Grounding wires on table I/O

[bullethead67]

I am wiring up my limits to my Table I/O card from Candcnc and i am going to be using a high freq machine. The wire for the limits is shielded. I have the wire ran. Problem I have is There doesnt seem to be anywhere to connect the bare grounding wire. I am using 4 strand wire and have the unused 2 strands coupled withe the ground wire at one end in hopes of adding a little extra help against high freq.

Next issue. there are home connections but only one that is labeled limit. is the one labeled limit for the Z axis only. It appears to be in the Z axis area. do i just wire the limits to the home switches??

[Torchhead]

There are no "grounds" because the inputs are on an isolated supply. Grounding them to a table side connection will guarantee that noise from the plasma side will get into the system. There are all kinds of noise suppression built in the Table I/O. By keeping the switches isolated through opto isolators and using an isolated power source (no common ground any common mode noise is not conducted across. Shielding the switch wires adds little to the noise prevention especially if the shield is connected to anything on the table/plasma side of the setup.

Covered in the manual, the Limits are for a string of series connected NC switches. A limit is designed to do one thing only: Stop the machine when it's activated. It's a waste of valuable inputs to have 6 switches to 6 inputs that do the same thing

Only problem the Tablr I/O limits approach is that the Limits stop MACH, but if it's on a servo based machine, sending an e-stop to MACH only stops the pulses from MACH and turns off the output signals. A motor running away from a bad encoder or bad connection will send the axis screaming off on it's own with no signals from MACH. Either you need to let the power supply to the motors be controlled by MACH or you need to have the e-stop from the limits turn off the power and THAT shuts down MACH to preserve position.

You can get more product specific answers by posting on the CandCNCSupport Yahoo Forum. Having been through hundreds of installs with all kinds of plasma cutters we have a pretty good understanding of how to deal with noise and run with HF start machines. Right now I am dealing with helping two different users get their old ESAB units to work. Not only are they HF start but also HV (High voltage) so it tends to eat up any thing directly connected to the Raw Arc Volts (like the THC Sensor Card. We just released a new THC Sensor card (REV14) and it's got added suppression for both HF and HV start machines. We even added a spark gap across the input that will stop really high voltage. There are only a few machines that use the HV (Capacitor Discharge) start approach so the REV14 is not needed but it insures our DTHC will work with any plasma unit.

TOM Caudle
www.CandCNC.com

[bullethead67]

The manual says that homes are normally open and limits are normally closed. Am I reading it wrong? I was thinking it would be all normally closed wired in series and mach would determine if it was a home or limit depending on the direction of travel

[bullethead67]

ok I got it. all limits to the limit pin and separate homes.