The Evolution of RFID in Metalworking

RFID – A key technology in modern production

It’s not just IIoT that has focused attention on RFID as a central component of automation. As a key technology, radio frequency identification has been long established in production. The inductive operating principle guarantees ruggedness and resistance to environmental stress factors. This makes the system highly reliable in function and operation. With unlimited read/write cycles and real-time communication, RFID has become indispensable. The beginnings for the industrial use of RFID go far back. RFID was first successfully used on machine tools in the mid-1980’s. Since the usage of RFID tags on cutting tool holders has been internationally standardized (ISO 7388 for SK shanks, ISO12164 for HSK shanks), there has been strong growth of RFID usage in cutting tool management.

Cutting tool in tool taper with RFID chip

Track-and-trace of workpieces

Modern manufacturing with a wide bandwidth of batch sizes and ever compressed production times demands maximum transparency. This is the only way to meet the high requirements for flexibility and quality, and to minimize costs. Not only do the tools need to be optimally managed, but also the finished parts and materials used must be unambiguously recognized and assigned.

Workpiece tracking with RFID on pallet system

RFID frequencies LF and HF – both RFID worlds come together

In terms of data transmission for cutting tool identification, established systems have settled on LF (Low Frequency), as this band has proven to be especially robust and reliable in metal surroundings. Data is read with LF at a frequency of 455 kHz and written at 70 kHz.

When it comes to intralogistics and tracking of workpieces, HF (High Frequency) has become the standard in recent years. This is because HF systems with a working frequency of 13.56 MHz offer greater traverse speeds and a more generous read/write distance.

As a result, RFID processor units have been introduced that offer frequency-independent application. By using two different read-/write heads (one for tool identification and one for track-and-trace of workpieces) that each interface to a single processor unit, the communication to the control system is achieved in an economical manner.

RFID processor for both tool identification and workpiece tracking

New Hybrid Read-Write Head

Industrial equipment is designed for a working life of 20 years or even more. Therefore, in production you often find machines which were designed in the last century next to new machines that were installed when the production capacity was enlarged. In such a brown field factory you have the coexistence of proven technology and modern innovative equipment. For the topic of industrial RFID, it means that both low frequency and high frequency RFID tags are used. To use both the existing infrastructure and to introduce modern and innovative equipment, RFID read/write heads have been recently developed with LF and HF technology in one housing. It does not matter whether a LF RFID tag or a HF RFID tag approaches the RFID head. The system will automatically detect whether the tag uses LF or HF technology and will start to communicate in the right frequency.

This hybrid read-write head adds flexibility to the machine tools and tool setters as you can use the entire inventory of your cutting tools and tool holders.

RFID Tool ID tag ready for the Cloud

The classical concept of data storage in Tool ID is a decentralized data storage, which means that all relevant data (tool dimensions, tool usage time, machining data, etc.) of a tool/tool holder is stored on the RFID tag which is mounted on the single tool holder. The reliability and availability of this concept data has been proven for more than 25 years now.

With the Internet of Things IIOT, the concept of cloud computing is trendy. All — tool setter, machine tool and tool stock systems — are connected to the cloud and exchange data. In this case only an identifier is needed to move and receive the data to and from the cloud. For this type of data management Tool ID tags with the standard (DIN 69873) size diameter 10 x 4,5 mm are available now in a cost effective version with a 32 Byte memory.

Evergreen – more modern than ever: RFID Tool ID in Metalworking

Learn more about the Evolution of RFID in Metalworking from true experts at  or at  Balluff events worldwide

Robot Collaborative Operation

In previous blogs, we discussed how “Safety Over IO-Link Helps Enable Human-Robot Collaboration” and “Safety & Productivity”. We’ll build on these blogs and dive more deeply into two robot collaborative operating modes: Safety-Rated Monitored Stop (SRMS) and Speed & Separation Monitoring (SSM).

Human-Robot Collaboration

Human-robot collaboration has received a lot of attention in the media, yet there is still confusion about the meaning and benefits of various types of collaboration. In a previous blog we briefly discussed the four collaborative modes defined by the global standard ISO/TS 15066. The most well-known mode is “power & force limiting”, which includes robots made by Universal Robots and Rethink. As the name implies, these robots are designed with limited power and force (and other ergonomic factors) to avoid injury or damage, but they are also slower, less precise and less powerful than traditional robots, reducing their usefulness in many common applications.

