IO-Link vs. Analog in Measurement Applications

IO-Link is well-suited for use in measurement applications that have traditionally used analog (0…10V or 4…20mA) signals. This is thanks in large part to the implementation of IO-Link v1.1, which provides faster data transmission and increased bandwidth compared to v1.0. Here are three areas where IO-Link v1.1 excels in comparison to analog.

1

Fewer data errors, at lower cost

By nature, analog signals are susceptible to interference caused by other electronics in and around the equipment, including motors, pumps, relays, and drives. Because of this, it’s almost always necessary to use high-quality, shielded cables to transmit the signals back to the controller. Shielded cables are expensive and can be difficult to work with. And even with them in place, signal interference is a common issue that is difficult to troubleshoot and resolve.

2

With IO-Link, measurements are converted into digital values at the sensor, before transmission. Compared to analog signals, these digital signals are far less susceptible to interference, even when using unshielded 4-wire cables which cost about half as much as equivalent shielded cables. The sensor and network master block (Ethernet/IP, for example) can be up to 20 meters apart. Using industry-standard connectors, the possibility for wiring errors is virtually eliminated.

3

Less sensor programming required

An analog position sensor expresses a change in position by changing its analog voltage or current output. However, a change of voltage or current does not directly represent a unit of measurement. Additional programming is required to apply a scaling factor to convert the change in voltage or current to a meaningful engineering unit like millimeters or feet.

It is often necessary to configure analog sensors when they are being installed, changing the default characteristics to suit the application. This is typically performed at the sensor itself and can be fairly cumbersome. When a sensor needs to be replaced, the custom configuration needs to be repeated for the replacement unit, which can prolong expensive machine downtime.

IO-Link sensors can also be custom configured. Like analog sensors, this can be done at the sensor, but configuration and parameterization can also be performed remotely, through the network. After configuration, these custom parameters are stored in the network master block and/or offline. When an IO-Link sensor is replaced, the custom parameter data can be automatically downloaded to the replacement sensor, maximizing machine uptime.

Diagnostic data included

A major limitation of traditional analog signals is that they provide process data (position, distance, pressure, etc.) without much detail about the device, the revision, the manufacturer, or fault codes. In fact, a reading of 0 volts in a 0-10VDC interface could mean zero position, or it could mean that the sensor has ceased to function. If a sensor has in fact failed, finding the source of the problem can be difficult.

With IO-Link, diagnostic information is available that can help resolve issues quickly. As an example, the following diagnostics are available in an IO-Link magnetostrictive linear position sensor: process variable range overrun, measurement range overrun, process variable range underrun, magnet number change, temperature (min and max), and more.

4

This sensor level diagnostic information is automatically transmitted and available to the network, allowing immediate identification of sensor faults without the need for time-consuming troubleshooting to identify the source of the problem.

To learn about the variety of IO-Link measurement sensors available, read the Automation Insights post about ways measurement sensors solve common application challenges. For more information about IO-Link and measurement sensors, visit www.balluff.com.

IO-Link Measurement Sensors Solve Application Challenges

In industrial distance and position measurement applications, one size definitely does not fit all.  Depending on the application, the position or distance to be measured can range from just a few millimeters up to dozens of meters.  No single industrial sensor technology is capable of meeting these diverse requirements.

Fortunately, machine builders, OEM’s and end-users can now choose from a wide variety of IO-Link distance and position measurement sensors to suit nearly any requirement.  In this article, we’ll do a quick rundown of some of the more popular IO-Link measurement sensor types.

(For more information about the advantages of IO-Link versus traditional analog measurement sensors, see the following blog posts, Solving Analog Integration Conundrum, Simplify Your Existing Analog Sensor Connection, and How Do I Make My Analog Sensor Less Complex?)

 

Short Range Inductive Distance Sensors

These sensors, available in tubular and blockScott Image1.JPG style form factors are used to measure very short distances, typically in the 1…5 mm range.  The operating principle is similar to a standard on/off inductive proximity sensor.  However, instead of discrete on/off operation, the distance from the face of the sensor to a steel target is expressed as a continuously variable value.  Their extremely small size makes them ideal for applications in confined spaces.

Inductive Linear Position Sensors

Inductive linear position sensors are available in several block style form factors, and are used for position measurement over stroke lengths up to about 135 mm.  These types of sensors use an array of inductive coils to accurately measure the position of a metal target.  Compact form factors and low stroke-to-overall length factor make them well suited for application with limited space.

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Magnetostrictive Linear Position Sensors

IO-Link Magnetostrictive linear position sensors are available in rod style form factors for hydraulic cylinder position feedback, and in external mount profile form factors for general factory automation position monitoring applications.  These sensors use time-proven, non-contact magnetostrictive technology to provide accurate, absolute position feedback over stroke lengths up to 4.8 meters.

