Condition monitoring of critical components on machines delivers enormous benefits to productivity in a plant. Rather than have a motor, pump, or compressor unexpectedly fail and the machine be inoperable until a replacement part is installed, condition monitoring of those critical pieces on the machine can provide warning signs that something is about to go terribly wrong. Vibration measurements on rotating equipment can detect when there is imbalance or degrade on rolling bearing elements. Temperature measurements can detect when a component is getting overheated and should be cooled down. Other environmental detections such as humidity and ambient pressure can alert someone to investigate why humidity or pressure is building up on a component or in an area. These measurement points are normally taken by specific accelerometers, temperature probes, humidity and pressure sensors and then analyzed through high end instruments with special analysis software. Typically, these instruments and software are separate from the PLC controls system. This means that even when the data indicates a future potential issue, steps need to be taken separately to stop the machine from running.
Using smart condition monitoring sensors with IO-Link allows these measured variables and alarms to be available directly onto the PLC system in real time. Some condition monitoring sensors now even have microprocessors onboard that immediately analyze the measured variables. The sensor can be configured for the measurement limit thresholds of the device it’s monitoring so that the sensor can issue a warning or alarm through the IO-Link communications channel to the PLC once those thresholds have been hit. That way, when a warning condition presents itself, the PLC can react immediately to it, whether that means sending an alert on a HMI, or stopping the machine from running altogether until the alarmed component is fixed or replaced.
Having the condition monitoring sensor on IO-Link has many advantages. As an IEC61131-9 standard, IO-Link is an open standard and not proprietary to any manufacturer. The protocol itself is on the sensor/actuator level and fieldbus independent. IO-Link allows the condition monitoring sensor to connect to Ethernet/IP, Profinet & Profibus, CC-Link & CC-Link IE Field, EtherCAT and TCP/IP networks regardless of PLC. Using an IO-Link master gateway, multiple smart condition monitoring sensors and other IO-Link devices can be connected to the controls network as a single node.
The picture above shows two condition monitoring sensors connected to a single address on the fieldbus network. In this example, a single gateway allows up to eight IO-Link condition monitoring sensors to be connected.
Through IO-Link, the PLC’s standard acyclic channel can be used to setup the parameters of the measured alarm conditions to match the specific device the sensor is monitoring. The PLC’s standard cyclic communications can then be used to monitor the alarm status bits from the condition monitoring sensor. When an alarm threshold gets hit, the alarm status bit goes high and the PLC can then react in real time to control the machine. This relieves the burden of analyzing the sensor’s condition monitoring data from the PLC as the sensor is doing the work.
IO-Link is a point-to-point communication standard [IEC61131-9]. It is basically a protocol for communicating information from end devices to the controller and back. The beauty of this protocol is that it does not require any specialized cabling. It uses the standard 3-pin sensor cable to communicate. Before IO-Link, each device needed a different cable and communication protocol. For example, measurement devices needed analog signals for communication and shielded cables; digital devices such as proximity sensors or photo eyes needed 2-pin/3-pin cables to communicate ON/OFF state; and any type of smart devices such as laser sensors needed both interfaces requiring multi-conductor cables. All of these requirements and communication was limited to signals.
With IO-Link all the devices communicate over a standard 3-pin (some devices would require 4/5 pin depending if they need separate power for actuation). And, instead of communicating signals, all these devices are communicating data. This provides a tremendous amount of flexibility in designing the controls architectures for the next generation machines.
IO-Link data communication can be divided into 3 parts:
- Process data: This is the basic functionality of the sensor communicated over cyclical messages. For example, a measurement device communicating measurement values, not 4-20mA signals, but the engineering units of measurement.
- Parameter data: This is a cyclic messaging data communication and where IO-Link really shines. Manufacturers can add significant value to their sensors in this area. Parameter data is communicated only when the controller wants to make changes to the sensor. Examples of this include changing the engineering units of measurement from inches to millimeters or feet, or changing the operational mode of a photoelectric sensor from through-beam to retro-reflective, or even collecting capacitance value from a capacitive sensor. There is no specific parameter data governed by the consortium — consortium only focuses on how this data is communicated.
- Event data: This is where IO-Link helps out by troubleshooting and debugging issues. Event messages are generated by the sensor to inform the controller that something has changed or to convey critical information about the sensor itself. A good example would be when a photoeye lens gets cloudy or knocked out of alignment causing a significant decrease in the re-emitted light value and the sensor triggers an event indicating the probable failure. The other example is the sensor triggering an event to alert the control system of a high amperage spike or critical ambient temperatures. When to trigger these events can be scheduled through parameter data for that sensor.
Each and every IO-Link device on the market offers different configurations and are ideally suited for various purposes in the plant. If inventory optimization is the goal of the plant, the buyer should look for features in the IO-Link device that can function in different modes of operation such as a photo eye that can operate as through-beam or retro-reflective. On the other hand, if machine condition monitoring is the objective, then he should opt for sensors that can offer vibration and ambient temperature information along with the primary function.
In short, IO-Link communication offers tremendous benefits to operations. With options like auto-parameterization and cable standardization, IO-Link is a maintenance-friendly standard delivering major benefits across manufacturing.