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  • #61
    Originally posted by Evan
    Wow! Another victim of hoof in mouth disease. It boggles the mind. The difference (a derivative) in position in time of something is not a property of anything. It is a purely mathematical concept. It has no realizable existence.

    Even the values required to determine a phase difference are not properties of anything. Location is not a physical or mechanical property. Location can only be described as relative to something else as there is no such thing as absolute location in time and space.

    Tell me, from what property is a phase difference derived, in your mind? RPM, Torque? You will need to show that both of those are also mechanical or physical properties. That will prove very problematic since a property of something cannot be defined by when it happens. That is called an "Event".

    You would do well to avoid pursuing this line of argument further as it can only reflect badly on your knowledge and judgement.
    This borders on the insane. There is NO other way to describe it..... Evan presumably is not insane, but his argument here is basically insane.

    The most obvious and central point of the issue is that while the label you place on the measurement may NOT refer to something you can pick up and handle........ the EFFECT IS PHYSICAL

    The shaft material may be pressed dog$hit, but the torque on it produces a PHYSICAL effect on the shaft, which YOU CHOOSE to measure/quantify by something we agree to call phase.

    The effect you are measuring, whether measuring absolutely, or relatively, is physical, and each different shaft sample will be slightly different, requiring a calibration to produce results which are meaningful when related to something outside that section of shaft..... You have to know that phase results from full torque, half torque, or whatever. In fact, you really need to know two points and make an assumption of linearity.

    Since you insist, the phase difference *in this case* (you must be measuring relative to something, by your own admission) derives at base from the twisting of the shaft under load. That means the "phase" derives from a PHYSICAL relative change of position at one end of a section of shaft vs the other.

    Evan, let the philosophical implications go, and concentrate your mind on the fact that physical things are happening... no matter in what airy realm of "concept and 'event" you want to describe them.

    The "event" here is that you are just measuring the twist of the shaft, in relative units...... Which are then, in some way related to actual physical torque so that the meter dial has meaning....
    1601

    Keep eye on ball.
    Hashim Khan

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    • #62
      The most obvious and central point of the issue is that while the label you place on the measurement may NOT refer to something you can pick up and handle........ the EFFECT IS PHYSICAL
      Why yes, it is. So what? You just nailed down my argument and you don't realize it. It is an EFFECT. That does not constitute a PROPERTY of anything.

      Thank you.
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      • #63
        Yikes, its a battle of the Irresistable Force against the Immoveable Object.

        This makes it a battle of a PROPERTY versus an EFFECT, with so much at stake!

        Comment


        • #64
          There is more than that. There is also the difference between Physical properties and mechanical properties.

          Then there is the entire concept of phase, phase differences and phase shift.

          Phase has a number of definitions depending on the subject. Materials may undergo a "phase change" which is a change in a physical property of the material. However, that has no applicability to this situation.

          In this case the applicable definition of Phase is: A particular point in the time of a cycle; measured from some arbitrary zero and expressed as an angle. That is not in any way a property, only the description of the state of a system in motion. Going further, we may measure that state at more than one place and compare the results. Disregarding the fact that it is impossible to measure two separated events at the same time we can subtract one value of phase from the other and the result is the difference in phase.

          A difference in phase is a derivative of the measured state of a system in motion when measured at more than one location. It is derived from measurements that do not represent properties, either physical or mechanical. Note that the measurement of phase requires the establishment of an ARBITRARY reference. Arbitrary means: Random or without a specific bias, cause or reason.

          One cannot describe a physical or mechanical property by using arbitrary values. Since phase is based entirely on an arbitrary starting point for the measurement that starting point can be assigned to any point in time and any state of the system. That makes it impossible for the concept of phase difference to be used to define a mechanical property.
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          • #65
            Originally posted by Evan
            There is more than that. There is also the difference between Physical properties and mechanical properties.

            Then there is the entire concept of phase, phase differences and phase shift.

            Phase has a number of definitions depending on the subject. Materials may undergo a "phase change" which is a change in a physical property of the material. However, that has no applicability to this situation.

            In this case the applicable definition of Phase is: A particular point in the time of a cycle; measured from some arbitrary zero and expressed as an angle. That is not in any way a property, only the description of the state of a system in motion. Going further, we may measure that state at more than one place and compare the results. Disregarding the fact that it is impossible to measure two separated events at the same time we can subtract one value of phase from the other and the result is the difference in phase.

