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Waterways: the Many Routes of Water Detection

 

Water is everywhere, in most things living and not, and the amount of this precious resource is always important. The simplest form of monitoring water is if it is there or not. In your body, you feel the effects of dehydration, in your car the motor overheats, and on your lawn, you see the dryness of the grass. What about your specialty machine or your assembly process? Water and other liquids are inherently clear so how do you see them, especially small amounts of it possibly stored in a tank or moving fast? Well, there are several correct answers to that question. Let’s dive into this slippery topic together, pun intended.

While mechanical float and flow switches have been around the longest, capacitive, photoelectric, and ultrasonic sensors are the most modern forms of electronic water detection. These three sensing technologies all have their strong points. Let’s cover a few comparisons that might help you find your path to the best solution for your application.

Capacitive sensors

Capacitive sensors are designed to detect nonferrous materials, but really anything that can break the capacitive field the sensor creates, including water, can do this. This technology allows for adjustment to the threshold of what it takes to break this field. These sensors are a great solution for through tank level detection and direct-contact sensing.

Ultrasonic sensors

Want to view your level from above? Ultrasonic sensors give you that view. They use sound to bounce off the media and return to the sensor, calculating the time it takes to measure distance. Their strong point is that they can overcome foam and can bounce off the water where light struggles when there is a large distance from the target to the receiver. Using the liquid from above, ultrasonics can monitor large tanks without contact.

Photoelectric sensors

Use photoelectric sensors when you’re looking at a solution for small scale. Now, this might require a site tube if you are monitoring the level on a large tank, however, if you want to detect small amounts of water or even bubbles within that water, photoelectric sensors are ideal. Using optical head remote photoelectric sensors tied to an amplifier, the detail and speed are unmatched. Photoelectric sensors are also great at detecting liquid levels on transparent bottles. In these applications with short distances, you need speed. Photoelectric sensors are as fast as light.

So, have you made up your mind yet? No matter which technology you choose, you will have a sensor that gives you accurate detail and digital outputs and is easy on the budget. Capacitive, ultrasonic, and photoelectric sensors provide all this and they grow with your application with adjustability.

Liquids are everywhere and not going away in manufacturing. They will continue to be an important resource for manufacturing.  Cherish them and ensure you account for every drop.

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Simplified Sensing Over a Complex Headache

The constant need for more data and higher accuracy has pushed sensing technologies to the extreme. Advancements in factory automation have created a perfect storm of innovation and new capabilities. This is probably an unpopular opinion but, do we always need all of this?

I started my career in factory automation in the late 90s. This was a time of technology transitions. PLCs had been around for ages but had never been so affordable. Technologies, such as time-of-flight laser measurement, industrial cameras, and inductive coupling, were new and exciting, and they were becoming more affordable, too.

As a controls engineer, I remember using these advanced technologies and systems as a way of keeping my projects future-proof – or so I thought. In reality, sometimes they just made things more complicated.

Let me explain this using an example where tried, true and affordable sensors could have made the project more reliable and future-proof from the start.

Photoelectric sensors have earned their place in the automation hall of fame. I don’t see a time when their use will not be necessary as a reliable way to conduct presence detection.

I was working on a project that required tracking several washing machine cabinet bases to be counted and orientated correctly on a conveyor. I wanted to use an industrial camera because the technology was getting better and better. I paid $7,000  for the camera and accessories. After several days and iterations, the camera system was working perfectly.  It continued working for about a week before it was knocked out of alignment by a production worker who was using it as a leaning post. It took another day or so to dial back in.

Tried, true and affordable win out

The solution I ultimately chose was the easiest. I strategically placed seven basic photoeyes underneath the conveyor to identify what base it was looking at and if certain characteristics were present for quality tracking. My investment was around $400, and it was extremely protected from failure. And, if a sensor went out, rather than calling an engineer in the middle of the night, a maintenance electrician could simply replace it with a new one.

Another huge benefit of using photoeyes was the avoidance of buyer’s remorse. Camera technology is always evolving. From one day to the next they get better and more capable, but also might have proprietary comms or software. Basic photoelectric sensors with a PNP or NPN output can easily be swapped out by almost any brand for decade to come.

