communication problems

[burri]

I'm not a expert on this fields , but I'm working in maintenace in a construction company and I'm having a problem in one plant of concrete.

The communication between the pcd and the computer is only possible with a laptop . when I'm using a normal desktop pc there are always a lot of communication problems.


The electricity comes from a diesel generator, the plc is conected to a ups , like the desktop pc. (both grounded)

I think maybe is some noise in the electricity or something like that , does anyone know something about that? how to solve the problem .

thank you in advance

 

[Skogsgurra]

There is a difference between the PC and the Laptop.

Even if both have grounded plugs (are you sure? Laptops often have that thin two-prong plug) the Laptop per se is not grounded (the power adapter is isolated) and the PC is connected to ground (chassis AND internal signal ground). That means that you will have currents flowing in your signal ground and those currents usually disturb the communication.

It sounds like you have a poorly defined ground system somewhere. Make sure (measurement, not inspection) that all your equipment is grounded.

If, after grounding everything, you still have problems, there are three ways out of this: Use galvanic isolation (transformer). Connect PC and PLC grounds with a heavy copper conductor. Use fiber optics or an optocoupler isolator.



Gunnar Englund

http://www.gke.org