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Author Topic: spindle load feedback to mach3  (Read 13084 times)

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Re: spindle load feedback to mach3
« Reply #30 on: July 19, 2013, 12:56:12 PM »
Putting a voltmeter on the VFD will tell you nothing of value.  You need to be looking at current, which means putting an ammeter *in series* with one phase of the motor.  The Tormach load meter is nothing but an analog ammeter.  An analog ammeter contains a shunt, which is a very small, precisely known resistance.  When current passes through it, it creates a small voltage drop (typically 50mV at maximum allowed current), and the meter itself is a very sensitive voltmeter, connected across the shunt, that reads full-scale with 50mV across it.  Look at digikey, mouser, and other electroincs supply houses, and find one with a suitable full-scale reading.  But, a good analog ammeter will not be cheap.  However, a digital meter, in this application, would be completely useless.


Putting a amp meter in series, or using a clamp on type with a VFD 3 phase output to the motor is useless. The VFD voltage is not a true sine wave and the frequency varies the motor speed. This will cause the amp meter to read incorrectly. All amp digital displays on VFD's are a calculated value corrected to 60 or 50Hz. The only way is use the 0-10V analog output or modbus. 
Re: spindle load feedback to mach3
« Reply #31 on: July 19, 2013, 01:44:04 PM »
Putting a amp meter in series, or using a clamp on type with a VFD 3 phase output to the motor is useless. The VFD voltage is not a true sine wave and the frequency varies the motor speed. This will cause the amp meter to read incorrectly. All amp digital displays on VFD's are a calculated value corrected to 60 or 50Hz. The only way is use the 0-10V analog output or modbus. 

An analog ammeter really doesn't much care what the waveform looks like, within reasonable limits, and they certainly don't care about the frequency, as it is FAR above the frequency the meter movement can react to - they'll still read a pretty good approximation of the RMS current.  And most modern VFDs will output something close to a sine wave anyway - after it gets filtered by the motor impedance.  Digital meters are pretty much useless with a VFD, whether you're looking at voltage or current.

Regards,
Ray L.
Regards,
Ray L.
Re: spindle load feedback to mach3
« Reply #32 on: July 19, 2013, 02:16:42 PM »
I'm a drives field service engineer and work on VFD's up to 5000 hp. AC drives today including cheap Chinese knock off use IGBT's in the power output sections. Clamp on amp meters on the motor t-leads will not give accurate readings. Drives setup in V/Hz mode as are most low cost drive used in CNC application (not vector mode) will output without a motor connected... motor impedance (xd') has very little effect on drive filtering. I could debate drive theroy with you but I think it would be beyond most of the forum readers. I've had a number of customers state their clamp on amp meters don't agree with the drive digital display...
Re: spindle load feedback to mach3
« Reply #33 on: July 19, 2013, 03:07:12 PM »
I'm a drives field service engineer and work on VFD's up to 5000 hp. AC drives today including cheap Chinese knock off use IGBT's in the power output sections. Clamp on amp meters on the motor t-leads will not give accurate readings. Drives setup in V/Hz mode as are most low cost drive used in CNC application (not vector mode) will output without a motor connected... motor impedance (xd') has very little effect on drive filtering. I could debate drive theroy with you but I think it would be beyond most of the forum readers. I've had a number of customers state their clamp on amp meters don't agree with the drive digital display...

I don't think anyone here mentioned clamp-on meters but you - When I say "analog ammeter" I'm talking about a true analog panel-mount ammeter, with a shunt and D'Arsonval meter movement.  Think 1930's technology.  Even most clamp-on meters these days will have digital internals - Hall Effect sensors feeding into a (probably sigma-delta) A/D converter, etc.

Regards,
Ray L.
Regards,
Ray L.

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Re: spindle load feedback to mach3
« Reply #34 on: July 19, 2013, 04:22:34 PM »
I will certainly be doing this when/if Brian ever gets his finger out his arse
What!!! - You mean he's typing one handed?  FM - that's gotta slow things down alright ;D

Ian

;D
Re: spindle load feedback to mach3
« Reply #35 on: July 19, 2013, 05:36:38 PM »
so do I or don't I use the analog output of the VFD to show motor load.  what wopuld be best would be if I can use teh 0-10V outputs on all teh drivers in my cabiunet including VFD to some input card that has a program on my compuer that shows all those load meters.   
Re: spindle load feedback to mach3
« Reply #36 on: October 23, 2017, 02:26:48 AM »