Evolution of Magnetic Field Sensors

When I visit customers, within a few minutes into our conversation they indicate to me they “must decrease their manufacturing downtime.” We all know an assembly line or weld cell that is not running is not making any money or meeting production cycle times. As we have the conversation regarding downtime the customer is always wanting to know what new or improved products are available that can increase uptime or improve their current processes.

A major and common problem seen at the plant level is a high amount of magnetic field sensor failures. There are many common reasons for this ranging from low quality sensors being used such as Reed switches that have a mechanical contact. Reed switch offerings typically have a lower price point than a discrete solid state offering with AMR or GMR technology however these low cost options will cost much more in the long run due to inconsistent trigger points and failure resulting in machine downtime. Another big part of failure is the location of the pneumatic cylinder position. It is not uncommon to see a cylinder located in a very hostile area resulting in sensor abuse and cable damage. In some cases the failure is simply associated to a cut cable or a cable that has been burned through from weld spatter.

Below are some key tips and questions that can be helpful when selecting a magnetic field sensor.

  • Do I need a T or C slot?
  • Do I need an NPN or PNP output?
  • Do I need a slide in style or a drop in type?
  • Do I need an offering that has an upgraded cable for harsh environment such as silicone tubing?
  • Do I need a duel head offering that only has one cable to simplify cable connections?
  • Do I need options like IO-Link that can provide multiple switch points and hysteresis changes?
  • Do I need one teachable sensor head that can read extended and retracted position?

If the tips above are put into practice you will sure have a better experience selecting the correct product for the application. Magnetic field sensors have evolved over the years with improved internal technology that make them much more reliable and user friendly for a wide range of applications. For example if the customer has magnetic field sensors installed in a weld cell they would want to select a magnetic field sensor that has upgraded cable materials or perhaps a weld field immune offering to deal with welding currents. Another example could be a pick and place application where the customer needs a sensor with multiple switch points or a hysteresis adjustment. In this case the customer could select a single head multiple teach sensor, offering the ability to fine tune the sensor using IO-Link.

For more information on all the various types of magnetic field sensors click here.

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Non-Contact Infrared Temperature Sensors with IO-Link – Enabler for Industry 4.0

Automation in Steel-Plants

Modern production requires a very high level of automation. One big benefit of fully automated plants and processes is the reduction of faults and mishaps that may lead to highly expensive downtime. In large steel plants there are hundreds of red hot steel slabs moving around, being processed, milled and manufactured into various products such as wires, coils and bars. Keeping track of these objects is of utmost importance to ensure a smooth and cost efficient production. A blockage or damage of a production line usually leads to an unexpected downtime and it takes hours to be rectified and restart the process.

To meet the challenges of the manufacturing processes in modern steel plants you need to control and monitor automatically material flows. This applies especially the path of the workpieces through the plant (as components of the product to be manufactured) and will be placed also at locations with limited access or hazardous areas within the factory.

Detection of Hot Metal

Standard sensors such as inductive or photoelectric devices cannot be used near red hot objects as they either would be damaged by the heat or would be overloaded with the tremendous infrared radiation emitted by the object. However, there is a sensing principle that uses this infrared radiation to detect the hot object and even gives a clue about its temperature.

Non-contact infrared thermometers meet the requirements and are successfully used in this kind of application. (The basics of this technology were discussed in a previous post.) They can be mounted away from the hot object so they are not destroyed by the heat, yet they capture the Infrared emitted as this radiation travels virtually unlimited. Moreover, the wavelength and intensity of the radiation can be evaluated to allow for a pretty accurate temperature reading of the object. Still there are certain parameters to be set or taught to make the device work correctly. As many of these infrared thermometers are placed in hazardous or inaccessible places, a parametrization or adjustment directly at the device is often difficult or even impossible. Therefore, an intelligent interface is required both to monitor and read out data generated by the sensor and – even more important – to download parameters and other data to the sensor.

