Questions about 7i76e External Connections

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17 Nov 2022 22:21 - 17 Nov 2022 22:28 #256972 by dlv
I have a few questions as I'm about to start hooking up my machine to the Plasma cutter I'm going to be using (Primeweld Cut60).   It is a blowback start but still I want to have the best EMI resistance I can.

I must apologize somewhat.  This subject gets covered a lot and I've seen a lot of guidance on the topic but I want to be sure I'm going in the right direction on some specifics.

I should point out *everything* external to my control box (which is metal and grounded) in my wiring is shielded with shields star grounded at the control box to earth.  Even some of my wiring in the box is shielded. 

I've read Tommy's excellent "complete guide" and one thing I picked up there is to use relays to isolate *all* input and output going to the table.  Even home/limit switches.  I bought a bunch of DIN rail SS relays for this purpose.  (and one physical relay for the ohmic probe supply)

Focusing on external connections to/from my control box and the table & plasma cutter, here's some questions;

1)  I came up with the attached diagram to illustrate my understanding of Tommy's guide and I'd like feedback if that looks like I'm going in the right direction.   Also attached a spreadsheet to track how many relays I need.   Any feedback?

2)  Wondering about using a single shielded multi-core cable to connect to the CNC port on the Primeweld.   Is it ok to run those signals, including the divided voltage back through the same multi-core cable or should I run a separate shielded cable for the divided arc voltage?

3) Last question (for now) is about Arc OK. Do I need it if I'm using a THCAD? The Primeweld has the signal. I think it's just a reed switch or a relay that closes when the arc is established. Is it better to rely on the divided arc voltage going to the THCAD for Arc OK?

Cheers and thanks!

-Dave
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Last edit: 17 Nov 2022 22:28 by dlv.

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17 Nov 2022 22:31 #256974 by rodw
I don't think its necessary to use the relays given you have a non HF blowback start. I never have used relays as you propose. The fewer failure points the better in my book!
If the machine has an ArcOK, then I strongly suggest you use it so you don't get an arcOK signalled when its not actually the case. This can cause grief.

There should be no reason to run more than one single cable to your control box to the CNC port. Keep the THCAD in your control box. the single shielded cable is fine.
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17 Nov 2022 22:56 #256977 by tommylight
I agree with ROD, if you are sure the plasma is a blowback type.
No, it does not matter what it says in the papers if it is china made, they just slap stuff at random on everything.
As for drawings, the input on one of the drawings is wrong, no use from using a relay and wiring input and output pins together, they are used for isolation, that implies having their own power supply.
--
P.A.
Relays on the inputs are used for isolation from interference, but also do not allow starting a homing procedure if there is no power going to sensors or any of the sensors failed or signal lines are cut.
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18 Nov 2022 10:24 - 18 Nov 2022 10:53 #257023 by Clive S
Just for clarity for others:
@Dave.. It is a blowback start
.
@Rod.. given you have a non HF blowback start
.
@Tom.. sure the plasma is a blowback type.
Last edit: 18 Nov 2022 10:53 by Clive S.
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18 Nov 2022 15:18 #257042 by dlv
Thanks all.

Tommy good catch, using field power from the 7i76 to power the limit switches is not really isolating.  If I did go with relays on inputs, I'd need to use another isolated power supply to truly have isolation for those limit switch connections.  Might also need to replace the non-isolated 5v supply with an isolated power supply as well.

That said I do feel better about going forward without using relays in this manner given the guidance you guys have provided and the fact many of you do not use them with a non-HF blowback start machine.  I do know the Primeweld machine is non-HF blowback start and I've been very particular about shielding and grounding so I'll leave my wiring as is with direct connections. 

As an aside here I am compelled to put a plug in for Primeweld.   In the course of researching connections I've run across some forum threads about a few folks with Primeweld Cut60 machines having some issues with the CNC port.  Possibly limited to a particular brand of table but Primeweld has made modifications to the design to reduce EMI and stabilize the DIV voltage in response.   I bought mine a year ago and from my serial number I found it's a a gen prior to the latest.  

So not even knowing yet if I have any issues with that I contacted Primeweld to ask about the changes they made.  Without even blinking they shipped out a brand new machine to replace mine free of charge!   So if anyone with a Primeweld on this forum stumbles across this, don't hesitate to reach out to them.  They're truly top shelf when it comes to customer service.
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