Stacklights deliver versatile multi-status indication in real time

With advanced communication technology, stacklights can provide valuable information to operators and floor managers.

Rainer3It’s a new world for real-time, point-of-use information. Stacklights and indicators can provide much more feedback to operators and plant floor managers than ever before.

Using colored lights, stacklights can convey a wide range of information. While red, yellow, green and blue are the standard stacklight colors, a variety of other colors can be used to indicate specific conditions and needs.  It is important to develop a communication plan to clearly identifies what each color and flashing pattern represents.

Figure 1

Color overload can be a problem if not planned out properly. The best planning utilizes a dual color approach where colors are defined by personnel responsible and machine/process status at the point of use. An example would be yellow/blue indication wherein yellow = process slowdown and blue = line supervisor is responsible. This responsibility is clearly on the line supervisor to fix the slowdown at the point of indication. Flashing multiple colors is one method to dual color indication, but that has proven to be confusing. A much more intuitive approach is to segment the indicators based on your communication plan. Even small, point-of-use indicators can be segmented to exceed your goals.

OwnerWe have also seen customers mixing their own colors to achieve a level of differentiation. This differentiation could be simple appearance preference or adherence to their corporate color identity. All very achievable with the new class of smart, LED based stacklights and indicators.

By providing continuously variable information, also referred to as analog information, stacklights can be used to indicate current level status in tanks, hoppers, feeders, flow racks and so on. Continuously variable information is also ideal to use in pacing for operators in manual assembly areas. They can quickly see how much time each individual person has for their process step. If someone is struggling, others can visibly see the situation and step in and help.


Another popular use is simply displaying that the machine is in idle state, like the spinning icon on computers. This would typically suspend all other forms of indication.  Basically, it indicates the machine is not ready. The color indicators can be used as part of a communication plan to indicate the reason for the idle time and call for specific personnel to respond. As soon as the machine is ready, the indicators and stacklights revert to normal operations, just like your computer.

Stacklights can additionally provide operational status such as flow rates, pressure values and process speed.

To learn more about stacklights and indicators, visit

Choosing the Best Position Sensor: Does Yours Measure Up?

Reliable electronic measurement is something that is always needed in industrial automation. Production interruptions and unexpected downtime will cripple even the best manufacturers if they do not have the appropriate measurement technology in place.

Whether it’s monitoring the position of a hydraulic jack or determining the proper position of a flood gate on a dam, be sure to choose the best option for precision, accuracy, and most importantly, reliability.

Strings Holding Down Production 

String potentiometers, also known as string pots, yo-yo sensors, cable-extension transducers, and a few other names, have been used for electronic measurement for the last 40 years.

These devices use braided steel wires (“strings”) wrapped around spools and require the release of the coiled string.


In an industrial assembly application, a typical scenario might involve wire being integrated into a manufacturing platform that moves from one assembly station to the next. As the string pot’s spool extends or retracts, position is measured by a rotational sensor/potentiometer that rests outside the spool and will trigger based on the position of the metal wire.

While string pots are often used in many sectors (heavy industry, crude oil processing, waste water treatment, etc.), they come with potential issues that make then unsuitable for others:

  • The wire will eventually jam from rust, mechanical glitches, or other environmental factors
  • The springs in the reel often fail over time
  • The high contact nature of the devices causes friction among the components, which leads to excessive wear and failure after a few thousand rotations

Combined, these things lead to expensive downtime/loss of production and costly repairs. A measurement system should not be a consumable item or an item with an expected but unpredictable maintenance interval. A measurement system should be designed with longevity and reliability in mind.

Right Solution for Your Industry

The assembly industry is not the only one that benefits from highly accurate position measurement. Whether it’s metallurgy, plastics and rubber, energy, or woodwork —­  the advanced, versatile, and resilient technology is required to thrive in high speed and demanding applications.

Fortunately, magnetostrictive linear transducers were developed to provide the kind of reliable position measurement that industry demands.