Keep it simple

At the end of the day, sometimes it is best to keep the solution simple, clean, and backed by the tried-and-true technologies in factory automation. Next time you dig into a project, take a moment to think about my example. Melt the solution down to the lowest common denominator and build up the complexity from there. You might just save more than just money; you might save a headache or two.

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Choosing a Contactless Sensor to Measure Objects at a Distance

Three options come to mind for determining which contactless sensor to use when measuring objects at a distance: photoelectric sensors, ultrasonic sensors, and radar detection. Understanding the key differences among these types of technologies and how they work can help you decide which technology will work best for your application.

Photoelectric sensor

The photoelectric sensor has an emitter that sends out a light source. Then a receiver receives the light source. The common light source LED (Light Emitting Diodes), has three different types:

    • Visible light (usually red light) has the shortest wavelength, but allows for easy installment and alignment as the light can be seen.
    • Lasers are amplified beams that can deliver a large amount of energy over a distance into a small spot, allowing for precise measurement.
    • Infrared light is electromagnetic radiation with wavelengths longer than visible light, generally making them invisible to the humans. This allows for infrared to be used in harsher environments that contain particles in the air.

Along with three types of LEDs, are three models of photoelectric sensors:

    • The retro-reflective sensor model includes both an emitter and receiver in one unit and a reflector across from it. The emitter sends the light source to the reflector which then reflects the light back to the receiver. When an object comes between the reflector and the emitter, the light source cannot be reflected.
    • The through-beam sensor has an emitter and receiver in two separate units installed across from the emitter. When an object breaks the light beam, the receiver cannot receive the light source.
    • The diffuse sensor includes an emitter and receiver built into one unit. Rather than having a reflector installed across from it the light source is reflective off the object back to the receiver.

The most common application for photoelectric sensors is in detecting part presence or absence. Photoelectric sensors do not work well in environments that have dirt, dust, or vibration. They also do not perform well with detecting clear or shiny objects.

Ultrasonic sensor

The ultrasonic sensor has an emitter that sends a sound wave at a frequency higher than what a human can hear to the receiver.  The two modes of an ultrasonic sensor include:

    • Echo mode, also known as a diffused mode, has an emitter and receiver built into the same unit. The object detection works with this mode is that the emitter sends out the sound wave, the wave then bounces off the target and returns to the receiver. The distance of an object can be determined by timing how long it takes for the sound wave to bounce back to the receiver.
    • The second type of mode is the opposed mode. The opposed mode has the emitter and receiver as two separate units. Object detection for this mode works by the emitter will be set up across from the receiver and will be sending sound waves continuously and an object will be detected once it breaks the field, similarly to how photoelectric sensors work.

Common applications for ultrasonic sensors include liquid level detection, uneven surface level detection, and sensing clear or transparent objects. They can also be used as substitutes for applications that are not suitable for photoelectric sensors.

Ultrasonic sensors do not work well, however, in environments that have foam, vapors, and dust. The reason for this is that ultrasonic uses sound waves need a medium, such as air, to travel through. Particles or other obstructions in the air interfere with the sound waves being produced. Also, ultrasonic sensors do not work in vacuums which don’t contain air.

Radar detection

Radar is a system composed of a transmitter, a transmitting antenna, a receiving antenna, a receiver, and a processor. It works like a diffuse mode ultrasonic sensor. The transmitter sends out a wave, the wave echoes off an object, and the receiver receives the wave. Unlike a sound wave, the radar uses pulsed or continuous radio waves. These wavelengths are longer than infrared light and can determine the range, angle, and velocity of objects. radar also has a processor that determines the properties of the object.

Common applications for radar include speed and distance detection, aircraft detection, ship detection, spacecraft detection, and weather formations. Unlike ultrasonic sensors, radar can work in environments that contain foam, vapors, or dust. They can also be used in vacuums. Radio waves are a form of electromagnetic waves that do not require a transmission medium to travel. An application in which radar does not perform well is detecting dry powders and grains. These substances have low dielectric constants, which are usually non-conductive and have low amounts of moisture.