Technical basics of Infrared Hot-Metal-Detectors

Traditional photoelectric sensors generate a signal and receive in most cases a reflection of this signal. Contrary to this, an infrared sensor does not emit any signal. The physical basics of an infrared sensor is to detect infrared radiation which is emitted by any object.
Each body, with a temperature above absolute zero (-273.15°C or −459.67 °F) emits an
electromagnetic radiation from its surface, which is proportional to its intrinsic
temperature. This radiation is called temperature or heat radiation.

By use of different technologies, such as photodiodes or thermopiles, this radiation can be detected and measured over a long distance.

Key Advantages of Infrared Thermometry

This non-contact, optical-based measuring method offers various advantages over thermometers with direct contact:

  • Reactionless measurement, i.e. the measured object remains unaffected, making it possible to measure the temperature of very small parts
  • Very fast measuring frequence
  • Measurement over long distances is possible, measuring device can be located outside the hazardous area
  • Very hot temperatures can be measured
  • Object detection of very hot parts: pyrometers can be used for object detection of very hot parts where conventional optical sensors are limited by the high infrared radiation
  • Measurement of moving objects is possible
  • No wear at the measuring point
  • Non-hazardous measurement of electrically live parts

IO-Link for smarter sensors

IO-Link as sensor interface has been established for nearly all sensor types in the past 10 years. It is a standardized uniform interface for sensors and actuators irrespective of their complexity. They provide consistent communication between devices and the control system/HMI.  It also allows for a dynamic change of sensor parameters by the controller or the operator on the HMI thus reducing downtimes for product changeovers. If a device needs to be replaced there is automatic parameter reassignment as soon as the new device has been installed and connected. This too reduces manual intervention and prevents incorrect settings. No special device-proprietary software is needed and wiring is easy, using three wire standard cables without any need for shielding.

Therefore, IO-Link is the ideal interface for a non-contact temperature sensor.

All values and data generated within the temperature sensor can be uploaded to the control system and can be used for condition monitoring and preventive maintenance purposes. As steel plants need to know in-process data to maintain a constant high quality of their products, sensors that provide more data than just a binary signal will generate extra benefit for a reliable, smooth production in the Industry 4.0 realm.

To learn more about this technology visit www.balluff.com.

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Difficulties Faced in Externally Mounted Magnetic Transducer Applications

In a previous blog post, we looked at the basic operating principle of magnetostriction and how it is applied in a linear position transducer. In this post we’re going to take a more in-depth look at this popular sensing technique and the factors that can contribute to its usability in transducer applications.

magnetostricive response

Figure 1: Magnetostrictive response (λ) as the absolute value of the Magnetic Field (H) changes.

As we’ve seen, the magnetostrictive effect is produced using a permanent magnet that is fixed either around or mounted some distance away from the ferromagnetic alloy that is being used. Now, if you’re like me and you’ve spent countless nights lying awake wondering how the effect of magnetostriction in a transducer is changed by the strength of the applied magnetic field and how that pertains to the output of a magnetostrictive transducer, then there isn’t need to look much further than this blog post. The strength of the magnetic field (which is directly related to distance through an inverse cubed relationship) projected onto the ferromagnetic material plays an incredibly critical role in the effect of magnetostriction. In Figure 1 you can see a depiction of the how the magnetostrictive effect varies at differing values of magnetic field strength.

Since magnetostriction does not behave perfectly linearly, some consideration must be taken into account when choosing a magnet and mounting system for your transducer. Potential problems occur if the magnet is mounted too far away from or too close to the transducer (thus producing either too much or too little magnetic field). But before we explore why too much or too little magnetic field is a problem, let’s compare it to the most desirable magnetic conditions.

Figure 2: Standard Application in which a magnet is in a fixed position therefore, allowing no variance in the strength of the magnetic field seen by the ferromagnetic material.

