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  1. #1
    Has anyone achieved linearity between Mach3 PWM signal and a VFD spindle??

    My VFD display matches the actual spindle pretty closely as checked with a laser tacho.

    When i request 24,000rpm, I get it, when I request 10,000rpm i get something like 8,000 instead - it's not a linear scale so need calibrating.

    I know it can be done, using the motor steps-per & velocity plus the spindle pulley settings but I cant find any concrete way of how its done.
    Last edited by Davek0974; 23-03-2016 at 08:21 PM.

  2. #2
    Well, spent an hour messing tonight, i have no doubt it can be done, but its not going to happen by trial and error i think - too many variables and unless you know what effect each one has your'e just pissing in the wind Wink

    Pretty certain now that steps/per and acceleration does nothing, this makes sense as we are on PWM so I think that can be taken out of the equation.

    That just leaves Min PWM, base frequency, pulley min and pulley max.

    Unless there is a setting on the VFD, i guess there might be, might be worth checking that 5v does give 50% speed.

  3. #3
    Been messing again - it all seems relative to the spindle pulley settings.

    I set the min as whatever I got after setting a M03 S1 command - this was 1500rpm.

    The max was then tried setting above the actual limit - this made things worse.

    Then I went below the limit - 20,000 actually did a good job at the 5,000 to 15,000 range and was pretty close BUT it means you cannot command full speed as you have limited it to 20,000 so not good Sad

    I am leaving this at present as I am unsure it actually be done without a lot more knowledge and maybe some VFD tweaks too.

  4. #4
    Should it be possible to measure the 0-10v signal?

    I thought so, but I tried measuring the input to the VFD from the BOB and as soon i touched the VI & ACOM pins in the VFD the motor stopped as if the input was being shorted out?

    This was with an expensive Fluke DMM on DC volts, i was expecting to see something 0 and 10v here??

    Odd?

  5. #5
    Clive S's Avatar
    Lives in Marple   Stockport, United Kingdom. Last Activity: 14 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 2,309. Received thanks 403 times, giving thanks to others 35 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    Quote Originally Posted by Davek0974 View Post
    Should it be possible to measure the 0-10v signal?

    I thought so, but I tried measuring the input to the VFD from the BOB and as soon i touched the VI & ACOM pins in the VFD the motor stopped as if the input was being shorted out?

    This was with an expensive Fluke DMM on DC volts, i was expecting to see something 0 and 10v here??

    Odd?
    Was it on auto ranging !! could be capacitance !!
    ..Clive
    The more you know, The better you know, How little you know

  6. #6
    Yes autorange but only Volts DC, it has no capacity ranges - too basic.

  7. #7
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 13 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    Quote Originally Posted by Davek0974 View Post
    Should it be possible to measure the 0-10v signal?
    Disconnect the VFD and measure it.
    Gerry
    ______________________________________________
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  8. #8
    will try that tomorrow, thanks

  9. #9
    What you using for Speed control Dave.? On-board Bob or separate board.?

  10. #10
    Its a cnc4you CP 0-10v breakout board with on-board converter.

    I fired the question at cnc4you and just got a reply - yes i should be able to measure 0-10v there, so i have no idea why i cannot.

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