            A difference in phase is a derivative of the measured state of a system in motion when measured at more than one location. It is derived from measurements that do not represent properties, either physical or mechanical. Note that the measurement of phase requires the establishment of an ARBITRARY reference. Arbitrary means: Random or without a specific bias, cause or reason.

            One cannot describe a physical or mechanical property by using arbitrary values. Since phase is based entirely on an arbitrary starting point for the measurement that starting point can be assigned to any point in time and any state of the system. That makes it impossible for the concept of phase difference to be used to define a mechanical property.
            I, in my ignorance, fail to see the revelance of this to the original post. Evan (and others?) have gone off on a tangent. While I can't dispute the above treatise, I can say that I don't need the information to build a practical torque sensing device, because I have already done it.

            I hearken back to Darryl:

            from darryl post #21:
            Have the piece of shaft, the drive couplings on both ends, and two pieces of reasonably close fitting tubes placed end to end between the couplings. Clamp the ends of the tubes to the shaft at the ends where the couplings are. While at rest, scribe a mark across both tubes where they meet. If you twist the shaft, those marks will go out of alignment. How far out is determined by how much you twist the shaft.

            You can calibrate that by putting a known force on the end of a known length of bar that's attached to one end of the shaft. Scratch the mating marks across for each torque value you apply. In this case, you might want a range up to maybe 1200 ft/lbs if you'll be routinely measuring roughly 800 ft/lb.

            In operation, you read it using a strobe light to freeze the markings, or you could trigger the strobe from the rotating shaft.
            The strobe represents a point in time where the shaft is flexed. The fact that the whole shaft is rotating is inconsequential, and also inconvenient. We just want to know how much it is twisted at that moment, as the twist represents the torque applied. The strobe is only a method of gathering data, just as gear teeth and sensors, or strain gauges and RF links, or even slip rings are methods of getting the data off the rotating shaft. THey all convey the same information: the shaft is twisting to some degree or another. That is all that needs to be known.

            Perhaps Evan's assertions are true - if you neet to be splitting infinite fine hairs.
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

            Comment


            • #66
              I, in my ignorance, fail to see the revelance of this to the original post.
              It isn't relevant. I simply mentioned that the properties of the shaft were irrelevant to the method that I proposed to measure the torque. Jerry immediately siezed what he thought was an opportunity to try and show that I was mistaken. He then took this discussion to where it is now. I have better things to do than engage in this sort of argument but I refuse to let an alleged error in fact stand as if it were true, especially if it relates to information that I have provided.

              Perhaps Evan's assertions are true - if you neet to be splitting infinite fine hairs.
              It isn't splitting hairs. Knowing the difference between the physical properties, the mechanical properties and the effects that materials are subject to is the difference between structures that fall down or don't.
              Last edited by Evan; 04-15-2010, 06:45 PM.
              Free software for calculating bolt circles and similar: Click Here

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              • #67
                [quote=Evan]That does not constitute a PROPERTY of anything.[/b]

                SO WHAT.....? Your phase results from a property of the shaft, which you MUST USE to get the measurement.....

                basically, its a "load"...... of crap to argue differently, so why do you?

                the facts are, the shaft twists, you measure it. Call it "phase" and say it is an "event" and not related to a "property" if you want, that's just wrong and a red herring to boot.

                Go there if you want to try to "faze" the audience, but that's all a crock...... That BS about "phase as an event" has no relation to engineering reality......

                Squeal and kick as much as you want, the answer is the same.....You are measuring twist, and you need to relate 'amount of twist" to 'amount of torque".

                Evan, people are LAUGHING AT YOU for this...... just let it drift away and preserve some shreds of dignity here.......



                BTW, for once there is a real relevance to the HSM in the argument, since lot of folks do build engines, and some of them are interested in measuring properties of those engines, including torque, power etc. it's best to not obscure the subject with the "philosphy of phase".........
                Last edited by J Tiers; 04-15-2010, 08:28 PM.
                1601

                Keep eye on ball.
                Hashim Khan

                Comment


                • #68
                  Evan, people are LAUGHING AT YOU for this...... just let it drift away and preserve some shreds of dignity here.......
                  Why should I preserve your dignity? You have done this to yourself. I said originally that you didn't need to know anything about the shaft and you have nearly turned yourself inside out to justify your mistaken assertion otherwise. In the process you have revealed an astounding and troubling lack of knowledge about basic matters of physics. This has not been a good day for you Jerry.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #69
                    Originally posted by Evan
                    Why should I preserve your dignity? You have done this to yourself. I said originally that you didn't need to know anything about the shaft and you have nearly turned yourself inside out to justify your mistaken assertion otherwise. In the process you have revealed an astounding and troubling lack of knowledge about basic matters of physics. This has not been a good day for you Jerry.

