On Sat, 2011-10-01 at 12:14 +0100, andy pugh wrote: ... snip > I have an idea for a way to use a second opto to discharge the cap > through the same resistor during the low portion of the PWM, which > should be linear at all frequencies, but have never bothered trying > it.
After having more experience with getting my PWM to VFD input working, it comes to my mind that what is behind the VFD input is an ADC, which I think takes a snap shot (sample/hold) at a frequency. I seem to recall one VFD manual stating the sample frequency at something around 500 Hz, and others in the tens of kilohertz. This seems to indicate that the input will sample whatever voltage happens to be on the input at a given, but regular, instant in time. With raw PWM this is typically either 0 or 10 Volts. With filtered PWM, the voltage could be anywhere along the charge/discharge ramps. It seems with a push/pull on the input, it may actually make things worse by making the input more like raw PWM. If my thinking is correct, ideally each PWM cycle would be used as a data point to drive a stable voltage output for that particular cycle. Even then, it might be better to block a sample that happens right on a cycle change or filter only close to that point to smooth the change. Or, I could be completely wrong. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ All of the data generated in your IT infrastructure is seriously valuable. Why? It contains a definitive record of application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-d2dcopy2 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