Ideally, the goal is to choose a magnet and mounting distance which can produce a magnetic field that will fall within the green region from Figure 1. In this region, the magnetostrictive effect can be approximated as linear, thus being used to produce a strong and consistently predictable output response. As for what actual magnetic field strength values fall within this range, that is almost entirely dependent on the properties of the ferromagnetic alloy that you are using. In a standard application, for instance, one in which a magnet and transducer is fixed inside of a hydraulic cylinder where the magnet is mounted in a fixed position relative to the transducer rod (as shown in Figure 2.), this magnetic field value will not vary so there is no reason to worry about how the magnetostrictive response could vary. The device is designed to operate in Figure 1’s green region.

Figure 3: Externally mounted magnets that are not fixed to the transducer typically need to have stronger magnetic properties for the field to reach the device. However, if it is too strong the magnetostrictive effect can saturate and cause a loss of output.

Problems can arise when dealing with externally mounted transducers in which the user has a significant amount more freedom in the selection of magnet and its mounting design. These instances could look incredibly different depending on the application. However, Figure 3 shows how this sort of design would come into play in a “floating” magnet application. At greater distances or when using weaker, non-standard magnets, the magnetic field will fall into the first red zone on Figure 1. In this region, the magnetic strength is too weak for a signal to be processed as an output by the transducer. This is primarily caused by the effect of magnetic hysteresis which is essentially a “charge up” zone and creates an exponential relationship in this zone, rather than the desired linear relationship. On the other hand, if you attempt to use a strong, rare-earth magnet too close to the transducer, it will produce too strong of a magnetic field and move beyond the green region into the second red zone. The problem here is that the magnetostriction will saturate and can potentially cause output loss. Also, similarly to the weaker magnetic field strength, the behavior cannot be approximated using the same linear relationship that we see in the green zone of Figure 1. As with the green region of the graph, the magnetic field strength values that lie in the red zones are dependent on the properties of the material as well as the response processing electronics of the transducer.

Due to these issues, there are many things to consider if you’re using an externally mounted transducer and choosing a non-standard mounting method in your application. You need to be careful when mounting a magnet too far away or using a rare-earth magnet too close to the transducer.

For more information visit www.balluff.us.

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IO-Link Sensors in Tire Manufacturing

Much has been written here on Sensortech about IO-Link, and the advantages that an IO-Link-based architecture offers. In this article, we’ll take a look at a specific application where those IO-Link advantages are clear.

Tire manufacturing machinery in general, and tire curing presses in particular, incorporate numerous sensors and indicators that contribute to machine efficiency. As an example, tire curing presses often use magnetostrictive linear position sensors for feedback and control of mold open/close. Overwhelmingly, sensors that provide an analog, 4-20 mA signal are used. But maybe there’s a better alternative to typical analog feedback.

As discussed HERE and HERE, migration away from typical analog sensor signals to network-capable IO-Link interfaces makes a great deal of sense in many areas of application.

In a tire manufacturing operation, there are typically numerous, essentially identical curing presses, lined up in a row, all doing essentially the same job. Each press uses multiple analog position sensors that need each need to be connected to the press control system. As with pretty much analog device, the use of individual shielded cables is critical. Individual shielded cables for every sensor is a costly a time-consuming proposition. An Engineering Manager at a machine builder told us recently that wiring each press requires around 300 man hours(!), a significant portion of which is spent on sensor and indicator wiring.

Which brings us to IO-Link. Replacing those analog sensors with IO-Link sensors, allows feedback signals from multiple machines to be consolidated into single cable runs, and connected to the network, be it Ethernet/IP, EtherCat, Profinet, or Profibus. The benefits of such an approach are numerous:

  • Wiring is simple and much more economical
    • Eliminates need for shielded sensor cables
  • Integrated diagnostics allow remote machine status monitoring
  • Reduces more expensive analog IO on the controller side
  • Over-the-network configuration and the ability to store those configurations reduces setup time

And, by the way, the IO-Link story doesn’t end with position sensors. The ever-growing list of IO-Link enabled sensors and indicators allows the benefits to be rolled into many areas of machine automation, such as:

  • Intelligent IO-Link power supplies with HeartBeat technology that monitor their own “health” and report it back over the network (think Predictive Maintenance)
  • Highly-configurable IO-Link stack light alternatives that can be set up to display a number of machine and process condition states
  • IO blocks, memory modules, pressure sensors, discrete (on/off) sensors of all type, and more

To learn more about IO-Link, visit Balluff.com

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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.