Instead of a trouble-prone mechanism, magnetostrictive non-contact linear transducers work with a movable free-floating or captive magnet that rides the length of a sensing rod as it follows the target object.

During operation, a very short-duration pulse is generated along the sensing element. This is known as the waveguide. The resulting magnetic field interacts with the magnetic field of the position magnet and generates a mechanical force on the sensing element. This force ripples along the waveguide at a faster-than-sound velocity that is detected by the sensor electronics, and is converted into an electrical pulse.

Using a very accurate high-speed clock, the time interval between the initial current pulse and return pulse is measured and converted into an absolute position value.

The end result is constant, precise, accurate, and smooth position measurement.


As an example: A high speed punch press requires position monitoring down to the millisecond. The punch press is designed to move very quickly back and forth in rows, punching holes in precise locations. When one row is finished, the unit moves forward and does the next. As the punch continues back and forth and up the rows, the sensor follows the position of the press, transmitting position feedback to the control system. This ensures the press stays on the appropriate track and punches where it should.

A contact device would not be suitable for this kind of operation, as the amount of friction caused from the speed and repetition would wear the sensor down too quickly and cause failure.

Fortunately, magnetostrictive linear sensors are widely available, come in a variety of form factors, and are truly non-contact, with some “floating” versions riding as much as 15mm off the surface of the transducer body. No contact means no wire binding issues and the lack of contact also means a lack of impact damage, which will help the sensor survive longer than a string potentiometer.

A measuring distance from 1 to 300 inches, offers short and long range capabilities.

Moreover, compared to string pots, magnetostrictive linear sensors, require fewer components. This means fewer parts to replace and maintain, which results in a reduction in overall equipment and maintenance costs.

Adaptable to nearly any industrial control system, these sensors are available in common analog (0….10V or 4….20 mA), as well as a variety of digital interfaces. This includes digital start/stop, synchronous serial interface, as well as network interfaces (IO-Link, Ethernet/IP, Profinet).

Tying it All Together

Though both string pots and magnetostrictive linear transducers are employed for electronic measurement, selecting the one that is best for your application will maximize manufacturing efficiency, increase machine uptime, and cut costs. All while ensuring your process keeps running smoothly and your customers get the parts and products they need on time.

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.


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.


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.


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.


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

A Gap Opens for Magnetic Linear Encoders

Innovation sometimes explodes onto the scene as a disruptive technology. More often, though, it arrives quietly in the form of continuous improvement that enhances performance and expands the scope of application capabilities. Sometimes evolutionary improvements are subtle, but once in a while they are game-changing.

When it comes to magnetic linear encoders, there have been steady improvements over the years in terms of resolution and linearity, enabling them to replace optical linear encoders in many applications at a fraction of the cost. One stubborn limitation, however, has been the trade-off between measuring performance and tape-to-sensor gap distance, sometimes called simply the gap distance or the ride height. Generally speaking, the higher the resolution and/or linearity specification, the smaller the allowable gap distance or ride height becomes. This reduction in ride height requires a corresponding tightening of machine tolerances in order to ensure that the maximum allowable gap distance is not exceeded.

Magnetic linear encoder

Recent breakthroughs in magnetic encoder design and technology have resulted in a new class of linear encoder systems that offer greatly expanded ride height. For example, an incremental system with 1 μm resolution and a system accuracy of ± 10 μm required a typical maximum tape-to-sensor gap distance of 0.35 mm. Now, the new generation of encoder technology can deliver the same 1 μm resolution and a similar ± 12 μm system accuracy, but with a maximum gap distance of 1.0 mm, nearly a threefold increase in ride height. That means far better tolerance of variability in the gap distance as the machine goes through its motions.

What’s more, encoder functionality can be assured even when the gap distance increases to as much as 1.8 mm, albeit with some loss of accuracy at these extreme distances. The ability to tolerate expanded variation in ride height ensures that machine operation will not be disrupted by loss of the encoder signal, even when gap tolerances occasionally exceed design maximums. That translates directly into greater design freedom for the engineer, and more machine uptime with fewer nuisance stoppages for the end user.

