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Miniature Sensors With Monumental Capabilities

Application requirements solved by miniature optical sensors.Application requirements solved by miniature optical sensors.The requirement for miniature optical sensors to meet the demands of medical and semiconductor automation equipment often exceeds the capabilities of standard self-contained optical sensors. In some cases, other industry application requirements can be best solved by these same miniature optical sensors with advanced capabilities. So, what do these optical sensors offer that makes them so much better?

Application requirements solved by miniature optical sensors.Applications

Let’s begin with some of the applications that require these capabilities: medical applications, such as lab-on-a-chip microfluidics, liquid presence or level in drip chambers or pipettes, turbidity, drop detection, and micro or macro bubble detection, to name a few. Semicon applications include wafer presence on end-effectors, wafer mapping, wafer centering, and wafer presence in transfer chambers. Other applications that benefit from these sensors include packaging pharmaceuticals, detecting extremely small parts, and spray detection. In addition, these sensors are frequently used in customer-specific designs because they can be customized for specific applications.

Application requirements solved by miniature optical sensors.These sensors require an amplifier which sometimes is not popular with design engineers. They are associated with additional cost and extra work during installation; however, the remote amplifier offers real advantages. The optical function is separate from the control unit which allows it to be incorporated into an extremely tiny sensor head. Since the LEDs are mounted in the sensor heads, we now have a small wired connection back to the amplifier. Unlike fiber optics, this wired connection to the emitting LED and receiver allows for very minimal or no bending radius because of the cable in use.

Features

The new generation of amplifiers offers tremendous flexibility with advanced features, including:

    • OLED displayoptical sensors.
    • Intuitive menu structure
    • LEDs for status, communication, and warnings
    • Teaching/Parametrization
    • Single-point, two-point, window, dynamic, and tracking operating modes
    • Multiple teach modes: direct, dynamic, external, automatic and I/O-Link
    • Selectable power modes
    • Selectable outputsminiature optical sensors
    • Selectable speed settings
    • Auto-sync up to 8 amplifiers
    • Configurable delays and hysteresis
    • Compatible with existing all sensor heads

The sensor heads or optical heads come in a wide variety of housings, including the ability to customize them to meet specific requirements. And they are available in small precision LEDs, photodiodes, phototransistors, and complete laser modules according to a patented manufacturing process. Due to the high optical quality, additional lenses or apertures are no longer necessary.

Application requirements solved by miniature optical sensors.A multitude of special characteristics completely differentiates these sensors from the products made by standard optical sensor manufacturers. The range of products includes extraordinary miniature optical sensors as standard products, optimally adapted customized solutions, and precision optoelectronic components, such as LEDs, photodiodes, and laser modules. High optical quality, and unique modular designs, in connection with the greatest possible manufacturing flexibility, guarantee solutions that are exactly adapted to the respective problems and needs of the users.

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Capacitive, the Other Proximity Sensor

What is the first thing that comes to mind if someone says “proximity sensor?” My guess is the inductive sensor, and justly so because it is the most used sensor in automation today. There are other technologies that use the term proximity in describing the sensing mode, including diffuse or proximity photoelectric sensors that use the reflectivity of the object to change states and proximity mode of ultrasonic sensors that use high-frequency sound waves to detect objects. All these sensors detect objects that are in close proximity to the sensor without making physical contact. One of the most overlooked or forgotten proximity sensors on the market today is the capacitive sensor.

Capacitive sensors are suitable for solving numerous applications. These sensors can be used to detect objects, such as glass, wood, paper, plastic, or ceramic, regardless of material color, texture, or finish. The list goes on and on. Since capacitive sensors can detect virtually anything, they can detect levels of liquids including water, oil, glue, and so forth, and they can detect levels of solids like plastic granules, soap powder, sand, and just about anything else. Levels can be detected either directly, when the sensor touches the medium, or indirectly when it senses the medium through a non-metallic container wall.

