Understanding the Use and Function of MEMS Piezoresistive Pressure Sensors

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In this interview, AZoSensors talks to Scott Sidwell, Engineering Manager at Merit Sensor Systems, about MEMS piezoresistive pressure sensors, silicon dies, and how these are all utilized across a range of industries.

Could you provide us with some background information on pressure sensors and their significance in various industries?

Pressure sensors are vital components that play a crucial role in various industries. The pressure sensor market is projected to see remarkable growth, as indicated by recent research, and it is expected to reach nearly 24.5 billion dollars by 2028.

They find applications in automotive, industrial automation and process control, consumer products like diving, e-bikes, and, importantly, in the medical field.

Pressure sensors work based on the principle of the force of a fluid divided by area. To put it into perspective, consider a syringe – a smaller one can generate more pressure than a larger one with the same force applied. Understanding this concept is crucial when dealing with pressure sensors.

Atmospheric pressure is a term we often hear. Could you explain what it is and its relevance in the context of pressure sensors?

Atmospheric pressure is essentially the weight of the air pressing down on us. As you ascend in an airplane or spacecraft, the air becomes less dense, with fewer molecules and less oxygen. It is important to consider atmospheric pressure when measuring the pressure in your application, because it will determine the type of pressure sensor needed.

Image Credit: Mi Sketch/Shutterstock.com

What other applications besides the automotive industry benefit from pressure sensors, and how are they used?

Pressure sensors find applications across a diverse spectrum of industries, expanding far beyond their traditional use in the automotive sector. One of the sectors where pressure sensors play a critical role is the diving industry. In this field, pressure sensors are employed to monitor the depth of divers underwater, enabling them to calculate ascent and descent times accurately. The hostile underwater environment necessitates reliable pressure measurements to ensure diver safety.

Pressure sensors have made their way into the consumer product market. For instance, in the realm of bicycles, especially the emerging category of e-bikes, pressure sensors are integrated into various components. These sensors may be utilized on bike shocks, tires, and other critical parts to enhance the overall performance and user experience.

What are the typical applications of piezoresistive pressure sensors, and how do they work?

Piezoresistive pressure sensors are a subtype of pressure sensors known for their versatility and use in various applications. Piezoresistive sensors function on a principle involving doped, semiconductor silicon crystal, which allows them to measure pressure more repeatably than other technologies.

To understand their typical applications, it is worth highlighting that piezoresistive pressure sensors are not constrained to a single field. They are used in an array of industries, including the medical sector. In medical procedures like angioplasty, where surgeons inflate balloons inside arteries, pressure sensors play a crucial role. In these procedures, the pressure sensor’s output helps the surgeon monitor the level of inflation inside the balloon, and assess the overall status of the procedure.

Can you explain what MEMS technology is and its advantages in the context of pressure sensors?

MEMS stands for Micro-Electrical-Mechanical Systems, and there are many different types of MEMS. The deposition, ion implantation, and diffusion steps are all fundamental to semiconductor manufacturing, as well as the photolithography and etching of MEMS pressure sensors. MEMS pressure sensors feature an elastic silicon diaphragm, which means they are free from hysteresis and creep.

This elasticity benefits the sensor because it allows it to undergo repeated pressure cycling without altering its properties. When things tend to creep or change, it is almost always a result of how they are packaged, not necessarily the silicon chip itself. Putting thousands of pressure sensors onto one wafer also significantly helps to reduce costs.

Merit Sensor has its wafer fab in Utah. There are many advantages to working with a vendor that has its wafer fab. When it comes to developing a new product, having your wafer fab is a huge advantage, as it allows you to control the supply chain. Keeping the design in-house is often considered the key to the successful development and launch of any product.

Can you give us a basic understanding of the MEMS pressure sensor?

The key design characteristic of a MEMS pressure sensor is the Wheatstone bridge diffused into the silicon diaphragm. The change in output from this bridge corresponds to a change in applied pressure.  When a customer needs a higher pressure range, the sensor requires a thicker diaphragm to handle the increased pressure. Conversely, for measuring low pressures, like inches of water or low pascals, a thin diaphragm suffices.

After the manufacturing process, the silicon is bonded to a piece of glass. The glass may have a hole to create a vent for various pressure applications, or it can be sealed without a hole. In the latter case, the glass and silicon are bonded together in a vacuum.

When there is no hole in the glass, it is known as an absolute sensor because the space between the silicon and glass represents zero pressure absolute.

There are two types of absolute sensors made from MEMS dies. The traditional type has no hole in the back glass, creating a sealed vacuum reference for absolute pressure. However, this design requires protection for the circuitry on the top side to prevent corrosion and shorts from humidity or moisture.

