Mach3 VFD PWM signal...

[Clive S]

I think he meant a proctoscope

I think you meant a endoscope

[cropwell]

I think you meant a endoscope

No I meant a proctoscope ! Happy Easter Clive..


Serious suggestion now - If you have an analogue meter these can have impedances as low as 5000 ohms per volt. All electrical measuring devices draw current from the circuit and this affects the circuit (experts can get precious here, but I am simplifying !). Having said that, I would not expect the BoB to be such a high impedance source as to have a drastic voltage drop when meter is put on it.

As Jazz says, it could be a dodgy Bob. I have never met a Dodgy Bob, but I do know a bloke called Dodgy Dave.

[Clive S]

Yep happy Easter Rob I was just jesting Avo 7 days and valve volt meters.

[Davek0974]

LOL:)

Anyways, I disconnected the BOB from the VFD and I can get sensible measurements from 0 - 10v so it seems the BOB is fine, the output is not linear though.

When connected to the VFD, no voltage again and the motor stops as soon as the meter is connected.

Very odd.

I did make a lookup table of speeds so I can easily set what i really want even though its not what it displays.

[routercnc]

If you only use a few speeds to cover your jobs I wonder if a relay module board with each relay connected to a trim pot and resistor pair from a 10v supply (each of which was fine tuned to give the right volts for that speed) could be used?
I guess you would need a gcode command in the code to switch the right relay on instead of the speed command. Just a different take on it.

[Davek0974]

I have done a similar thing at work with an awkward interface for a temperature controller - works well.
It used a 10 channel bargraph chip to take a 0-10v signal and convert to 10 adjustable resistance outputs using 10 miniature relays and 10 trim-pots - the relays were needed to give isolation.

trouble with using Mach it would need multiple outputs to do it directly and thats not so easy.

The bargraph / relay / pot system would work though - it just converts 0-10v variable into 0-10v stepped signals.

I think the lookup table will work for now until a proper fix comes up.

I see we have 15 spindle pulleys - could they be set up to do this?
I'm not sure the ratio does anything when using PWM though.

[Doddy]

Having just come in from the shed doing very much the same thing:

BOBs, or cheap ones at least, may not have a linear output from the PWM drive. I had very much the same experience as the OP.

You absolutely should be able to measure the voltage at the VFD with a DVM/DMM/etc. If you can't, then I'd look for possible dry-joints (as you prod the terminals with the meter leads it may crack the joint open). Try prodding each terminal in turn with a single lead to rule out mechanical play. Other than that - hand-held or bench meter? (I'm wondering if a bench meter if you've got a grounded common line... unlikely, but I can't think of any explanation why, having confirmed not on current-input on meter, why you couldn't read the voltage at the analogue input to the VFD).

What I can recommend as a very cheap alternative solution is one of the 2-pin USB/RS485 adapters (I picked up 3 for less than a tenner, UK) - use one to control the spindle (direction, speed, on/off) digitally, using the Mach3 plugin. (assuming HuanYang VFD).

Or, google mach3 linearity.dat