Reaping The Benefits Of Custom Optical Sensors

Reaping The Benefits Of Custom Optical Sensors

Sensors Insights by Mike Lander

SENSORS EXPO 2018 - TT ElectronicsBooth #830

We live in a complex world dominated by increasingly unique applications.  The advent and adoption of the Internet of Things (IoT) and asset intelligence continues to fuel the importance of optical sensors as the baseline building block for a complete solution.  With an estimated 23 billion IoT connected devices installed in 2018, the need for customised optoelectronic sensor solutions is becoming not only a reality, but a necessity. 

Finding an off-the-shelf solution for a specific optical sensor application becomes extremely challenging and requires a certain level of optical, electrical and mechanical engineering expertise to ensure the solution functions consistently and reliably.  Designing compatible light emitters, sensor sensitivity, optical power, and electrical characteristics, while balancing stack-up tolerances and overall cost is difficult, even for the simplest development projects.

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Benefits of a custom optical sensor solution

Each application is unique, and integrating commercial off-the-shelf (COTS) sensor components oftentimes does not produce the desired outcome given the countless parameters being considered.  COTS solutions may provide too wide or too little detection sensitivity, and could lead to a false reading or inconsistent results.  Designing the optimum sensor solution with the appropriate sensitivity range, opto-electrical performance and footprint becomes critical to ensure precise, consistent and reliable performance always. 

These custom optical sensor solutions are fine-tuned with compatible LEDs, sensors, housing dimensions and with factory matched testing and configuration to produce the desired results for a turn-key solution.  Adding cables, connectors, passive circuit components and custom PCBs also complement and enhance the flexibility and reliability of the desired solution. There are real tangible benefits with customised optical sensor assemblies as shown in the summary table below:

Table 1

 

Optical sensor solution building blocks

The options to achieve your sensor solution are quite broad.  They range from simply procuring discrete components, through simple packaged COTS solutions to higher-level custom assemblies.  Let’s take a quick look at the building blocks across the continuum of optical sensor solutions:

 

Discrete components:

The discrete sensor is the most basic element of the sensor solution, though selecting the appropriate additional components is certainly no trivial task.  For example, matching an appropriate LED with the sensor element becomes challenging with multiple options: including basic photo transistors, photo diodes and even smart detectors that provide some level of intelligence along with the sensor element itself.  Intelligent sensors can integrate functionality such as temperature-compensation, auto-gain control or autonomous decision-making capabilities, for example.  The right sensor depends on the needs of your specific application.  Furthermore, you will need to consider requirements such as wavelength, sensitivity, possibly the size of the photo-sensor, and other parameters.

For most designs, you also need to select a discrete emitter.  The most common emitters are LEDs, but vertical-cavity surface-emitting lasers (VCSELs) are also used in some designs.  Again, there are many parameters to consider when selecting your emitter including, but not limited to wavelength, optical output power, angular optical output and forward voltage.  Lastly, the pairing of the emitter and sensor is typically also not a trivial task.  Wavelength, power levels, and sensitivity to mechanical alignment are all among the critical considerations for an effective solution. 

 

Housing: 

The housing (or packaging) of your sensor solution is the next step up the hierarchy.  Many sensor solutions require both photo-sensors and emitters.  For example, basic reflective sensors and transmissive sensors (such as slotted switches) integrated both elements.  Reflective sensors are typically used to detect the presence or proximity of an object by detecting reflected optical power.  Transmissive sensors typically have a line-of-sight between the emitter and the sensor and sense objects that break the optical “circuit”.

The optical and mechanical housing requirements are quite broad because each application has unique requirements.  Considerations include spacing between the sensor and emitter, aperture size, through-hole vs. surface mount, mounting bracket and so forth.  Designers must be cognizant of the mechanical stack-up tolerances involved with each design.  The discrete components and housing design all contribute to the overall system performance.  The customised optical sensor solution design must be able to accommodate variability in the location mounting, types of media being detected, environmental conditions and detection distance just to name a few.

 

Wiring and Connectors: 

Often, these optical sensors are mounted remotely from the main printed circuit board (PCB) or microcontroller in a system.  Connectivity becomes critical for input power and communications, so the integration of wiring and connectors becomes beneficial.  The appropriate determination of the wire length and connector types are essential in designing a robust solution.  Procuring these custom assemblies with pre-attached wiring and connectors saves time and money and fosters ‘plug-n-play’ compatibility resulting in faster time-to-market and increased manufacturing efficiencies.  The value-add labour and assembly is done in high-volumes at the factory instead of further downstream in the assembly process.

 

Higher-Level Assemblies:

It’s possible that your optical sensor requirement goes beyond the simple need of just a detector and emitter.  You might require multiple sensors and/or emitters.  You may even need other passive and active components (such as a voltage regulator), or even other mechanical components.  This often requires multiple components to be placed on a common PCB.  That PCB may require additional wiring and connectors as well.  Sometimes a common substrate with multiple discrete die components might be ideal.  The point is, higher-level assemblies can take on many different forms, which are dictated by your requirements around functionality, performance and size requirements of your need.

 
​​Fig. 1: Simple to complex

The value of working with a trusted partner

As stated earlier, bringing all the sensor solution building blocks together in a way that meets the optical, electrical and mechanical performance requirements together is not a simple task.  This is especially true when trying to detect challenging media or operating in difficult conditions. 

Finding the right partner for your customisation is critical.  You want to work with a team with expertise across the appropriate engineering disciplines and with a long and proven track-record of providing reliable solutions.  You need a team that can review your application, specify the appropriate optical sensor performance, select and design the proper components and understand what it takes to bring your solution to mass production.  In short, you want a partner who understands your challenges and knows how to solve your problems.

 

Look like a hero while simplifying your life

Providing robust optical sensor solutions that function reliably is challenging, and designing them in today’s fast-paced environment is no small task.  Remember, you are not alone.  Look for a proven partner to mitigate your risk and provide the optimal solution quickly.  In doing so, you will look like a hero, while simplifying your life. For more information visit TT Electronics.

 

About the author(s)

Mike Lander is Vice President of Product Management for Sensor Products at TT Electronics.  Most of his career has focused on sensor technologies, providing solutions that bridge the analog physical world with the digital computing world.  He received his BSEE from the University of Cincinnati and his MBA from the University of Dallas.

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