Sensors are used to measure and convert physical quantities into equivalent electrical signals. During any calculative process, we all aim for a perfect result. However, when it comes to sensor measurement, “perfection” is an illusion. There will always be factors, however miniscule, that affect a sensor’s performance. Our aim with this article is to make you aware of what those factors are and what challenges they present, so you will know what to look for when you’re optimizing your solution. We will also show how FUTEK’s sensors and electronics have been designed to solve them.

Here at FUTEK, we believe in continuous improvement. That means that we always strive to get as close to “perfect” as possible. This starts with our sensors — we’re laser-focused on minimizing their imperfections in order to maximize their performance and make them an optimal match for your application. But no matter how solid our sensors’ capabilities are, they can’t perform in isolation. We know that there are common challenges when sensors are matched with electronics. The more components that are added to a measuring solution, the more errors will be introduced. We also know that electronics can help solve sensor challenges. That’s why we feel that it’s our responsibility to make sure that our sensors are optimized to the fullest by delivering complete solutions in the form of a system that includes sensor, electronics, and calibration.

Excitation: We will mostly focus on strain gauge-based sensors, which require an external power supply (excitation) to operate. In other words, the excitation signal is used by the sensor to produce the output signal. This brings up a very important fact about working with strain gauge-type sensors, as the quality of their output is directly related to the quality their input (excitation), which implies how critical it is to properly design the circuitry that provides a clean, low drift, and stable excitation signal.

Below are some facts about strain gauge sensors:

Sensitivity Error: The slope of the characteristic output curve of a sensor usually defines the sensor’s sensitivity. Hence, the amount of deviation from the ideal curve defines the sensitivity error, which could result in the sensor to be non-symmetric and also directly impact the dynamic range (the total range, from minimum to maximum, that could be measured during normal operation). For example, an ideal sensor does not have sensitivity error thus, it is fully symmetrical. However, in practice, the output of a real sensor could deviate up to 20% (sometimes even more) from each direction. In order to minimize the error, this deviation needs to be addressed by the electronics connected to the sensor.

Precision: The degree of reproducibility of a measurement is defined as precision. This means that an ideal sensor would be able to measure the same exact value over and over with the same stimuli. In practice, the output of a real sensor could be impacted by external factors that we cannot fully control, such as the nature of the material that the sensors are made from, or some processes that the sensors need to go through during manufacturing. This shows the importance of keeping the errors introduced by the electronics being at least one order of magnitude lower than errors introduced by the sensor. At FUTEK, we have invested a lot of time investigating and analyzing our manufacturing process to identify these errors, finding a solution for every step in the process, and addressing them in our electronics design process as well. The same concept is valid for the Accuracy characteristic of the sensor.

Sensor Resolution: The definition of resolution can be expressed as the smallest detectable change of the input that can be presented in the output. It means that the electronics must be designed to have a higher level of precision that is capable of resolving the output of the sensor to provide a precise measurement.

Offset Error: As we already established that there is no perfect or ideal sensor, we can expect to see some errors when it comes to the sensor output. In other words, the offset error of a sensor is defined as the output that exists when there is no load. FUTEK minimizes the offset error of the sensors during the manufacturing process, but it is important to understand that this error cannot be eliminated 100%.

Linearity Error: The linearity of the sensor could be identified as how much the actual measured output curve of a sensor could deviate from its ideal straight-line curve. As we know, the electronics will also have some linearity errors, so it is important to consider designing a circuit that provides extremely low error in comparison to the sensor error. This makes sure that the overall system non-linearity remains close to the sensor error. It should be mentioned that in some extreme cases, the electronics are designed to provide linearization. This approach usually involves a lot of complications, such as additional digital/firmware development and enhanced calibration that need to be implemented on the electronics side by understanding the unique nonlinearity characteristic error of every sensor.

There are other factors related to the sensor specs that should be considered during the electronics design such as Hysteresis, Response Time, Bridge Resistance, Sensor Drift, etc.

FUTEK’s focus is on complex high-performance applications, such as those found in the medical, aerospace, and manufacturing industries. We take every action to ensure that our systems (sensor + electronics) are fully optimized per the needs of the application by offering analog and digital embedded and external solutions:

Analog: Current, voltage output devices (single ended and differential).

Digital: UART, USB, SPI, RS232, Ethernet IP, Display devices, etc.

So far, we have discussed the important factors related to the sensor that must be considered during the electronics design for strain gauge applications. In the following discussion, we will focus on the topics that are directly related to the electronics design. If these factors are not considered, they could significantly downgrade the sensor’s performance.

Design aspects:

Calibration: When it comes to calibration of a system, it is important to understand the offset and span calibration in detail as they play an important role in the output performance. Calibration of the system could be done with both analog and digitally controlled components. The design for both methods is tied to several factors such as: bridge resistance, sensitivity of the sensor, optimum gain of the system, requirements of the power consumption, available real estate, excitation source, dynamic range of the system, the impact of the offset calibration on the span and vice versa, and bandwidth. Here at FUTEK, we have developed and designed several advanced calibration methods that suit different applications. For some of our medical applications where the calibration is vital, we have developed a method that offers a fully independent offset and span calibration with a precision of 200µV out of 10V.