Tom K Blog

The safety-rated monitored stop (SRMS) and speed & separation monitoring (SSM) modes are very interesting because they allow larger, more powerful, traditional robots to be used collaboratively — though in a different manner than power & force limited robots. The updated standards allow the creation of a shared workspace for the robot and human and define how they may interact in this space. Both SRMS and SSM require this shared workspace to be monitored using advanced safety sensors and software, which create a restricted space and a safeguarded space. With SRMS, the robot stops before the operator enters the collaborative workspace — this requires a safety sensor to detect the operator.  Similarly, in SSM the goal is to control the separation distance between the human and robot, but it can be dynamic, rather than static as in SRMS. The SRMS separation distance can never be less than the protective distance and this requires sensors to verify the separation.


The robot’s restricted space is a 3-dimensional area created to limit where the robot can operate. In the past this was done through limit switches, hard stops or sensors such as Balluff’s BNS; now the standards have been updated to allow this to be done in software with internal robot feedback that can dynamically change to adapt to the robot’s programmed operation. The robot controller can now restrict the robot’s motion to a specific envelope and monitor its actual position against its programmed position within this envelope using software tools such as Safe Move or Dual Check Safety.

The safeguarded space is defined and monitored using safety sensors. The robot might know and assure its own safe position within the restricted space, but it doesn’t know whether or not a person or obstruction is in this space, therefore a safeguarded space needs to be created using safety sensors. Advanced sensors not only detect people or obstructions, but can also actively track their position around the robot and send warning or stop signals to the safety controller and robot. Safety laser scanners, 3D safety cameras and other safety sensors can create zones, which can also be dynamically switched depending on the operating state of the robot or machine.

Closely coordinating the restricted space and safeguarded space creates a flexible and highly productive system. The robot can operate in one zone, while an operator loads/unloads in a different zone. The robot sensors monitor the restricted space while the safety sensors monitor the safeguarded space – and when the robot moves to the next phase of operation, these can dynamically switch to new zones. Warning zones can also be defined to cause the robot to slow down if someone starts to approach too closely and then stop if the person comes too close.


System Linkages

Linking the restricted space and safeguarded space to create an effective, closely coordinated human-robot SSM/SRMS collaborative system requires several elements: a high performance robot and controller with advanced software (e.g. Safe Move), a fieldbus and a variety of built-in and external sensors (standard and safety).

Significant growth in robot collaborative applications utilizing safety-rated monitored stop (SRMS) and speed & separation monitoring (SSM) will occur as robot users strive to improve productivity and safety of traditional robot systems – especially in applications requiring faster speed, higher force and more precision than that offered by power & force limited robots.

Set your sights on IO-Link for machine vision products

While IO-Link is well addressed in an automated production environment, some have overlooked the benefits IO-Link can deliver for machine vision products.

PLC Gateway-Modus

Any IO-Link device can be connected and controlled by the PLC via fieldbus interface. Saving installation costs and controlling and running IO-Link components are the key values. All the well-known IO-Link benefits apply.


Camera-Modus – without PLC

However, with IO-Link that operates in this mode, the IO-Link-interfaces Rainer2are directly controlled. IO-Link I/O-Modules are automatically detected, configured and controlled.

In a stand-alone situation where an optical inspectionRainer3 of a component is performed without PLC, the operator delivers the component, hits a trigger button, the SmartCamera checks for completeness of production quality, sends a report to a separate customer server, and controls directly via IO-Link interface the connected vision product.

For more information about machine vision and optical identification see


Process Audits – the most powerful tool you probably aren’t using

For a myriad of reasons, when industrial machinery is being designed and constructed, the right sensing/connectivity product with the right application-specific attributes doesn’t always get designed into the zone of the machinery for the function it’s intended to perform.  This can result in consumption, excessive and expensive machine downtime and increased overall cost to operate the machinery.  A process audit, which is used in end-user environments to document specific sensing/electronic measurement/network/connectivity issues, can assist with reducing machine downtime, increasing productivity and reducing material consumption on the plant floor.

