Distance Measurement with Inductive Sensors

When we think about inductive sensors we automatically refer to discrete output offerings that detect the presence of ferrous materials. This can be a production part or an integrated part of the machine to simply determine position. Inductive sensors have been around for a long time, and there will always be a need for them in automated assembly lines, weld cells and stamping presses.

We often come across applications where we need an analog output at short range that needs to detect ferrous materials. This is an ideal application for an analog inductive proximity sensor that can offer an analog voltage or analog current output. This can reliably measure or error proof different product features such as varying shapes and sizes. Analog inductive sensors are pure analog devices that maintain a very good resolution with a high repeat accuracy. Similar to standard inductive sensors, they deal very well with vibration, commonly found in robust applications. Analog inductive proximity sensors are also offered in many form factors from M12-M30 tubular housings, rectangular block style and flat housings. They can also be selected to have flush or non-flush mounting features to accommodate specific operating distances needed in various applications.

Application Examples:



For more specific information on analog inductive sensors visit www.balluff.com.

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 www.balluff.com.

The Evolving Technology of Capacitive Sensors

In my last blog post, Sensing Types of Capacitive Sensors, I discussed the basic types of capacitive sensors; flush versions for object detection and non-flush for level detection of liquids or bulk materials.  In this blog post, I would like to discuss how the technology for capacitive sensors has changed over the past few years.

The basic technology of most capacitive sensors on the market was discussed in the blog post “What is a Capacitive Sensor”.  The sensors determine the presence of an object based on the dielectric constant of the object being detected.  If you are trying to detect a hidden object, then the hidden object must have a higher dielectric constant than what you are trying to “see through”.

Conductive targets present an interesting challenge to capacitive sensors as these targets have a greater capacitance and a targets dielectric constant is immaterial.  Conductive targets include metal, water, blood, acids, bases, and salt water.  Any capacitive sensor will detect the presence of these targets. However, the challenge is for the sensor to turn off once the conductive material is no longer present.  This is especially true when dealing with acids or liquids, such as blood, that adheres to the container wall as the level drops below the sensor face.

Today, enhanced sensing technology helps the sensors effectively distinguish between true liquid levels and possible interference caused by condensation, material build-up, or foaming fluids.  While ignoring these interferences, the sensors would still detect the relative change in capacitance caused by the target object, but use additional factors to evaluate the validity of the measurement taken before changing state.

These sensors are fundamentally insensitive to any non-conductive material like plastic or glass, which allows them to be utilized in level applications.  The only limitation of enhanced capacitive sensors is they require electrically conductive fluid materials with a dipole characteristic, such as water, to operate properly.

Enhanced or hybrid technology capacitive sensors work with a high-frequency oscillator whose amplitude is directly correlated with the capacitance change between the two independently acting sensing electrodes.  Each electrode independently tries to force itself into a balanced state.  That is the reason why the sensor independently measures  the capacitance of the container wall without ground reference and the capacitance of the conductivity of the liquid with ground reference (contrary to standard capacitive sensors).


Up to this point, capacitive sensors have only been able to provide a discrete output, or if used in level applications for a point level indication.  Another innovative change to capacitive sensor technology is the ability to use a remote amplifier.  Not only does this configuration allow for capacitive sensors to be smaller, for instance 4mm in diameter, since the electronics are remote, they can provide additional functionality.

The remote sensor heads are available in a number of configurations including versions image2that can withstand temperature ranges of -180°C up to 250°C.  The amplifiers can now provide the ability to not only have discrete outputs but communicate over an IO-Link network or provide an analog output.  Now imagine the ability to have an adhesive strip sensor that can provide an analog output based on a non-metallic tanks level.

For additional information on the industry’s leading portfolio of capacitive products visit www.balluff.com.

How to Develop and Qualify Sensors for Arctic Conditions

The climatic conditions in the arctic are characterized by cold winters and short summers. There is a large variability in climate and weather: Some regions face permafrost and are ice covered year-round with temperatures down to -40°C / -40°F (and lower), other land areas face the extremes of solar radiation up to +30°C / +86°F in summer.

As oil and gas exploration, as well as renewable energy (e.g. cold climate versions of wind turbines) move into arctic areas, the need grows for sensors designed to deal with the extreme conditions and to perform reliably over their whole life cycle.

One option is the implementation of a Highly Accelerated Life Test (abbreviation HALT) in the development process. The basic idea of HALT is the accelerated aging of electronic products (including sealing gaskets, potting compound, housing etc.) with the aim of detecting their possible weak spots as early as possible and to correct them at the development stage.

