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Question on index pulse
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washcomp
I notice that "index pulse" can be checked on the parallel input to
pick up the true speed of a machine. Can the PWM frequency of a VFD be used for this? If so, can it be scaled in MACH2 to correspnd to the speed (I believe speed is a linear function to frequency, but the numeric value of one will not be the same as the other. Jeff |
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Not enough precision for threading. Even if you could do a PWM to pulse
convertor it will not work. You will need a true encoder, home made or not. More, it will be simpler. For threading you don't only need the exact speed of the spindle, but his absolute position too with a good accuracy. Can only be done with an encoder with index + eventually other pulses for low or medium speed applications. Olivier. |
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washcomp
Olivier:
Actually, this question revolved around my Bridgeport mill. In this case I'd like to get "feedback" to MACH2 and to a readout of RPM, but I don't think the number is as critical as in a lathe. I just thought it made sense to use the pulses from the VFD to drive the readout. An error of a percent or two probably wouldn't matter for this application. It's just that the number of pulses would have to be able to be scaled to make the read out make sense in RPM. Is there a way to scale in MACH2 between the pulses and the RPM? Jeff --- In mach1mach2cnc@..., "Digital audio Pro" <digitalaudiopro@w...> wrote: Not enough precision for threading. Even if you could do a PWM topulse convertor it will not work. You will need a true encoder, home madeor not. More, it will be simpler.but his absolute position too with a good accuracy. Can only be done withan encoder with index + eventually other pulses for low or medium speedapplications.
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Art
Jeff:
there a way to scale in MACH2 between the pulses and the RPM?the read out make sense in RPM. Is YEs, Mach2 will scale the input automatically and display RPM. I believe even Mill can do this as long as the index or timing mark inputs are hooked up and activated. Have you hooked them up yet?? Thanks, Art www.artofcnc.ca ----- Original Message ----- From: "washcomp" <jeff@...> To: <mach1mach2cnc@...> Sent: Monday, March 01, 2004 10:32 AM Subject: [mach1mach2cnc] Re: Question on index pulse Olivier: |
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Andy Wander
Of course, VFD means Variable Frequency, so is this actually a PWM signal?
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I'm so confused... Andy Wander Verrex Corporation -----Original Message-----
From: washcomp [mailto:jeff@...] Sent: Monday, March 01, 2004 8:42 AM To: mach1mach2cnc@... Subject: [mach1mach2cnc] Question on index pulse I notice that "index pulse" can be checked on the parallel input to pick up the true speed of a machine. Can the PWM frequency of a VFD be used for this? If so, can it be scaled in MACH2 to correspnd to the speed (I believe speed is a linear function to frequency, but the numeric value of one will not be the same as the other. Jeff Yahoo! Groups Sponsor ADVERTISEMENT Click HereClick Here < /S=:HM/A=2019528/rand=446470174> _____ Yahoo! Groups Links * To visit your group on the web, go to: <> * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of <> Service. |
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washcomp
Unless I'm mistaken, (wouldn't be the first time), the way the
frequency variation manifests itself is by modulating the pulse width. Pulses shorter and closer together = higher frequency. Please correct me if I'm wrong. Jeff --- In mach1mach2cnc@..., Andy Wander <awander@v...> wrote: Of course, VFD means Variable Frequency, so is this actually a PWMsignal? I'm so confused...VFD be used for this? If so, can it be scaled in MACH2 to correspnd tothe numeric value of one will not be the same as the other.M=274551.4550177.5761904.1261774/D=egroupweb /S=:HM/A=2019528/rand=446470174>subject=Unsubscribe> of <> Service. |
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No, it is the same base frequency. The width of the pulse ( length of time
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it is high ) determines the energy it can deliver. 80% PWM = 80% of the time it high and 20% is low. Jim ----- Original Message -----
From: "washcomp" <jeff@...> To: <mach1mach2cnc@...> Sent: Monday, March 01, 2004 11:36 AM Subject: [mach1mach2cnc] Re: Question on index pulse Unless I'm mistaken, (wouldn't be the first time), the way the |
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Andy Wander
I can't speak about the intricacies of the VFD, but PWM is Pulse Width
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Modulation, where the ONLY thing that is varied is the width of the "ON" pulse(not both ON and OFF). This means that the frequency of the pulses does NOT change, just the ratio of ON-time to OFF time of a (quasi) square wave. If the width of both the ON and the OFF pulse changed(and was identical, you would NOT have PWM, you would have FM(frequency modulation) of a square wave. Andy Wander Verrex Corporation -----Original Message-----
From: washcomp [mailto:jeff@...] Sent: Monday, March 01, 2004 12:36 PM To: mach1mach2cnc@... Subject: [mach1mach2cnc] Re: Question on index pulse Unless I'm mistaken, (wouldn't be the first time), the way the frequency variation manifests itself is by modulating the pulse width. Pulses shorter and closer together = higher frequency. Please correct me if I'm wrong. Jeff --- In mach1mach2cnc@..., Andy Wander <awander@v...> wrote: Of course, VFD means Variable Frequency, so is this actually a PWMsignal? I'm so confused...VFD be used for this? If so, can it be scaled in MACH2 to correspnd tothe numeric value of one will not be the same as the other.M=274551.4550177.5761904.1261774/D=egroupweb /S=:HM/A=2019528/rand=446470174><> <<> > subject=Unsubscribe> of < <> >Service. _____ Yahoo! Groups Links * To visit your group on the web, go to: <> * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of <> Service. |
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Andy Wander
Of course, by changing the width of the ON pulkse, while the frequency stays