Capacitive sensors overview

Like any other sensor, there are certain considerations to account for when applying capacitive, multipurpose sensors, including:

1 – Target

    • Capacitive sensors can detect virtually any material.
    • The target material’s dielectric constant determines the reduction factor of the sensor. Metal / Water > Wood > Plastic > Paper.
    • The target size must be equal to or larger than the sensor face.

2 – Sensing distance

    • The rated sensing distance, or what you see in a catalog, is based on a mild steel target that is the same size as the sensor face.
    • The effective sensing distance considers mounting, supply voltage, and temperature. It is adjusted by the integral potentiometer or other means.
    • Additional influences that affect the sensing distance are the sensor housing shape, sensor face size, and the mounting style of the sensor (flush, non-flush).

3 – Environment

    • Temperatures from 160 to 180°F require special considerations. The high-temperature version sensors should be used in applications above this value.
    • Wet or very humid applications can cause false positives if the dielectric strength of the target is low.
    • In most instances, dust or material buildup can be tuned out if the target dielectric is higher than the dust contamination.

4 – Mounting

    • Installing capacitive sensors is very similar to installing inductive sensors. Flush sensors can be installed flush to the surrounding material. The distance between the sensors is two times the diameter of the sensing distance.
    • Non-flush sensors must have a free area around the sensor at least one diameter of the sensor or the sensing distance.

5 – Connector

    • Quick disconnect – M8 or M12.
    • Potted cable.

6 – Sensor

    • The sensor sensing area or face must be smaller or equal to the target material.
    • Maximum sensing distance is measured on metal – reduction factor will influence all sensing distances.
    • Use flush versions to reduce the effects of the surrounding material. Some plastic sensors will have a reduced sensing range when embedded in metal. Use a flush stainless-steel body to get the full sensing range.

These are just a few things to keep in mind when applying capacitive sensors. There is not “a” capacitive sensor application – but there are many which can be solved cost-effectively and reliably with these sensors.

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Evolution of Pneumatic Cylinder Sensors

Today’s pneumatic cylinders are compact, reliable, and cost-effective prime movers for automated equipment. They’re used in many applications, such as machinery, material handling, assembly, robotics, and medical. One challenge facing OEMs, integrators and end users is how to detect reliably whether the cylinder is fully extended, retracted, or positioned somewhere in between before allowing machine movement.

A widely used method for cylinder position detection is to attach magnetically actuated switches or sensors to the sides of the cylinder using brackets, or by inserting them into a slot extruded into the body of the cylinder. Magnetic field sensors detect an internal magnet that is mounted on the moving piston through the aluminum cylinder wall.

The selection of which type of magnetic sensors to use depends on your application needs and specific data requirements.

Magnetic Sensor Types

Reed switches

The reed switch is the most simplistic and most often used end-of-stroke sensor available on the market. It consists of two flattened ferromagnetic nickel and iron reed elements enclosed in a hermetically sealed glass tube. The tube aids in minimizing contact arcing and prevents moisture from getting to the switch elements. As an axially aligned magnet approaches the switch element, the reed elements are magnetized and attracted together completing the circuit.

AMR and GMR sensors

Most cylinder manufacturers and OEMs use electronic sensors with either magnetoresistive technology (AMR) or giant magnetoresistive (GMR). Both versions are based on a change in resistance. One advantage of these sensors is that they will work with the axially magnetized magnet and, in some cases, the radially magnetized magnet. GMR sensors can be physically smaller than the AMR sensors. They are more sensitive, more precise and have a better hysteresis. Versions exist that provide reverse polarity protection, overload protection, and short circuit protection.

The initial cost of an AMR or GMR sensor may be slightly more than a reed sensor, however, this cost is increasingly less, especially if you figure the cost of downtime when the reed switch fails. AMR and GMR sensors are also three-wire devices, unlike the two-wire reed switches. In the end, the AMR and GMR sensors are the better solution since there are no moving parts and they typically last much longer than the reed switch.

