Technical Article

Three Things About IO-Link Sensors That May Shock You

August 15, 2023 by David Peterson’s Director of Engineering got to explore IO-Link sensors and what he found might surprise you! Although still considered an “emerging” technology, it’s clear IO-Link technology boasts several bonafide benefits over traditional sensors.

Sensors. Very few automation systems can reliably function without some sort of feedback or information from the operating environment. Industrial sensors provide broad functionality detecting all sorts of things, including objects, motion, temperature, pressure, color, and many other important properties including flow and turbulence of liquids in process.


Enter the Versatile IO-Link

In the past, information from the system followed one of two signal options, it was either discrete or analog. Discrete sensors indicate the presence of an object or a parameter rising or falling around a set threshold. Analog sensors offer a continuous range of values following a linear voltage or current change as the property changes.

Enter the IO-Link. Since its debut, IO-Link has been getting pretty good press, reportedly having the ability to be configured remotely, but also providing an exciting list of benefits not usually found in sensors with a simple electrical output.


Is IO Link worth the hype?

Figure 1. IO-Link versus standard discrete sensors? Do the benefits outweigh vendor hype and is it worth the premium price?


What is IO-Link?

Because IO-Link is a network structure, extra hardware is not required—which can be intimidating. All gone are devices like master distribution blocks, hubs, extra power supplies, as well as the familiar lineup of innovative sensor technologies. IO-Link networked sensors may not be the best fit for basic systems, but for those needing extra utility and functionality, it’s certainly worth a look. Plus, system engineers won’t need to invest in spare I/O modules to build or expand their advanced IO-Link sensing innovation!


SICK IO-Link Technology

With a name like SICK, you can trust this vendor to provide great products that exhibit some pretty useful features for both design and maintenance engineers. Thanks to our friends at SICK, I recently got a chance to thoroughly explore the company’s line of IO-Link sensor technology. What I found revealed some truly amazing features and capabilities rarely found in more simple feedback systems.


Multiple Output Signals for Different Sensing Ranges

Virtually every industrial sensor has a teach adjustment, either by potentiometer or by team buttons embedded in the housing. For example, operators can adjust the sensing range of an optical sensor to ensure that the detection distance is correct to control a conveyor system properly.

However, those other sensors, adjustable as they are, can only provide a single output signal when the range threshold is broken. Because the IO-Link is a byte-organized protocol, different bits can be transmitted to correspond to various distances.


Inductive sensor with adjustable ranges

Figure 2. A small inductive sensor (which already has a limited sensing distance) can be set to provide various output signals depending on the distance to the target.


This may be helpful if three different product widths are expected along the conveyor. A different output signal is taught for each width. This is far more cost-effective than buying three sensors, each one adjusted to one fixed product width.


Built-in On or Off Delay Timers to Energize Outputs

I have seen some sensors with added timer capabilities, but they are rare and usually quite specialized. I also fully realize that a good PLC programmer can add a delay timer into a ladder line to ensure that no false readings are obtained (they sometimes call this “debouncing”).

But what if you could measure the size of an object with just a single discrete sensor, and omit the PLC programming? That would be a very helpful use of a timer function.

By fixing one or two timers to the sensor element, the device can be trained to energize multiple outputs respectively after a pre-set time, just like an on-delay timer. The result? As an object moves down a conveyor with a fixed speed, one output can energize to indicate one product length, while a second output is energized shortly after to detect a second length or similar variation.


IO Link with separate output timers

Figure 3. With a single input signal (Qint. 1), two timers set to 2000 and 1000 ms respectively, can issue separate control signals, reflecting two target detection durations.


To perform this same operation using traditional sensors generally requires either an analog sensor and input module or a set of two sensors to perform AND logic comparison in the ladder rungs. A single IO-Link sensor offers a less complicated and cost-effective solution.


Analyze the Quality of the Teach Point Settings

“Ok, well, I guess it works.” Those aren’t the words you want to hear when setting up a million-dollar manufacturing line. Often, when teaching a sensor, you press a series of buttons to teach a first limit, then a second limit. If the object breaks the threshold of the set limits, the output will energize.

This process is certainly reliable, but in many cases, the difference between the two limits is very small. It may work functionally when the conditions are perfect, but over time, more and more errors and false triggers are received.

It would be nice if there was some way to determine the reliability (or quality) of the teaching threshold difference using commonly available sensors. What’s great is that many IO-Link sensors provide this numerical quality metric, thus offering real confidence that the teaching process is delivering an accurate, long-lasting result.


IO Link teach quality monitor

Figure 4. Teach-in quality is important to know. It may work at first, but what about those intermittent failures because the threshold is not in the right place?


IO-Link Sensors in Automated Systems

Sensors are always a critical decision for automation engineers. It’s important to keep up with the newest technologies shaping the industrial/manufacturing landscape and learn about the best technologies to build the best systems. We’re engineering the future after all! Just like any other type of commercial sensing technology, IO-Link is offered by several vendors. And so while not every sensor provides all of the features I’ve mentioned here, SICK’s IO-Link product line offers innovative capabilities that can certainly help you engineer the best features into your next design.