Choosing from an ultrasonic sensor, photoelectric sensor, or radar comes down to the technology being used. LEDs are great at detecting part presences and absence of various sizes. Sound waves are readily able to detect liquid levels, uneven surfaces, and part presence. Electromagnetic waves can be used in environments that include particles and other substances in the air. It also works in environments where air is not present at all. One technology is not better than the other; each has its strengths and its weaknesses. Where one cannot work, the others typically can.

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Shedding Light on Different Types of Photoelectric Sensors

Photoelectric sensors have been around for more than 50 years and are used in everyday things – from garage door openers to highly automated assembly lines that produce the food we eat and the cars we drive.

The correct use of photoelectric sensors in a manufacturing process is important to ensure machines can perform their required actions. Over the years they have evolved into many different forms.

But, how do you know which is the right sensor for your application?  Let’s take a quick look at the different types and why you would choose one over another for your needs.

Diffuse sensors

    • Ideal for detecting contrast differences, depending on the surface, color, and material
    • Detects in Light-On or Dark-On mode, depending on the target
    • Economical and easy to mount and align, thanks to visible light beams
    • Shorter ranges as compared to retroreflective and through-beam sensors
    • IR (Infrared) light beams available for better detection in harsh environments
    • Laser light versions are available for more precise detection when needed
    • Mounting includes only one electrical device

Diffuse sensor with background suppression

    • Reliable object detection with various operating ranges, and independent of surface, color, and material
    • Detects objects against very similar backgrounds – even if they are very dark against a bright background
    • Almost constant scanning range even with different reflectance
    • Only one electrical device without reflectors or separate receivers
    • Good option if you cannot use a through-beam or retroreflective sensor
    • With red light or the laser red light that is ideally suited for detecting small parts

Retroreflective sensors

    • Simple alignment thanks to generous mounting tolerances
    • Large reflectors for longer ranges
    • Reliable detection, regardless of surface, color, and material
    • Polarized light filters are available to assist with detecting shiny objects
    • Mounting includes only one electrical device, plus a reflector
    • Most repeatable sensor for clear object detection; light passes through clear target 2X’s giving a greater change in light received by the sensor

Through-beam sensors

    • Ideal for positioning tasks, thanks to excellent reproducibility
    • Most reliable detection method for objects, especially on conveyor applications
    • Extremely resistant to contamination and suitable for harsh environments
    • Ideally suited for large operating ranges
    • Transmitter and receiver in separate housings

Fork sensors

    • Different light types (red light, infrared, laser)
    • Robust metal housing
    • Simple alignment to the object
    • High optical resolution and reproducibility
    • Fork widths in different sizes with standardized mounting holes
    • Identical mechanical and optical axes
    • The transmitter and receiver are firmly aligned to each other, yielding high process reliability

The next time you need to choose a photoelectric sensor for your manufacturing process, consider these features of each type to ensure the sensor is performing optimally in your application.

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Choosing Sensors Suitable for Automation Welding Environments

Standard sensors and equipment won’t survive for very long in automated welding environments where high temperatures, flying sparks and weld spatter can quickly damage them. Here are some questions to consider when choosing the sensors that best fit such harsh conditions:

    • How close do you need to be to the part?
    • Can you use a photoelectric sensor from a distance?
    • What kind of heat are the sensors going to see?
    • Will the sensors be subject to weld large weld fields?
    • Will the sensors be subject to weld spatter?
    • Will the sensor interfere with the welding process?

Some solutions include using:

    • A PTFE weld spatter resistant and weld field immune sensor
    • A high-temperature sensor
    • A photoelectric diffuse sensor with a glass face for better resistance to weld spatter, while staying as far away as possible from the MIG welding application

Problem, solution

A recent customer was going through two sensors out of four every six hours. These sensors were subject to a lot of heat as they were part of the tooling that was holding the part being welded. So basically, it became a heat sink.

The best solution to this was to add water jackets to the tooling to help cool the area that was being welded. This is typically done in high-temperature welding applications or short cycle times that generate a lot of heat.