Position detection sensors for both C-slots and T-slots

Pneumatic cylinders typically have either a C-slot or T-slot feature in the extrusion of the cylinder body. Many sensor housings have these same housing profiles and the sensor can either be dropped into the slot from above and tightened with a screw or slid in from the end of the cylinder provided there is no end plate. For round cylinders or tie rod cylinders, additional brackets are available that can use either a C-slot or T-slot sensor. This allows for commonality of sensors for end users and OEMs to meet the needs of many applications and reduce the number of sensor part numbers and inventory.

Today, there are more options than ever for piston position detection in pneumatic cylinders, including different housing styles to meet the cylinder extrusions. Also available are two sensors – one for extended and one for retracted – that share a single, four-pin connection. These magnetic sensors are also available now with weld field immunity for harsh welding applications.

Technology has advanced as well. Now cylinder sensors can be taught to trigger at certain points along the travel of the piston. The user simply moves the piston to a desired location and presses a button to set the switching location. This teachable sensor can also be connected to IO-Link, allowing up to eight switching points for flexibility in several applications.

Over the years, many users have abandoned reed switches, due to their failure rate, in favor of mechanical or inductive sensors to detect pneumatic cylinder position. AMR and GMR sensors are smaller, faster, easy to integrate, and are much more reliable. With the vast improvements in sensor technology, AMR and GMR sensors should now be considered the primary solution for detecting cylinder position.

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Today’s Pressure Sensors: More Options to Meet Your Application Needs

Pressure sensing devices are prevalent in industrial machinery.  

 

There are three types of pressure measurements, each with their advantages and disadvantages. 

Absolute pressure (psia) is referenced to a perfect vacuum. This pressure measurement is always positive and is used in measuring barometric pressure or in altimeters.  

 

Gauge pressure (psig) measurement is measured relative to ambient pressure. Examples of gauge pressure include blood pressure and intake manifold vacuum in an engine. Typically, these types of sensors have an atmospheric vent hole located somewhere in the housing. An advantage to this type of sensor is it can measure both positive and negative, thus it can be used in vacuum applications such as robots picking up glass or other products with suction cups.  

 

Differential pressure (psid) measurement is the difference between two pressure sources. The gauge pressure measurement is really a differential measurement as one side is open to the ambient pressure and the other side is connected to the process pressure. However, for most differential pressure sensors the second pressure source is not the ambient air. 

In the past, pressure sensing was accomplished by mechanical switches that typically used Bourdon tubes, diaphragms or bellows. These devices caused a mechanical movement in the switch as the pressure increased or decreased. A course adjustment screw was used to set the desired set point to actuate the various controls. In addition to the switch, some sort of indication was needed so an analog gauge was also typically required. While these devices solved the control requirement, accuracy was not as reliable as the controls required or what was preferred. 

To convert pressure into an electrical output, several different technologies are used in electronic pressure sensors. The first type of strain gauge technology — Piezoresistive technology — is based on measuring the resistance of a deforming silicon semiconductor. A stainless steel housing protects the silicon chip as pressure is indirectly transferred to the membrane with a liquid that is usually silicon oil. This type of measurement is most often used in high dynamic pressures.

Thin film technology utilizes a stainless steel carrier. The resistors and other circuitry are placed on the membrane, and measurement is based on the strain gauge technology. The advantage of the thin stainless steel film is its ability to withstand high peak pressures and burst pressures.  

Thick film technology, which also utilizes strain gauge concepts, uses a ceramic carrier. The resistors and other associated circuitry are placed on a membrane using a thick film process. Ceramic cells offer long-term stability and good corrosion resistance. 

In capacitive measuring cells, one electrode is fitted to an elastic membrane and the other electrode is on the support or housing surface on the opposite side. This forms a capacitor in which one electrode follows the movement of the membrane. As the pressure increases or decreases the distance between the electrodes change causing a change in capacitance. 