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.

  1. Is decreasing production time an objective of your organization? I assume the answer to this is yes in most cases. Decreasing production time means an increase in line speed which means the RFID system has to be able to read and write faster. Some RFID systems are designed for reading a tag while the part is static or sitting in front of the reader for a period of time, while others are designed for reading a tag dynamically as it flies by the read head. Taking the time to determine if a system is capable of reading on the fly is worth the extra research time to avoid the “trap”.
  2. Will you use more data in the future than you do today? Basically, will you need to write more data to the tag as the line matures? That seems like another no-brainer considering the huge demand for data storage in other realms of our life. Countless times I have heard customers say all they want to write to the tag is a four digit identifier and a year later they want to add quality information, lineage data, build data, process data and so on to the tag. Couple that with an increase in line speed and now you are talking about some serious throughput. It is imperative to make sure the tag has the necessary capacity and the reader has the necessary cycle time to handle the increase in demand for throughput.
  3. Will you ever expand the line to have more read/write stations? This is a big one especially in quality intensive applications where multiple inspections throughout the process are required. The critical error here is lack of foresight into the networking capabilities of the system. Whether the processor is capable of handling multiple readers or it is just a single read point solution it is important to know how the system is expanded. Some systems are expanded by daisy chaining processors which is less complicated than adding additional switching equipment to expand the system.

None of us are capable of telling the future, but we can put a pretty good plan together to accommodate growth. Keep it simple and ask as many questions as you can dream up before you pull the trigger. Just make sure the three questions above are addressed and the technology trap can be avoided.

To learn more about RFID solutions visit www.balluff.com.

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4 (More) Smart Applications for Process Visualization

In a previous post, 3 Smart Applications for Process Visualization, we discussed how the term “process visualization” has evolved since the introduction of the SmartLight. While it can definitely be used as a stack light, its additional modes can be applied for all sorts of different operation/ process visualization tasks. Below are a few more examples we’ve come across.

Use Case #4:  Fill Level Status: From micro-breweries to steel-mills and oil refineries, all have state-of-the art tack fill level detection systems measuring fill levels to the last millimeter or in some cases cubic inches. But when you want to take peek at the how much the reservoir is full at any given time- you have to go to the HMI in some corner to see that value. Nine times out of ten this fill indication provides you only with numerical value. What if SmartLight shows you the value visually using the level mode of operation? Then the decision to run another batch of bottle filling can be taken without going to that corner and punching some numbers. Additionally, the colors of the segments can be changed to indicate the temperature or pressure inside the tank or just different fill levels so the line supervisors can take decisions promptly on the next action.

Use Case #5: Interactive Operator Status: Several times plants invest in huge TV monitors to provide a real-time visual feedback to their employees on how their operations are progressing compared to the quota assigned. At one plant, they found no increase in employee productivity with such investment because the TV monitors failed to provide a visual feedback. The television sets indicated 112/300 – which meant nothing to the operators. The SmartLight, however, provided them the feedback using the level mode of operation on how they are performing to the quota. The moment SmartLight turns yellow was an indication to the operator(s) that they are falling behind the level of the lighted LED indicated that they are closing the gap to their daily quota. If the operator notices problems with the batch of components or machine itself they could change the SmartLight to a run light mode with a push of a button indicating trouble in the workcell – the supervisor then can deploy the right maintenance person to the cell. Utilizing the SmartLight light not only provided instantaneous feedback on performance but also added efficiency in handling production issues.

