On 9/29/2011 9:24 PM, Kirk Wallace wrote: > I'm trying to get my Shizuoka going after being idle during the Summer. > Some of the parts had "fallen" off. So, in putting it back together I > attended to an issue that bothered me from before. The SPI DAC I use to > feed the 0-10 V input to the spindle VFD wanders a bit and is enough to > notice the speed change at the spindle. I suspect the problem is that > the VFD and DAC have different supplies and grounds. I decided to try a > different approach and rigged up an opto-isolator which switches the 10V > speed supply to the 0-10V input. I feed the transmit side of the > opto-isolator with a PWM signal. I get much less wander, but after > adjusting the scale, I realized only the first 10% of the PWM range is > used to get 0 to 100% RPM (10V). I would like to have 100% pwm > correspond to 100% RPM or 10V input. I tried various resistors to limit > the input current or to pull the input down, but I still get the same > problem. > > Has anyone setup a PWM input to a VFD that utilizes the full PWM range? > If so, please let me know how it can be done. There is a 20mA input > also, but I don't know how it is supposed to work. I'll check the > manual, but hints would be appreciated. Otherwise, I my need to resort > to a digital potentiometer. Thanks for any help. > >
0-20 ma or 4-20 ma inputs are usually easy to setup in the drive. It is just a variation of an analog input. There is usually some provisions for scaling the analog inputs to the speed command, ie 4-20ma = 0-120 hz. The idea behind the 4-20 ma signal is that a wire break can be detected since 0 ma is an illegal value. There are converters commercially available to convert between 0-10 volts and 0-20 or 4-20 ma signals. I'm sure there are ways to do the conversion with an op amp and a few resistors also - setup a voltage controlled current regulator. If you have an unused analog out available on your servo board, it should not be difficult to setup. Dave ------------------------------------------------------------------------------ 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