Getting to Root Cause of Failure

Finding out and documenting exactly why things prematurely fail in specific electronic locations by Cell Number and OPS Number, photographing each problematic sensor location and offering solutions to areas where components are prematurely failing is the heart and soul of an audit. It’s pretty amazing, but once problem areas are documented, and shared with every pertinent player from the corner office to the operator, it’s hard to refute and even harder to ignore.

Understanding the problem and why it is happening, allows a company to establish a timeline and an action plan for retrofitting sensor locations and developing best practice solutions that will enhance productivity, decrease machine downtime, build better parts with efficiency, and save the organization money.

Pictured below is a plain Jane, plastic faced, M5 inductive proximity sensor with minimal rated sensing distance (Sn) in a hostile spot that a customer is using to detect small “L” brackets on a huge welded panel.  If five of these are used per day (common), and the purchase price for the device is approximately $56 each, this equates to $280 per day or $1,680 per six-day work week. That totals to $84,000 spent per year for one inductive sensor in one individual sensor location.  If machine downtime is a nominal $250/minute (a very low estimation) and it takes five minutes to change out this sensor, machine downtime equates to $375,000 (1,500 sensors x $250).  One sensor can potentially cost this customer $459k per 50 week manufacturing year when factoring in material and downtime.

Dave Bird

If best practice solutions save the customer 50% (In fairness, most customers will only go so far to improve the process.), the business will see a savings of $229,500!

This is a significant payoff for the relatively small cost of an audit. Some businesses will provide them at no charge in the hope that the customer will then use that business to implement the best practice solutions — a win-win situation.

A small price to pay

Audits aren’t reserved for only harsh manufacturing environments like metal stamping and robotic welding. Any end-user manufacturing discipline that integrates sensors, connectivity, RFID, and networking systems that are consumed in the process of a hostile manufacturing environment is a candidate for an audit.

Hostile manufacturing can show up in all industries in all parts of the country.  The process audit can be a valuable tool for you and for your customers.

Reviewing options for optimized level detection in the food & beverage industry

Level detection plays an important role in the food and beverage industry, both in production and filling. Depending on the application, there are completely different requirements for level detection and, therefore, different requirements for the technologies and sensors to solve each task.

In general, we can differentiate between two requirements — Do I want to continuously monitor my filling level so that I can make a statement about the current level at any time? Or do I want to know if my filling level has reached the minimum or maximum?

Let’s look at both requirements and the appropriate level sensors and technologies in detail.

Precisely detecting point levels

For point level detection we have three different options.

A through-beam fork sensor on the outside of the tank is well suited for transparent container walls and very special requirements. Very accurate and easy to install, it is a good choice for critical filling processes while also being suitable for foaming materials.

Image 1
One point level detection through transparent container walls

For standard applications and non-metallic tank walls, capacitive sensors, which can be mounted outside the tank, are often the best choice. These sensors work by detecting the change of the relative electric permittivity. The measurement does not take place in direct contact with the medium.

Figure 2
Minimum/maximum level detection with capacitive sensors

For applications with metal tanks, there are capacitive sensors, which can be mounted inside the tank. Sensors, which meet the special requirements for cleanability (EHEDG, IP69K) and food contact material (FCM) required in the food industry,  are mounted via a thread and a sealing element inside the tank. For conductive media such as ketchup, specially developed level sensors can be used which ignore the adhesion to the active sensor surface.

Figure 3
Capacitive sensors mounted inside the tank

Continuous level sensing

Multiple technologies can be used for continuous level sensing as well. Choosing the best one depends on the application and the task.

Continuous level detection can also be solved with the capacitive principle. With the aid of a capacitive adhesive sensor, the level can be measured from the outside of the tank without any contact with the sensor. The sensor can be easily attached to the tank without the use of additional accessories. This works best for tanks up to 850 mm.

Figure 4
Continuous level detection with a capacitive sensor head

If you have fast and precise filling processes, the magnetostrictive sensing principle is the right choice. It offers very high measuring rate and accuracy. It can be used for tank heights from 200 mm up to several meters. Made especially for the food and beverage  industry, the sensor has the Ecolab, 3A and FDA certifications. Thanks to corrosion-free stainless steel, the sensor is safe for sterilization (SIP) and cleaning (CIP) in place.

