RS Logix 500 comms problem

Hi

I have a ML1000 plc. My laptop has no serial comms port. I use a Moxa USB to serial converter. Sometimes it works fine and sometimes not. At the moment I go online with the plc and when the motors on the machine starts the comms to the plc fails. Can any body help ?

Thank.

get a laptop with a serial port.

or use a qualified usb to serial converter

Aftech said:

Hi

I have a ML1000 plc. My laptop has no serial comms port. I use a Moxa USB to serial converter. Sometimes it works fine and sometimes not. At the moment I go online with the plc and when the motors on the machine starts the comms to the plc fails. Can any body help ?

Thank.

Click to expand...

Definetely a noise issue.
Shielding will help but you could separate the comms cables from the rest of the wiring for a quick fix.

On the Micro Logix 1000there is an earth terminal do you have a large size earth wire connecting it to a good solid earth, earth bar

The motors coming on should not create enough noise in the right frequency to interfere with comms yes they create noise but its rare to have that noise interfere with the Comms I would check all grounding to the motors. Make sure your using a single ground point and not creating ground loops. Also just as a cautionary check for harmonic triplens. The normal hertz frequency noise generated from most motors shouldn't interfere with the megahertz range on a comm signal. So I highly suspect you may have a harmonic related problem. Either that or your USB converter has very poor noise filtering. I would check all neutral and ground bonds make sure all connections are secure. Phase to phase imbalances are an indictation of a harmonic issue though 9 times out of 10 its a high resistance connection thats easily corrected by clenaing the wires and studs and re terminating. If your motors are generating enough noise to interfere with your Comms then its a highly good chance they are causing other problems with nearby equipment and signals on other machines in the area.

Forgot to add one other remote possibility as we do not have a complete list of components involved or a wiring diagram. Its also possible that the current draw to the motors is pulling available current from your system comms though this is highly unlikely it is a remote possibility again eliminating high resistance points will help correct this.