Centroid Community CNC Support Forum

To start, i've read all the threads regarding EMI, proper shielding, grounding, snubbers, etc.

Im using a DYN4/Servo spindle.

When i have the DYN4 analog connected to Acorn's analog (shielded and grounded via drain) i get a strange 0.19V across the terminals. This wreaks havoc on the DYN4. This voltage is not linear. If i feed it 10V i get 10.1V, 5V i get 5.19V. Its a mess. Spindle bench test passes. Tried snubbers, ferrites, no change.

Heres where things get strange. If i unplug the analog, Acorn and DYN4 terminals show 0V on a volt meter. If i plug the analog cable (same cable) into a DC power supply, 0V, voltage offset goes away. I can FULLY control the DYN4 via DC power supply with no voltage anomalies. However, if i take another acorn board and plug the same cable into it, 2nd acorn is outside of the cabinet, not even powered up, but plugged in, voltage offset is back. If i unplug this board from the wall, offset goes away.

What the heck is happening here? Im loosing my mind.

The ground / COM is probably slightly different between DYN4 and ACORN. ACORN analog output is not isolated. Your DC power supply probably is. Disconnect the wires between ACORN and DYN4 and measure COM to COM. If it is not the same, the ground wiring needs work.

The analog output may also oscillate, which is not obvious without viewing on an oscilloscope. Measuring using the meter's AC scale may show voltage from oscillation. The AC reading should be 0. Here is a post about analog output oscillation: viewtopic.php?p=46032#p46032

I ended up redesigning my mill to eliminate the dmm as a spindle drive. I had issues with it faulting out after a stop command and creep after a stop command. Both were solved through plc programming changes...however I found my particular choice if servo and drive to be weak in torque and not sufficient for my application. I also was unable to get the dmm encoder to work with the acorn....never did solve that issue. I think the general consensus was try to avoid dmm as a spindle drive. As a servo I hear good things about them. All the best Sean

Are you using the recommended 18ga twisted pair (shielded) wire?

Have you installed the often noted 0.10 mfd capacitor across the analog terminals?

Also, I do not have the confidence in DMM products that Sean has. I have been burned by them in too many instances.

This could be either the DMM analog input stage being influenced by acorn or vice versa. Snubbers, etc are not going to solve that. As this is a (slow) analog signal and not a high-frequency changing signal. Another potential issue is that both suppliers are not on the same reference . In that case you get weird offsets between them which might not be fixed and can change due to other influences.

That is one of the reason why i like full digital such as you get with ethercat implementations.

eng199 wrote: ↑Wed May 15, 2024 8:41 am The ground / COM is probably slightly different between DYN4 and ACORN. ACORN analog output is not isolated. Your DC power supply probably is. Disconnect the wires between ACORN and DYN4 and measure COM to COM. If it is not the same, the ground wiring needs work.

The analog output may also oscillate, which is not obvious without viewing on an oscilloscope. Measuring using the meter's AC scale may show voltage from oscillation. The AC reading should be 0. Here is a post about analog output oscillation: viewtopic.php?p=46032#p46032

As measured:

DYN4 Analog common to Acorn Analog common, 0V
Across Acorn Analog terminals, with DYN4 connected, 0.19V (spindle off)
Acorn Analog common to Acorn H9 Ground, 0.02v
Acorn Analog VOUT to Acorn H9 Common, 0.19V
AC reading for acorn analog out is 0.

These values are all with a snubber in place. Removing snubber makes no difference.

SpacedmanSpiff wrote: ↑Wed May 15, 2024 9:01 am I ended up redesigning my mill to eliminate the dmm as a spindle drive. I had issues with it faulting out after a stop command and creep after a stop command. Both were solved through plc programming changes...however I found my particular choice if servo and drive to be weak in torque and not sufficient for my application. I also was unable to get the dmm encoder to work with the acorn....never did solve that issue. I think the general consensus was try to avoid dmm as a spindle drive. As a servo I hear good things about them. All the best Sean

So far the motor has been good. I can use the DMM software to tune the deadzone so the motor comes to a stop. Unfortunately this wont work with non-linear offsets which is what im experiencing. I completely understand your frustration with DMM, however their product works perfectly with a cheap lab power supply, in this case its not their fault.

spikee wrote: ↑Wed May 15, 2024 9:48 am This could be either the DMM analog input stage being influenced by acorn or vice versa. Snubbers, etc are not going to solve that. As this is a (slow) analog signal and not a high-frequency changing signal. Another potential issue is that both suppliers are not on the same reference . In that case you get weird offsets between them which might not be fixed and can change due to other influences.

That is one of the reason why i like full digital such as you get with ethercat implementations.

Could be. Doesnt look good in the case of Acorn. Centroid should be designing a product that is compatible with this sort of thing. If a cheap DC lab power supply can do better than the expensive acorn board then something is wrong.

I thought of the reference idea and tried grounding the DMM analog neg with no improvement. It seems as if the DYN4 is influencing the Acorn Analog OPAMP in some way i don't understand. Whatever it is it seems its not the best choice from a design standpoint. Ready to get flamed by Centroid employees but sorry not sorry, i shouldn't be having this problem and its going to make recommending this kit difficult.

Gary Campbell wrote: ↑Wed May 15, 2024 9:21 am Are you using the recommended 18ga twisted pair (shielded) wire?
Have you installed the often noted 0.10 mfd capacitor across the analog terminals?
Also, I do not have the confidence in DMM products that Sean has. I have been burned by them in too many instances.

As i mentioned i've read all the recommendations and propper practices. Shielded cables with twisted pairs, foil with drains grounded, snubbers, no difference. DMM product works well with DC power supply, problem is Acorn.

After all best practices have been employed (twisted pair shielded wire, proper grounds, bypass caps, etc.), you might want to look into a signal isolator:

https://www.amazon.com/Isolator-Insulat ... B09TJTCDQ8