 

Today’s pressure sensors incorporate both the switching functions and the display of the current pressure. Since these devices are electronic, there are a multitude of output functions available as opposed to the simple on-off functionality of the mechanical pressure switch. These include multiple discrete PNP or NPN outputs from one sensor with multiple functionalities. In many cases a sensor will provide a single discrete output plus a continuous analog output proportional to the pressure value. The discrete output can provide an alarm function while the analog output provides a dynamic value of the process.

The discrete outputs can be programmed for various operations. First and most important are the set points, sometimes referred to as hysteresis, of when the output should activate (SP) and when the output should reset or turn off (RP). Hysteresis keeps the switching outputs stable even if the system pressure fluctuates around the set point.

In some applications it is desirable to know if the pressure is within operating range for machine functions to continue. The output or outputs can be programmed with a window function. The output will be active as long as the measured values fall between the defined low pressure and the defined upper pressure.

Pressure spikes can cause problems not only with the mechanics of the system but with the logic of electrical controls including outputs changing states quickly or chattering. The electronic sensors offered today include the ability to delay the switching outputs of the sensor. Typically, the delays are programmable up to 50 seconds. 

Pressure is usually measured in PSI or bar with one bar of pressure being equal to 14.5 PSI. When applying pressure sensors various pressures should be taken into consideration. First is the nominal operating pressure of the system. The pressure sensor applied to the system should in the 50 – 60% maximum rating of the sensor as this will provide a safety margin.  

 

Overload pressure can be caused by pressure spikes in the system from valves opening or closing or pump cavitation. These spikes can exceed the specified sensor limit, however, no permanent damage or change will occur. Burst pressure is the pressure that can cause permanent damage to the sensing device or mechanical damage to the sensor.   

 

What if the application involves a paste or thick substance that could potentially clog the orifice or dead space of the sensor? Some pressure sensor manufacturers offer flush mounted pressure sensors. These devices are perfect for detecting pastes, greases or thick substances as the bottom of the sensor has a protective membrane, typically stainless steel.  

 

Today’s display is multifunctional as not only does it display dynamic values but it is also used for programming or configuring the sensor. Included on the display is the pressure, parameters, parameter values, scaling of the device, and output(s) status. Also included are programming keys and, in some cases, keypad lock out functionality. 

The true epitome of a pressure sensor is one that can have all of capabilities I’ve mentioned as well as the ability to provide additional functionality and parameterization. Pressure sensors that connect to networks such as IO-Link can optimize processes allowing process monitoring, configuration and error analysis to take place through the system controller. Digital transmission of analog values ensures high signal quality over longer distances and signal delays and distortions are eliminated.  

 

Networkable sensors, such as IO-Link, reduce downtimes and possible configuration errors with plug-and-play functionality. Maximum system flexibility can be achieved during operation as parameters can be modified quickly and remotely. In addition, process diagnostics, data, and errors are reported directly to the controller and displayed on man-machine interfaces. 

 

Pressure sensors have come a long way from the multiple mechanical based components used in the past in both functionality and capabilities. 

 

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AMR and GMR: Better Methods to End of Travel Sensing

Today’s pneumatic cylinders are compact, reliable, and cost-effective prime movers for automated equipment. Unfortunately, they are often provided with unreliable reed or Hall Effect switches that fail well before the service life of the cylinder itself is expended. Too often, life with pneumatic cylinders involves continuous effort and mounting costs to replace failed cylinder position switches. As a result, some OEMs and end users have abandoned magnetic cylinder switches altogether in favor of more reliable — yet more costly and cumbersome — external inductive proximity sensors, brackets, and fixed or adjustable metal targets. There must be a better way!

One position sensing technique is to install external electro-mechanical limit switches or inductive proximity switches that detect metal flags on the moving parts of the machine. The disadvantages of this approach include the cost and complexity of the brackets and associated hardware, the difficulty of making adjustments, and the increased physical size of the overall assembly.

