Simple circuit with a PLC

I have done a rewire on a machine and need blocking relays as I am unable to change the original configuration. I have done one machine and used relays. I am not happy with the result. Is there an easier way to program this with a PLC. The drawing I posted is too small. So please follow this link
https://www.dropbox.com/sh/yqub1x9v9gu0ia2/GmcGzfbH1A

Still small? click on options right hand side lower corner of screen and click view original.
Thanks

Don't make sense man!

So in your diagram you are dropping the neutral to each relay and subsequent relays before the next one. You can accomplish the same thing in the PLC just understand everything in a PLC is done on the power rail side, not the neutral. So to replicate your first rung of K1 would have an XIO of K2 K3 and K4 in series. The second rung of K2 would have XIO of K3 and K4. K3 just K4, and K4 no XIO.

I do not understand Why you are breaking the neutral or Neg.
what is the order you need things to happen.
What do you mean by "Blocking"

I am also confused on why you would want to switch the Neutral or Ground side of the Relay coil. I have seen it done but hate the practice.

What it looks like to me is R1 can be activated if R2 and R3 and R4 are all not activated. R2 can be activated if R3 and R4 are not activated. R3 can be activated if R4 is not activated. R4 can be activated anytime regardless of the state of the other relays.

If so here is what I would do with some PLC logic to make that happen:
| C1 R2 R3 R4 R1
|-------||--|/|--|/|--|/|--------()--|
| C2 R3 R4 R2 |
|-------||--|/|--|/|-------------()--|
| C3 R4 R3 |
|-------||--|/|------------------()--|
| C4 R4 |
|-------||-----------------------()--|

You can use the XIO (true if off) of the R coils or the C contacts to make the logic work.

Edit: The diagram doesn't look right because the tags are off. For some reason the spaces are not posting like I want them too. Hope this doesn't mess you up too bad.

The output from the machine uses the same logic as used on VSD's x0 speed 1, x0 and x1 speed 2, x0 x1 x2 speed 3, x0 x1 x2 x3 x4 speed 4. So by breaking the neutral I am able to drop out the previous relay. I hope this makes sense, and no I can't use a VSD. But you guys have got me thinking about logic gates on the input side( and or nor etc)
thanks

PS hate breaking neutrals too

iant said:

I do not understand Why you are breaking the neutral or Neg.
what is the order you need things to happen.
What do you mean by "Blocking"

Click to expand...

It's quite common in old school relay logic to break neutrals...As you can see, to accomplish the same thing on the power rail, you would need a relay with multiple NC contacts (in the case of R4). By breaking the neutral leg, you only need a relay with one NC contact on each, thereby reducing hardware and wiring costs.

I have seen it before - FYI I started in this industry in 1976 learning
Relay logic very early.
But I didn't like switching neutrals then (might be Ok in control Panels)
But in the early days most control circuits here were 240 VAC.
the Neutral was bonded to earth -
If an earth fault occurred the neutral switch could fail.

Electronic control - NPN logic is different

iant said:

I have seen it before - FYI I started in this industry in 1976 learning
Relay logic very early.
But I didn't like switching neutrals then (might be Ok in control Panels)
But in the early days most control circuits here were 240 VAC.
the Neutral was bonded to earth -
If an earth fault occurred the neutral switch could fail.

Electronic control - NPN logic is different

Click to expand...

Huh? Who said anything about NPN logic? It's quite common to break neutrals still in control circuits. 120VAC neutrals are bonded to ground also...at least they should be at the control transformer. If you buy an MCC Centerline motor starter from AB they are still breaking the neutral to the starter contactor through the OL contact.

The OP said he was rewiring an original machine and the schematic he posted I assume was from the HARD rewire. His question posed how to do it in PLC. I don't think anyone is advocating breaking neutrals with a PLC, although many still do through relay output modules.

robertmee,


1.) Speed selection using relay for VSD ?

2.) what model VSD ?

3.) Present what source activate the relay ?