Why Measure Torque?
Knowing torque accurately is essential in monitoring the performance of rotating machinery and to disclose the need for maintenance. Whereas the limit of heat loss calculations is generally 5%, direct measurement routinely provides 1% or better (1/2% on test stands).
In selecting a system, the following needs to be considered:
Environment – Will heat, dirt and oil, high speeds, and g-forces compromise performance?
Performance – What accuracy is required? Is long-term stability needed? What are the allowable maintenance intervals?
Applicability – Can it use an existing coupling, or are major changes needed? What is the effect upon machine dynamics, such as torsional stiffness?
One type of system measures the phase displacement of toothed wheels mounted at each end. Since unwanted deflections can otherwise be interpreted as torque, the effects of bending or misalignment of the coupling, as well as motions of the sensors (which may be due to temperature changes), needs to be considered. The smaller deflections of short or stiff shafts can reduce performance, and calibration at zero speed is difficult.
Strain gage systems directly measure the deflections, or strains, in the shaft material itself. They have the ability to work with short shafts and at zero speed, making possible direct static calibration using load cells. The output of strain gages is low, so processing is required before transmission from the rotating shaft.
Properly designed rotary transformers afford a reliable way of accomplishing this without the use of radio signals, slip rings, or bearings. The Riverhawk Torque Meter is designed with a generous gap between rotating and stationary members. This enables the Torque Meter to accommodate both the radial and axial misalignments normally present in an operating machine.
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