A more popular and widely used method is to attach magnetically actuated switches or sensors to the sides of the cylinder, or into a slot extruded into the body of the cylinder. Through the aluminum wall of the pneumatic cylinder, magnetic field sensors detect an internal magnet that is mounted on the moving piston. In most applications, magnetic sensors provide end-of-stroke detection in either direction; however, installation of multiple sensors along the length of a cylinder allows detection of several discrete positions.

The simplest magnetic field sensor is the reed switch. This device consists of two flattened ferromagnetic nickel and iron reed elements enclosed in a hermetically sealed glass tube. The glass tube is evacuated to a high vacuum to minimize contact arcing. As an axially aligned magnet approaches, the reed elements attract the magnetic flux lines and draw together by magnetic force, thus completing an electrical circuit. The magnet must have a strong enough Gauss rating, usually in excess of 50 Gauss, to overcome the return force, i.e. spring memory, of the reed elements.

The benefits of reed switches are that they are low cost, they require no standby power, and they can function with both AC and DC electrical loads. However, reed switches are relatively slow to operate, therefore they may not respond fast enough for some high-speed applications. Since they are mechanical devices with moving parts, they have a finite number of operating cycles before they eventually fail. Switching high current electrical loads can further cut into their life expectancy.

Hall Effect sensors are solid-state electronic devices. They consist of a voltage amplifier and a comparator circuit that drives a switching output. It might seem like an easy solution to simply replace reed switches with Hall Effect sensors, however, the magnetic field orientation of a cylinder designed for reed switches may be axial, whereas the orientation for a Hall Effect sensor is radial. The result? There is a chance that a Hall Effect sensor will not operate properly when activated by an axially oriented magnet. Finally, some inexpensive Hall Effect sensors are susceptible to double switching, which occurs because the sensor will detect both poles of the magnet, not simply one or the other.

Today, solid-state magnetic field sensors are available either using magnetoresistive (AMR) or giant magnetoresistive (GMR) technology.  Compared to AMR technology, GMR sensors have an even more robust reaction to the presence of a magnetic field, at least 10 percent.

The operating principle of AMR magnetoresistive sensors is simple: the sensor element undergoes a change in resistance when a magnetic field is present, changing the flow of a bias current running through the sensing element. A comparator circuit detects the change in current and switches the output of the sensor.

In addition to the benefits of rugged, solid-state construction, the magnetoresistive sensor offers better noise immunity, smaller physical size, less susceptibility to false tripping, speed and lower mechanical hysteresis (the difference in switch point when approaching the sensor from opposite directions). Quality manufacturers of magnetoresistive sensors incorporate additional output protection circuits to improve overall electrical robustness, such as overload protection, short-circuit protection, and reverse-connection protection. Some manufacturers also offer lifetime warranty of the sensors.

Over the years, many users have abandoned the use of reed switches due to their failure rate and have utilized mechanical or inductive sensors to detect pneumatic cylinder position. AMR and GMR sensors are smaller, faster, and easer to integrate and are much more reliable however; they must overcome the stigma left by their predecessors. With the vast improvements in sensor technology, AMR and GMR sensors should now be considered the primary solution for detecting cylinder position.

 

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Capacitive Prox Sensors Offer Versatility for Object and Level Detection

When you think of a proximity sensor, what is the first thing that comes to mind? In most cases it is probably the inductive proximity sensor and justly so because they are the most widely used sensor in automation today. But there are other types of proximity sensors. These include diffuse photoelectric sensors that use the reflectivity of the object to change states and proximity mode of ultrasonic sensors that use high frequency sound waves to detect objects. All of these sensors detect objects that are in close proximity of the sensor without making physical contact.

