Portable dynamic electronic speed-torque indicator

The concept of instantaneous observation of the complete speed-torque characteristic of a motor while it accelerates from standstill to full speed is based on the assumption that a large percentage of the torque is utilized in acceleration of the inertia if the motor is otherwise unloaded. The basic instrument needed is an accelerometer with dynamic response capable of indicating the true starting torque and the transient cusps of the torque curve. This paper discusses the application of a 2-phase a-c instrument tachometer and active high-gain operational amplifiers to the design of a portable speed-acceleration instrument. The tachometer utilizes a drag-cup rotor and produces a constant frequency carrier output that has a minimum of ripple with frequency proportional to speed, thus eliminating the problem at low speeds of ripple amplification by differentiation encountered when using conventional tachometers. The constant frequency carrier output simplifies the problem of amplification and noise found with the homopolar-type generator. The use of stabilized operational amplifiers for differentiation and amplification after demodulation both provide the necessary dynamic response for the torque signal and virtually eliminates the problem of drift in the d-c stages. Operational applications of the instrument including torque versus speed, acceleration versus time, and speed versus time are included from the engineering laboratories of Robbins and Myers, Inc., Springfield, Ohio.