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Practical Communication Optimization of PLCs in Factory Information Systems

Last week, the newly installed automated production line in the workshop encountered issues right after it went into operation. The data collection was unstable, intermittently dropping, and the production reports were filled with missing data. The factory manager was furious and rushed to find me. Having repaired electrical equipment for over twenty years, I’ve seen this situation many times. The problem is actually due to improper PLC communication configuration. Now, let me explain to everyone, so that next time you encounter a similar issue, you won’t panic; just follow my advice and you won’t go wrong.

PLC communication is like the nervous system of a factory, responsible for connecting various devices and ensuring smooth data flow. Our factory has now implemented an MES system, requiring interconnectivity from top to bottom, making PLCs a critical data transfer station. If communication fails, it’s like a nerve blockage in a human, causing the entire system to collapse.

I remember one night shift when the injection molding workshop suddenly stopped production. After half a day of troubleshooting, we discovered it was due to a communication timeout. If I had understood these basic concepts, it could have been resolved in ten minutes, but we ended up struggling until dawn.

Choosing the right communication protocol is the first hurdle. The main protocols commonly used in our factory are Modbus, Profinet, and Ethernet/IP. Don’t be fooled by their fancy names; they are quite easy to understand. Modbus is like Mandarin, simple and widely accepted, with good device compatibility, suitable for basic data exchange; Profinet and Ethernet/IP are like dialects, offering high transmission efficiency and richer functionalities within their own circles.

Recently, Old Wang was responsible for the packaging line, which connected over 20 frequency converters using Modbus serial communication, but the data updates were always lagging. When I looked at his program:

// Old Wang's communication code

READ_VAR(#Slave_addr:=1, #DB_addr:=3001, #Len:=10...);

READ_VAR(#Slave_addr:=2, #DB_addr:=3001, #Len:=10...);

READ_VAR(#Slave_addr:=3, #DB_addr:=3001, #Len:=10...);

// There are a dozen similar instructions following

This is a typical polling method, asking each device one by one, which is definitely slow. I suggested he change it to group reading, separating important parameters from non-critical ones, reading key data every 100ms and general data every second. After the change, the communication load was significantly reduced, and the system became much smoother.

Little Wang, remember, the communication cycle and data volume must be reasonably allocated, just like eating; taking big bites can lead to choking, while small bites can leave you hungry. For PLCs, both communication and control logic consume CPU resources. If you query too frequently, the main control program will slow down, which is counterproductive.

Another important point is that when configuring communication parameters, they must match strictly. Last time, Master Li’s production line kept reporting communication errors. Upon inspection, I found that one side was set to a baud rate of 9600, while the other was set to 19200. That’s like speaking different languages!

// Correct communication parameter configuration

#Port_Config.Baud := 19200;    // Baud rate

#Port_Config.Parity := 0;      // Parity

#Port_Config.DataBits := 8;    // Data bits

#Port_Config.StopBits := 1;    // Stop bits

These parameters are like agreed-upon codes; both sides must be consistent. A mismatch in baud rates is like two people speaking at different speeds; one fast and one slow, making it hard to understand.

Speaking of factory informatization, we now basically need to upload PLC data to connect to MES or ERP systems. OPC UA servers are the best data bridges, as they can unify the data formats from different brands of PLCs before sending them to upper-level systems. Our factory’s MES system, which was launched two years ago, initially had frequent data transmission interruptions. We later discovered that the OPC server’s buffer was set too small, causing overflow during busy times. After increasing the buffer size, the problem was resolved.

Some older devices do not support Ethernet communication and only have 485 interfaces. In such cases, a communication gateway can be added for protocol conversion. It’s like finding a translator, allowing old devices to communicate in a language that the upper-level systems can understand. Last month, I added a few gateways to the old machines in the injection molding workshop, enabling them to connect to our data collection system, and the boss was very pleased.

// Simple example of gateway configuration

Device_CF.Protocol := "Modbus RTU"; // Device-side protocol

Gateway_CF.Protocol := "Modbus TCP"; // Upper-level machine protocol

Gateway_CF.IP_Address := "192.168.1.100"; // Gateway IP address

Another crucial point is that the network topology must be reasonably planned; don’t underestimate this. We divide the network segments by functional areas, strictly separating control networks from office networks, and with redundant switch configurations, communication across the factory has become much more stable. I remember during last year’s typhoon when the power went out; after power was restored, the system had almost no data loss and automatically returned to normal.

Experienced technicians have a habit of checking the physical layer first when there are communication issues. This means checking for poor connections and whether the network port lights are flashing normally before examining software configurations. Years of experience have taught me that more than half of the problems arise from the most basic issues. Software debugging may have countless lines, but hardware stability is the first priority, and that is absolutely true.

In short, PLC communication in factory informatization is not some esoteric technology; the key lies in understanding the basic principles and mastering practical skills. As long as you grasp the key points of communication protocol selection, parameter configuration, and network planning, the data flow in the factory can be smooth, and the management system can achieve maximum efficiency.