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Thread: extending "galvo amp" wires for 1 or 2 metres ? is it possible ?

  1. #1
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    Default extending "galvo amp" wires for 1 or 2 metres ? is it possible ?

    toying with an idea of a housing in which the galvo block is in a different box
    from the galvo amps !

    ........ rather than reinvent the wheel :-)

    has anyone else done this , might need to run the galvo amp wires
    for 1 or 2 meters ?

    anybody any thoughts on this , is it possible

    what about a buffer to push signal if you think is might degrade ?

    any input appreciated

    paul
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    I don't know how far "normal" scanner amps will get you; but TurboTrack 2 amps are good for 10ft of signal cable.
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    Many thanks daniel , that info means experimentation is certainly on the cards , however turbo track amps bring up little information on google, ebay and indeed here , so further , i would be interested in hearing from anyone who has extended or experimented with standard cheaper galvos and amps and in particular DTs

    cheers

    paul
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    Paul
    Use good quality sheilded cable - if doing DTs then you will see the lead is made of a pair of wires, one 2 way + sheild one 3 way + shield. Use similar cable and keep the wires separated as they are from the factory. One lead conducts the motor drive current the other the feed and signal for the optical position sensor. Its more important that the position sensor wires are good as noise or bad signal on this will mean an incorrect position will be detected and the amp will try n drive the scanner wrongly.
    Make up some long leads and test first with the signal inputs grounded not no signal in - actually ground them. This will give a clean 'no signal' to the amps and the scanners should rest in the home position. Fire a laser at the scanners and make sure you see a static spot, any wiggle on it will be pickup from the position sense lead.
    If this is ok then put a signal in and bring up the scale from zero very carefully, that way if its going wrong you shouldnt do any damage.
    hope it helps
    Rob

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    Given the sharp drive currents involved, I would imagine this could at the very least necessitate a re-tune of the PID loop. I would be thinking thicker shielded cables for the galvo drive signals to minimise current losses.

    I have little knowledge of the DT feedback signals, but these could be effected by longer cables too, so be careful!
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    Ok. I deal with this one all the time. Six to ten feet is the normal maximum foir high speed scanners. Six feet is pushing the limits unless you have true Cambridge amps or Turbotracks with the input low pass filters. I've seen industrial grade Cambridge galvos go about 20 feet, but those are ones with better amp front ends.

    You have to beef up and shield the driver cables, they handle 4-6 amps peak for a few milliseconds at a time. Because of this, you need large diameter stranded wire.

    The dual position sensor photodiodes are operated in transimpedance mode, ie using currents, instead of voltages. The photosensor is running differential, so you ground the photosensor cable shield at the amp end. Currents are ranging from a few nanoamps at rest to a milliamp at peak swing.
    The led driver current is a few tens of mA.

    So each cable is broken into two halves, the driver half and the sensor half.

    Your limit is driver cable inductance and crosstalk from the driver cable to the sensor.
    Most drivers are already using paralleled wire to the coils, lowering the inductance by paralleling wires can't hurt.

    The easiest way to find out is to built a test cable, and splice in more driver cable till you see a image degrade. Then back off by at least half on the max length.

    Bad cables usually lead to nasty oscillation.

    See attached PDF "678xxCable1A.pdf" from a Cambridge manual for a example extension cable. Note "rings" on schematic diagram are the shield braid. Note that on a actual galvo cable, the shield on the two conductor wire would NOT be connected at the galvo end. This is shown in the second PDF attached, called "678xxCable2A.pdf".



    Steve
    Attached Thumbnails Attached Thumbnails 678XXCable2A.pdf  

    678XXCable1A.pdf  

    Last edited by mixedgas; 08-19-2012 at 10:57.

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    Thanks for replies guys , lots of ideas to check and experiment with

    Paul
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    Heya bro,
    Kiwi tinker and I talked about this idea a few years ago. Never amounted to anything. We where thinking of an amp rack with the diode drivers and scanner amps. Perhaps a multicore cable going to a really small enclosure for the scanners/diodes. Keen to hear how you get on.

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    Hi,

    it is impotent to separate the signals. one cable for the current from the amp to the galvo coils and the other one for the position signal back to the amp. the second one neat a good shield quality.

    lobo has extent her galvo signal more then 5m with the lobo amp 3.

    best regards

    thomas

  10. #10
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    Perhaps this might work with the pangolin rack mount unit. Just like a pa?

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