To learn more about the new generation of magnetic linear encoders, visit


Where Discrete Position Sensing Belongs in the Manufacturing Process

Unlike continuous position sensors which provide near real-time position feedback throughout the stroke of the cylinder, discrete position sensors are equipped with a switching functionality at one or more designated positions along the cylinder’s stroke. Typically, these positions are set to detect fully retracted and extended positions but one can also be used to detect mid-stroke position.

To determine which is right for you requires a review of your application and a determination of how precisely the movement of the cylinder needs to be controlled. Some hydraulic cylinder applications require no position sensing at all. These applications simply use the cylinder to move a load, and position control is either done manually or by some other external switch or stop. Moving up a step, many applications require only that the beginning and end of the cylinder stroke be detected so that the cylinder can be commanded to reverse direction. These applications are ideal for discrete position sensing.

Several types of sensors are used for discrete position detection, but one of the most common is high-pressure inductive proximity sensors, which are installed into the end caps of the cylinder. The sensors detect the piston as it reaches the end of the cylinder stroke in either direction.

These sensors are designed to withstand the full pressure of the hydraulic system. Inductive sensors are extremely reliable because they operate without any form of mechanical contact and are completely unaffected by changes in oil temperature or viscosity.

High-pressure inductive sensors installed in hydraulic cylinder

Discrete position sensors are used in applications such as hydraulic clamps, detection of open/closed position in welding operations, and in hydraulic compactors and balers for compacting materials until end of cylinder stroke is reached, at which point the cylinder retracts.

Additionally, it is quite common for pneumatically-actuated clamps and grippers to use discrete sensors to indicate fully extended and fully retracted positions, and in many cases, in-between positions as well. There are even applications where multiple discrete sensors are used in grippers for gauging and sizing work pieces.

By far, the most common method of providing discrete position in an air cylinder is to use externally-mounted switches that react to a magnet installed around the circumference of the piston. These magnetically-actuated switches can sense the field of a magnet embedded in the cylinder’s piston through the aluminum body of the cylinder.

magnetically actuated
Magnetically actuated sensor installed into cylinder C-slot

There are several different operating principles used in these magnetically-actuated switches, ranging from simple, low-cost reed switches and Hall-effect switches to significantly more reliable sensors that use magnetoresistive technology. One of the big advantages of magnetoresistive sensors is that they will reliably detect both radial and axial magnetic fields, making them ideal replacements for reed or Hall-effect switches.

Check out our previous blog to learn more about continuous position sensors.

When and Where to Use Continuous Cylinder Position Sensing

The role of smart cylinders — hydraulic or pneumatic cylinders with integrated position detection capability — has increased as manufacturers constantly strive to improve efficiency through automation. Smart cylinders can use either continuous or discrete position sensing, providing manufacturers with options, but possibly leaving them with questions on which is best for their application.

In this post we will review the benefits of continuous position sensors and list the applications where this is the best fit.

Continuous position sensors provide near real-time position feedback throughout the entire stroke of the cylinder making them the ideal choice for applications at the higher end of the control spectrum. Closed-loop servohydraulic systems can achieve sophisticated, dynamic control of motion across the entire cylinder stroke.

Continuous position sensors are commonly used when the application calls for closed-loop servo control, where the position, speed, acceleration, and deceleration of the cylinder must be controlled. Closed-loop servohydraulics have been widely used in industrial applications, such as sawmills, steel processing and tire manufacturing, and more recently in cylinders in off-highway equipment.

Magnetostrictive linear position sensors are the most commonly used continuous position sensors in hydraulic cylinders. These sensors are installed into the back end of the cylinder. The sensor detects the position of a magnet attached to the piston and provides a continuous, absolute position signal.

