Test Technology - DIGITORQUE ® Testing
What began as a project to develop a better torque transducer/load test method soon developed into a rethinking of how torque is measured. As in all good research, the basic principles of physics were reexamined and, although all prior methods were studied, thinking was not allowed to simply begin where previous research had ended. The result was the invention of the digital torque measurement method. Now referred to as Digitorque®.
Digitorque®’s revolutionary method has all the advantages of load testing without its calibration / maintenance woes, typical slowness and high costs. Indeed, the Digitorque® method can measure hundreds of torque / speed points - enough to characterize the entire torque / speed curve including locked-rotor, pull-up, breakdown, and full load points - in just a few seconds. About the same amount of time most no-load and signature methods require. Simply put, this all-digital method renders laboratory results at no load speeds.
The Digitorque® method is founded upon a basic physics principle: The torque applied to a rotating mass of known inertia can be calculated by measuring the change in speed
over a fixed period of time.
Torque = Inertial Load X Acceleration
or
Torque = Inertial Load x change in speed/time
Generally, this formula is used to determine the torque required of a motor to accelerate an "Inertial Load" from zero speed to full speed in a finite time. The Digitorque® method utilizes it to calculate torque. In a system employing the Digitorque® method, the motor under test is mechanically connected to the test system via a test fixture consisting primarily of a rotating shaft supported upon high-quality bearings and a flywheel of known inertia and a high-resolution rotary digital encoder mounted on the shaft
The flywheel is used as an "inertial load." Its value is a constant in the above equation. The measurement time interval is also a fixed value generated by a crystal oscillator. Time is measured from one zero line crossing to the next on the AC line cycle. Thus, the only remaining parameter required to calculate torque is the change in speed.
The change in speed is determined via the industrial grade digital optical encoder which, together with support electronics, is capable of resolving extremely small changes in speed. Torque and speed are computed using this method for each line crossing from the time power is applied to the motor until it reaches its maximum "no-load speed." The flywheel size is selected so it will take about four seconds for the motor to accelerate to that speed from a standstill. The exact time is not critical. The result is, that about 480 torque and speed measurements are made during this acceleration time. This is more than enough points to accurately describe the entire torque versus speed curve of the motor from locked-rotor to full load.
Motor power and current are also continually measured during the Digitorque® test and both are plotted along with torque versus speed curve The test system computer then employs algorithms to instantly pick out each specific point of interest (locked-rotor torque and current, pull-up torque, breakdown torque and speed, full load speed, current and power for induction motors) from the curves.
The system also allows limits for torque or speed to be set at up to 5 user-defined points.
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