On Sat, 2011-11-05 at 14:09 +0200, Viesturs Lācis wrote: > 2011/11/5 Slavko Kocjancic <[email protected]>: > > Hello... > > > > I think the 1'st thing is to check what is wrong. Not to do something to > > eliminate problem but not know what problem it is. > > Yes, that is exactly my question - is there anything I can do to > diagnose the cause of problem?
My experience seems to indicate: _Always_ have a filter on VFD power inputs. They are not that expensive. Proximity of a VFD to sensitive parts doesn't really indicate much. If the hardware is not configured properly (and what is?), the VFD interference can travel through metal frames, conduit, unrelated wires, shielding, etcetera, and come out on the far side of the machine. Sometimes, beads on the output wires can help. Most stepper and servo drives are very similar to VFD's, so they may need power input filters, or output beads too. Most break-out-board inputs (and others) have very high impedance, therefore are very susceptible to induced fields on the input wiring, so even minor interference can show up at the input pin. Think of hitting something hard like a bell. It doesn't absorb or convert the energy very well so it rings until the energy gets converted to sound. Hitting dry sand converts the all of the energy instantly, so it is hard to drive a signal into it,let alone induce noise. I've found that plain buffer inputs have very high impedance and often need some some sort of filter (lowers impedance, adds sand) that matches the type of signal being read. Opto-isolated inputs seem to have more impedance, so are not as much of a problem. Switches and relays with real contacts go from very high impedance to very low, and bounce, so most likely need filtering. Most real machines (my opinion) use 12 Volts for control signals to help push the noise into the OFF voltage region. Others have more experience with this, but I have found that connecting a short piece of wire on my oscilloscope probe picks up interference. I can wave it around my machine and find the noisy spots. It seems some amount noise is inevitable and normal, so expect to need to deal with it, rather than eliminate it. I've heard an AM radio is also good for scanning for interference. I recently set up HALscope to trigger on a suspicious signal. After forcing a trigger on the scope to clear the traces, I sat and watched HALscope until it triggered, then preesed stop to keep the traces form getting written over. This indicated that this signal was on the edge of ON and OFF. A resistor in the line (current limit) and capacitor to ground (low impedance, sand, RC filter) cleared it up. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