Example of a sensor in the HALT test facility (Balluff magnetostrictive linear position sensor BTL)

The item under test is subjected to higher and higher thermal and mechanical stress in order to cause failures. The limits where the product will fail functionally or be destroyed are determined in order to push these limits as far out as possible, and so achieve a higher reliability for the product.

Product operational specs = data sheet values

The HALT procedure – in brief:

a) Analysis of weaknesses already known, definition of failure criteria, establishing the stress factors

b) Stressing the test specimen beyond the specification to find the “upper and lower operating limits”, and the “upper and lower destruct limit” for temperature, rapid change of temperature, vibration, combined vibration and temperature stress

c) Determination of the causes of failure

d) Devising a solution to eliminate the weaknesses

e) Repeating of steps b) to c)

Example: Temperature step test – cold and hot
Example: Combined vibration test and rapid temperature changes
Example: Cowan Dynamics E2H Electro-Hydraulic valve actuator Photo: Cowan Dynamics (Canada)

In contrast to other environmental tests, HALT is not qualification testing according to specific technical standards (as  ISO/IEC etc.), but it applies stimuli to the items under test until they fail, so weak spots will be revealed. A HALT test is not an exam you can pass!

However, if sensors are implemented into more complex automation systems that will be operated in remote areas, this method may help to prevent major faults in the field and is therefore also used in the aircraft and automotive industry.

For more information about Balluff testing methods and the laboratory, please visit www.balluff.com or download our brochure “The Balluff Testing Laboratory”.


How Hot is Hot? – The Basics of Infrared Temperature Sensors

Detecting hot objects in industrial applications can be quite challenging. There are a number of technologies available for these applications depending on the temperatures involved and the accuracy required. In this blog we are going to focus on infrared temperature sensors.

Every object with a temperature above absolute zero (-273.15°C or -459.8°F) emits infrared light in proportion to its temperature. The amount and type of radiation enables the temperature of the object to be determined.

In an infrared temperature sensor a lens focuses the thermal radiation emitted by the object on to an infrared detector. The rays are restricted in the IR temperature sensor by a diaphragm, to create a precise measuring spot on the object. Any false radiation is blocked at the lens by a spectral filter. The infrared detector converts radiation into an electrical signal. This is also proportional to the temperature of the target object and is used for signal processing in a digital processor. This electrical signal is the basis for all functions of the temperature sensor.

There are a number of factors that need to be taken into account when selecting an infrared temperature sensor.

  • What is the temperature range of the application?
    • The temperature range can vary. Balluff’s BTS infrared sensor, for example, has a range of 250°C to 1,250°C or for those Fahrenheit fans 482°F to 2,282° This temperature range covers a majority of heat treating, steel processing, and other industrial applications.
  • What is the size of the object or target?
    • The target must completely fill the light spot or viewing area of the sensor completely to ensure an accurate reading. The resolution of the optics is a relationship to the distance and the diameter of the spot.

  • Is the target moving?
    • One of the major advantages of an infrared temperature sensor is its ability to detect high temperatures of moving objects with fast response times without contact and from safe distances.
  • What type of output is required?
    • Infrared temperature sensors can have both an analog output of 4-20mA to correspond to the temperature and is robust enough to survive industrial applications and longer run lengths. In addition, some sensors also have a programmable digital output for alarms or go no go signals.
    • Smart infrared temperature sensors also have the ability to communicate on networks such as IO-Link. This network enables full parameterization while providing diagnostics and other valuable process information.

Infrared temperature sensors allow you to monitor temperature ranges without contact and with no feedback effect, detect hot objects, and measure temperatures. A variety of setting options and special processing functions enable use in a wide range of applications. The IO-Link interface allows parameterizing of the sensor remotely, e.g. by the host controller.

For more information visit www.balluff.com

Basic Sensors for Robot Grippers

Robot gripper with inductive proximity sensors mounted
Robot gripper with inductive proximity sensors mounted

Typically when we talk about end-of-arm tooling we are discussing how to make robot grippers smarter and more efficient. We addressed this topic in a previous blog post, 5 Tips on Making End-of-Arm Tooling Smarter. In this post, though, we are going to get back to the basics and talk about two options for robot grippers: magnetic field sensors, and inductive proximity sensors.

