On Thu, 2011-09-29 at 20:44 -0700, Karl Cunningham wrote: ... snip > The PWM output (duty cycle) is 0 to 1.0. Is it possible you're telling > it to go from 0 to 10, and by the time it reaches 10% of full scale it's > already at 1.0? The 10 volts is only between the opto and the VFD input, > nothing else needs to know about it. What about changing the scale.
Thanks for your reply Karl. I am using a Pluto-P to get the PWM, so I didn't have HALscope to check the actual PWM output. I had to drag out my real oscilloscope and attached it to the opto-isolator transmitter and verified that the PWM to the opto was about 10% with the VFD display indicating 100% RPM (60 Hz). It seems the input doesn't need much of a charge to keep it topped up. I tried a resistor in series with the input pin, but this just lowered the maximum signal rather than spreading it out on the PWM range. > On ours (PWM driving a 0-10V output, which feeds the VFD's 0-10V input) > we have the following in the ini file for a motor max speed of 2500 RPM. > > MAX_VELOCITY = 2500.0 > OUTPUT_SCALE = 2500.0 > OUTPUT_OFFSET = 0.0 > MAX_OUTPUT = 2500.0 I think I got this part sorted out. My maximum of 3700 RPM gives me 1.00 into the PWM generator. It's just that the real maximum RPM kicks in much earlier. I can make it look like it works by fiddling with the scale value, but then I get .04 going to the PWM generator at 3700 RPM. It works okay, in fact it took me a while to realize there was a problem, but then most of the available PWM resolution gets lost. I wish I knew what circuit is behind the VFD's 10V supply, input, and common control terminals. Then I might be able to figure out what it needs. The one example that I know that works properly is a potentiometer on the three terminals, so it seems to me that all three terminals are needed in some fashion. So far, I'm switching the high side to the input, which corresponds to having the pot turned fully up during the PWM high period. It may be that I need another opto to switch the input to the low side for the pot turned fully down, or PWM low. I would need an inverter chip to get PWMnot for the low side opto, and then I am worried about getting shoot through as the high side shuts down and the low side turns on. Another thing comes to mind, my serial DAC uses it's own voltage reference - I wonder if I should use the VFD 10V terminal instead. http://www.wallacecompany.com/machine_shop/EMC2/serial_dac/ (U2 on schematic) A digital potentiometer might be the easiest solution, but could potentially have it's own issues. Besides it's not like I am the first person to hook a PWM signal to a VFD. I must be missing something simple. PS, this VFD doesn't have Modbus or other communication port, or I would have used it already. :( -- 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
