The environment of an industrial site can be complex and constantly changing. Engineers often encounter mixed and chaotic signals that are difficult to interpret. It can be challenging to trace the source of the signal due to various ground connections. Is the correct connection identified?

The CAN bus is widely used in the industrial and automotive industries due to its high reliability, real-time capabilities, flexibility, and rigorous data processing mechanism. However, as the number of nodes increases and environmental interference becomes more prevalent, the stability of the CAN bus is put under higher demands. This raises questions about how to deal with different grounding methods, including power supply ground, signal ground, shielding ground, and enclosure ground.

Figure 1 shows the common symbols for the four types of ground: power ground, signal ground, shield ground, and earth ground.

Fig. 1 Four Grounding Symbols

Power Ground (GND)

1、Power Ground Concept

The power supply ground, also known as GND, ensures that the power supply forms a complete current loop.

2、Power Ground Handling

Connect to the negative terminal of the single power supply.

Fig. 2 CAN Transceiver Power Ground (GND) Wiring

Signal Ground (CAN-GND)

1. The Concept of Signal Ground

Signal ground, also known as isolated ground, is used to create a unified reference potential for electronic equipment. This helps to avoid interference from harmful electromagnetic fields and ensures stable and reliable equipment operation. The signal circuits within the equipment share a common reference ground, known as CAN-GND.

2. Signal Ground Processing

In practical applications, designers often connect the reference ground of each node directly to the local earth as the signal's return ground. While this may seem like a normal and reliable practice, it can pose significant hidden dangers.

The correct connection of the signal ground (CAN-GND) is divided into two main types:

Single Shield Cable: If the cable is a single shield, it is best to connect the signal ground using a special signal cable that connects all nodes to the signal ground, which serves as a reference ground. However, if there is a lack of signal ground, all nodes can also be connected to the signal ground shield, but the shielding effect may be unsatisfactory.

Fig. 3 Twisted pair with shield

Fig. 4 Twisted pair connection with signal earth wire

Fig. 5 Signal Ground and Shield Connection

Double Shielded Cable: When using double shielded cable, connect all node signal ground to the inner shield. When using double shielded cable, connect all node signal ground to the inner shield. When using double shielded cable, connect all node signal ground to the inner shield. If using unshielded cable for data transmission, keep the signal ground pin suspended.

Fig. 6 Double Shield Signal Ground Handling

Once all node signal grounds have been connected to the inner layer of the shield or double shield, ensure that the shield is grounded at a single point rather than multiple points. This will prevent the formation of ground loop currents on the signal ground.

Additionally, to enhance isolation resistance between the power supply ground and signal ground and prevent electromagnetic interference caused by coupling in the common ground impedance circuit, it is important to implement single-point grounding. It is also recommended to use isolation floating ground design and isolate the shielding layer and shell through capacitance-resistant means. Consistency in the use of terminology and units is crucial for clarity and coherence.

Fig. 7 Electromagnetic Interference for messages Without Single Point Grounding Processing

Shielded Ground (CAN-Shield)

1. The Concept of Shielded Ground

Shielded ground (CAN-Shield) can also be referred to as CAN shield. In some cases, it may also be marked as FG. The conductor outside the wrapped wire is called the shielded wire, while the wrapped conductor is called the shield. The shield is generally made of woven copper mesh or copper (aluminium), and it needs to be grounded to ensure that external interference signals can be introduced into the earth by the layer.   

Figure 8 Single-and Double-Shielded Cable Profiling

2. Shielded Ground Handling

When using a double shielded cable, connect the CAN-Shield to the outer shield and the shielding shell of the DB9 connector. Additionally, when using DB9 pin connectors, connect the outer shield to pin 5 to ensure reliable grounding when using connectors without a shield connection.

Multi-node buses require a single-point ground for the shield to prevent loops and are designed for floating ground.

Figure 9 shows the processing. CTM1051 module pin 3 is the shield ground and pin 5 is the signal ground.

Figure 9 Signal Ground, Shield Ground Handling in Double-Shielded Layer Lines

Shell Ground

1. Shell Ground Concept

Static electricity is the accumulation of electric charge on the surface of an object. When it encounters a circuit, it can form an electric current. In dry environments, the voltage generated can be very high. To prevent damage to electronics, the enclosure ground is used to quickly release the charge to earth.

2、Shell Ground Processing

Shell grounding serves two purposes: protecting human safety and preventing interference. The metal shell provides excellent shielding, blocking the majority of radiation interference. Ground isolation technology is used to address interference introduced through the ground, also known as common resistance to interference. This involves adding impedance to the enclosure grounding and implementing filtering.

Figure 10 Recommended Circuit for Signal Ground, Shield Ground, and Enclosure Ground Connection

3. Suggestions for improvement of the programme

If you have experienced occasional communication errors or data loss while debugging with the CAN bus, or if you have been using the bus normally and suddenly experienced widespread errors or node damage.

If you are currently using a basic CAN transceiver, please switch to an isolated CAN transceiver. ZLG Zhiyuan's CTM isolation module includes an isolated DC-DC converter, signal isolation circuits, CAN bus transceiver circuits, and basic bus protection.

Isolation transceivers can isolate the bus and control circuitry, preventing high voltage from reaching the control system. This ensures the safety of operators and the system. Additionally, isolation suppresses common mode interference caused by ground potential difference and ground loop, allowing uninterrupted and error-free operation of the bus even in the presence of serious interference and other system-level noise.