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Torque measurement of rotating shaft

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  • Torque measurement of rotating shaft

    Howdy--------- Local fabricator wanting ideas/hardware for measuring torque which is being transmitted by a rotating shaft. Max rpm is 3,000, max torque may be as high as 800 lb-ft and max HP is limited to 600.

    Strain guages come to mind, with attendant problems of getting a measurement signal off the spinning shaft. Any ideas or derivations of a localized signal transmitting/receiving device/system?

    All thoughts appreciated.

    --G

  • #2
    There are inline load cells with slip rings that do what you want. Omega should have what you need:

    http://www.omega.com/toc_asp/subsect...&book=Pressure

    Edit, maybe, maybe not. Biggest they have is rated for 10000 in/lb or 833ft/lb

    Part #TQ501-10K $4075
    Last edited by macona; 04-13-2010, 01:37 AM.

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    • #3
      Can you put instruments/strain gages on the driving motor mounts? Might save the problems associated with slip rings etc.

      Dave

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      • #4
        I think you would be asking for problems doing something like that.

        Heres a new in the box sensor on ebay:

        http://cgi.ebay.com/Himmelstein-MCRT...#ht_500wt_1182

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        • #5
          http://www.sensotec.com/torque.asp

          In particular the clamp-on torque cells look handy....

          - Bart
          Bart Smaalders
          http://smaalders.net/barts

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          • #6
            I imagine you would want a digital readout of some kind. In that case, some electronics will be required. It's not too much of a stretch to say that a shaft-mounted device could be battery powered and send a signal to a receiving and processing circuit. I don't know of any such device, but I'm sure it exists somewhere.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Omega has a line of readouts that connect to them as well as the others.

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              • #8
                Use an ampmeter to compare current between loaded and unloaded conditions?

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                • #9
                  Measure the twist in the shaft by using optical sensors at each end that pick up an index mark once per rev. I could throw something together like that in a few hours. Cheap and easy. A commercial frequency counter with a pulse duration mode will give an accurate readout of the time difference which can be referenced to a converson table developed during calibration. Or, you can design and build a direct reading unit like this one. With only a slight modification it would do the job. It counts the duration from pulse to pulse by preloading the counters to maximum count and counting down until the next pulse latches the count to the displays. By adjusting the clock generator it can be made to read in whatever units are convenient.

                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    The smartest idea may be to measure the reaction at the drive point. That requires virtually no calibration aside from physical measurements.

                    Measuring the twist of the shaft requires knowing things about the shaft, which is of course not impossible....... but.

                    Another approach, depending on precision and real-time requirements might be to measure the motor current... that can be one-time calibrated to the motor and will be good until the motor is re-wound or is damaged.
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      Meauring the twist doesn't require knowing anything about the shaft, only the load.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        Purpose?

                        [QUOTE=GuidoMax rpm is 3,000, max torque may be as high as 800 lb-ft and max HP is limited to 600.[/QUOTE]

                        Bodger has the right answer, motor current with maybe a slight correction for RPM (as in, higher frictional/cooling fan losses at 3000 rpm than 30 rpm)

                        Real question is, (800*3000)/5252 = 456 horsepower... So your peak torque and peak rpm seem to limit you well under your 600 limit. But I'm reading it as a 600 HP, 3000 rpm motor is bolted to a shaft or gearbox that'll shatter above 800 lb-ft, which is inadequate shaft for a 600 HP motor.

                        In my opinion you should replace the shaft/gearbox/whatever with one that'll survive at least 1600 lb-ft (and thats a factor of safety of only 50%). Alternately, program the VFD, or install a restrictor plate, or swap out the motor to maybe a 400 HP one.

                        Easy way to remember the HP equation, BTW, is to just memorize 5280 aka feet in a mile. Its close enough.

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                        • #13
                          Just 'thinking-----------

                          Been brainstorming this problem and a solution for years. Should have been more detailed with the problem of wanting to measure/display HP and torque on the dashboard of a Peterbuilt moving down the highway at speed. Idea popped up when we saw how turboprop engines display torque in real time. A nonlinear pressure guage is mounted on the panel, with pressure from engine compressor stage number so-and-so measured and displayed. The pressure guage displays in ft-lb of torque.

                          There's gotta be a market for a device to be added to an over the highway diesel truck tractor, which would reliably display torque/HP. Instant operator visual of motor performance.

                          Everyone's thinking and input is appreciated.

                          --G

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                          • #14
                            Motor mounts.

                            Put some type of transducer under the comporession side motor mount and figuure the distance to the opposite side motor mount. You then have a force and a distance which can calulate to torque. 800Lbs, and 24" spacing = 400 ft lbs.

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                            • #15
                              Originally posted by kf2qd
                              Put some type of transducer under the comporession side motor mount and figuure the distance to the opposite side motor mount. You then have a force and a distance which can calulate to torque. 800Lbs, and 24" spacing = 400 ft lbs.

                              Since the engine is trying to spin around the crankshaft, I think you would only need the distance from the center line of the crank to the load cell. Not the mount to mount distance. The cell could be placed on either side, I would say the side in tension, as it would be much easier to attach a cell to the top of the mount. Rather than having to lift an engine of that size out of its mounts. Less to disassemble that way too.

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