Transcript:
[0m:00s] Hey, I'm Mitchell, and welcome to another video in the RSP Education Series. Imagine hitting the emergency stop on a machine and nothing happens—or at least, not right away. That delay is the risk of non-deterministic communication in industrial automation. Welcome back to our series on industrial automation communication protocols. Today, we’re diving into the unpredictable world of non-deterministic communication. We’ll break down what it really means when data doesn’t arrive on time, why that’s okay sometimes—think SCADA monitoring and cloud data collection—and why it’s a disaster in other situations like motion control and safety shutdowns. We’ll also look at real-world examples, common protocols like Modbus, TCP/IP, and OPCUA, and how smart engineers design around these delays using hybrid networks and buffering strategies. If you like this content, please like and subscribe. This video is for educational purposes only. Always consult a professional for your application, as RSP Supply is not liable for any misuse of this information. Let’s get right into it.
[1m:18s] In our last video, we covered deterministic communication. Now we’re discussing non-deterministic communication, which is more unpredictable and delayed. Data may arrive with varying delays depending on network traffic conditions. In industrial automation, it’s used for non-time-critical tasks like data logging, SCADA monitoring, and sending reports. It works well for HMIs, cloud data collection, and remote monitoring. Think of non-deterministic communication like sending a letter through regular mail: it’ll probably arrive, but you don’t know exactly when. Deterministic communication is more like a scheduled courier drop-off.
[2m:00s] What makes this communication style non-deterministic? Delays happen due to packet collisions, network congestion, retransmissions, and variable routing times in Ethernet-based networks. Non-determinism often comes from shared Ethernet networks where packets compete for bandwidth. This leads to jitter—variation in latency—dropped packets, and retries, making timing unpredictable. In contrast, deterministic protocols like PROFINET or EtherCAT guarantee timely delivery within microseconds, which is essential for motion control and safety interlocks. Examples of non-deterministic protocols include Modbus TCP/IP, used for SCADA systems where data updates are not time-sensitive; Ethernet/IP in standard mode, which works for general industrial communication but isn’t real-time; and OPCUA, used for historical data storage, reporting, and automation systems.
[3m:00s] Why is non-deterministic communication not suitable for real-time control? If a sensor sends a delayed reading, a PLC might trigger the wrong action, causing waste or downtime. If an emergency stop signal is delayed, it could create safety hazards. Industrial systems handle non-determinism through buffering, timestamping data, and using hybrid networks that mix deterministic protocols for control with non-deterministic protocols for monitoring. Let’s discuss communication models that influence which protocol is used. In a master-slave system, one central controller (the master) sends commands and requests to devices (the slaves), which respond. Timing is controlled by the master, making deterministic communication easier. Examples include Modbus RTU or PROFIBUS. In a client-server model, the client—often an HMI or SCADA system—requests data from the server, like a PLC. Timing is less structured, making this model more non-deterministic. Examples include Modbus TCP/IP and OPCUA in client-server mode.
[4m:44s] Some applications like data logging, SCADA monitoring, sending reports, cloud data collection, and remote monitoring are better suited for non-deterministic communication. A quick recap: use deterministic protocols for motion control, safety, and time-critical systems, and non-deterministic protocols for SCADA, reporting, cloud monitoring, and similar tasks. Protocols aren’t one-size-fits-all; many systems use a mix. Avoid assuming that Ethernet always means real-time. Using non-deterministic protocols for control loops can cause jitter, downtime, or equipment damage. Always validate timing needs before choosing protocols. Choosing the wrong protocol can turn a smooth commissioning into weeks of troubleshooting.
[5m:21s] That wraps up video seven in our series on industrial automation communication protocols. We explored the unpredictable nature of non-deterministic communication, why delays occur, and why it’s fine for SCADA, data logging, and cloud monitoring but a serious problem for real-time control, safety interlocks, and motion systems. We looked at Modbus, TCP/IP, Ethernet/IP, and OPCUA, and discussed buffering, timestamping, and hybrid networks to work around delays. We also compared master-slave and client-server models, showing how system structure affects timing reliability. The big takeaway: use deterministic protocols when timing is critical and non-deterministic protocols for monitoring and reporting. Never assume Ethernet means real-time. Choosing the right protocol can make the difference between smooth commissioning and weeks of costly troubleshooting. For hundreds of thousands of industrial automation products, visit rpsupply.com, the internet’s top source for industrial hardware.