Use Case #6: Improving Hazard Awareness: In one automotive plant, the maintenance team designed an innovative solution with SmartLights for hazard communication. This plant has several automated guided vehicles (AGVs). The light indicators on these AGVs are the same type that was on the mast of most of the workcells in the plant. It was hard to notice when the AGVs were pulling out of and entering their parking stand. Maintenance engineers installed SmartLights on the mast of the AGV parking stand and with different color scheme and level mode indicated if the AGV is coming to stop or just starting the motion. This simple idea avoided daily occurrences of mishaps for the forklift drivers and operators.

Use Case #7: Identify Bottlenecks: With linear assembly process it can be difficult to detect bottlenecks in the production process. With increase complexity of today’s production flows the bottlenecks dynamically change under various conditions. Installing SmartLights programmed to change their mode of operation depending on certain conditions (on-demand change of mode) could help point out bottlenecks in the current environment. For example, these days the automation controllers are equipped to calculate its overall equipment effectiveness (OEE). That information can be directed to the SmartLight. A specified segment may turn green when OEE >80%, turns yellow when 60% < OEE < 80% and red if the OEE falls below 60%.  Now, the plant supervisors can see the overall picture of the entire floor to make informed and timely decisions.

Use Case #8: Time Lapse Counter: Wouldn’t it be nice to know how long it takes to replenish the stack of pallets in the robotic palletizing cell? Or how often the operator has to go into the cell (causing stop operations) for mis-fired sensor or dropped package? How about break-times for the operators? Well SmartLights can be used for all these types of operations. This can be done by changing the blinking frequency of the SmartLight segment, and changing the colors or modes of operations, a multitude of information can be displayed for various purposes.

We want to hear from you! Do you have a unique application for the SmartLight? Share your story with us here.

You can also learn more by visiting our website at www.balluff.us.

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Tool Identification in Metalworking

With the start of industry 3.0 (the computer based automation of production) the users of machine tools began to avoid routine work like manually entering tool data into the HMI.  Computerized Numerical Controlled CNC machine tools gained more and more market share in metalworking applications.  These machines are quite often equipped with automatic tool change systems. For a correct production the real tool dimensions need to be entered into the CNC to define the tool path.

Tool ID for Automatic and Reliable Data Handling

Rather than entering the real tool diameter and tool length manually into the CNC, this data may be measured by a tool pre-setter and then stored in the RFID tool chip via an integrated RFID read-/write system. Typically when the tool is entered in the tool magazine the tool data are read by another read-/ write system which is integrated in the machine tool.

Globally in most cases the RFID tool chips are mounted in the tool holder (radially mounted eg. in SK or HSK holders).

In some applications the RFID tool chips are mounted in the pull stud (which holds the tool in the tool holder). Especially in Japan this tag position is used.

Tool Data for Different Levels of the Automation Pyramid

The tool data like tool diameters and tool lengths are relevant for the control level to guarantee a precise production of the workpieces.  Other data like planned and real tool usage times are relevant for industrial engineering and quality control to e.g. secure a defined surface finish of the workpieces.  Industrial engineers perform milling and optimization tests (with different rotational spindle speeds and tool feed rates) in order to find the perfect tool usage time as a balance between efficiency and quality.  These engineering activities typically are on the supervision level.  The procurement of new tools (when the existing tools are worn out after e.g.  5 to 10 grinding cycles) is conducted via the ERP System as a part of the asset management.

 

Coming back to the beginning of the 3rd industrial revolution the concept of CIM (Computer Integrated Manufacturing) was created, driven by the integration of computers and information technology (IT).

With the 4th industrial revolution, Industry 4.0, the success story of the Internet now adds cyber physical systems to industrial production.  Cloud systems support and speed up the communication between customers and suppliers.  Tool Management covers two areas of the Automation pyramid.

