What communication protocols are best for sensor and actuator integration in industrial control systems?

First need to understand the sensor provides a signal, and the actuator adjusts based on that signal so it can determine the state of the controlled system and decide whether further control signals are needed. So as per my mind mostly used serial communication protocols for sensor & actuator integration are as below - RS – 232 ( for Point-to Point communication) - RS- 485 ( For Multi-point communication) - MODBUS.

The following networking protocols are well suited to such applications: 1. CAN 2. Profibus 3. DeviceNet 4. Profinet 5. HART (Highway Addressable Remote Transducer)

Labeling a communication protocol as 'the best' is challenging as it largely depends on the brand of equipment in use. In a Schneider sys, Modbus might be considered the best since it's Schneider's native protocol. Similarly, for Siemens equipment, Profibus is often preferred. Cost is another factor; Modbus tends to be cheaper than Profibus, but the latter's higher cost is justified by its advanced features and reliability. However, an additional complication arises when other system components, like sensors or actuators, need to support the exact protocol being used. Ultimately, the choice of protocol should be based on a balance of compatibility, cost, and the specific requirements of the system to ensure seamless and efficient operation.

Unfortunately, the best protocol for Actuator and Sensor integration is not named in the list. The AS-Interface is dedicated to do this task and saves in most cases 50-60% wiring efforts.

My mentor once told me, "IP will eat everything". He of course was talking about Internet Protocol and experienced in his lifetime the digital transition of telephony systems. This IP'fication was at this stage happening on SAN switches with Fibre Channel being the next technology that was consumed by IP. This trend has not stopped and we will see the full conversion of industrial protocols into IP (or components of the TCP stack) over the next 10 years. This transition has already started with Modbus-TCP, Profinet and Bacnet using parts of the TCP stack.

Industrial Ethernet protocols, like ProfiNet, Ethernet IP, EtherCat... are fine for demanding tasks like vision systems, motion control. They are to expensive and demanding for the majority of sensor and actuators. The easy wiring system AS-Interface solves many solutions and offers opportunities.

We are sitting in a strange place where factories need 5G type speeds for point in time condition monitoring and process optimization yet we are sitting with a mix of Serial, Ethernet, Wifi, Bluetooth, GSM and LORA connectivity in most cases. Equipment EMF and Thermal radiation wreaks havoc on most of this spectrum and laying cables from one OT zone to another can test the length limits of Cat6 cables operational parameters. Hopefully 5G costing can support digitization of factory equipment and processes so that we can reduce overall production operational costs, this we still need to see play out in the medium term. Just in time for 6G right :)

Generally in early days of ICS, OEMs have their own proprietary protocols. Customers are bound to use the same ( i.e. Seimens - Profibus, Rockwell- Ethernet/IP etc.) There's very limited interoperability and very high dependency to that particular OEM. As the need of interoperability and less OEM dependency came into picture. these protocols change to support some essential features and some become open source. Based on above discussion I think key criteria for a particular protocol selection depends on- 1. Bandwidth and supported distance requirements 2. Type of data, we need from device over that protocol 3. Security Features 4. Interoperability of that protocol with other PLCs 5. Integration with Other systems

The best protocol depends on the application, for easy installation it is AS-Interface mostly. For demanding tasks, it depends on the specs and your favorite supplier. You can solve many tasks in manifold ways. Eg.: You want to connect 10 Motor starters, 20 binary sensors, and some E-Stops, AS-Interface probably is your best deal. If you want to connect a vision system or a demanding motion control you'd better check the Ethernet Protocols.

I strongly believe to consider secure protocols at the initial stage of purchasing new projects or new services. Test and validate these protocols during SAT and FAT.

ASI interface is very useful for sensors and actuators. No complications for wiring, easy to configure, One module can cover 62 devices. Each node can have up to four inputs and/or four outputs for actuators or sensors.