Magnetostrictive linear position sensor installed in hydraulic cylinder

The sensor is rated to withstand the full pressure of the hydraulic system. Magnetostrictive technology offers the advantage of being completely non-contact, meaning it requires no mechanical contact between the sensor and the moving cylinder and is not subject to wear and performance degradation. In addition, numerous electrical interface options are available, from simple analog (0 to 10V or 4-20mA) to high-performance industrial fieldbus interfaces that offer advanced functionality.

Continuous position sensors can also be used in pneumatic cylinders. While closed-loop servo control with pneumatics is not as common as it is with hydraulics, there are situations where pneumatic cylinders require continuous position sensing capability. For example, low-pressure pneumatic cylinders are sometimes used as measurement probes, or touch probes, where the cylinder rod is extended until it touches a part to be measured or gaged. In these situations, it is beneficial to be able to get continuous position feedback, especially when there is variability in the measured part.

To learn more about cylinder position sensing, visit

Clamp Control of Tools and Workpieces

In Metalworking, the clamping status of tools and workpieces are monitored in many Image1applications. Typically, inductive sensors are used to control this.

Three positions are usually detected: Unclamped, clamped with object, and clamped without object. The sensor position is mechanically adjusted to the application so the correct clamping process and clamping status is detected with a proper switch point. Additionally, with the usage of several sensors in many cases the diagnostic coverage is increased.

For approximately 15 years, inductive distance sensors with analog output signals have been utilized in these applications with the advantage of providing more flexibility.

 Image2By using a tapered (conical) shape, an axial movement of the clamping rod can be sensed (as a change of distance to the inductive sensor with analog output). Several sensors with binary (switching) output can be replaced with a sensor using such a continuous output signal (0..10V, 4-20 mA or e.g. IO-Link). Let’s figure a tool in a spindle is replaced by another tool with a different defined clamping position. Now, rather than mechanically changing the mechanical position of the inductive sensor with binary output, the parameter values for the correct analog signal window are adjusted in the control system. This allows easy parameter setting to the application, relevant if the dimensions of the clamped object may vary with different production lots.

The latest state-of-the-art sensor solution is the concept of a compact linear position system which is built of several inductive sensor elements mounted in one single housing. Image3

Instead of a tapered (conical) shape, a disk shaped target moves lateral to the sensor. From small strokes (e.g. 14 mm) up to more than 100 mm, different product variants offer the best combination of compact design and needed lateral movement. Having data about the clamping force (e.g. by using pressure sensors to monitor the hydraulic pressure) will lead to additional information about the clamping status.

For more information on linear position sensors visit

For more information on pressure sensors, visit


Top 5 Automation Insights Posts from 2017

Kick off the New Year by taking a look at the top 5 Automation Insight blog posts from last year.

#5. Make sure your RFID system is future-proof by answering 3 questions

With the recent widespread adoption of RFID technology in manufacturing plants I have encountered quite a number of customers who feel like they have been “trapped” by the technology. The most common issue is their current system cannot handle the increase in the requirements of the production line. In a nutshell, their system isn’t scalable.5

Dealing with these issues after the fact is a nightmare that no plant manager wants to be a part of. Can you imagine installing an entire data collection system then having to remove it and replace it with a more capable system in 3 years or even less? It’s actually a pretty common problem in the world of technology. However, an RFID system should be viable for much longer if a few simple questions can be answered up front. Read more>>

#4. IO-Link Hydraulic Cylinder Position Feedback

Ready for a better mousetrap?  Read on…..

Some time ago here on Sensortech, we discussed considerations for choosing the right in-cylinder position feedback sensor.  In that article, we said:

“…….Analog 0-10 Vdc or 4-20 mA interfaces probably make up 70-80% of all in-cylinder feedback in use…..”


