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Troubleshooting Fieldbus Communication Loss with Miller Auto Deltaweld 350 (PolyScope 5)

Fix a lost Modbus TCP connection between your PolyScope 5 robot and the Miller Auto Deltaweld 350 power source — COMMUNICATION LOSS, welder not connected, weld program stops.

Written by Doug Ayers

This article is for robots running PolyScope 5. If your robot runs PolyScope X, see Troubleshooting Fieldbus Communication Loss with Miller Auto Deltaweld 350 (PolyScope X).

The Miller Auto Deltaweld 350 power source talks to the robot over a Modbus connection. When that connection drops, the teach pendant shows COMMUNICATION LOSS. This article will help you fix it.

What You'll See

  • COMMUNICATION LOSS on the teach pendant

  • Communication error between the welder and robot in the error details

  • The weld program stops

Teach pendant message reading COMMUNICATION LOSS, communication error between the welder and robot

Quick Fix

Restart the power source. This often brings the connection back.

If That Didn't Work

Check the Power Source's Ethernet Cable

Check that the Ethernet cable is plugged in firmly at the power source and at the port on the robot's cabinet. The power source comes with a screw-in Ethernet cable. Line up the pins, then screw the cable into place.

Screw-in Ethernet cable connected to the port on the robot cabinet

Check the Robot's USB-to-Ethernet Adapter

Inside the robot's cabinet, a USB-to-Ethernet adapter connects the cabinet's outside Ethernet port to the robot controller. Check that the Ethernet cable is plugged in firmly at the adapter. Check that the adapter is plugged in firmly at the robot controller.

The adapter's light should be solid or blinking. If the light is off, unplug the adapter from the USB port, then plug it back in.

USB-to-Ethernet adapter inside the robot cabinet

Check that Modbus TCP is Enabled

  1. On the teach pendant, open the menu, then tap Settings.
    ​

    PolyScope 5 menu with Settings

    ​

  2. Under the Security section, tap Services.
    ​

    PolyScope 5 Settings sidebar with Security expanded and Services selected

  3. Enter the admin password (default beaconbot), then tap Unlock. The Services interfaces list becomes active.
    ​

    PolyScope 5 Services Settings screen with the Admin Password field and Unlock button

  4. Enable Modbus TCP.
    ​

    PolyScope 5 Services Settings with Modbus TCP showing status Enabled

  5. If you enabled Modbus TCP, restart the robot so the change takes effect.

Check the Modbus Unit Setup

  1. On the teach pendant, tap Installation.
    ​

    PolyScope 5 toolbar with Installation

  2. Under the Fieldbus section, tap MODBUS.
    ​

    PolyScope 5 Installation sidebar with Fieldbus expanded and MODBUS selected

  3. There should be one MODBUS unit with one signal defined. Check its settings.

    1. The unit's IP address should be 192.168.181.151.

    2. The signal's Type should be Digital Input.

    3. The signal's Address should be 0.

    4. The signal's Name should be MODBUS_1.
      ​

    PolyScope 5 MODBUS client IO Setup with IP address 192.168.181.151, a green dot, Digital Input, address 0, and name MODBUS_1

  4. If you see other units, tap Delete Unit until only one unit remains.
    ​

    PolyScope 5 MODBUS client IO Setup with a second unit, MODBUS_2, and its Delete Unit button

  5. Look at the dot to the left of Type. A green dot means the robot and the power source are talking to each other. A gray dot means they are not.
    ​

  6. If the dot is gray, restart the power source. If it stays gray, check the robot's eth1 network settings.

Check that Fieldbus Profinet Device is Disabled

  1. On the teach pendant, tap Installation.
    ​

  2. Under the Fieldbus section, tap PROFINET.
    ​

  3. The Profinet IO Device should be disabled. If it reads Enabled, tap Disable.
    ​

  4. If you disabled the device, restart the robot so the change takes effect.
    ​

PolyScope 5 PROFINET screen with PROFINET IO Device reading Disabled

Check that Fieldbus EtherNet/IP Adapter is Disabled

  1. On the teach pendant, tap Installation.
    ​

  2. Under the Fieldbus section, tap EtherNet/IP.
    ​

  3. The EtherNet/IP Adapter should be disabled. If it reads Enabled, tap Disable.
    ​

  4. If you disabled the adapter, restart the robot so the change takes effect.
    ​

PolyScope 5 EtherNet/IP screen with EtherNet/IP Adapter reading Disabled

Check the Robot's eth0 and eth1 Network Settings

  1. On the teach pendant, tap Installation.
    ​

  2. Under the URCaps section, tap Beacon.
    ​

  3. You should see an eth0 and an eth1 setting, each with its own IP address.
    ​

    PolyScope 5 Beacon screen showing Online, eth1 at 192.168.181.149 for fieldbus and eth0 for internet

  4. If you don't see eth1, or eth1 is not set to 192.168.181.149, recreate the eth1 network interface.

To check or change the IP address on the power source itself, see How to Set the IP Address on the Miller Auto Deltaweld 350.

Still Need Help?

Tap the Support menu in Beacon to send us a message. It helps if you can share:

  • A photo of any error messages on the teach pendant or equipment

  • Your robot's serial number (printed on a label on the robot's base)

  • A photo of the MODBUS tab, showing the unit's IP address and the dot next to Type

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