I disagree. Grounding won't fix what is inherently a bad design. Might make it appear less often if that indeed is the reason but it's still a bad design.
Way back in 1993, before Philips had even released the P82C250 CAN driver, I worked on a system that had about 12 nodes on CAN bus. Although the resistance between the CAN wires was 60 ohms with the properly terminated network the input impedance on the receivers relative to ground was still in the 10K ohm range. It was on a 30 ton fly wheel press that used a stepper motor to close the frame to hold the forming tools. When the press ran without any leadframes there were no issues. When leadframes were formed and trimmed occasionally a node would report enough errors to cause the entire machine to fault. Although the bus looked noisy from a single ended perspective the differential was clean. I then put the scope on the TTL side of the bus receiver circuitry and it was also very clean. Until the press hit a leadframe. Then very narrow pulses that were normally below the detection threshold appeared randomly on the other side. Turns out that the SloSyn stepper motor that closed the Tool Holder frame under load would deflect just enough to cause the constant current into the stepper windings to increase enough to prevent the motor from turning further. That extra bit of 18kHz electrical noise was coupled onto the CAN bus resulting in the occasional failed message. CAN works as follows. For each transmitted message that fails, a counter is incremented by 8. For each successful message the counter is decremented by 1. There's a warning at 96, and then a mode called Error Passive at 128 and finally if the errors continue the node goes bus off at 256. The bus off was causing the system to stop. Eventually a hardware solution involving a brake and disable of the stepper solved the problem but the interim period was handled with dual core ferrite cores at each point where the network entered a node. One loop of each side of the CAN bus through the core. Looking at the signals showed a remarkable rounding of the corners as this massive amount of inductance on the CAN bus caused considerable loss in high frequency response. But it was also enough to completely suppress the stepper motor chopping frequency and no more partially completed or damaged Pentium-66 processors which at $600 each or so was expensive. So as always, try and remove the source of the noise if you can find where it's coming from. Good grounding is a no brainer and of course needs to be done. But running a high speed edges, single ended from 0.4V to perhaps 12V into a load that draws at most 5uA is bad design when the driver is capable of driving 10mA or more. Not to say that the DC load may be brought down to 1K with an opto-isolator input while the impedance due to wiring might still be at 50K Ohm at the interfering frequency. Which is why other types of filtering like ferrite cores around the wire are also useful solutions. To lower that impedance and block the signals. Differential instead of single ended so common mode noise is cancelled out. But running that 12V signal through a 1K resistor into what is essentially a 2.4M ohm load won't stop noise from being picked up and transmitted through the 74HC4050. My two cents. John > -----Original Message----- > From: Chris Albertson [mailto:albertson.ch...@gmail.com] > Sent: October-08-21 4:52 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Fwd: Rogue Index Pulses > > I'll say what Gene said. I'd bet on a groubing issue. The schmatic has an > error, a groubd wire ismissing and also shows random crossing grounds. > Run everything back to the power supply minus post. > > Also you be much better if the sheild was grounded to the controller end. > Never us a machine and it's mounting bolts as grounds. > > > -- > > Chris Albertson > Redondo Beach, California > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