    • Solution 1 was to use a 160 Deg C temp sensor to see if the life span would last much longer.
    • Solution 2 was to use a plunger prob mount to get more distance from the weld area.

Using both solutions was the best solution. This increased the life to one week of running before it was necessary to replace the sensor. Still better than two every 6 hours.

Taking the above factors into consideration can make for a happy weld cell if time and care are put into the design of the system. It’s not always easy to get the right solution as some parts are so small or must be placed in tight areas. That’s why there are so many choices.

Following these guidelines will help significantly.

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Looking Into & Through Transparent Material With Photoelectric Sensors

Advance automated manufacturing relies on sensor equipment to ensure each step of the process is done correctly, reliably, and effectively. For many standard applications, inductive, capacitive, or basic photoelectric sensors can do a fine job of monitoring and maintaining the automated manufacturing process. However, when transparent materials are the target, you need a different type of sensor, and maybe even need to think differently about how you will use it.

What are transparent materials?

When I think of transparent materials, water, glass, plexiglass, polymers, soaps, cooling agents, and packaging all come to mind. Because transparent material absorbs very little of the emitted red LED light, standard photoelectric sensors struggle on this type of application. If light can make its way back to the receiver, how can you tell if the beam was broken or not? By measuring the amount of light returned, instead of just if it is there or not, we can detect a transparent material and learn how transparent it is.

Imagine being able to determine proper mixes or thicknesses of liquid based on a transparency scale associated to a value of returned light. Another application that I believe a transparent material photoelectric senor would be ideal for is the thickness of a clear bottle. Imagine the wall thickness being crucial to the integrity of the bottle. Again, we would measure the amount of light allowed back to the receiver instead of an expensive measurement laser or even worse, a time-draining manual caliper.

Transparent material sensor vs. standard photoelectric sensor

So how does a transparent material sensor differ from a standard photoelectric sensor? Usually, the type of light is key. UV light is absorbed much greater than other wavelengths, like red or blue LEDs you find in standard photoelectric sensors. To add another level, you polarize that UV light to better control the light back into the receiver. Polarized UV light with a polarized reflector is the best combination. This can be done on a large or micro scale based on the sensor head size and build.

Uses for transparent material sensor include packaging trays, level tubes, medical tests, adhesive extrusion, and bottle fill levels, just to name a few. Transparent materials are everywhere, and the technology has matured. Make sure you are looking into specialized sensor technologies and working through best set-up practices to ensure reliable detection of transparent materials.

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Tire Industry Automation: When a Photo-Eye Is Failing, Try an Ultrasonic Sensor

Should you use a photo-eye or an ultrasonic sensor for your automation application? This is a great question for tire industry manufacturing.

I was recently at a tire manufacturing plant when a maintenance technician asked me to suggest a photoelectric sensor for a large upgrade project he had coming up. I asked him about the application, project, and what other sensors he was considering.

His reply was a little startling. He said he had always used photo-eyes, but he couldn’t find a dependable one, so he would continually try different brands. My experience in this industry, along with good sensor training and advice from my colleague Jack Moermond, Balluff Sensor Products Manager, immediately made me think that photo-eye sensors were not the right choice for this application.

As I asked more questions, the problem became clear. The tire material the technician was detecting was black and dull. This type of material absorbs light and does not reflect it reliably back to the sensor. Also, environmental factors, such as dust and residue, can diminish a photo-eye’s signal quality.

Ultrasonic sensors for non-reflective materials and harsh environments

The technician didn’t have much experience with ultrasonic sensors, so I went on to explain why these may be a better solution for his application.

While photoelectric sensors send light beams to detect the presence of or measure the distance to an object, ultrasonics bounce sound waves off a target. This means that ultrasonics can be used in applications where an object’s reflectivity isn’t predictable, like with liquids, clear glass or plastic, or other materials. Dust build up on the face of an ultrasonic sensor does not give a false output. Ultrasonic sensors actually have a dead zone a few millimeters from the face where they won’t detect an object until the wave clears the dead zone, so take this into consideration when planning where to install an ultrasonic sensor.