Figure 5
Level detection via magnetostrictive sensing principle

If the level must be continuously monitored from outside the tank, hydrostatic pressure sensors are suitable. Available with a triclamp flange for hygienic demands, the sensor is mounted at the bottom of the tank and the level is indirectly measured through the pressure of the liquid column above the sensor.

Figure 6
Level detection via hydrostatic pressure sensor

Level detection through ultrasonic sensors is also perfect for the hygienic demands in the food industry. Ultrasonic sensors do not need a float, are non-contact and wear-free, and installation at the top of the tank is easy. Additionally, they are insensitive to dust and chemicals. There are even sensors available which can be used in pressurized tanks up to 6 bar.

Figure 7
Level detection via ultrasonic sensor

Product bundle for level monitoring in storage tanks

On occasion, both types of level monitoring are required. Take this example.

The tanks in which a liquid is stored at a food manufacturer are made of stainless steel. This means the workers are not able to recognize whether the tanks are full or empty, meaning they can’t tell when the tanks need to be refilled to avoid production downtime.

The solution is an IO-Link system which consists of different filling sensors and a light to visualize the filling level. With the help of a pressure sensor attached to the bottom of the tanks, the level is continuously monitored. This is visualized by a machine light so that the employee can see how full the tank is when passing by. The lights indicate when the tank needs to be refilled, while a capacitive sensor indicates when the tank is full eliminating overfilling and material waste.

Figure 8
Level monitoring in storage tanks

To learn more about solutions for level detection visit

What’s So Smart About a Smart Camera?

Smart “things” are coming into the consumer market daily. If one Googles “Smart – Anything” they are sure to come up with pages of unique products which promise to make life easier. No doubt, there was a marketing consortium somewhere that chose to use the word “smart” to describe a device which includes many and variable features. The smart camera is a great example of one such product where its name only leads to more confusion due to the relative and ambiguous term used to summarize a large list of features. A smart camera, used in many manufacturing processes and applications, is essentially a more intuitive, all-in-one, plug-and-play, mid-level technology camera.

OK, so maybe the marketing consortium is on to something. “Smart” does indicate a lot of features in a simple, single word, but it is important to determine if those smart features translate into benefits that help solve problems. If a smart camera is really smart it should include the following list of benefits:

  • Intuitive: To say it is easy to use just doesn’t cut it. To say it is easy for a vision engineer to use doesn’t mean that it is easy for an operator, a controls engineer, production engineer, etc. The camera should allow someone who has basic vision knowledge and minimal vision experience to select tools (logically named) and solve general applications without having to consult a manufacturer for a 2 day on-site visit for training and deployment.
  • All-In-One: The camera should house the whole package. This includes the software, manuals, network connections, etc. If the camera requires an external device like a laptop or an external switch to drive it, then it doesn’t qualify as smart.
  • Plug-and-play: Quick set up and deployment is the key. If the camera requires days of training and consultation just to get it up and running, then it’s not smart.
  • Relative technology: Smart cameras don’t necessarily need to have the highest end resolution, memory, or processing speed. These specs simply need to be robust enough to address the application. The best way to determine that is by conducting a feasibility study along with the manufacturer to make sure you are not paying for technology that won’t be needed or used.

Ultimately, a lot of things can be described as “smart”, but if you can make an effort to investigate what smart actually means, it’s a whole lot easier to eliminate the “gotchas” that tend to pop up at the most inopportune times.

Note: As with any vision application, the most important things to consider are lighting, lenses and fixtures. I have heard vision gurus say those three things are more critical than the camera itself.

How do I justify an IIoT investment to my boss?

Many engineers and managers I meet with when presenting at conferences on Smart Manufacturing ask some version of the question: “How can we justify the extra cost of Industrial Internet of Things (IIoT)?” or “How do I convince management that we need an Industry 4.0 project?” This is absolutely a fair and tough question that needs to be answered; without buy-in from management and proper budget allocation, you can’t move forward. While an investment in IIoT can deliver major payoffs, the best justification really depends on your boss.

I have seen three strong arguments that can be adapted to a variety of management styles and motivations.

