PncConf Open Loop test- very low analog output

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17 Sep 2016 19:40 #80535 by B.Reilly01
So I've gotten as far as open loop test, and at first I didn't think I was moving at all. Then I reached down and felt my ballscrew barely turning. Got out the multimeter and measured analog output. 25mV! upped the DAC to 10, same 25mV. It's responding to on/off commands (when jog isn't pressed there's no signal) but clearly I'm not getting the output I expected. I changed values in every field I could think of in pncconf, but didn't get a noticeable change in output. HALSCOPE says I'm getting the commanded value. Clearly I'm missing something. I'd appreciate any and all help. Unfortunately, I'm new not just to LinuxCNC, but to Linux in general, so I'm a bit crippled in general.

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17 Sep 2016 20:37 #80538 by PCW
What is the output scale? that is the output voltage should be 10V*analog_out/output_scale

Also I would make sure you have electrical connections correct (try the 7I77 without any connected load)
The reason I say this is that we have had people swap AOUT and GND pins to reverse the driver direction.
This is not a good thing with single ended input servo drives as it ends up shorting the 7I77s AOUT to ground
The following user(s) said Thank You: B.Reilly01

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17 Sep 2016 21:28 #80545 by B.Reilly01
Holy crap. I thought I had non-single ended drive, your post caused me to look again, and the diagram I have for my Hurco drives clearly shows it as single ended, but the colors on the diagram don't match the wires I have, so I guess I just figured it was a differential, not a signal and gnd. I switched them, and I clearly was sending AOUT to ground. Everything works as it should now. Thank you. I'm very glad MESA made their cards at least somewhat idiot-proof, I know many other ways I could have let the smoke out of a chip.

I'm going to owe a lot of people pints by the time I've got this thing running. I only hope I can be helpful to others at some point.

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