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Thread: Specs needed for GVM-3620

  1. #1
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    Default Specs needed for GVM-3620

    I am looking for specs for a General Scanning GVM 3620 or GVM 620 actuator. They have the same mounting foot print and shaft diameter as the GM-20, but the body is about twice as long. Queries to "The General" have been fruitless. Anyone?
    Thanks
    Last edited by glorocks; 04-04-2015 at 07:47. Reason: typo

  2. #2
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    See attached for the GVM "PEN MOTOR".

    You have a house marked, OEM GVM.

    We know from the data sheet the drive coil should be ~26 ohms.

    The open loop A102 amp will need the ratios of the sense bridge resistors adjusted for the 26 ohm GVM coils, plus the coupling capacitor C3 in the bridge difference loop will need to be larger. I'd also change out the cascaded transistor pairs to TIP series Darlingtons for far better performance. A102 creates damping signal by taking the difference in signals between a non-inductive load (R22,R23) and the inductive load which is the Galvo and the sense resistor R25. C8 (HF Rolloff) may need to be made larger as well.

    Otherwise try the amp in the patent that uses the feedback coil.

    Steve
    Attached Thumbnails Attached Thumbnails Open_Loop_DataSheet_736-49506.pdf  

    GS-A102.gif  

    Last edited by mixedgas; 04-08-2015 at 08:32.
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  3. #3
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    Thank you, Steve, thank you very much. Your points about the A-102 amp are very helpful.
    I need to measure the resistances in the connector to see where to go next. If these are V feedback, I should find two more coils besides the drive coil.
    Cheers,
    Jay

  4. #4
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    Well, looks like these are are house marked GM 734. The GM 734's have started cropping up on E-bay for as low as $10 ea.
    There are two coils- Pins 1 & 2 (viewed with the connector at the bottom) show a resistance of 27 ohms, which would be the drive coil, and pins 4-5 show 14.6 ohms, which would be the feedback coil. Pin 3 appears to be NC.
    Inductances are 57 mH and .8 mH, respectively. (these readings may be off a little)
    US patent 4,186,332 details the galvo and contains a suggested drive circuit. Time to get the soldering iron out. More to follow

  5. #5
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    OK- The GVM 3620's I have are NOT GVM 734's. I just picked up a few 734's, and they are much wider and heavier than the 3620's I have. Mounting hole layout is wider, and the internal threads are 6-32 as opposed to 4-40. Apples and oranges.
    So, I'm still looking for info about the GVM-3620 part.





    Quote Originally Posted by glorocks View Post
    Well, looks like these are are house marked GM 734. The GM 734's have started cropping up on E-bay for as low as $10 ea.
    There are two coils- Pins 1 & 2 (viewed with the connector at the bottom) show a resistance of 27 ohms, which would be the drive coil, and pins 4-5 show 14.6 ohms, which would be the feedback coil. Pin 3 appears to be NC.
    Inductances are 57 mH and .8 mH, respectively. (these readings may be off a little)
    US patent 4,186,332 details the galvo and contains a suggested drive circuit. Time to get the soldering iron out. More to follow

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