Tire detection for process reliability with BUS ultrasonic sensors

Tire industry applications

The following are some popular tire industry applications where it might be better to choose an ultrasonic sensor over a photo-eye sensor.

    • The tire building process requires a lot of winding and unwinding of material to build the different layers of a tire. As this material is fed through the machines it starts to sag and loop. An ultrasonic sensor in this location will monitor how much sag and loop is in the process.
    • When tires are being loaded into curing presses, the press needs to confirm that the correct size tire is in place. An ultrasonic sensor can measure the height or width of the tire from the sides or top for confirmation.
    • Ultrasonic sensors are great at detecting if a tire or material is in place before a process starts.
    • Hydraulic systems are common in tire manufacturing. Ultrasonic sensors are good for hydraulic fluid level monitoring. Tying them to a SmartLight offers a visual reference and alarm output if needed.
    • Everyone knows the term “wig-wag” in tire mixing and extrusion. The sheets of wig-wag require monitoring as they are fed through the process. When this material gets close to being used up, a new wig-wag must be used.
Wig-wag stacks

So, when there is an application for a photo-eye, especially in a tire manufacturing plant, keep in mind that, rather than a photoelectric sensor, an ultrasonic may be a better option.

The maintenance technician I spoke with is now looking at different options of ultrasonics to use. He said I gave him something new to think about for his machines and opened the door for adding this technology to his plant.

Happy hunting!

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Protecting photoelectric and capacitive sensors

Supply chain and labor shortages are putting extra pressure on automation solutions to keep manufacturing lines running. Even though sensors are designed to work in harsh environments, one good knock can put a sensor out of alignment or even out of condition. Keep reading for tips on ways to protect photoelectric and capacitive sensors.

Mounting solutions for photoelectric sensors

Photoelectric sensors are sensitive to environmental factors that can cloud their view, like dust, debris, and splashing liquids, or damage them with physical impact. One of the best things to do from the beginning is to protect them by mounting them in locations that keep them out of harm’s way. Adjustable mounting solutions make it easier to set up sensors a little further away from the action. Mounts that can be adjusted on three axes like ball joints or rod-and-mount combinations should lock firmly into position so that vibration or weight will not cause sensors to move out of alignment. And mounting materials like stainless steel or plastic can be chosen to meet factors like temperature, accessibility, susceptibility to impact, and contact with other materials.

When using retroreflective sensors, reflectors and reflective foils need similar attention. Consider whether the application involves heat or chemicals that might contact reflectors. Reflectors come in versions, especially for use with red, white, infrared, and laser lights, or especially for polarized or non-polarized light. And there are mounting solutions for reflectors as well.

Considering the material and design of capacitive sensors

Capacitive sensors must also be protected based on their working environment, the material they detect, and where they are installed. Particularly, is the sensor in contact with the material it is sensing or not?

If there is contact, pay special attention to the sensor’s material and design. Foods, beverages, chemicals, viscous substances, powders, or bulk materials can degrade a sensor constructed of the wrong material. And to switch perspectives, a sensor can affect the quality of the material it contacts, like changing the taste of a food product. If resistance to chemicals is needed, housings made of stainless steel, PTFE, and PEEK are available.

While the sensor’s material is important to its functionality, the physical design of the sensor is also important. A working environment can involve washdown processes or hygienic requirements. If that is the case, the sensor’s design should allow water and cleaning agents to easily run off, while hygienic requirements demand that the sensor not have gaps or crevices where material may accumulate and harbor bacteria. Consider capacitive sensors that hold FDA, Ecolab, and CIP certifications to work safely in these conditions.

Non-contact capacitive sensors can have their own special set of requirements. They can detect material through the walls of a tank, depending on the tank wall’s material type and thickness. Plastic walls and non-metallic packaging present a smaller challenge. Different housing styles – flat cylindrical, discs, and block styles – have different sensing capabilities.

Newer capacitive technology is designed as an adhesive tape to measure the material inside a tank or vessel continuously. Available with stainless steel, plastic, or PTFF housing, it works particularly well when there is little space available to detect through a plastic or glass wall of 8mm or less. When installing the tape, the user can cut it with scissors to adjust the length.

