcome is a bit more complicated as compared to the normal testing. There are myriad arrangements that require adjusting the shaft before testing with different types of motors. The diverse types of motors include small, low-power motor, automotive DC motor, DC starter motor.
