Stepping motor driven constant-shear-rate rotating viscometer
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2004-10-08
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Despite the frequent use of stepping motors in robotics, automation and in a variety of precision instruments, they can hardly be found in rotational viscometers. This paper proposes the use of a stepping motor to drive conventional constant-shear-rate laboratory rotational viscometer, in order to avoid the use of velocity sensor and gearbox and, thus, simplify the instrument design. To investigate this driving technique, a commercial rotating viscometer has been adapted to be driven by a stepping motor, which is controlled via PC. Special circuitry has been added in order to microstep the stepping motor at a selectable step size, and to condition the torque signal. Tests have been carried out using the prototype to produce three flow curves for a standard Newtonian fluid (920 mPa.s at 25°C) but employing a different microstep size for each of them, within the shear rate range from 50 s-1 to 500 s-1. The results indicate the feasibility of the proposed driving technique.
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Conference Record - IEEE Instrumentation and Measurement Technology Conference, v. 2, p. 1373-1377.