📋 Case Study

AGCO Fendt 1100 Vario — CAN Bus Interference Causing Intermittent SCR Deactivation

SCR disabled randomly during auto-steer operations; correlated with ISOBUS implement handshake activity

🏗️ Project Overview

Precision tillage contract in Brandenburg, Germany

🎯 Challenge

SCR disabled randomly during auto-steer operations; correlated with ISOBUS implement handshake activity

🔧 Design Approach

CAN bus topology audit → discovered unterminated stub > 0.3 m on J1939 backbone → installed 120Ω terminator + ferrite choke on display harness

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

Stub Reflection Delay

t_ref = 2 × L_stub × √(LC)

Result: 2.1 ns

Exceeds bit time at 250 kbps (4000 ns), causing edge jitter

Termination Power Dissipation

P = V² / R

Result: 0.25 W

Confirms 120Ω resistor rating adequacy

📊 Results

Zero SCR deactivations over 1,800 field hours; J1939 error frames reduced from 12/min to 0.1/min

💡 Lessons Learned

• •All CAN stubs > 0.1 m require impedance matching
• •J1939 and ISO11783 networks must be isolated with gateway filtering when sharing physical layer

✅ Key Takeaways

• 1All CAN stubs > 0.1 m require impedance matching
• 2J1939 and ISO11783 networks must be isolated with gateway filtering when sharing physical layer