Joining Two Circuits

[ergs]

Hi,I'm new here. I'm looking to connect a robot(one of those big 6 axis robotic arms) and a machine (a plastic injection moulder) together. This should be very easy, but I am struggling. Both are 24v DC.

I really thought if I connected a single wire from the 24v of the machine to the neutral of the robot using a single wire I would get a 24v reading on the multimeter. This was not the case. Do I need two wires to make a loop? Do I need relays or contacts thrown in there for isolation? Any help on the best practice to wire this would be greatly, greatly appreciated. I check every hour or so I'm awake so any further clarification will be responded to immediately. Thank again.

 

[MacGyverS2000]

A practicing EE that doesn't grasp the concept of a basic electrical loop?

!Aye, dios mio!

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ergs]

Yeah I definitely deserve that. I'm actually a mechanical engineer but by some cruel twist of fate I got employed in a role that's primarily electrical. No complaints though, I enjoy it, but I obviously have a steep learning curve. I was hoping that the 0v of the robot and the machine would be connected somewhere in the mains, creating said loop.

Alright so I need two wires. I'm guessing one for the 24v signal coming from the loop with the limit switch, and another connecting the neutrals of the two circuits. Is this correct?

 

[MikeHalloran]

You probably need an isolated current loop so the machines can pass a one-bit signal, or two loops so they can pass data.

Do not try to connect their power supplies or control circuits to each other in any direct way. Machine tools often have control circuits that are not grounded in the usual way, and simple direct connections can burn out expensive pieces of one or both.

Example: A friend of mine burned out a milling machine's motherboard simply by connecting its printer output to a printer that was plugged into the wall, not to the orange ungrounded receptacle that was provided on the machine for the sole purpose of powering an attached printer.

I.e., stop, and RTFM. Again.



Mike Halloran
Pembroke Pines, FL, USA

 

[ergs]

Thanks heaps Mike. Sounds like I need a single isolated current loop. That gives me something to google, an extremely good start.

I just need to be able to mimic the switch within a program from the robots plc, which is a 24v on or off.

If a machine is not grounded in the usual way, does that mean there would be a voltage differential between the two grounds and when they are connected together directly a large current would flow. Is that kind of what destroyed your friend's motherboard? I always just thought ground is always 0v.

 

[MikeHalloran]

In my friend's case, the milling machine's motherboard was connected between two phases of a three phase supply, so it's 'ground' was nowhere near 0V, and was actually alternating to boot.

I forgot to mention that the incident also killed the printer, but that was a minor expense.

The orange receptacle would have been a clue to an electrician, but my friend is a machinist.

That was an extreme case, but in general, for high powered machines, 'ground' is never actually 0 volts.

In your case, yes you need some kind of isolated link, and in general any connection to a machine tool should be isolated, just because of the expense and delay involved in getting even minor problems fixed.

One other option, if both machines are connected to a network, is to establish a logical connection between them over the network, which should require no additional hardware.

I used to recommend a company called Black Box, now at blackbox.com, as a source of special cables, isolators, converters, and such, but their product line has become so extensive that it may take you a year of study just to figure out which kind of stuff applies to your problem. Have you got access to an EE or controls guy who can help you in person?





Mike Halloran
Pembroke Pines, FL, USA

 

[ergs]

I understand how connecting it to 3 phase would cause a major issue.

On high powered machines ground is never actually 0 volts. Why is that?

I don't have a real EE that can come in and have a look in person, but I have a store room with pretty much every type of relay, contactor, converters and a whole bunch of other things that I don't really know what they are. I'm sure there will be something in there to do the job. I've spent the time since your first reply reading up on isolating current and I'm slowly starting to get the idea. Thanks again. I'm sure you get told this a lot but by taking a few minutes to explain this simple concept to me you've really helped out.