Today, let’s discuss an important communication method in the field of industrial automation – Profibus FMS. Although this technology sounds very professional, it is not difficult to understand; it is like a “WeChat group” in a factory, allowing various devices to freely exchange information.
What is Profibus FMS?
Profibus FMS (Fieldbus Message Specification) is an industrial communication protocol primarily used for data exchange between PLCs, industrial computers, and other intelligent devices. To put it simply, if we compare the automation devices in a factory to team members, Profibus FMS is the “instant messaging tool” they use to communicate with each other.
Key Hardware Connections
To achieve Profibus FMS communication, the following key hardware is required:
- Profibus communication module (required for each PLC)
- Profibus dedicated cable (purple twisted pair, do not use ordinary network cables)
- Bus termination resistors (must be installed at both ends, with a resistance of 220Ω)
Wiring points:
- Termination resistors must be connected at both ends of the bus
- Do not use T-branch wiring
- The distance between each station should not exceed 100 meters
- The shielding layer must be properly grounded
Communication Parameter Configuration
When configuring Profibus FMS communication, the following basic parameters need to be set:
- Station address (0-125, must not be duplicated)
- Baud rate (commonly 9.6kbps to 12Mbps)
- Timeout (recommended to set to 1000ms)
For example, suppose there are 3 PLCs on site that need to communicate with each other:
Copy
Master PLC: Station No. 1, Baud Rate 187.5kbps
Slave 1: Station No. 2, Baud Rate 187.5kbps
Slave 2: Station No. 3, Baud Rate 187.5kbps
Data Exchange Methods
Profibus FMS supports various data exchange methods:
- Cyclic data exchange (similar to sending WeChat messages at regular intervals)
- Non-cyclic data exchange (similar to sending messages only when necessary)
- Broadcast communication (similar to sending group messages)
Common Issues and Solutions
- Communication interruption issues
- Check if the termination resistors are correctly installed
- Confirm that the communication rate settings are consistent
- Investigate if the cable is subject to interference
- Data anomaly issues
- Check if the station addresses are duplicated
- Verify if the data format matches
- Test if the communication distance exceeds limits
Practical Application Case
In a beverage production line, there are 3 PLCs controlling filling, labeling, and packaging. Through Profibus FMS communication, the following is achieved:
- The filling PLC notifies the labeling PLC upon completion
- The labeling PLC notifies the packaging PLC upon completion
- Each PLC exchanges equipment status information in real-time
Debugging experience sharing:
During a field debugging session, communication was frequently interrupted, initially thought to be a program issue. Later, it was discovered that the Profibus cable was laid parallel to the variable frequency drive power cable, causing interference. Switching to metal cable trays for separation resolved the issue.
Safety Precautions
- Communication cables must use dedicated Profibus cables
- Regularly back up communication parameter configurations
- Design should consider emergency handling for communication interruptions
- Do not plug or unplug communication modules while powered
Practical exercise suggestions:
Build a simple Profibus FMS communication system with 2 PLCs to achieve cyclic data exchange and broadcast communication functions. Use an oscilloscope to observe communication signals, deepening the understanding of protocol timing. Complete debugging in a laboratory or testing platform first, familiarizing with various fault phenomena and solutions.