On 09/30/2011 09:27 AM, Kirk Wallace wrote: [snip] > The only reason I was thinking about a push-pull (half bridge) is > because it would incorporate the common terminal. > > I haven't connected my oscilloscope to the VFD terminals yet, this may > shed some light on how the input works. I suspect for an SCR speed > controller, the input provides a voltage level for triggering the SCR, > but for a VFD it may be a PLL or "Maybe it's something really cool that > I don't even know about" (tree of trust).
Kirk, You might try a pull-down resistor between the analog input and common of the VFD. Is there an input resistance (impedance) spec on the VFD? Of you could put an op-amp voltage follower in between the opto and the VFD. You'd have to use a pull-down resistor on the input of the op-amp. Only trouble is if you don't have a -15V supply to run the op-amp, you have to use one that can drive to the negative rail and tie it's -Vps to ground. Karl ------------------------------------------------------------------------------ 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