One of the most overlooked proximity sensors on the market today is the capacitive sensor. Why? For some, they have bad reputation from when they were released years ago as they were more susceptible to noise than most sensors. I have heard people say that they don’t discuss or use capacitive sensors because they had this bad experience in the past, however with the advancements of technology this is no longer the case.

Today capacitive sensors are available in as wide of a variety of housings and configurations as inductive sensors. They are available as small as 4mm in diameter, in hockey puck styles, extended temperature ranges, rectangular, square, with Teflon housings, remote sensing heads, adhesive cut-to-length for level detection and a hybrid technology that is capable of ignoring foaming and filming of liquids. The capability and diversity of this technology is constantly evolving.

Capacitive sensors are versatile in solving numerous 1applications. These sensors can be used to detect objects such as glass, wood, paper, plastic, ceramic, and the list goes on and on. The capacitive sensors used to detect objects are easily identified by the flush mounting or shielded face of the sensor. Shielding causes the electrostatic field to be short conical shaped much like the shielded version of the inductive proximity sensor. Typically, the sensing range for these sensors is up to 20 mm.

Just as there are non-flush or unshielded inductive sensors, there are non-flush capacitive sensors, and the mounting and housing2 looks the same. The non-flush capacitive sensors have a large spherical field which allows them to be used in level detection. Since capacitive sensors can detect virtually anything, they can detect levels of liquids including water, oil, glue and so forth and they can detect levels of solids like plastic granules, soap powder, sand and just about anything else. Levels can be detected either directly with the sensor touching the medium or indirectly where the sensor senses the medium through a non-metallic container wall. The sensing range for these sensors can be up to 30 mm or in the case of the hybrid technology it is dependent on the media.

The sensing distance of a capacitive sensor is determined by several factors including the sensing face area – the larger the better. The next factor is the material property of the object or dielectric constant, the higher the dielectric constant the greater the sensing distance. Lastly the size of the target affects the sensing range. Just like an inductive sensor you want the target to be equal to or larger than the sensor. The maximum sensing distance of a capacitive sensor is based on a metal target thus there is a reduction factor for non-metal targets.

As with most sensors today, the outputs of a capacitive sensor include PNP, NPN, push-pull, analog and the increasing popular IO-Link. IO-Link provides remote configuration, additional diagnostics and a window into what the sensor is “seeing”. This is invaluable when working on an application that is critical such as life sciences.

Most capacitive sensors have a potentiometer to allow adjustment of the sensitivity of the sensor to reliably detect the target. Today there are versions that have teach pushbuttons or a teach wire for remote configuration or even a remote amplifier. Although capacitive sensors can detect metal, inductive sensors should be used for these applications. Capacitive sensors are ideal for detecting non-metallic objects at close ranges, usually less than 30 mm and for detecting hidden or inaccessible materials or features.

Just remember, there is one more proximity sensor. Don’t overlook the capabilities of the capacitive sensor.

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Do Your Capacitive Sensors Ignore Foam & Condensation for True Level Detection?

Capacitive sensors detect any changes in their electrostatic sensing field. This includes not only the target material itself, but also application-induced influences such as condensation, foam, or temporary or permanent material build-up. High viscosity fluids can cause extensive delays in accurate point-level detection or cause complete failure due to the inability of a capacitive sensor to compensate for the material adhering to the container walls. In cases of low conductive fluids such as water or deionized water and relatively thin container walls, the user might be able to compensate for these sources of failure. Potential material build-up or condensation can be compensated for by adjusting the sensitivity of the sensor, cleaning of the container, or employing additional mechanical measures.

However, this strategy works only if the fluid conductivity stays low and no other additional influencing factors like temperature, material buildup, or filming challenge the sensor. Cleaning fluids like sodium hydrochloride, hydrochloric acid, chemical reagents, and saline solutions are very conductive, which cause standard capacitive sensors to false trigger on even the thinnest films or adherence. The same applies for bodily fluids such as blood, or concentrated acids or alkaline.