Alternatively, there is the absolute sensor with backside pressure. In this design, a piece of glass is added to the top of the silicon, creating a sealed vacuum reference on the top side and allowing for backside pressure on the MEMS element. This type is commonly used in automotive and high-temperature applications, as well as with liquids.

Cross Section of a MEMS Silicon Die with Top Glass

Can you tell us more about offset pressure and other factors like pressure non-linearity and hysteresis?

Offset pressure is the zero pressure measurement at room temperature. Pressure non-linearity measures how linear or nonlinear the sensor’s output is from zero pressure to full-scale pressure, and hysteresis reflects the difference between the initial zero and return zero, when pressure is applied and then relieved. The MEMS sensing element is designed to minimize these sources of error.

How do temperature-related factors, such as TCR and TCS, influence the behavior of pressure sensors?

It is possible to use the TCR, the Temperature Coefficient of Resistance, in conjunction with the pressure sensing to determine the temperature, because the TCR changes significantly with temperature. The Temperature Coefficient of Span/Sensitivity, or TCS, is important to take into account, especially in applications for wide operating temperature ranges. The TCS is negative, and when using the MEMS piezoresistive pressure sensor, the sensitivity or span decreases as the temperature rises.

Can you explain the importance of accuracy in pressure sensors and how it can be achieved?

Accuracy in pressure sensors is often measured as the total error band, which includes errors related to temperature and pressure. Achieving accuracy involves calibration, and fully compensated sensors with onboard ASICs simplify this process and provide higher accuracy. Accuracy is vital, especially in applications where precise measurements are critical.

How do stress and other external influences impact pressure sensors?

We take great pride in understanding and characterizing the sources of error that our customers can’t compensate for:  thermal hysteresis and long-term stability. The last thing our customers want is a part failure in their hands, which can occur due to long-term stability issues.

It’s important to keep in mind, that the MEMS sensing element is also a good stress sensor.  For example, a torque, or bending moment on the MEMS element will change the output of the Wheatstone bridge.  Stress can be induced during packaging and assembly processes, impacting sensor performance. Over time, any package-related stresses will relieve themselves and come back to equilibrium.  This stress-relief will manifest as a change in the offset of the sensor, in other words, offset drift and long-term stability. Careful handling and packaging are essential to maintain sensor stability.

Could you explain how MEMS dies are suitable for a wide range of applications, both specific and general, and what factors should customers consider when selecting a pressure sensor?

MEMS dies are common in pressure transducer or pressure transmitter applications where the MEMS die is on a header. The header gets welded into a stainless-steel housing with a stainless-steel diaphragm. Stainless steel is an excellent choice since it is very media-friendly, and most people are usually very familiar with stainless steel’s capabilities. This package is suitable for many industrial applications.

After welding the stainless-steel diaphragm and package together, there’s a back-filling of oil into this housing. A clean silicon oil surrounds the MEMS die, transmitting pressure between the stainless-steel diaphragm and the silicon diaphragm of the MEMS element.

In the HVAC industry, the MEMS die can be purchased separately or packaged into our LP series and placed on a control board. These control boards are found in large buildings, either atop the building near the air intake or in the building’s utility room, where heat exchangers and air airflow systems are located.

Another common application is in transportation. Pressure sensors are widely used in various types of automobiles. This area continues to grow as legislation drives the demand for higher efficiency and cleaner emissions.

To learn more, watch the full webinar below:

Understanding MEMS Piezoresistive Pressure Sensors: A Close Look at a Silicon Die from Merit Medical on Vimeo.

 

About the interviewee

Scott joined Merit Sensor in September of 2003. Before joining Merit Sensor, he worked in a variety of engineering roles with semiconductor companies, such as ON Semiconductor and Motorola. In his current role he works closely with customers to provide pressure-sensing solutions and technical support.

Scott received a chemical-engineering degree and MBA from Brigham Young University. He speaks Spanish and enjoys volunteering his time.

Choosing the Right Sensor for Harsh Environments in Fuel Cell Technology

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Electric vehicles (EVs) have recently gained a huge amount of attention in the evolving transportation landscape.

According to the latest statistics, an estimated 14 million EVs are projected to be sold in 2023, reflecting a 35% year-on-year increase.1 Fuel cell EVs have also attracted attention from major players in the auto industry, including Toyota, Honda, and BMW.2,3,4

However, manufacturing fuel cell EVs poses significant challenges. Their reputation for being clean and eco-friendly, a remedy for our polluted past, is hard-earned.

This article will elaborate on the various internal components of a fuel cell EV, which must maintain different pressures to ensure optimal performance and safety. The pressure sensors, situated amidst these components, play a crucial role in monitoring the system.

 

 

 

 

 

Understanding Hydrogen Fuel Cells

Hydrogen fuel cells represent pioneering technology in sustainable energy. These cells harness the power of hydrogen, combining it with oxygen from the air to produce electricity, with only water vapor as the emission.