1) Showing a ROI through Reducing Downtime

“Show me the money!” I think everyone has a manager with this expectation. It may seem like a daunting task to calculate or capture this information, but by using a team, knowing your KPIs and applying anecdotal feedback, you can get a good initial picture of the ROI that an IIoT project will bring to the organization. Many people have shared with me that their initial project’s ROI has “funded the next project.” There is a really great article from MetalForming Magazine that discusses how exactly to do this with the tables and forms they used at ODM Tool & Manufacturing.


2) Corporate Goals for Productivity and Utilization

We can be successful getting support for a project when we link corporate goals to project goals. Smart Industry publishes a research project each year that investigates trends in the manufacturing space in regards to digital transformation initiatives. This report cites that the three top benefits manufacturers are seeing are: improving worker productivity (3rd 2016), reducing costs (1st 2016) and optimizing asset utilization (2nd 2016). These goals are driving investments and showing actual results for manufacturers both large and small. However, the report also revealed that more than half of manufacturers cite workforce skills-gap issues as their largest roadblock and this is, I believe, why we saw improving worker productivity move to the top spot. We must bring efficiency and effectiveness to the people we have.


3) Your Competitors are Investing in IIoT!

If you have a boss that worries about falling behind, this can be a motivating argument. Control Engineering recently published a study of manufacturers and how they are investing in IIoT technologies. The largest investments are coming with sensors, connectivity and data analytics. But what is most shocking is that on average IIoT budgets are $328,160, with 18% budgeting more than a half-million dollars. If you want to keep up with the rapid pace of change in the global market, an investment in IIoT is a requirement to remain competitive.

If you are looking for support and partnership on your IIoT projects, we are experienced at utilizing IO-Link, smart sensors and RFID to enable Industry 4.0 and Smart Manufacturing projects.

Changing the Paradigm from Safety vs. Productivity to Safety & Productivity

In a previous blog, we discussed how “Safety Over IO-Link Helps Enable Human-Robot Collaboration”. It was a fairly narrow discussion of collaborative robot modes and how sensors and networks can make it easier to implement these modes and applications. This new blog takes a broader look at the critical role safety plays in the intersection between the machine and the user.

In the past, the machine guarding philosophy was to completely separate the human from the machine or robot.  Unfortunately, this resulted in the paradigm of “safety vs. productivity” — you either had safety or productivity, but you couldn’t have both. This paradigm is now shifting to “safety & productivity”, driven by a combination of updated standards and new technologies which allow closer human-machine interaction and new modes of collaborative operation.

Tom_Safety1.pngThe typical machine/robot guarding scheme of the past used fences or hard guards to separate the human from the machine.  Doors were controlled with safety interlock switches, which required the machine to stop on access, such as to load/unload parts or to perform maintenance or service, and this reduced productivity.  It was also not 100% effective because workers inside a machine area or work cell might not be detected if another worker restarted the stopped machine.  Other drawbacks included the cost of space, guarding, installation, and difficultly changing the work cell layout once hard guarding had been installed.

We’ve now come to an era when our technology and standards allow improved human access to the machine and robot cell.  We’re starting to think about the human working near or even with the machine/robot. The robot and machinery standards have undergone several changes in recent years and now allow new modes of operation.  These have combined with new safety technologies to create a wave of robot and automation suppliers offering new robots, controllers, safety and other accessories.

Machine and robot safety standards have undergone rapid change in recent years. Standard IEC 61508, and the related machinery standards EN/ISO 13849-1 and EN/IEC 62061, take a functional approach to safety and define new safety performance levels. This means they focus more on the functions needed to reduce each risk and the level of performance required for each function, and less on selection of safety components. These standards helped define, and made it simpler and more beneficial, to apply safety PLCs and advanced safety components. There have also been developments in standards related to safe motion (61800-5-2) which now allow more flexible modes of motion under closely controlled conditions. And the robot standards (10218, ANSI RIA 15.06, TS15066) have made major advances to allow safety-rated soft axes, space limiting and collaborative modes of operation.

