Adding Smart Condition Monitoring Sensors to Your PLC Control Systems Delivers Data in Real Time

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.


Reduce the Number of Ethernet Nodes on Your Network Using IO-Link

Manufacturers have been using industrial Ethernet protocols as their controls network since the early 1990s. Industrial Ethernet protocols such as Ethernet/IP, ProfiNet, and Modbus TCP were preferred over fieldbus protocols because they offered the benefits of higher bandwidth, open connectivity and standardization, all while using the same Ethernet hardware as the office IT network. Being standard Ethernet also allows you to remotely monitor individual Ethernet devices over the network for diagnostics and alarms, delivering greater visibility of the manufacturing data.

With Ethernet as the key technology for Industry 4.0 and digitalization, more and more devices will have Ethernet capabilities. Typical industrial Ethernet nodes on a plant floor could include PLC controllers, robots, I/O devices for sensors, actuators, flowmeters, transducers and manifolds. While, it’s great getting all the data and diagnostics of the entire manufacturing process, having every device connected via Ethernet has some downfalls. It can lead to larger Ethernet networks, which can mean more costs in hardware such as routers, switches and Ethernet cables, and some Ethernet software license costs are based on the number of Ethernet nodes being used in the network.

Also, as more Ethernet devices are added to a network, the Ethernet network itself can get more complex. Each individual Ethernet device requires an IP address. If an Ethernet node stopped working and needed to be replaced, an operator would need to know the previous IP address of the device and have quick access to the manual with instructions on how to assign the previous IP address to the new device. Someone must also manage the IP addresses on the network. There will need to be a list of the IP addresses on the network as well as the available ones, so when a new Ethernet device is added to the network, a duplicate address is not use

One way to reduce the number of Ethernet nodes while still getting device data and diagnostics is by using IO-Link for field device communications. IO-Link is an open point-to-point communication standard for sensors and actuators published by IEC (International Electrotechnical Commission) as IEC 61131-9. Since it’s fieldbus and manufacturer independent, there is a long list of manufacturer devices that come with IO-Link. Each IO-Link device can then be brought back to a single Ethernet node, through an IO-Link to Ethernet gateway. Since it’s open technology, there are also multiple manufacturers that make different IO-Link to industrial Ethernet gateways.

On the IO-Link to Ethernet gateway, each channel has an IO-Link master chipset. It is designed to automatically communicate and provide data as soon as an IO-Link device is connected to a port. So, there is no addressing or additional setup required. IO-Link is point to point, so it’s always a single IO-Link device connected to a single port on the gateway using a standard sensor cable. Depending on the number of IO-Link devices to be connected to a single Ethernet node, IO-Link gateways can come in 4, 8 or 16 device channels. This graphic (image 1) shows six IO-Link devices connected to a single 8-channel Ethernet gateway. This gateway then communicates back to the Ethernet PLC controller as a single IP address with a standard Ethernet cable. Without using IO-Link, this might require all six devices to be industrial Ethernet devices. Each device would have its own IP address to set up, along with six Ethernet cables going back to a 6-port managed switch before going to the PLC controller.


Image 1: Six IO-Link devices connected to a single 8-channel Ethernet gateway.

IO-Link Devices Connected:

  1. Device I/O Hub used to connect to 16 standard discrete sensors/photoeyes.
  2. Valve Manifold used to control up to 24 coils.
  3. Visual Indicator Light
  4. RFID Processor System
  5. Pressure Sensor
  6. IO-Link to Standard Analog (0-10V or 4-20ma) Converter