Advantages of Using Microcomputers in Dynamometer Controllers

Dynamometer controllers incorporating digital microcomputers are generally more accurate and hold their accuracy longer than their analog counterparts. Furthermore, the digital microcomputer can perform a multitude of other tasks normally not possible with an analog controller. This paper describes the implementation and the results of the following four microcomputer functions. 1. Digital Speed Measurement. This requires a shaft encoder and a digital signal conditioner in addition to a microcomputer. The speed signal obtained with this system is free of drift, requires no calibration and has a resolution of 0.01% of reading. 2. Automatic Calibration of Parasitic Losses and Torque Signal. This is a procedure fully implemented in software, requiring approximately three minutes to execute. The automatic calibration and the drift-free speed measurement make it unnecessary to calibrate the dynamometer controller manually. 3. Torque Signal Linearization. This is accomplished by using a lookup table and a linear curve fitting technique. The linearization substantially increases the measurement accuracy at low torque values. 4. Dynamometer Set-up Procedure. This is simplified by recalling all the necessary test parameters with one control key. Some of the test parameters included are the three road load coefficients, electric inertia, flywheel combination, parasitic losses compensation and coast down speed trigger points. The possible number of sets of test parameters is essentially unlimited. They are stored in a battery back-up, nonvolatile CMOS memory.