CB Radio problem with Master/Slave Comm.

[Ken Talley]

Hello all,

After almost a year of work, I have actually had the machine work.  It consists of two TM100MD+ in a master/slave config.  All works well with one MINOR problem.   The system is on a Peterbilt truck.  When I use the CB Radio it shuts the system down while I am talking.  This is not good because the system controls a road oil spreading apparatus on the back of the truck.  Therefore when I am spreading and talk on the CB it shuts the unit off then on again and leaves a blank spot in the road.  This is not good.  I do not have the luxury of just not talking on the radio.  I am currently using and foil wrapped and wire braided shielded cable for communication and power from the slave to the master PLC.  Any ideas?

Thanks,
Ken

[support]

Do you mean that during the period when you are talking on the CB radio, the PLC(s) shut down? Are you able to figure out which PLC is affected (Master or Slave) or is it because of RS485 communication being affected? Knowing which part of your system has been affected can help you identify the cause.

If it affects either one of the PLCs, then most likely the noise come from the power supply. Is your CB radio drawing large current from the 12V supply? Can you consider using a separate battery for the the PLCs so that it is not affected by the truck's power supply fluctuation?

If it is RS485 communication being affected, then you may like to add biasing resistors to the RS485 network to put it in a known state and make it less suspectible to RF noise when none of the PLC is communicating.