Using MicroSpot LEDs for Precise Evaluations in Life Science

Handling microfluidics and evaluating samples based on light is a precise science. And that precision comes from the light source, not the actual detection method. But too many times we see standard LEDs being used in these sensing and evaluation applications. Standard LEDs are typically developed for lighting and illumination applications and require too many ancillary components to achieve a minimum level of acceptability. Fortunately, there is an alternate technology.

First, let’s look at a standard LED. Figure 1 shows a typical red LED. You can see the light emission surface is cluttered with the anode pad (square in the middle) and its bond wire. These elements are fine for applications like long-range sensing, lighting and indications, but for precise, up-close applications they cause disturbances.

Figure 1: Typical red LED showing the intrusion of the anode and bond wire into the light emission

Most notable is the square hole in the middle of the emission pattern. There are two typical methods to reduce the effect of the hole: lensing and apertures. An aperture essentially restricts the emitted light to a corner of the die, substantially reducing the light energy causing difficulties with low-contrast detections. Using a lens only will maintain the light energy, but the beam will have a fixed focused point that is not acceptable for many applications. But even the bond wire produces reflections and causes spurious emissions. These cannot be tolerated with microfluidics as adjacent channels will become involved in the measurement. An additional aperture is typically used to suppress the spurious emissions.

Fortunately, there is an alternative with MicroSpot LEDs. Basically, the anode and emission areas are inverted as shown in the Figure 2 comparison.

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Figure 2: Comparison of the typical LED with the MicroSpot’s clean, powerful and collimated emission

This eliminates the need for the anode and bond wire to interfere with the emitted light. This produces a clean, powerful and collimated emission that will produce consistent results without additional components. This level of beam control is typically reserved for lasers. However, lasers also require more components, are much larger and cost more. The MicroSpot LED is the best choice for demanding life science applications.

Try the MicroSpot for yourself in select Balluff MICROmote miniature photoelectric sensors.

Learn more at www.balluff.com.

Imagine the Perfect Photoelectric Sensor

Photoelectric sensors have been around for a long time and have made huge advancements in technology since the 1970’s.  We have gone from incandescent bulbs to modulated LED’s in red light, infrared and laser outputs.  Today we have multiple sensing modes like through-beam, diffuse, background suppression, retroreflective, luminescence, distance measuring and the list goes on and on.  The outputs of the sensors have made leaps from relays to PNP, NPN, PNP/NPN, analog, push/pull, triac, to having timers and counters and now they can communicate on networks.

The ability of the sensor to communicate on a network such as IO-Link is now enabling sensors to be smarter and provide more and more information.  The information provided can tell us the health of the sensor, for example, whether it needs re-alignment to provide us better diagnostics information to make troubleshooting faster thus reducing downtimes.  In addition, we can now distribute I/O over longer distances and configure just the right amount of IO in the required space on the machine reducing installation time.

IO-Link networks enable quick error free replacement of sensors that have failed or have been damaged.  If a sensor fails, the network has the ability to download the operating parameters to the sensor without the need of a programming device.

With all of these advancements in sensor technology why do we still have different sensors for each sensing mode?  Why can’t we have one sensor with one part number that would be completely configurable?

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Just think of the possibilities of a single part number that could be configured for any of the basic sensing modes of through-beam, retroreflective, background suppression and diffuse. To be able to go from 30 or more part numbers to one part would save OEM’s end users a tremendous amount of money in spares. To be able to change the sensing mode on the fly and download the required parameters for a changing process or format change.  Even the ability to teach the sensing switch points on the fly, change the hysteresis, have variable counter and time delays.  Just imagine the ability to get more advanced diagnostics like stress level (I would like that myself), lifetime, operating hours, LED power and so much more.

Obviously we could not have one sensor part number with all of the different light sources but to have a sensor with a light source that could be completely configurable would be phenomenal.  Just think of the applications.  Just think outside the box.  Just imagine the possibilities.  Let us know what your thoughts are.

To learn more about photoelectric sensors, visit www.balluff.com.

Back to the Basics – Photoelectric Light Source

Welcome to the first in a series of getting back to the basic blogs about photoelectric sensors.

LightTypeAll photoelectric sensors require a light source to operate. The light source is integral to the sensor and is referred to as the emitter. Some light sources can be seen and may be of different colors or wavelengths for instance red, blue, green, white light or laser or one you cannot see, infrared. Many years ago photoelectric sensors used incandescent lights which were easily damaged by vibration and shock. The sensors that used incandescence were susceptible to ambient light which limited the sensing range and how they were installed.

Today light sources use light emitting diodes (LED’s). LED’s cannot generate the light that the incandescent bulbs could. However since the LED is solid state, it will last for years, is not easily damaged, is sealed, smaller than the incandescent light and can survive a wide temperature range. LED’s are available in three basic versions visible, laser and infrared with each having their advantages.

Visible LED’s which are typically red, aid in the alignment and set up of the sensor since it will provide a visible beam or spot on the target. Visible red LED’s can be bright and should be aimed so that the light will not shine in an operator’s eyes. The other color visible LED’s are used for specific applications such as contrast, luminescence, and color sensors as well as sensor function indication.

Laser LED’s will provide a consistent light color or wavelength, small beam diameter and longer range however these are generally more costly. Lasers are often used for small part detection and precision measuring. Although the light beam is small and concentrated, it can be easily interrupted by airborne particles. If there is dust or mist in the environment the light will be scattered making the application less successful than desired. When a laser is being used for measuring make sure the light beam is larger than any holes or crevasses in the part to ensure the measurement is as accurate as possible. Also it is important to ensure that the laser is installed so that it is not aimed into an operator or passerby’s eyes.

Lastly, the infrared LED will produce an invisible, to the human eye, light while being more efficient and generating the most light with the least amount of heat. Infrared light sources are perfect for harsh and contaminated environments where there is oil or dust. However, with the good comes the bad. Since the light source is infrared and not visible setup and alignment can be challenging.

LED’s have proved to be robust and reliable in photoelectric sensors. In the next installment we will review LED modulation.

You can learn more about photoelectric sensors on our website at www.balluff.us