                    LOL, way to try to turn it inside out....

                    You are truly incorrigible. I am actually a bit worried about you... certain observable trends are not so good.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #70
                      How many people have told Evan he is mistaken?????

                      This whole phase voodoo is beginning to be a ramble. A repetition of the same information. I believe the accepted definition of crazy is: doing the same thing over and over again and expecting different results.

                      Comment


                      • #71
                        How many people have told Evan he is mistaken
                        How many people with actual experience agreed with me? Saying the same thing over and over is the only option when you are right. Just because you don't understand it doesn't make me wrong.

                        I will make it very simple for your benefit.

                        We have a box. We have no idea what is inside the box and are given absolutely no information about it. But, there is an external coupling at each end of the box. One end is locked in place and not free to turn. The other end is mounted on a bearing and free to rotate with a stub shaft to which we may apply torque.

                        There is a small slot at each end of the box into which we may insert a small rod so that it protrudes very slightly from the slot to act as an indicator. We apply a torque to the output with a torque wrench. We then are able to observe how much the indicator rod at each end moves. We find that at a torque of 100 ft lbs the indicator at the end with the torque wrench moves twice as far as the indicator at the other end.

                        That tells us how much relative deflection of the pointers occurs when a torque of 100 ft lbs is applied to the one end of the stub shaft sticking out of the box.

                        Now, what does it tell us about what is in the box? No assumptions are permitted. You must justify your answers based on the available evidence.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #72
                          It tells you the torsional rigidity of the item in the box. So simple what's the problem.

                          Phil

                          Originally posted by Evan

                          I will make it very simple for your benefit.

                          We have a box. We have no idea what is inside the box and are given absolutely no information about it. But, there is an external coupling at each end of the box. One end is locked in place and not free to turn. The other end is mounted on a bearing and free to rotate with a stub shaft to which we may apply torque.

                          There is a small slot at each end of the box into which we may insert a small rod so that it protrudes very slightly from the slot to act as an indicator. We apply a torque to the output with a torque wrench. We then are able to observe how much the indicator rod at each end moves. We find that at a torque of 100 ft lbs the indicator at the end with the torque wrench moves twice as far as the indicator at the other end.

                          That tells us how much relative deflection of the pointers occurs when a torque of 100 ft lbs is applied to the one end of the stub shaft sticking out of the box.

                          Now, what does it tell us about what is in the box? No assumptions are permitted. You must justify your answers based on the available evidence.

                          Comment


                          • #73
                            It tells you the torsional rigidity of the item in the box. So simple what's the problem.
                            No it doesn't. You don't know the radius of gyration. There is no reason to assume that the radius is the same as the couplings.

                            If it isn't then you are also dealing with bending forces.

                            That also means that you don't know how much it has twisted or even if it has twisted. You also don't know what the mechanism of force transfer is.

                            To be more specific it doesn't inform you in any way as to the contents of the box. All you can deduce is that the box is able to transmit torque from one end to the other with a phase difference.
                            Last edited by Evan; 04-16-2010, 12:48 PM.
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                            • #74
                              Definition of torsional rigidity.

                              (mechanics) The ratio of the torque applied about the centroidal axis of a bar at one end of the bar to the resulting torsional angle, when the other end is held fixed.

                              No radius of gyration involved in torsional rigidity. If you study the equation it may help you with your misunderstanding.

                              Phil


                              Originally posted by Evan
                              No it doesn't. You don't know the radius of gyration. There is no reason to assume that the radius is the same as the couplings.

                              If it isn't then you are also dealing with bending forces.

                              That also means that you don't know how much it has twisted or even if it has twisted. You also don't know what the mechanism of force transfer is.

                              To be more specific it doesn't inform you in any way as to the contents of the box. All you can deduce is that the box is able to transmit torque from one end to the other with a phase difference.

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                              • #75
                                Are we having fun yet?

                                Regardless of who is right or wrong these banterings get pretty tiring. Isn't this stuff supposed to be fun or at least enjoyable?

                                We all know or work with someone we get tired of listening to so you just learn to ignore them after a while. Fortunately here you can just update your "Buddy / Ignore Lists" and the rest is magic ;-)
                                "Work hard. Tell everyone everything you know. Close a deal with a handshake. Have fun!"

                                -- Harold "Doc" Edgerton

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