  1. Machine Control: From sensor / actuator level up to the control level (real time )
  2. Asset Management: Up to enterprise level and beyond (even to the “Cloud”)

To learn more about Tool ID visit www.balluff.com

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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

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Project Uptime – Pay Me Now or Pay Me Later

Back when I worked in the tier 1 automotive industry we were always trying to find time to break into our production schedule to perform preventative maintenance. The idea for this task was to work on the assembly machines or weld cells to improve sensor position, sensor and cable protection and of course clean the machines. As you all know this is easier said than done due to unplanned downtime or production schedule changes, for example. As hard as it is to find time for PM’s (preventative maintenance) it is a must to stay ahead and on top of production. PM’s will not only increase the production time, but it will also help maintain better quality parts by producing less scrap and machine downtime due damaged sensors or cables.

If you have read any of my previous posts you have probably noticed that I refer to the “pay me now or pay me later” analogy. This subject would fall directly into this category, you have to take the time to prevent machine crashes and damaged sensors and cables on the front side rather than being reactive and repairing them when they go down. It has been proven that a properly bunkered or protected proximity sensor will outlast the machine tooling when best practices are executed. It’s important to take the time and look at the way a sensor is mounted or protected or acknowledge when a cable is routed in harm’s way.

Click to enlarge

PM’s should be an important task that is part of a schedule and followed through in any factory automation or tier 1 production facility. In some cases I have seen where there is a complete bill of material (BOM) or list of tasks to accomplish during the PM time. This list will help maintenance personnel and engineering know what to look for and what are the hot spots that create unplanned downtime.  This list could also indicate some key sensors, mounting brackets and high durability cables that can improve the process.

For more information on a full solution supplier or products that can improve and decrease downtime click here.

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Level Sensing in Machine Tools

Certainly the main focus in machine tools is on metal cutting or metal forming processes.

To achieve optimum results in cutting processes coolants and lubricants are applied. In both metal cutting and metal forming processes hydraulic equipment is used (as hydraulics create high forces in compact designs). For coolant, lubricant and hydraulic tanks the usage of level sensors to monitor the tank level of these liquids is required.

Point Level Sensing

For point level sensing (switching output) in many cases capacitive sensors are used. These sensors detect the change of the relative electric permittivity (typically a change of factor 10 from gas to liquid). The capacitive sensors may be mounted at the outside of the tank wall if the tank material is non metallic like e.g. plastic or glass. The installation may even be in retrofit applications yet limited to non metallic tanks up to a certain wall thickness.

When using metal tanks the capacitive sensors enter the inner area of the tank via a thread and a sealing component. Common thread sizes are: M12x1, M18x1, M30x1,5, G 1/4″, NPT 1/4″ etc. For conductive liquids specially designed capacitive level sensors may be used which ignore build up at the sensing surface.

Continuous Level Sensing

Advanced process control uses continuous level sensing principles. The continuous sensor signals e.g. 0..10V, 4…20mA or increasingly IO-Link deliver more information to better control the liquid level, especially relevant in dynamic or precise applications.

When using floats the magnetostrictive sensing principle offers very high resolution of the level value. Tank heights vary from typically 200 mm up to several meters. Another advantage of this sensor principle is the high update rate (supporting fast closed loop systems for level sensing)

In many applications the  requirements for the level control solutions are not too demanding. In these cases the ultrasonic principle has gained significant market share within the last years. Ultrasonic sensors do not need a float, installation on the top of the tank is pretty easy, there are even sensor types available which may be used in pressurized tanks (typically up to 6 bar). As ultrasonic sensors quite often are used in special applications, field tests during the design in process are recommended.

Finally hydrostatic pressure transducers are an option for level sensing when using non pressurized tanks (typically  connected to ambient pressure through a bore in the upper area of the tank). With the sensor mounted at the bottom of the tank the level is indirectly measured through the pressure of the liquid column above the sensor (e.g. 10m of water level resembles 1 bar).

Summary

Concerning level sensing in metalworking applications in the first step it should be decided whether point level sensing is sufficient or continuous level sensing is required. Having chosen continuous level sensing there are several sensor principles available (selection depending on the application needs and features of the liquids and tank properties). It is always a good engineering practice to prove the preselected sensing concept with field tests.

To learn more visit www.balluff.com

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