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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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Tackling the Most Demanding Applications With Precision Sensors

Standard industrial sensors can solve a lot of automation challenges. Photoelectric, capacitive, and inductive technologies detect presence, distances, shapes, colors, thicknesses, and more. To satisfy these general applications, there are a few reputable manufacturers in the market that design and produce such products. In many instances, it is possible to interchange them from manufacturer to manufacturer, due to similar mounting patterns, technical specifications, connectors, and even common pin assignments.

But some applications require more precision – where standard sensors will not do.  Some examples include:

    • The target may be too small or difficult material to detect
    • The target may move very slowly, or very quickly
    • The target may have a minimal displacement, as in valve feedback
    • The sensor must have low mass, for high-acceleration applications
    • The sensor location has severe space constraints or material constraints

Applications that must detect particles that can’t be seen with the naked eye, or something as small as sensing the thin edge of a silicon wafer or the edge of a clear glass microscope slide, require sensors with exceptional precision.

Many precision sensing applications require a custom-designed sensor to meet the customer’s expectations. These expectations typically involve a quality sensor with robust attributes, likely coupled with difficult design parameters, such as high switch-point repeatability, exceptional temperature stability, or exotic materials.

What constitutes a precision sensing application? Let’s take a look.

Approximately 70% of all medical decisions are based on lab results. Our doctors are making decisions about our health based on these test outcomes. Therefore, accurate, trustworthy results, performed quickly, are priorities. Many tests rely on pipetting, the aspirating and dispensing of fluids – sometimes at a microscale level – from one place to another. Using a manual pipette is a time-consuming, labor-intensive process. Automating this procedure reduces contamination and eliminates human errors.

To satisfy the requirements of an application such as this requires a custom-manufactured LED light source, with a wavelength chosen to best interact with the fluids, and an extremely small, concentrated light emission that approaches laser-like properties (yet without the expense and power requirements of the laser). This light source verifies pipette presence and dispensing levels, with a quality check of the fluids dispensed down to the nanoliter scale.

So, the next time you face an application challenge that cannot be tackled with a standard sensor, consider a higher precision sensor and rest assured you will get the reliability you demand.

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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 the Right Sensor for Measuring Distance

Distance-measuring devices help with positioning, material flow control, and level detection. However, there are several options to consider when it comes to choosing the correct sensor technology to measure distance. Here I’ll cover the three most commonly used types in the industrial automation world today, including photoelectric, ultrasonic, and inductive.

Photoelectric sensors

Photoelectric sensors use a light source, such as a laser or light-emitting diode, to reflect the light off an object’s surface to calculate the distance between the face of the sensor and the object itself. The two basic principles for how the sensor calculates the distances are the time of flight (TOF) and triangulation.

    • Time of flight photoelectric distance measurement sensors derive the distance measurement based on the time it takes the light to travel from the sensor to the object and return. These sensors are used to measure over long distances, generally in the range between 500 millimeters and up to 5 meters, with a resolution between 1 to 5 millimeters, depending on the sensor specifications. Keep in mind that this sensor technology is also used in range-finding equipment with a much greater sensing range than traditional industrial automation sensors.

    • In the triangulation measurement sensor, the sensor housing, light source, and light reflection form a triangle. The distance measurement is based on the light reflection angle within its sensing range with high accuracy and resolution. These sensors have a much smaller distance measurement range that is limited to between 20 and 300 millimeters, depending on the sensor specifications.

The pros of using photoelectric distance measurement sensors are the range, accuracy, repeatability, options, and cost. The main con for using photoelectric sensors for distance measurement is that they are affected by dust and water, so it is not recommended to use them in a dirty environment. The object’s material, surface reflection, and color also affect its performance.

Photoelectric distance measurement sensors are used in part contouring, roll diameter measurement, the position of assemblies, thickness detection, and bin-level detection applications.

Ultrasonic sensors

Ultrasonic distance sensors work on a similar principle as photoelectric distance sensors but instead of emitting light, they emit sound waves that are too high for humans to hear, and they use the time of flight of reflecting sound wave to calculate the distance between the object and the sensor face. They are insensitive to the object’s material, color, and surface finish. They don’t require the object or target to be made of metal like inductive position sensors (see below). They can also detect transparent objects, such as clear bottles or different colored objects, that photoelectric sensors would have trouble with since not enough light would be reflected back to reliably determine the distance of an object. The ultrasonic sensors have a limited sensing range of approximately 8 meters.