Laser Optical Distance Sensors

 

Scott Image 4.JPGLaser distance sensors use either a time-of-flight measuring principle (for long range) or triangulation measuring principle (for shorter range) to precisely measure sensor to target distance from up to 6 meters away.  Laser distance sensors are especially useful in applications where the sensor must be located away from the target to be measured.

 

Magnetic Linear Encoders

IO-Link magnetic linear encoders use an absolute-codedScott Image 5 flexible magnet tape and a compact sensing head to provide extremely accurate position, absolute position feedback over stroke lengths up to 8 meters.  Flexible installation, compact overall size, and extremely fast response time make magnetic linear encoders an excellent choice for demanding, fast moving applications.

IO-Link Measurement Sensor Trends

The proliferation of available IO-Link measurement sensors is made possible, in large part, due to the implementation of IO-Link specification 1.1, which allows faster data transmission and parameter server functionality.  The higher data transfer speed is especially important for measurement sensors because continuous distance or position values require much more data compared to discrete on/off data.  The server parameter function allows device settings to be stored in the sensor and backed up in the IO-Link master.  That means that a sensor can be replaced, and all relevant settings can be downloaded from master to sensor automatically.

To learn about IO-Link in general and IO-Link measurement sensors in particular, visit www.balluff.com.

Magnetic Linear Encoders – Tape Magnetization Technology

bmlPrecision Tape Magnetization Leads to Precision Position Measurement

The key to ultimate accuracy for any magnetic linear encoder system is the precision of the magnetic encoding on the tape (sometimes called a scale). Sensors inside the encoder read head respond to the strength and position of the magnetic flux coming from the magnetic poles encoded onto the tape. Precise placement of these poles – and just as importantly, the precise shape of these poles – is critical to the ultimate level of accuracy that can be delivered by the encoder system. Any inaccuracy in the position, strength, or shape of these fields will directly influence the accuracy of the encoder’s indicated position. This effect is amplified with increasing gap distance between the tape and the encoder read head. The further away from the tape, the weaker and more indistinct the shape and position of the magnetic poles becomes.

Not All Magnetic Tapes Are Created Equal

Many magnetic encoder tapes on the market are surface magnetized utilizing the conventional parallel magnetization process. This is a straightforward technique that results in an encoder tape that meets performance specifications at close gap settings between the read head and the tape.

A more recent tape magnetization process called Permagnet® produces magnetic poles with improved control over their strength, shape, and location on the tape. The best way to appreciate the advantages of this technology is to compare magnetic scans of some conventionally magnetized tapes to some examples of tapes encoded with the Permagnet® process. Note the visible difference in sharp definition of the magnetic poles that is produced by the newer technology.

Conventionally Magnetized Tape – Sample #1

Sample #1 - Conventionally magnetized tape: 2 mm pole spacing, scanned at a distance of 0.2mm from the tape surface
Sample #1 – Conventionally magnetized tape: 2 mm pole spacing, scanned at a distance of 0.2 mm from the tape surface
Sample #1 - Conventionally magnetized tape: 2mm pole spacing, scanned at a distance of 0.8 mm from the tape surface
Sample #1 – Conventionally magnetized tape: 2 mm pole spacing, scanned at a distance of 0.8 mm from the tape surface

Tape Magnetization with Permagnet® Technology – Sample #2

Sample #2 - Permagnet tape: 2mm pole spacing, scanned at a distance of 0.2 mm from the tape surface
Sample #2 – Permagnet tape: 2mm pole spacing, scanned at a distance of 0.2 mm from the tape surface

Sample #2 – Permagnet® tape: 2 mm pole spacing, scanned at a distance of 0.8 mm from the tape surface.
Sample #2 – Permagnet® tape: 2 mm pole spacing, scanned at a distance of 0.8 mm from the tape surface.

The stronger, more sharply-defined magnetic poles produced by Permagnet® technology enables encoders to be more tolerant of variation in the working distance between the encoder read head and the tape. Reduced dispersion and distortion of the magnetic fields at any distance within the specified working range reduces the influence of distance variation on the accuracy of the position measurement in real-world applications.

Summary of Application Benefits

  • Improved linearity at close working distances for ultimate system accuracy
  • Improved linearity at longer working distances
  • Higher tolerance to deviations in the working distance, with reduced non-linearity
  • Less need to closely control the working distance in the application, saving cost by reducing painstaking setup and alignment effort
  • Full system accuracy, even if gap distance varies during operation
  • Better linearity for any given pole spacing on the tape

Open- vs. Closed-loop Control

Several previous articles here on SENSORTECH have mentioned closed-loop control (Servo-Hydraulic Showcase, Linear Feedback Sensor Applications: The Three M’s). But exactly what does “closed-loop control” mean? How does it compare to open-loop control? I recently ran across an article in Control Engineering magazine that does an outstanding job of answering those questions.

Click over and have a look at this excellent article.