Whatever the setting, environmental factors and installation factors can affect the functionality of photoelectric and capacitive sensors, sometimes bringing them to an untimely end. Details like mounting systems and sensor materials may not be the first requirements you look for, but they are important features that can extend the life of your sensors.

 

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Detecting Liquid Media and Bubbles Using Optical Sensors

In my line of work in Life Sciences, we often deal with liquid media and bubble detection evaluation through a vessel or a tube. This can be done by using the absorption principle or the refraction principle with through-beam-configured optical sensors. These are commonly embedded in medical devices or lab instruments.

This configuration provides strong benefits:

    • Precise sensing
    • Ability to evaluate liquid media
    • Detect multiple events
    • High reliability

How does it work?

The refraction principle is based on the media’s refraction index. It uses an emitted light source (Tx) that is angled to limit the light falling on the receiver (Rx, Figure 1). When the light passes through a liquid, refraction causes the light to focus on the receiver as a beam (known as a “beam-make” configuration). All liquids and common vessel materials (silicon, plastic, glass, etc.) have a known refraction index. These sensors will detect those refraction differences and output a signal.

The absorption principle is preferred when a media’s absorption index is high. First, a beam is established through a vessel or tube (Figure 2). Light sources in the 1500nm range work best for aqueous-based media such as water. As a high absorption index liquid enters the tube, it will block the light (known as a beam-break configuration). The sensor detects this loss of light.

Discrete on-off signals are easily used by a control system. However, by using the actual light value information (commonly analog), more data can be extracted. This is becoming more popular now and can be done with either sensing principle. By using this light-value information, you can differentiate between types of media, measure concentrations, identify multiple objects (e.g., filter in an IV and the media) and much more.

There is a lot to know about through-beam sensors, so please leave a comment below if you have questions on how you can benefit from this technology.

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Avoid Downtime in Metal Forming With Inductive & Photoelectric Sensors

Industrial sensor technology revolutionized how part placement and object detection are performed in metal forming applications. Inductive proximity sensors came into standard use in the industry in the 1960s as the first non-contact sensor that could detect ferrous and nonferrous metals. Photoelectric sensors detect objects at greater distances. Used together in a stamping environment, these sensors can decrease the possibility of missing material or incorrect placement that can result in a die crash and expensive downtime.

Inductive sensors

In an industrial die press, inductive sensors are placed on the bottom and top of the dies to detect the sheet metal for stamping. The small sensing range of inductive sensors allows operators to confirm that the sheet metal is correctly in place and aligned to ensure that the stamping process creates as little scrap as possible.

In addition, installing barrel-style proximity sensors so that their sensing face is flush with the die structure will confirm the creation of the proper shape. The sensors in place at the correct angles within the die will trigger when the die presses the sheet metal into place. The information these sensors gather within the press effectively make the process visible to operators. Inductive sensors can also detect the direction of scrap material as it is being removed and the movement of finished products.

Photoelectric sensors

Photoelectric sensors in metal forming have two main functions. The first function is part presence, such as confirming that only a single sheet of metal loads into the die, also known as double-blank detection. Doing this requires placing a distance-sensing photoelectric sensor at the entry-way to the die. By measuring the distance to the sheet metal, the sensor can detect the accidental entry of two or more sheets in the press. Running the press with multiple metal sheets can damage the die form and the sensors installed in the die, resulting in expensive downtime while repairing or replacing the damaged parts.

The second typical function of photoelectric sensors verifies the movement of the part out of the press. A photoelectric light grid in place just outside the exit of the press can confirm the movement of material out before the next sheet enters into the press. Additionally, an optical window in place where parts move out will count the parts as they drop into a dunnage bin. These automated verification steps help ensure that stamping processes can move at high speeds with high accuracy.

These examples offer a brief overview of the sensors you mostly commonly find in use in a die press. The exact sensors are specific to the presses and the processes in use by different manufacturers, and the technology the stamping industry uses is constantly changing as it advances. So, as with all industrial automation, selecting the most suitable sensor comes down to the requirements of the individual application.