Challenges of this type of application are not obvious. This is especially true when the sensors performed well in the initial design phase but fail in the field for no obvious reason. An example of this would be when the sensors on the equipment are setup with deionized water however, the final process requires some type of acid  Difficult and time-consuming setup procedures and unstable applications requiring frequent readjustment are the primary reasons why capacitive level sensors have been historically avoided in certain applications.

Today, there are hybrid technologies employed in capacitive sensors for non-invasive level detection applications that would require little or no user adjustment after the initial setup process. They can detect any type conductive water based liquid through any non-metallic type of tank wall while automatically compensating for material build-up, condensation, and foam.

This hybrid sensing technology helps the sensors to distinguish effectively between true liquid levels and possible interferences caused by condensation, material build-up, or foaming fluids. While ignoring these interferences, the sensors still detect the relative change in capacitance caused by the media but use additional factors to evaluate the validity of the measurement taken before changing state. These sensors are fundamentally insensitive to any non-conductive material like plastic or glass, which allows them to be utilized in non-invasive level applications.

These capacitive sensors provide cost-effective, reliable point-level monitoring for a wide array of medical, biotechnology, life sciences, semiconductor processes, and other manufacturing processes and procedures. This technology brings considerable advantages to the area of liquid level detection, not only offering alternative machine designs, but also reduced assembly time for the machine builders.  Machine designers now have the flexibility to non-invasively detect almost any type of liquid through plastic, glass tubes, or other non-metallic container walls, reducing mechanical adaption effort and fabrication costs.

Discrete indication tasks like fluid presence detection in reagent supply lines, reagent bottle level feedback, chemical levels, and waste container overfill prevention are now a distinct competence for capacitive sensors. Reagents and waste liquids are composed of different formulas depending on the application.  The sensing technology has to be versatile enough to compensate automatically for changing environmental or media conditions within high tolerance limits. Applications that require precision and an extraordinary amount of reliability, such as blood presence detection in cardiovascular instruments or hemodialysis instruments, medical, pharmaceutical machine builders, equipment builders for semiconductor processes can rely now on these hybrid capacitive sensors

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Mini Sensors Add Big Capabilities to Life Science Applications

1Miniaturization is one of the essential requirements for medical instruments and laboratory equipment used in the life science industry. As instruments get smaller and smaller, the sensor components must also become smaller, lighter and more flexible. The photoelectric sensors that were commonly used in general automation and applied in life science applications have met their limitations in size and performance.

2.jpgSensors used in these complex applications require numerous special characteristics such as high-quality optics, unique housing designs, precise LEDs with the best suited wavelength and the ability to be extremely flexible to fit in the extremely small space available. Sensors have been developed to meet the smallest possible installation footprint with the highest optical precision and enough flexibility to be installed where they are needed. These use integrated micro-precision optics that shape and focus the light beam exactly on the object without any undesirable side-effects to achieve the reliability demanded in today’s applications.

Previously many life science applications used conventional plastic fiber optic cables that were often too large and not flexible enough to be routed through the instruments. An alternative to the classic fiber cables is a “wired” fiber with precision micro-optics and extremely flexible cables with essentially no minimum bending radius and no significant coupling losses. Similar to a conventional fiber optic sensor, an external amplifier is required to provide a wide variety of functionalities to solve the demanding applications.

These sensors can be used in applications such as:

  • Precise detection of liquid levels using either attenuation or refraction with a small footprint
  • Reliable detection of transparent objects such as microscope slides or coverslips having various edge shapes
  • Detection of transparent liquids in micro-channels or capillaries
  • Reliable detection of individual droplets
  • Recognition of free-floating micro-bubbles in a tube that are smaller than the tube diameter and that cannot be seen by the human eye
  • Recognition of macro-bubbles that are the diameter of small tubes

For more information on photoelectric sensors that have the capability to meet the demands of today’s life science applications visit www.balluff.com.