And while that 70-80% analog figure is still not too far off, we’re starting to see those numbers decline, in favor a of newer, more capable interface for linear position feedback:  IO-Link.  Much has been written, here on Sensortech and elsewhere, about the advantages offered by IO-Link.  But until now, those advantages couldn’t necessarily be realized in the world of hydraulic cylinder position feedback.  That has all changed with the availability of in-cylinder, rod-style magnetostrictive linear position sensors.  Compared to more traditional analog interfaces, IO-Link offers some significant, tangible advantages for absolute position feedback in hydraulic cylinders. Read More>>

#3. External Position Feedback for Hydraulic Cylinders

The classic linear position feedback solution for hydraulic cylinders is the rod-style magnetostrictive sensor installed from the back end of the cylinder. The cylinder rod is gun-drilled to accept the length of the sensor probe, and a target magnet is installed on the face of the piston. A hydraulic port on the end cap provides installation access to thread-in the pressure-rated sensor tube. This type of installation carries several advantages but also some potential disadvantages depending on the application. Read More>>


#2. 3 Smart Applications for Process Visualization

Stack lights used in today’s industrial automation haven’t changed their form or purpose for ages: to visually show the state (not status) of the work-cell. Since the introduction of SmartLight, I have seen customers give new2 meaning to the term “process visualization”. Almost every month I hear about yet another innovative use of the SmartLight. I thought capturing a few of the use-cases of the SmartLight here may help others to enhance their processes – hopefully in most cost effective manner.

The SmartLight may appear just like another stack-light.  The neat thing about it is that it is an IO-Link device and uses simply 3-wire smart communication on the same prox cable that is used for sensors in the field. Being an IO-Link device it can be programmed through the PLC or the controller for change of operation modes on demand, or change of colors, intensity, and beeping sounds as needed. What that means is it can definitely be used as a stack light but has additional modes that can be applied for all sorts of different operation/ process visualization tasks. Read More>>

#1. What is a Capacitive Sensor?

Capacitive proximity sensors are non-contact devices that can detect the presence or absence of virtually any object regardless of material.  1They utilize the electrical property of capacitance and the change of capacitance based on a change in the electrical field around the active face of the sensor.

A capacitive sensor acts like a simple capacitor.  A metal plate in the sensing face of the sensor is electrically connected to an internal oscillator circuit and the target to be sensed acts as the second plate of the capacitor.  Unlike an inductive sensor that produces an electromagnetic field a capacitive sensor produces an electrostatic field. Read More>>

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.


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

Measurement Fundamentals: Position Measurement vs. Distance Measurement

Continuous measurements on industrial machines or the materials that these machines are making, moving, or processing can be categorized into two main types of sensors:  position measurement sensors, and distance measurement sensors.  It’s a somewhat subtle distinction, but one that is important when evaluating the best measurement sensor for a particular application.

Position Measurement: When we speak in terms of position measurement, we’re typically talking about applications where a the sensor is installed onto a machine, and mechanically coupled to the moving part of the machine – or is installed into a hydraulic cylinder that is moving the machine – and is reporting the continuous position of the machine.  In a positioning application, the questions that need to be answered are: “Where is it?  Where is it now?  And now?”.

Scott image1

Examples of position measurement sensors include magnetostrictive linear position sensors and magnetically encoded linear sensors.  With each of these sensor types, either the sensor itself, or the position marker, is typically attached to the moving part of the machine.

Distance Measurement: Distance measurement sensors, on the other hand, are used in applications that require accurate measurement of a target that is typically no part of the machine.  A good example would be an application where parts or components are moving along a conveyer belt, and the position of those parts needs to be accurately measured.  In this example, it wouldn’t be practical, or even possible, to attach a sensor to the moving part.  So its position needs to be measured from a DISTANCE.  In a distance measuring application, the question being answered is: “How far away is it?”.

Scott image2

Examples of distance measuring sensors include photoelectric (laser) sensors and inductive distance sensors.  These types of sensors are usually mounted on the machine, or in the immediate vicinity of the machine, and are aimed at a point or a path where the object to be measured is, or will be, located.

In summary, while both position and distance sensors do much the same thing – provide continuous indication of position – the applications for each are generally quite different.  Gaining an understanding of the application and its requirements will help to determine which type of sensor is the best choice for the task.

For more information on position and distance measurement sensors, visit