Intelligent Interfaces and IO-Link Innovation

I recently had the opportunity to attend Hannover Fair in Germany and was blown away by the experience… buildings upon buildings of automation companies doing amazing things and helping us build our products faster, smarter and cheaper.  One shining topic for me at the fair was the continued growth of new products being developed with IO-Link communications in them.

All in all, the growth of IO-Link products is being driven by the need of customers to know more about their facility, their process and their production.  IO-Link devices are intelligent and utilize a master device to communicate their specific information over an industrial network back to the controller.  To learn more about IO-Link, read my previous entry, 5 Things You Need to Know about IO-Link.

Continue reading “Intelligent Interfaces and IO-Link Innovation”

3 Production Problems Solved by Intelligent Sensors

In typical sensors all you get is ON or OFF… we just hope and assume that the prox is working, until something doesn’t work properly.  The part is seated but the sensor doesn’t fire or the operator can’t get their machine to cycle.  This can sometimes be tricky to troubleshoot and usually causes unplanned interruptions in production while the maintenance teams attempt to replace the sensor.  On some recent customer visits on the east coast, I have had a number of  interesting conversations about the customer’s need to collect more information from their sensors; specifically questions like:

  • How do I know the sensor is working?
  • How do I predict sensor failure?
  • How do I know something has changed in the sensor application?
  • How do I get my sensor to provide adaptive feedback?
  • How do I plan preventative maintenance?
  • How can I increase the overall equipment throughput?
  • How can I increase my process reliability?

Continue reading “3 Production Problems Solved by Intelligent Sensors”

You can be doing MORE with Your Sensors!

Recently Hank Hogan published an article in Control Design titled “Sensor, Diagnose Thyself.”  (To be honest, I really wanted to steal his title for my blog entry.)   I think Hank did a great job dissecting the key benefits of smart sensors and the amazing things you can do with them.  Utilizing the technology IO-Link (that we have discussed in many past Blog Entries), sensors can communicate more with the controller and provide more data than ever before.

Some of the key points that I really thought are useful to maintenance and engineers at end-user facilities or machine builders:

  • Being able to detect and notify about pending failures; for example a photoeye’s lens is dirty and needs to be cleaned.
  • A failed sensor needs to be swapped out quickly; IO-Link allows for the smart sensors settings to be cloned and the swap to be executed super fast.
  • Configure a sensor before installation; program with your laptop: sample rate, response time, measurement settings, on/off switch points, anything!
  • One platform can be used for many sensor types;  this gives familiarity to a single interface while using multiple sensor types and technologies.
  • In the future sensors in a wireless cloud would self-heal;  this is an amazing concept and if we can figure out the price for radios and batteries to make it cost-effective, I think this could be a game changer someday.

But all that being said, it really comes down to the total cost of ownership doing it the standard sensor way versus the smart sensor way.  I think you will pay more upfront in capital but down the line there will be less cost in maintenance and downtime.

To learn more about about IO-Link visit www.balluff.us

The Best Way to Communicate with Smart Sensors

When I am discussing with customers the use of smart sensors and smart devices in industrial automation, I always get posed with these questions:

  • How do the smart sensors interface with the controller?
  • How do you configure the device?
  • How do you get diagnostics out of it?
  • What other information can it provide?

This is sort of solved in a muddled world of proprietary communications or expensive network enabled sensors.  But John and I have been talking for a long time about IO-Link, which can easily and cost effectively answer all these questions!

Continue reading “The Best Way to Communicate with Smart Sensors”

Visit Automation Tradeshows for Free!

I am experiencing the future of tradeshows; a networking & educational conference without the travel, the expense, and the suit!  I can sit at my desk and make contact with future vendors and customers.  The online database GlobalSpec hosts multiple times per year industry specific virtual tradeshow events.  There are presentations and exhibitors.  A place to sit and drink virtual coffee with your peers and of course the token giveaway raffles.

Today I am working the Balluff booth in the Sensors and Switches Virtual show.  It is a collection of companies and attendees from many different industries.  I really enjoy these events because we can contact quickly with potential customers and potential vendors right from the comfort of our conference room and at a much reduced cost. Here you can see our hard working staff chatting with customers.

Check out the Balluff booth at the  Sensors & Switches Virtual Tradeshow, it will be available to visit for 90 days from today.

Do Photoelectric Sensors Really Measure Up?

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I recently spent the week at the IMTS show in Chicago. If you have never been to this show I highly recommend you go in 2012. The show occupied over 1.1 million square feet and there were over 1700 manufacturers and or vendors. If you do attend this show I think, you really need take at least two days to go through it. No matter how comfortable you think your shoes are I guarantee that your feet will hurt after going through the four buildings of exhibits.

While I was working at our booth, I had several customers ask me about using photoelectric sensors in measuring applications. The questions ranged from the basic how they work, what are some of the application concerns to the infamous what is the accuracy of the sensor.

Here are some of the highlights to summarize our conversations:

Continue reading “Do Photoelectric Sensors Really Measure Up?”