A few things to keep in mind that negatively affect the ultrasonic sensor is when the object or target is made of sound-absorbing material, such as foam or fabric, where the object absorbs enough soundwave emitted from the sensor making the output unreliable. Also, the sensing field gets progressively larger the further away it gets from the sensing face, thus making the measurement inaccurate if there are multiple objects in the sensing field of the sensor or if the object has a contoured surface. However, there are sound-focusing attachments that are available to limit the sensing field at longer distances making the measurements more accurate.

Inductive sensors

Inductive distance measurement sensors work on the same principle as inductive proximity sensors, where a metal object penetrating the electromagnetic field will change its characteristics based on the object size, material, and distance away from the sensing face. The change of the electromagnetic field detected by the sensor is converted into a proportional output signal or distance measurement. They have a quick response time, high repeatability, and linearity, and they operate well in harsh environments as they are not affected by dust or water. The downside to using inductive distance sensors is that the object or target must be made of metal. They also have a relatively short measurement range that is limited to approximately 50 millimeters.

Several variables exist to consider when choosing the correct sensor technology for your application solution, such as color, material, finish, size, measurement range, and environment. Any one of these can have a negative effect on the performance or success of your solution, so you must take all of them into account.

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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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Sensor Mounting Made Easy

So, you’ve figured out the best way to detect the product shuttle paddle in your cartoning/packaging machine needs a visible red laser distance sensor. It’s taken some time to validate that this is the right sensor and it will be a reliable, long-term solution.

But then you realize there are some mechanical issues involved with the sensor’s placement and positioning that will require a bit of customization to mount it in the optimal location. Now things may have just become complicated. If you can’t design the additional mounting parts yourself, you’ll have to find someone who can. And then you have to deal with the fabrication side. This all takes time and more effort than just buying the sensor.

Or does it?

Off-the-shelf solutions

It doesn’t have to be that complex. There are possible off-the-self solutions you can consider that will make this critical step of providing a reliable mounting solution – possibly as straightforward as choosing the right sensor. Multiple companies offer sensor mounting systems that accommodate standard sensor brackets. Over the years, companies have continued to develop new mounting brackets for many of their sensor products, from photoelectric sensors and reflectors to proximity sensors to even RFID heads and linear transducers.

So it’s only natural to take that one step further and create a mounting apparatus and system that not only provides a mounting bracket, but also a stable platform that incorporates the device’s mounting bracket with things like stand-off posts, adjustable connection joints, and mounting bases. Such a flexible and extensive system can solve mounting challenges with parts you can purchase, instead of having to fabricate.

Imagine in the example above you need to mount the laser distance sensor off the machine’s base and offset it in a way that doesn’t interfere with the other moving parts of the cartoner. Think of these mounting systems and parts as a kind of Erector Set for sensing devices. You can piece together the required mounting bracket with a set of brace or extension rods and a mounting base that raises the sensor up and off the machine base and even angles it to allow for pointing at the target in the most optimal way.

The following are some mounting solutions for a variety of sensors:

These represent only a small number of different ways to mix and match sensor device brackets and mounting components to find a solid, reliable and off-the-shelf mounting solution for your next mounting challenge. So before considering the customization route, next time take a look at what might already be out there for vendors. It could make your life a lot simpler.

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Choosing Between M18 and Flatpack Proxes

Both M18s and flatpacks are inductive or proximity sensors that are widely used in mechanical engineering and industrial automation applications. Generally, they are similar in that they produce an electromagnetic field that reacts to a metal target when it approaches the sensor head. And the coil in both sensors is roughly the same size, so they have the same sensing range – between 5 to 8 millimeters. They also both work well in harsh environments, such as welding.

There are, however, some specific differences between the M18 and flatpack sensors that are worth consideration when setting up production.

M18

One benefit of the M18 sensor is that it’s adjustable. It has threads around it that allow you to adjust it up or down one millimeter every time you turn it 360 degrees. The M18 can take up a lot of space in a fixture, however. It has a standard length of around two inches long and, when you add a connector, it can be a problem when space is an issue.

Flatpack

A flatpack, on the other hand, has a more compact style and format while offering the same sensing range. The mounting of the flatpack provides a fixed distance so it offers less adjustability of the M18, but its small size delivers flexibility in installation and allows use in much tighter fixes and positions.

The flatpack also comes with a ceramic face and a welding cable, especially suited for harsh and demanding applications. You can also get it with a special glass composite protective face, a stainless-steel face, or a steel face with special coatings on it.

Each housing has its place, based on your detection application, of course. But having them both in your portfolio can expand your ability to solve your applications with sensor specificity.

Check out this previous blog for more information on inductive sensors and their unlimited uses in automation.

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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.