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the same, the width of the OFF pulse is changed also, in the opposite direction. For example a 50% PWM pulse train will look just like a square wave at that frequency, because the ON pulse will be 50" of the period, and so will the OFF pulse. A 20% PWM will have the ON time at 20" of the period, and the OFF at 80%. Etc.. Andy Wander Verrex Corporation -----Original Message-----
From: Andy Wander [mailto:awander@...] Sent: Monday, March 01, 2004 12:40 PM To: 'mach1mach2cnc@...' Subject: RE: [mach1mach2cnc] Re: Question on index pulse I can't speak about the intricacies of the VFD, but PWM is Pulse Width Modulation, where the ONLY thing that is varied is the width of the "ON" pulse(not both ON and OFF). This means that the frequency of the pulses does NOT change, just the ratio of ON-time to OFF time of a (quasi) square wave. If the width of both the ON and the OFF pulse changed(and was identical, you would NOT have PWM, you would have FM(frequency modulation) of a square wave. Andy Wander Verrex Corporation -----Original Message----- From: washcomp [mailto:jeff@...] Sent: Monday, March 01, 2004 12:36 PM To: mach1mach2cnc@... Subject: [mach1mach2cnc] Re: Question on index pulse Unless I'm mistaken, (wouldn't be the first time), the way the frequency variation manifests itself is by modulating the pulse width. Pulses shorter and closer together = higher frequency. Please correct me if I'm wrong. Jeff --- In mach1mach2cnc@..., Andy Wander <awander@v...> wrote: Of course, VFD means Variable Frequency, so is this actually a PWMsignal? I'm so confused...VFD be used for this? If so, can it be scaled in MACH2 to correspnd tothe numeric value of one will not be the same as the other.<> > M=274551.4550177.5761904.1261774/D=egroupweb /S=:HM/A=2019528/rand=446470174><> < <> > <<> < <> > > subject=Unsubscribe> of < <> <<> > > Service. _____ Yahoo! Groups Links * To visit your group on the web, go to: <> < <> > * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of < <> > Service. Yahoo! Groups Sponsor ADVERTISEMENT Click HereClick Here < /S=:HM/A=2019528/rand=704545992> _____ Yahoo! Groups Links * To visit your group on the web, go to: <> * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of <> Service. |
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Les Newell
A VFD creates an approximation of a sine wave by pulse width modulating a high frequency carrier. The carrier frequency is high enough that the motor effecively filters it out, leaving the sine wave. The frequency of the sine wave is varied to control the speed of the motor.
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This is not really much use to Mach2 as it is only the commanded speed to the motor. It does not mean the motor will actually turn at that speed. The best thing to do is fit a sensor on the spindle and have done with it. That way Mach2 always knows the true speed of the spindle. Les Andy Wander wrote: I can't speak about the intricacies of the VFD, but PWM is Pulse Width |
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Andy Wander
Les:
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Thanks for the explanation-what I still don't understand about it is how the "Sine Wave", which is generated by the "filtering" of the motor, will vary in frequency, if the only thing that is done to it is to change the PWM duty cycle. This would seem to me to get us to a "Sine wave" which has different values for it's Positive and Negative half-cycles, but I can't see how the frequency would change unless the frequency of the PWM changed. Andy Wander Verrex Corporation -----Original Message-----
From: Les Newell [mailto:les@...] Sent: Monday, March 01, 2004 12:54 PM To: mach1mach2cnc@... Subject: Re: [mach1mach2cnc] Re: Question on index pulse A VFD creates an approximation of a sine wave by pulse width modulating a high frequency carrier. The carrier frequency is high enough that the motor effecively filters it out, leaving the sine wave. The frequency of the sine wave is varied to control the speed of the motor. This is not really much use to Mach2 as it is only the commanded speed to the motor. It does not mean the motor will actually turn at that speed. The best thing to do is fit a sensor on the spindle and have done with it. That way Mach2 always knows the true speed of the spindle. Les Andy Wander wrote: I can't speak about the intricacies of the VFD, but PWM is Pulse Widthdoes NOT change, just the ratio of ON-time to OFF time of a (quasi) squarewave. you would NOT have PWM, you would have FM(frequency modulation) of a square Yahoo! Groups Sponsor ADVERTISEMENT Click HereClick Here < /S=:HM/A=2019528/rand=293473797> _____ Yahoo! Groups Links * To visit your group on the web, go to: <> * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of <> Service. |
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Les Newell
Hi Andy,
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If you average a steady state PWM signal (apply a low pass filter) you get a DC voltage. At 0% PWM you get 0V, at 50% PWM you get 1/2 voltage and at 100% PWM you get full voltage and so on. Now if you slowly change the pulse width your DC voltage will slowly change to follow it. A VFD changes the pulse width in a sinusoidal pattern and the motor inductance acts as the filter. As long as the PWM frequency is much higher than the sine wave frequency (say 10kHz or highter) all the motor will see is the sine wave. By varying the pattern the VFD can control the sine wave frequency and voltage. Les Andy Wander wrote: Les: |
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Art
Jeff:
pick up the true speed of a machine. Can the PWM frequency of a VFDnotice that "index pulse" can be checked on the parallel input to be used for this? If so, can it be scaled in MACH2 to correspnd No. This can only be gotten for a once per rotation pulse from the spindle sensor.. Art www.artofcnc.ca |
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Ed Gilbert
Hi Andy,
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Are you actually talking about the signals on the wires to the motor or about a PWM signal generated by the VFD to indicate the frequency it is running at? Mach2 uses the index pulse to determine RPM and is probably based a number of pulses per interrupt cycle. It may be based on the speeds you define in the pulley setup of the spindle. You would have to ask ART specifically. Best, Ed Gilbert Gilbert Engineered Systems 632 Warrenton-Embro Road Macon, NC 27551 252-257-0539 -----Original Message----- ------------------------------------- This message has been scanned for viruses and dangerous content by NCOL.NET, and is believed to be clean. |
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