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.

Linear Measurement Sensors for Short Stroke Applications

We’ve posted numerous articles here on the Sensortech blog about linear position sensors used for applications such as hydraulic cylinder position feedback, plastic injection molding machinery, tire manufacturing machinery, etc.  What all of the applications have in common is that we’re generally talking about fairly long linear travels, usually longer than 12″, sometimes up to 300″.spindle

But in applications such as spindle clamp positioning on machine tools or positioning of
linear movements on automated assembly machinery, travels are sometimes only a couple of inches, and the available space to mount a position sensor is extremely limited.  Fortunately, there are highly capable linear position sensors that are perfectly suited for such applications.

For example, there are sensors that use an array of inductive coils to detect the bips
precise linear position of a simple metal target.  These sensors, with working strokes ranging from < 1″ up to around 5″ have are extremely compact, with very little dead zone.  That means they fit into very tight spaces, where other type of linear position sensors simply couldn’t.

Typically, these types of sensors provide a position signal in the form of an analog voltage (0-10V) or current (4-20 mA).  Increasingly though, IO-Link interfaces are gaining in popularity, offering simplified wiring, better noise immunity, built-in diagnostics, and the ability to easily get the position data into virtually any industrial field-bus architecture.

For more information, visit www.balluff.com

What’s best for integrating Poka-yoke or Mistake Proofing sensors?

Teams considering poka-yoke or mistake proofing applications typically contact us with a problem in hand.  “Can you help us detect this problem?”

We spend a lot of time:

  • talking about the product and the mistakes being made
  • identifying the error and how to contain it
  • and attempting to select the best sensing technology to solve the application.

However this can sometimes be the easy part of the project.  Many times a great sensor solution is identified but the proper controls inputs are not available or the control architecture doesn’t support analog inputs or network connections.  The amount of time and dollar investments to integrate the sensor solution dramatically increases and sometimes the best poka-yoke solutions go un-implemented!”

“Sometimes the best poka-yoke solutions go un-implemented!”

Many of our customers are finding that the best controls architecture for their continuous improvement processes involves the use of IO-Link integrated with their existing architectures.  It can be very quickly integrated into the existing controls and has a wide variety of technologies available.  Both of these factors make it the best for integrating Poka-yoke or Mistake Proofing due to the great flexibility and easy integration.

Download this whitepaper and read about how a continuous improvement technician installed and integrated an error-proofing sensor in 20 minutes!

For Industrial Controls, What’s Next After Analog?

Analog signals have been part of industrial control systems for a very long time.  The two most common signals are 0-10V (“voltage”) and 4-20mA (“current”), although there are a wide variety of other voltage and current protocols.  These signals are called “analog” because they vary continuously and have theoretically infinite resolution (although practical resolution is limited by the level of residual electrical noise in the circuit).

Measurement sensors typically provide analog output signals, because these electronic circuits are well-understood and the designs are relatively economical to produce.  But that doesn’t mean it’s easy to design and build a good-quality analog sensor: in fact it is very difficult to engineer an analog signal that is highly linear over its measuring range, has low noise (for high-resolution), is thermally stable, (doesn’t drift as temperature changes), and is repeatable from sample to sample.  It takes a lot of careful engineering, testing, and tweaking to deliver a good analog sensor to the market.

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Cable Length for Analog Sensors

A question came in recently concerning the maximum recommended cable length for analog sensors.  Even as digital interfaces gain popularity, sensors with analog interfaces (0-10V, 4-20 mA, etc.) still represent the overwhelming majority of continuous position sensors used in industrial applications.

The question about maximum cable length for analog sensors comes up pretty frequently.  Generally speaking, the issue is that electrical conductors, even good ones, have some resistance to the flow of current (signals).  If the resistance of the conductor (the cable) gets high enough, the sensor’s signal can be degraded to the point where accuracy suffers, or even to the point where it becomes unusable.  Unfortunately, there is no hard and fast answer to the question.  Variables such as wire gauge, whether or not the cable is shielded, where and how the cable is routed, what other types of devices are nearby, and other factors come into play, and need to be considered.  A discussion about all of these variables could fill a book, but we can make some general recommendations:

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E = IR: It’s Not Just a Good Idea, it’s the Law

I recently had a conversation with a customer that resulted in one of those forehead-slapping “duh” moments for me, and I thought it might be worth passing along. Here’s the story:

The customer had an application that required an analog linear feedback sensor that provided an output of 1 volt to 5 volts over the linear stroke range. Now, a 1-5V output is not very common, and the particular sensor he was interested in was only available with either a 0-10V or a 4-20 mA output. What to do? Perhaps the answer should have been obvious to me, but it was the customer who provided the solution this time: “couldn’t I use a 4-20 mA output and 250 ohm resistor to get my 1-5V output?” Why, yes….yes you could (smack…..duh!). And I know it will work, because we have the law on our side. Ohm’s Law, that is: E = IR, or voltage equals current x resistance.

Let’s check it:

4 (mA) x 250 (ohms) = 1 (volt)

20 (mA) x 250 (ohms) = 5 (volts)

So there you have it. Take a very common 4-20 mA output and drop it across a 250 ohm resistor and, lo and behold, you have your less common 1-5V signal. And, if you do this conversion right at the input to the controller, you get the added benefit of increased noise immunity of the 4-20 mA signal.

And, yes, I’m sure I knew of this little trick at one time. Maybe the part of my brain where this information was stored got overwritten by the names of the contestants on The Amazing Race or by the rollout plans for my million dollar consumer product idea: Dehydrated Water (just add water). But let’s keep that just between us, ok?

To learn more about analog feedback sensors visit www.balluff.us

Analog Inductive Sensors

In his post, When Do You Specify An Inductive Sensor?, Shawn Day (Market Manager, Inductive Sensors) discusses selection criteria and application for inductive proximity sensors.  In that article, Shawn focuses on what are sometimes referred to as discrete sensors – sensors that detect the presence of a metal target, and then turn on (or turn off).  As Shawn points out, there are many, many applications for this type of discrete sensing.

But what if just indicating the presence or absence of a part is not enough?  What if you need to know not only if a part is in a particular position or not, but rather you need to know exactly where the part is at any given point along its entire range of travel?  That’s where analog, or continuous, inductive position sensors come into play.

Analog inductive sensors employ basically the same technology as discrete proximity sensors.  That is, they use inductive coils to generate eddy currents that respond to a metal target.  But, unlike discrete sensors, analog inductive sensors provide a continuously variable output, not just an on/off change of state.

Tubular Analog Inductive Sensors

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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.

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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?

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To Avoid Trouble Later, Consider Your Application Conditions Up Front

Hardly a day passes by where we are not contacted by a desperate end-user or equipment manufacturer seeking assistance with a situation of sensors failing at an unacceptably high rate.  Once we get down to the root cause of the failures, in almost every case it’s a situation where the specific sensors are being applied in a manner which all but guarantees premature failure.

Not all sensors are created equal.  Some are intentionally designed for light-duty applications where the emphasis is more on economical cost rather than the ability to survive in rough service conditions.  Other sensors are specifically designed to meet particular challenges of the application environment and as a result may carry a higher initial price.

Some things to think about when choosing a sensor for a new application:

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