One of the basic differences is that detection method that each solution utilizes. Magnetic field sensors use an indirect method by monitoring the mechanism that moves the jaws, not the jaws themselves. Magnetic field sensors sense magnets internally mounted on the gripper mechanism to indicate the open or closed position. On the other hand, inductive proximity sensors use a direct method that monitors the jaws by detecting targets placed directly in the jaws. Proximity sensors sense tabs on moving the gripper jaw mechanism to indicate a fully open or closed position.

Robot gripper with magnetic field sensors mounted

Additionally, each solution offers its own advantages and disadvantages. Magnetic field sensors, for example, install directly into extruded slots on the outside of the cylinder, can detect an extremely short piston stroke, and offer wear-free position detection. On the other side of the coin, the disadvantages of magnetic field sensors for this application are the necessity of a magnet to be installed in the piston which also requires that the cylinder walls not be magnetic. Inductive proximity sensors allow the cylinder to be made of any material and do not require magnets to be installed. However, proximity sensors do require more installation space, longer setup time, and have other variables to consider.

The Latest Trend in the Stamping and Die Industry

compact-sensor-blogOne trend we see today in many applications is the need for smaller low profile proximity sensors. Machines are getting much smaller and the need for error proofing has ultimately become a must for such applications in the Stamping and Die industry. Stamping Die processes can be a very harsh environment with excessive change overs to high speed part feed outs when running production. In many cases these applications need a sensor that can provide 5mm of sensing range however they simply do not have the room for an M18 sensor that is 45 to 50mm long. This is where the “FlatPack” low profile sensor can be a great choice due to their low profile dimensions.

Proximity sensors have proven time and time again to reduce machine crashes, part accuracy and proper part location. Sensors can be placed in multiple locations within the application to properly error proof “In Order Parts” (IO) for example detecting whether a punched hole is present or not present to ensure a production part is good. All of this adds up to reduced machine downtime and lower scrap rates that simply help a plant run more efficiently.

So when selecting proximity sensors and mating cables it is very important to select a sensor that A) mechanically fits the application and B) offers enough sensing range detection to reliably see the target without physical damage to the sensor. Remember, these sensors are proximity sensors not positive machine stops. Cables are also key to applications, it is important to pick a the proper cable needed for example an abrasion resistant cable may be needed due to excessive metal debris or a TPE cable for high flex areas.

Below both sensors have 5mm of sensing range:


Below both sensors have 2mm of sensing range:


You can see that in certain process areas “FlatPack” low profile sensors can provide benefits for applications that have space constraints.

For more information on proximity sensors click here.

Hydraulic Cylinder Position Feedback, Revisited

In a previous Sensortech post entitled “Hydraulic Cylinder Position Feedback“, we discussed the basic concept of hydraulic cylinder position feedback.  In case you might have missed that post, here it is for an encore appearance.

Magnetostrictive linear position transducers are commonly used in conjunction with hydraulic cylinders to provide continuous, absolute position feedback.  Non-contact magnetostrictive technology assures dependable, trouble-free operation.  The brief video below illustrates how magnetostrictive position sensors are used with hydraulic cylinders.

Continue reading “Hydraulic Cylinder Position Feedback, Revisited”

Back to the Basics: How Do I Wire a DC 2-wire Sensor?

In one of my previous post we covered “How do I wire my 3-wire sensors“. This topic has had a lot of interest so I thought to myself, this would be a great opportunity to add to that subject and talk about DC 2-wire sensors. Typically in factory automation applications 2 or 3 wire sensors are implemented within the process, and as you know from my prior post a 3 wire sensor has the following 3 wires; a power wire, a ground wire and a switch wire.

A 2-wire sensor of course only has 2 wires including a power wire and ground wire with connection options of Polarized and Non-Polarized. A Polarized option requires the power wire to be connected to the positive (+) side and the ground wire to be connected to the negative side (-) of the power supply. The Non-Polarized versions can be wired just as a Polarized sensor however they also have the ability to be wired with the ground wire (-) to the positive side and the power wire (+) to the negative side of the power supply making this a more versatile option as the sensor can be wired with the wires in a non – specific location within the power supply and controls.

In the wiring diagrams below you will notice the different call outs for the Polarized vs. Non-Polarized offerings.

PolarizedDiagramsnon-polarized diagramsNote: (-) Indication of Non-Polarized wiring.

While 3-wire sensors are a more common option as they offer very low leakage current, 2 wire offerings do have their advantages per application. They can be wired in a sinking (NPN) or sourcing (PNP) configuration depending on the selected load location. Also keep in mind they only have 2 wires simplifying connection processes.

For more information on DC 2- Wire sensors click here.