Fixing Schneider TM238LFDC24DT CANopen Failures and ATV312 Node Loss

In modern industrial automation, integrating programmable logic controllers (PLCs) with variable frequency drives (VFDs) via CANopen streamlines machine architecture. Connecting a Schneider Electric Modicon TM238LFDC24DT PLC to an Altivar ATV312 drive eliminates costly discrete wiring. However, field technicians often encounter node dropouts and communication loss during commissioning. Powergear X Automation provides this practical engineering guide to solve CANopen network instability, focusing on bus termination and physical layer issues.

The Critical Role of 120-Ohm Termination Resistors in CAN Physics

According to the ISO 11898 standard, CANopen networks require a 120-ohm termination resistor at each physical end. The CAN bus uses differential voltage signals across CAN_H and CAN_L lines. Omitting termination resistors causes signal reflections at the line ends. As a result, signal noise distorts frame structures, triggering frequent Process Data Object (PDO) timeouts. B2B engineers must verify that the total bus resistance measures approximately 60 ohms when powered down.

Matching Software Configuration with ATV312 Drive Parameters

Establishing physical connectivity alone does not guarantee drive operation. Schneider SoMachine or EcoStruxure Machine Expert software requires precise slave node configuration. Moreover, engineers must update internal ATV312 drive parameters to grant control access to the CANopen card. For instance, setting command channel (CMD) and frequency reference (FR1) to CANopen remains essential. Otherwise, the PLC may read drive status without being able to start the motor.

Mitigating Noise Interference Across Long Cable Runs

High-power switching from VFD pulse-width modulation (PWM) introduces severe electromagnetic noise into nearby signal lines. Industrial field reports show that unshielded cabling increases CAN error counters significantly. Therefore, installers must utilize dedicated shielded twisted-pair cables designed specifically for CAN networks. In addition, routing CAN communication wires parallel to high-voltage motor lines must be strictly avoided to maintain signal integrity.

Step-by-Step Commissioning Procedure for CANopen Communication

1. Inspect Physical Wiring: Verify correct polarity for CAN_H, CAN_L, and CAN_GND signal lines.
2. 저항 측정: Power off the network and measure resistance across CAN_H and CAN_L using a multimeter.
3. Verify Baud Rates: Ensure both the TM238 PLC master and ATV312 drive slaves use identical baud rates.
4. Assign Node IDs: Confirm each ATV312 drive possesses a unique CANopen Node ID on the network segment.
5. Set Control Channels: Configure drive parameters FR1 and CMD to prioritize CANopen control signals over local terminals.

Best Practices for Maintenance and Physical Cable Routing

Long-term network reliability requires careful physical Installation and adherence to grounding standards. Engineers should ground cable shielding at a single point according to system EMC guidelines. Furthermore, avoid placing excessive termination resistors on intermediate nodes. Installing more than two 120-ohm resistors overloads the bus transceiver, causing sudden network collapse. Maintaining a clear topology map simplifies future troubleshooting and system expansions.

B2B Procurement Guidelines for CANopen Components

When selecting control components for factory automation projects, buyers must evaluate hardware compatibility early. Modern distributed control systems (DCS) rely on standardized fieldbus protocols for seamless integration. Investing in certified CANopen cables, ruggedized connectors, and genuine communication modules reduces long-term maintenance costs. Additionally, purchasing properly tested hardware prevents unexpected line stoppages during high-volume production cycles.

Application Scenario: Packaging Machinery Conveyor Line

A bottling plant encountered intermittent “Node Lost” faults on three ATV312 drives controlled by a TM238LFDC24DT PLC. The conveyor line stopped randomly twice per shift, disrupting overall equipment effectiveness. During field inspection, engineers discovered that the installer left off the 120-ohm termination resistor at the farthest drive node.

The technical team installed a standard 120-ohm termination resistor at the end-of-line ATV312 terminal. Furthermore, they separated the CANopen communication cables from the main 400V motor power conduits. After checking that the total de-energized bus resistance dropped to 61.2 ohms, the system resumed operation. The conveyor system has operated for over six months without a single communication dropout.

To explore reliable industrial control systems, PLCs, and drive components for your production lines, visit 파워기어 X 자동화 for technical product support and procurement options.

자주 묻는 질문 (FAQ)

Q1: Can a short CANopen network function without 120-ohm termination resistors?
A short bench test might temporarily work without resistors due to low capacitance. However, production environments generate electromagnetic noise that causes immediate packet loss without proper termination.

Q2: What is the ideal multimeter resistance reading for a healthy CANopen bus?
With the system completely powered off, measuring resistance between CAN_H and CAN_L should yield approximately 60 ohms, representing two 120-ohm resistors in parallel.

Q3: Why does my ATV312 drive show “Operational” status in the PLC but refuse to run?
This issue occurs when drive parameters FR1 or CMD remain set to local terminals instead of CANopen. You must update the drive control source parameters via the keypad.