On the technology side, innovations in sensors, controllers and drives have changed the way humans interact with machines and enabled much closer, more coordinated and safer operation. Advanced sensors, such as safety laser scanners and 3D safety cameras, allow creation of work cells with zones, which makes it possible for an operator to be allowed in one zone while the robot performs tasks in a different zone nearby. Controllers now integrate PLC, safety, motion control and other functions, allowing fast and precise control of the process. And drives/motion systems now operate in various modes which can limit speed, torque, direction, etc. in certain modes or if someone is detected nearby.

Sensors and Networks
The monitoring of these robots, machines and “spaces” requires many standard and safety sensors, both inside and outside the machine or robot. But having a lot of sensors does not necessarily allow the shift from “productivity vs. safety” to “productivity & safety” — this requires a closely coordinated and integrated system, including the ability to monitor and link the “restricted space” and “safeguarded space.” This is where field busses and device-level networks can enable tight integration of devices with the control system. IO-Link masters and Safety Over IO-Link hubs allow the connection of a large number of devices to higher level field busses (ProfiNet/ProfiSafe) with effortless device connection using off-the-shelf, non-shielded cables and connectors.

Balluff offers a wide range of solutions for robot and machine monitoring, including a broad safety device portfolio which includes safety light curtains, safety switches, inductive safety sensors, an emergency stop device and a safety hub. Our sensors and networks support the shift to include safety without sacrificing productivity.

Back to the Basics: Measuring

In the last post about the Basics of Automation, we discussed how objects can be detected, collected and positioned with the help of sensors. Now, let’s take a closer look at how non-contact measurement—both linear and rotary—works to measure distance, travel, angle, and pressure.

Measuring travel, distance, position, angle and pressure are common tasks in automation. The measuring principles used are as varied as the different tasks.

Sensor Technologies

  • Magnetostrictive enables simultaneous measurement of multiple positions and can be used in challenging environments.
  • Magnet coded enables the highest accuracy and real-time measurement.
  • Inductive is used for integration in extremely tight spaces and is suitable for short distances.
  • Photoelectric features flexible range and is unaffected by the color or surface properties of the target object.

Different Sensors for Different Applications

Distance measurement

Janni1Disc brakes are used at various locations
in wind power plants. With their durability and precise measurement, inductive distance sensors monitor these brake discs continuously and provide a timely warning if the brake linings need to be changed.

In winding and unwinding equipment, a photoelectric sensor continuously measures the increasing or decreasing roll diameter. This means the rolls can be changed with minimal stoppages.

Linear position measurement

Janni4Workpieces are precisely positioned on the slide of a linear axis. This allows minimal loss of production time while ensuring quality. Magnetic encoders installed along the linear axis report the actual slide position to the controller (PLC) continuously and in real time — even when the slide is moving at a speed of up to 10 m/s.

In a machine tool the clamping state of a spindle must be continuously monitored during machining. This improves results on the workpiece and increases the reliability of the overall system. Inductive positioning systems provide continuous feedback to the controller: whether the spindle is unclamped, clamped with a tool or clamped without a tool.

Rotational position measurement

Janni5Workpieces such as a metal plate are printed, engraved or cut on a cut/print machine. This demands special accuracy in positioning it on the machine. Magnetic encoders on both rotating axes of the machine measure the position of the workpiece and ensure an even feed rate.

In a parabolic trough system,
sunlight is concentrated on parabolic troughs using parabolic mirrors allowing the heat energy to be stored. To achieve the optimal energy efficiency, the position of the parabolic mirror must be guided to match the sun’s path. Inclination sensors report the actual position of the parabolic mirror to the controller, which then adjusts as needed.

Pressure and Level Measurement

Janni7Consistently high surface quality of the machined workpiece must be ensured in a machine tool. This requires continuous monitoring of the coolant feed system pressure. Pressure sensors can reliably monitor the pressure and shut down the machine within a few milliseconds when the defined pressure range is violated.

Janni8In many tanks and vats, the fill height of the liquid must be continually measured. This is accomplished using ultrasonic sensors, which note levels regardless of color, transparency or surface composition of the medium. These sensors detect objects made of virtually any material (even sound-absorbing) including liquids, granulates and powders.

Stay tuned for future posts that will cover the essentials of automation. To learn more about the Basics of Automation in the meantime, 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.