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Make Clear Water Visible to Your Sensors

In some industries such as life sciences it is necessary to detect clear water or clear liquids in a container or tube. This is even more challenging when the diameters of the tube are small, and the tube thickness is nearly as large as the stream of liquid.

The attenuation or gradual reduction of the intensity of the light beam in water and air can be directly compared. The attenuation of light in water can be attributed to light entering water at any angle other than at a right angle and can be refracted. The measurement of light through a tube is different because not only is the light attenuated by the liquid, but depending on where the light passes through the tube it can be refracted, diverted and or focused. As a result, the signal differences can be low.

Attenuation is typically the first choice if the liquids are opaque or colored. The requirements of the shape of the light beam and the alignment of the sensor add more complication to the application. The attenuation effect appears weaker in clear liquids. The principle does not work with reflective sensors since reflection is a surface effect and the light must pass through the liquid.OPTO_appl_08_sw-water

From spectral analysis it’s has been determined that the attenuation characteristics of water are heavily dependent on the wavelength of the light that is conducted through it. Sensors were developed for such applications. Typically, these sensors utilize LED’s in the upper infrared range of 1,450 nm. At this wavelength water literally absorbs the light and becomes opaque making detection more simplified and reliable.

This principle even works for fine capillaries and microchannels. Liquid detection can be very precise depending on the sensor size and the effective light beam. Light beams as small as 0.4mm can provide high resolution for small thin tubes typically found in microfluidics applications.

Versions of these sensors exist for applications that involve less transparent or semi-transparent vessels. Light at the 1450nm wavelength can pass through these containers or tubes and can be attenuated by the water. The main factor is that enough light makes its way through the walls of the container.

Through-beam sensors were developed for applications such as detecting clear liquids. These sensors are also available in extremely small dimensions and usually require an amplifier, or they can be supplied in a rugged fork sensor housing. The required sensor dimensions conform to the geometry of the vessel or container.

For more information on sensors for these types of applications contact your local Balluff representative or contact us at www.balluff.com.

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Capacitive Sensors: Versatile enough for most (but not all) detection applications

capacitive 1

Capacitive sensors are versatile for use in numerous applications. They can be used to detect objects such as glass, wood, paper, plastic, ceramic, and more. Capacitive sensors used to detect objects are easily identified by the flush mounting or shielded face of the sensor. This shielding causes the electrostatic field to be short and conical shaped, much like the shielded version of an inductive proximity sensor.

capacitive 2Just as there are non-flush or unshielded inductive sensors, there are non-flush capacitive sensors, and the mounting and housing look the same. The non-flush capacitive sensors have a large spherical field which allows them to be used in level detection, including detection of liquids and granular solids. Levels can be detected either directly with the sensor making contact with the medium, or indirectly with the sensor sensing the medium through a non-metallic container wall.

Capacitive sensors are discrete devices so once you adjust the sensitivity to detect the target while ignoring the container, the sensor is either on or off. Also remember that the sensor is looking for the dielectric constant in the case of a standard capacitive sensor or the conductivity of a water based liquid in the case of the hybrid technology.

Recent technology advances with remote amplifiers have allowed capacitive sensors to provide an analog output or a digital value over IO-Link. As previously mentioned, these sensors are based off of a dielectric constant so the analog value being created is dependent on the media being sensed.

While capacitive sensors are versatile to work in many applications, they are not the right choice for all applications.

Recently a customer inquired if a capacitive sensor could detect the density of an substance and unfortunately the short answer is no, though in some applications the analog sensors can detect different levels of media if it can be separated in a centrifuge. Also, capacitive sensors may not detect small amounts of media as the dielectric constant of the media must be higher than the container that holds the media.

There are three important steps in applying a capacitive sensor — test it, test it and test it one more time. During your testing procedures be sure to test it under the best and worse conditions. Also like any other electronic device temperature can have an affect although it may be negligible there will be some affect.

For more information on capacitive sensors visit www.balluff.com.