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#1
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"mindenpilot" wrote We do all kinds of little tricks like putting a notch in the crankshaft to use as a phase reference. Then we can determine at what point in the cycle an anomaly occurs, which can lead to different diagnoses. How does the notch help in telling the rotational position? -- Jim in NC |
#2
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"Morgans" wrote in message
... "mindenpilot" wrote We do all kinds of little tricks like putting a notch in the crankshaft to use as a phase reference. Then we can determine at what point in the cycle an anomaly occurs, which can lead to different diagnoses. How does the notch help in telling the rotational position? -- Jim in NC It takes a little nick out your finger as it goes by? Rich "Ow ow ow ow owow ow ow ow ow owow" S. |
#3
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On Fri, 11 Mar 2005 20:25:16 -0500, "Morgans"
wrote: "mindenpilot" wrote We do all kinds of little tricks like putting a notch in the crankshaft to use as a phase reference. Then we can determine at what point in the cycle an anomaly occurs, which can lead to different diagnoses. How does the notch help in telling the rotational position? A little magnet and associated coil sees a difference in flux as the slot goes by. This is a variable reluctance sensor. Your auto engine may be timed from something like this, any more. Brian W |
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Morgans wrote:
"mindenpilot" wrote We do all kinds of little tricks like putting a notch in the crankshaft to use as a phase reference. Then we can determine at what point in the cycle an anomaly occurs, which can lead to different diagnoses. How does the notch help in telling the rotational position? It adds a known vibration to the system? ;-) Presumably, it gets used as a timing mark of some kind. I guess that monitoring the spark time to the No 1 cylinder would almost give you the same. "Almost" because of course the spark can be advanced/retarded. Frank |
#5
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"Morgans" wrote in message ... How does the notch help in telling the rotational position? -- Jim in NC Without giving too much away... The notch depth is more significant than any vibration. If using a proximity measurment, it is easy to determine when the notch occurs. The notch is aligned with a known position (engineer inserts notch when pistons/crank is in known position). This gives a phase reference. You can compare where in the cycle a disturbance (knock, rub, etc) occurs with relation to the notch. On recip applications, often a multi-tooth wheel is used in addition to a phase reference for more accuracy. Adam N7966L Beech Super III |
#6
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#7
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"sleepy6" wrote That notch causes a much larger timing blip in the signal than any crank movement will cause. By measureing the time between the timing blips you can determine the amount of rotation after a timing blip that you see an up or down crank movement event. What sort of technology does a proxomity detector use? Magnetics, sonic, radio waves? -- Jim in NC |
#8
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Yes, all of the below.
Sometimes you drill a hole in a small magnet and use a small screw to hold it to the propeller backing plate. Sometimes you use a strip of reflective tape on the prop itself. Sometimes you use a pulse from the #1 magneto lead. Jim "Morgans" wrote in message ... "sleepy6" wrote That notch causes a much larger timing blip in the signal than any crank movement will cause. By measureing the time between the timing blips you can determine the amount of rotation after a timing blip that you see an up or down crank movement event. What sort of technology does a proxomity detector use? Magnetics, sonic, radio waves? -- Jim in NC |
#9
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"RST Engineering" wrote in message ... Yes, all of the below. Sometimes you drill a hole in a small magnet and use a small screw to hold it to the propeller backing plate. Sometimes you use a strip of reflective tape on the prop itself. Sometimes you use a pulse from the #1 magneto lead. Jim This guy was talking about a notch and proximity detector for the phase detection. I know about all of the things you mentioned, but the proximity detector's workings are new to me. -- Jim in NC |
#10
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In article ,
Morgans wrote: "RST Engineering" wrote in message ... Yes, all of the below. Sometimes you drill a hole in a small magnet and use a small screw to hold it to the propeller backing plate. Sometimes you use a strip of reflective tape on the prop itself. Sometimes you use a pulse from the #1 magneto lead. Jim This guy was talking about a notch and proximity detector for the phase detection. I know about all of the things you mentioned, but the proximity detector's workings are new to me. Think of a proximity detector as 'ultra short-range radar'. grin It may use reflected RF energy, or 'optical'. where the 'excursions' you're trying to measure are smaller than the wavelength of the measuring 'beam', you can use simple phase-shift between outgoing and returning signal, to determine distance. where the distance is much larger than the wavelength, you have to impress a carrier on the beam, and measure phase-shift in the carrier frequency. this gets an 'approximate' distance, that can be further refined by phase angle measurements of the beam itself. Capacitance tracking is also a possible approach. and/or "Hall effect". These can get 'messy', due to inherent non-linearity in the technology, that has to be compensated for, in 'reading' the signals. Capacitance tracking works best where there are *very*small* vibrations involved, and a very _smooth_ surface to measure against. The technique is capable of mapping individual atoms/molecules in a crystal lattice. Scientific American had a write-up -- at least 15 years ago -- about a new 'super microscope' (successor generation to the scanning electron microscope) that worked in that manner. a _very_fine_ 'needle' was carefully moved, raster-style, across the object being 'scanned', and the capacitance changes between the needle and the object were mapped. |
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