Sensors

IO-link enables Industrial IoT (IIoT)

4th November 2016
Joe Bush
0

IO-link is a relatively new standard for industrial sensors, that is showing a phenomenal growth trajectory. From about 250,000 installed IO-Link sensors in 2009, it is now estimated that over three million IO-Link sensors are now deployed. Suhel Dhanani, Principal MTS, Industrial Strategy, Maxim Integrated explains.

One reason that this standard is enjoying rapid adoption in factories in Europe first and increasingly around the world is that connected, smart sensors underpin the Industrial IoT (IIoT) that is beginning to be deployed in factories.

Defining Industrial IoT
Industrial IoT is the Internet of Things within an assembly line, factory, oil field - even in a jet engine or any such industrial environment to help us better run that particular process.

While one day we may all want connected toasters and refrigerators (for a yet to be determined reason) - it is clear that connected factory/process automation systems can quickly deliver significant benefits. Understanding and measuring the heat profile of an actuator or the vibration over time of a motor allows us to wring out significant operational efficiencies from the assembly line. Over time, a connected, digital factory can also exploit new business models and adapt production to market needs in real time.

Above: Understanding industrial IoT in terms of a stack

Industrial IoT is an attempt to connect up all the pertinent data from a process or from an assembly line to be able to make intelligent decisions - such as predicative maintenance, running at optimum efficiency, better production scheduling, improving production mix, etc. As we start connecting up data from the myriad of different sensors across the production line, ever-improving software and algorithms promise to give us more insight and understanding of our production flows.

One way to visualise Industrial IoT is in terms of a stacked pyramid, as shown below. At the very bottom is sensor data - which must be detailed, actionable, as well as useful for analysis. The glue for Industrial IoT is data, or more specifically smart sensor data. This means more than just ON/OFF signals.

This can be illustrated with a few examples. It is not enough to detect proximity - we need to know how close the product gets to the motor. It is not enough to detect a light curtain breach, as we need to know which quadrant the breach seems to be happening in. In short, we need the sensor to transmit complex data and not just an ON/OFF signal. This is where the new IO-Link protocol for transmitting sensor date comes in.

What is IO-Link?
This is how the IO-Link Association defines this standard.

‘IO-Link is the first standardised IO technology worldwide (IEC 61131-9) for the communication with sensors and also actuators. The powerful point-to-point communication is based on the long established 3-wire sensor and actuator connection without additional requirements regarding the cable material. So, IO-Link is no fieldbus but the further development of the existing, tried-and-tested connection technology for sensors and actuators.’

The key thing to note here is that this is an open standard and is based on the legacy 3-wire sensor connector that everyone is used to. Over this cable the protocol supports communications at data rates up to 230kbit/s.

Above: An IO-link cable based on a (mostly) legacy M12 connector

The connection between an IO-Link Master and slave is via a maximum 20ft long 3-pin cable.

The IO-Link master establishes the connection between the IO-Link devices and the automation system. As a component of an I/O system, the IO-Link master is installed either in the control cabinet or as remote I/O which communicates via regular fieldbus networks to the controller.

Example IO-Link sensors
Today’s factories rely more on automation and less on manual labour. With this increased use of automation and robotics comes the increased need for proximity sensing. Proximity sensors are devices that can sense when an object is a specific distance away from a reference point location. They are able to act as a switch by flipping when the target object passes a predefined distance threshold. They can also provide continuous readings when objects are changing distances within a sensor’s range. Several types of proximity sensors exist today such as optical, inductive, capacitive, ultrasonic, magnetic and even mechanical.

Shown above is a tiny IO-Link proximity sensor with an IR receiver, matching IR LED driver, IO-Link transceiver and energy efficient step-down converter, all on an 8.2x31.5mm printed circuit (PC) board. The Maxim reference design here consists of an industry standard Maxim

Integrated IO-Link device transceiver (MAX14821), a tiny low dropout linear regulator (MAX8532), an efficient high voltage step-down converter (MAX17552), a Renesas ultra-low power 16-bit microcontroller (RL78) utilising TMG TE’s IO-Link device stack, and a Maxim Integrated proximity sensor (MAX44000).

This reference design highlights an ability to develop ultra-small IO-Link sensors that are versatile and powerful enough to be integrated within an actual assembly line.

Enabling IO-Link design
There are various types of IO-Link sensors that are becoming available in the market which range from temperature to distance and even light curtains with multiple light beams. To enable the interface of these sensors with legacy programmable logic controllers (PLCs) we see a host of gateways that can translate multiple IO-Link inputs to a single fieldbus. Some of the newer PLC designs are incorporating IO-Link master functionality built-in, so that they can communicate directly with the IO-Link sensors. This is enabled by the availability of integrated IO-Link transceiver devices in small, power efficient form factors.

For example, the MAX14824 is an IO-Link master interface that integrates an IO-Link physical layer transceiver with an auxiliary digital input and two linear regulators in a small 4x4mm, 24-pin TQFN package. The device supports all the IO-Link data rates and is compliant with IO-Link v.1.0 and v.1.1 Physical Layer. The chart below shows the typical operating circuit for IO-Link Master functionality with such a device.

Using this transceiver, Maxim has also built the first public and fully IO-Link-compliant, 4-port IO-Link master reference design.

Above: The first IO-Link master reference design for interfacing with up to four IO-Link sensors

The reference design has four robust female M12 connectors, the most common connector used for IO-Link, and ships with two black IO-Link cables to quickly connect to IO-Link compatible sensors and actuators. An AC-to-DC (24VDC/1A) power supply cube is capable of providing greater than 200mA simultaneously to each port and greater than four times that amount if the other ports are unused. A Micro-USB connector underneath the enclosure allows for quick connectivity to a Windows PC.

IO-Link reference designs such as the ones described here help speed up the design and development of IO-Link-based sensors for customers that are still beginning to embrace this fast growing technology.

Conclusion
Industrial IoT is at an inflection point - we see some factories that are getting hyper connected and many others which are still in the evaluation mode. As factories become digital, smart and relevant, sensor data will be the basis upon which manufacturing and even enterprise level software will run optimisation and other algorithms.

As sensors measure even more parameters and have to communicate with the controller/PLC, the need for a low cost, robust and open communication standard will be important. IO-Link checks all of these boxes and has the potential to become the dominant factory automation standard for the pervasive, smart sensor world that is emerging.

Right: IO-Link optical proximity sensor reference design from Maxim Integrated

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