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3 high-flying French SMEs serving the innovative application of one of them, CSTM, which is developing its own high-speed electric motor, has encountered a hard point in torque measurement. It must be contactless, precise, without added inertia, without constraint and in addition at very high speed (100,000 rpm) ......

Torque measurement without torque meter: oxymorons or paradoxes?

François Dugué, director of CSTM, explains in detail his engine and its requirements:
We are strongly concerned with high-speed rotating machines, particularly for aeronautics and space, whether for test benches or for prototypes of on-board equipment. In this context, we are developing an electric motor with a mechanical power of 52 kW at 100,000 rpm, which does not exist on the market, and which can meet the needs of several of our customers. For its development, we had to measure speed and torque. But, above 25,000 rpm there was no torque meter on the market.

To measure at these high speeds We obviously need a very fast and precise reference speed sensor for this: the world reference is OPTEL THEVON, designing its sensors in Paris. We chose the 152M model from OPTEL THEVON Cf. Figure 4, which has many advantages on the scientific and practical level with TTL and Analogue outputs; This standard product presents a truly exceptional dynamic, as well as an ease of assembly and use, (The installation simply requires for each sensor a marking on the shaft alternating a reflective surface and a matt surface, as well as an optical fiber support The installation and adjustment of the optical sensor is then of the order of 10 min). The advantages of these optical probes are their precision which makes it possible to put many marks on a small diameter as well as their insensitivity to electromagnetic pollution. No wonder Porsche, Toyota and all the other majors use OPTEL THEVON products around the world.
Thanks to the VIB 360 application from French Impédance, with its acyclism extraction algorithm created by Dr Hamid SAIAH, we can measure the speed, torque, acyclisms and eigenmodes of the shaft line, and with two sensors 152M each located on a tone wheel on either side of a shaft portion of known stiffness, the high speed torque meter is produced.

Hamid Sahia and his team have been developing and using algorithms for machine vibration diagnostics for many years in conjunction with CSTM. Its algorithms are really impressive as shown by validation tests with a commercial torque meter, tests carried out at Supélec where a precision better than 10-3 angular degrees was observed, ie 0.02% of the torque considered at low speed.
The strength of this torque meter, using very high dynamic OPTEL THEVON sensors, is that the measurement can be performed at low speed on large rotors and theoretically at speeds greater than 200,000 revolutions per minute with the same angular precision, if the acquisition frequency is suitable.
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Our recent tests up to 85,000 rpm, with two 152M sensors on an electric motor test bench designed and produced by CSTM, see Figure 1, have led to exceptional results. In fact, the torque measurements perfectly follow the predictions of the calculation. By comparing the torque measured against the braking torque of the aerodynamic brake that we calculated in digital fluid mechanics (CFD), we validate at high speed both the calculations and the torque meter which is of course the more precise of the two, such as This is shown by the low dispersion of the measurement points compared to their trend curve.

For more information, meet at our stand C10 during the MEASUREMENT WORLD trade fair…


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