Mesa 7i95t connection to Thermal Dynamics 60i

Hi,

I'm converting a Crossfire Pro to LinuxCNC using a Mesa 7i95t and THCAD2.  I have the automation interface card in the cutmaster 60i so it has the torch start/stop, voltage divider, ok to move, and ohmic sensing on the CPC connector.  I'm still waiting for the THCAD2 to come in but the wiring for it seems pretty straight forward.  I've attached the wiring diagram from the service manual and I'm not quite sure if I can just wire the start/stop directly to a 7i95t output or if I need to use a relay.  If I understand the qtplasmac docs I should be able to connect the ok to move directly to an input but may need a resistor if the current draw isn't enough.  I may hook up ohmic later but would I need another THCAD2 for it as well?

Thanks,

Kevin

You don't need a relay as your card has 2 amp relays built in to the high current outputs, Use one for the torch on. Adding a relay would just add an additional failure point and add some lag into the signal.
I think your plasma has the same divider as the TD  A120 I had. In which case, use a 30:1 divider without any scaling resistors on the THCAD's 10 volt scale. If you do have a 20:1 divider (I didn't)  you could use that. set the frequency divider to 1/32 and scale the sticker frequency by the same amount when configuring qtplasmac
You do need to use a pull down resistor on the ArcOK input which is discussed in the QTP manual.

Hi Rodw,

My automation card divider is 50:1 by default but can be set to 80:1, 40:1, 30:1, 20:1, and 16.7:1. Would you still suggest the 20:1 or would the default 50:1 work just as well?

50:1 would be OK with with thcad 5 volt scale.
on 10v scale, Use 20:1 which is 200 volt full scale. That will be more accurate. It will probably go off that scale briefly when piercing but  it won't matter as we don't care about the voltage until it settles back to cut voltage of about 130 volts. The THCAD can handle the over voltage.

Is it still recommended to mount the THCAD on the outside of the plasma power unit when the power unit has a voltage divider? I was thinking it wouldn't make much difference since the start and ok to move are coming directly into the electronics box.