The Benefits of Using Custom Optical Sensors

Our complex world is dominated by increasingly unique applications. The acceptance 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 customized optoelectronic sensor solutions is not only becoming a reality, but a necessity.

It is extremely challenging to find an off-the-shelf solution for a specific optical sensor application and it 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 tough, even for the simplest of development projects.

Benefits of a Custom Optical Sensor Solution

Every application is unique and assimilating commercial off-the-shelf (COTS) sensor components often does not produce the desired outcome, given the countless parameters to consider. COTS solutions may provide too wide or too little detection sensitivity and might lead to a false reading or unreliable results.

Designing the optimum sensor solution with a suitable sensitivity range, opto-electrical performance and footprint becomes critical to certify 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 yield the desired results for a turn-key solution. Adding cables, connectors, passive circuit components, and custom PCBs also complements and enhances the flexibility and reliability of the desired solution. There are real concrete benefits with customized optical sensor assemblies as shown in the summary table below:

Optical Sensor Solution Building Blocks

There is a broad spectrum of options to help achieve the desired sensor solution ranging 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 most basic element of the sensor solution is the discrete sensor, although choosing the proper additional components is certainly no trivial task. Matching an appropriate LED with the sensor element becomes challenging when faced with multiple options including basic photo transistors, photo diodes, and even smart detectors that provide a level of intelligence along with the sensor element itself.

Intelligent sensors integrate functionality such as temperature-compensation, auto-gain control, or autonomous decision-making capabilities. The correct sensor depends on the specific application and requirements such as wavelength, sensitivity, possibly the size of the photo-sensor, and other parameters will need to be considered.

For most designs, a discrete emitter is also selected, the most common being LEDs, but vertical-cavity surface-emitting lasers (VCSELs) are also used in some designs. Again, there are many constraints to consider when selecting your emitter including, but not limited to: wavelength, optical output power, angular optical output and forward voltage.

Finally, the pairing of the emitter and sensor can be difficult: wavelength, power levels, and sensitivity to mechanical alignment are among the other critical considerations to ensure an effective solution.

Housing or Packaging

The housing of your sensor solution is the next step up the ladder. Many sensor solutions require both photo-sensors and emitters. For example, basic reflective sensors and transmissive sensors (such as slotted switches) integrate both elements. Reflective sensors are normally used to detect the proximity of an object by detecting reflected optical power, while transmissive sensors have a line-of-sight between the emitter, the sensor, and sense objects that disrupt the optical circuit.

Optical and mechanical housing requirements are extensive because each application has unique requirements. Things to consider include the spacing between the sensor and emitter, aperture size, through-hole vs. surface mount, mounting bracket and so forth. Designers must be aware of the mechanical stack-up tolerances involved with each design.

The discrete components and housing design all contribute to the overall system performance. The customized optical sensor solution design must be able to accommodate changeability in the location mounting, types of media being perceived, environmental conditions, and detection distance just to name a few.

Wiring and Connectors

Optical sensors are often 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 valuable. The appropriate determination of the wire length and connector types are crucial factors to consider when 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 labor and assembly are carried out in high volumes at the factory instead of further downstream in the assembly process.

Higher-Level Assemblies

It may be that your optical sensor requirement goes beyond the simple need of just a detector and an emitter: multiple sensors and/or emitters might be needed. You may require other passive and active components (such as a voltage regulator), or even other mechanical components and this often necessitates multiple components being placed on a common PCB.

That PCB may need further wiring and connectors as well and 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 the size requirements of your need.

Simple to complex

​​Figure 1. Simple to complex

 

The Value of Working with a Trusted Partner

Gathering all the sensor solution building blocks together in a way that meets the optical, electrical and mechanical performance requirements at once is not an easy task, especially when trying to detect challenging media or when operating in difficult conditions.

Choosing the right partner for your customization is crucial: you want a team with expertise across the appropriate engineering disciplines and a long and proven track-record of providing reliable solutions.

A team that can review your application, postulate the appropriate optical sensor performance, choose, and design the proper components, and understand what it takes to bring your solution to mass production is required.  In short, you want a partner who understands your challenges and knows how to solve your difficulties.

Look Like a Hero While Simplifying your Life

Providing robust optical sensor solutions that function consistently 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 in the most efficient manner.

This information has been sourced, reviewed and adapted from materials provided by TT Electronics plc.

For more information on this source, please visit TT Electronics plc.

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