Amplification: This portion of the design is the most important and vital part of the electronics system as it is directly amplifying the output signal which is usually small and in the ranges of 0.2mV/V – 4mV/V. Thus, it is very critical to understand how to design a circuit that takes care of the amplification stage. This portion of the design could have many involvements such as: filtering, SNR/noise, component selection, impedance requirements, input common mode requirements, gain (single or multiple stages), power consumption, PCB routing, component location, protection circuitry, common-mode rejection ratio (CMRR), power supply rejection ratio (PSRR), bandwidth requirements, thermal and age-related drifts, etc. The engineers at FUTEK have drawn from their deep R&D experience to identify the issues above and develop both design and manufacturing solutions that address the challenges caused by them.

Filtering: A factor that could easily be overlooked in a design is the development of proper filters per the needs of the application. It is important to understand that proper filtering cannot be achieved if the reason for filtering is not well understood. Here at FUTEK we make sure that we always use the most advanced technology in the industry. We use the latest simulation tools to design the filters and we test them using our proprietary test equipment, which is more accurate and repeatable than what’s available in the market.

How has FUTEK gone above and beyond to solve these challenges?

As we have continued to iterate on our design and manufacturing processes to enhance the performance of our sensors and electronics, we have also developed proprietary features that make our sensors smarter and tell you more about your system. Depending on the system and the application, failures can be caused due to a variety of factors. To minimize these risks, we have tried to identify the most common failures and offer a solution for each of them. None of these features are standard in the market — we created them so you can benefit from having flexibility and efficiency as well as full confidence in our products.

Fault Detection: We have the capability to detect excitation faults (open/short) which can be indicated visually, through a digital pin or a data packet to be transferred.

Onboard Temperature: We utilize onboard temperature measurement to make sure the electronic devices operate in a nominal condition. This onboard temperature could be even more useful when embedded electronics are used. Since the distance between the bridge and the electronics is minimal in this scenario, the measured temperature could be a good estimation of the bridge temperature as well. This measurement can in turn be used for temperature compensation of the bridge.

Packet Acknowledgement Implementation: As a medical application supplier, we understand the importance of digital implementation in medical devices and we have tried to make our devices as safe as possible. With that being said, we make sure that all data transfers for digital communication have an acknowledgement (CRC/checksum) implemented.

Power Management: In some of our critical applications that require ultra-low power consumption, we have designed a feature that provides the controlling device with full control of the power consumption of the system. This important feature allows the controlling device to constantly monitor the overall power consumption and either shut down or put the FUTEK device in low power mode as needed.

Protection: We make sure that all of the exposed pins of our electronic designs have some sort of protection against unexpected events. It should be noted that the protection circuitry could impact the performance of the design, thus designing a proper protection system without sacrificing the performance is the key to this development. Depending on the types of applications, we go even further and provide standard certifications for our products such as CE, MTBF, etc.

PCB Design and Material Selection: In mixed system designs, proper isolation between analog and digital circuitry is one of the keys to good performance. Here at FUTEK we have many experienced PCB designers who understand the needs of these types of projects and they make sure that the maximum performance is achieved for the PCB design. Since we build our own sensors and design our own electronics, including the PCB, we can optimize our system even further by customizing our design with less restrictions. We also select the PCB material per the system requirements as the long-term performance of our systems is vital as our products are used in many different environments such as: high humidity, vibration, high/low temperature, etc.

Production and Manufacturing Process: Even if you have the best design in hand it doesn’t mean that final product could be as great as the design, so in order to make sure that our electronics design can function the way they are intended to, we control our manufacturing process from A to Z. Here at FUTEK, we identify qualified PCB manufacturing and assembly houses, evaluate them, and if acceptable, we add them to our approved vendor list. All these vendors go through periodic audits and assessments and the frequency of these audits is dependent on the criticality of the projects they support. With no exceptions, we evaluate first articles (FAs) for every single build and we then directly control the quality of the final part by identifying the inspection process for our suppliers. During our production process we test and calibrate all electronics 100% to make sure the final product reflects the design specification.

Capacity, Productivity and Efficiency: To have full control of the production process, we strive to optimize our productivity by automating where possible. This also helps us eliminate any potential human error in our system. Automation has allowed FUTEK to maintain full control on the manufacturing process for our high-mix low-quantity business model which is why we have been able to successfully deliver on time and meet our customers’ expectations.

FUTEK’s Engineering Service: We understand that the industries we serve are highly paced and dynamic, which can make things complicated during the design phase for both the supplier and the customer. We are fully aware of this challenge and to streamline the process for our customers we offer a dedicated team to work directly on our OEM accounts. This provides a lot of flexibility for our customers during any custom design requests, as we go through several design phases to make sure that we tackle all challenges from different angles and provide the best possible solutions.

Risk Mitigation: FUTEK has already developed solutions for all the above challenges which mitigates the client’s risk for their critical application. This also cuts the development time and takes the risk away from the engineer on the hardware and firmware fronts. The risks are usually even more critical on the firmware front as it is a more involved and complicated process.

Why we believe you should choose FUTEK

Even though sensor and electronics-related challenges are specific to each application, we have attempted to give you an overview of factors that should be considered for every application. Designing an optimal measurement solution is not a simple task, which is why we make sure that you don’t have to. From investing extra time and resources into our products’ developing phase to analyzing and improving our manufacturing processes, we know more about our systems, and how to optimize them, than any other provider. When you get your sensor and instrumentation solution from us, you will have a more efficient and accurate system that saves time and costs and gives you peace of mind.