Currently, hydrogen’s use as an energy carrier is mainly for road vehicles. As of June 2021, over 40,000 fuel cell EVs were operational globally, with nearly 90% concentrated in four countries: Japan, Korea, China, and the United States.5

The utilization of hydrogen fuel cells is expected to grow, with CEM H2I leading the efforts to promote fuel cell technologies worldwide through collaboration with governments and partners.6

The Vital Role of Decompressing Hydrogen

In a typical hydrogen fuel cell EV, hydrogen is stored in a high-pressure container. However, because the fuel cell stack operates optimally at significantly lower pressure, a decompression procedure is necessary to bridge the gap between the high-pressure hydrogen tank and the fuel cell stack.

The decompression of hydrogen is crucial for the fuel cell to function effectively.7 Hydrogen, being the smallest particle, does not affect the absolute TRVC function, making radial sealing critical in design due to TRVC and plug geometry.

Significance of Heat Management Systems in EVs

Heat management, such as efficient cooling systems, plays a key role in the performance and lifespan of fuel cells.8

Making sure heat dissipates effectively is essential to keep critical parts like the battery and electronic systems within the required temperature limits. For batteries, this often means using a dedicated battery thermal management system (BTMS).

Keeping the right pressure in cooling systems specific to each EV is vital to prevent coolant leaks and potential damage to components.9

Importance of Pressure Sensors in Fuel Cell Technology

Precise pressure measurement is essential during energy generation and heat management. Accurate pressure sensors are necessary to monitor gas flow in pipelines and maintain proper coolant levels in the cooling system.

Sensors face challenges in harsh environments with corrosive substances, temperature changes, and high-pressure fluctuations. Thus, pressure sensors deployed in these settings must be designed to endure harsh conditions.

Introducing Merit Sensor’s TRVF-Series of Pressure Sensors

Merit Sensor, a top player in piezoresistive pressure sensors, crafted the TRVF-Series to meet industry needs. These sensors seamlessly integrate into fuel cell systems’ hydrogen supply and coolant circuits, ensuring top-notch stability.

Capable of handling temperatures from -40 °C to 150 °C, the TRVF-Series boasts exceptional durability thanks to its trio of materials – silicon, glass, and ceramic. These sensors are built to endure the harsh conditions within fuel cell environments.

The aforementioned materials also guarantee compatibility with various liquids, vapors, and gases, from fuel to water, ensuring longevity and reliability in challenging operational settings.

Covering a pressure range of 2–15 bar, the TRVF-Series offers precise measurements and accurate analog voltage output, enabling effective monitoring of gas and liquid pressures for optimized energy generation and improved heat management processes.10

The graph illustrates the stability results of the TRVF Series measured at 150 °C for 1300 hours.

Enhanced Reliability in Coolant Circuit Measurements

TRVF sensors have been designed to collect pressure measurements from its posterior surface. This is achieved by hermetically sealing the MEMS silicon die on top of a ceramic port, ensuring that the media only touches the desired wetted materials.

This functionality allows the sensor to consistently provide dependable readings within the coolant system, ensuring efficient coolant control and contributing to the overall effectiveness and performance of the fuel cell system.10

Measured Under Pressure: Serving Fuel Cell Technology with the TRVF-Series

The introduction of Merit Sensor’s TRVF-Series marks a significant advancement in fuel cell technology, addressing the crucial need for durable and accurate sensors capable of enduring the tough conditions within fuel cell systems.
With its sturdy build and dependable performance, the TRVF-Series is positioned to have a significant impact on driving the advancement of sustainable transportation and energy solutions, establishing a new standard of excellence in sensing technology for harsh fuel cell environments.

References and Further Reading

  1. IEA. Global EV Outlook 2023: Executive Summary. Available at: https://www.iea.org/reports/global-ev-outlook-2023/executive-summary (Accessed on 31 August 2023).
  2. Toyota. Toyota Launches the New Mirai. Available at: https://global.toyota/en/newsroom/toyota/33558148.html (Accessed on 31 August 2023).
  3. Honda. Honda To Begin U.S. Production of Fuel Cell Electric Vehicles in 2024. Available at: https://hondanews.com/en-US/releases/honda-to-begin-us-production-of-fuel cell-electric-vehicles-in-2024 (Accessed on 31 August 2023).
  4. BMW. BMW Group brings hydrogen cars to the road: BMW iX5 Hydrogen pilot fleet launches. Available at: https://www.press.bmwgroup.com/global/article/detail/T0408839EN/bmw-group-brings-hydrogen-cars-to-the-road:-bmw-ix5-hydrogen-pilot-fleet-launches?language=en (Accessed on 31 August 2023).
  5. IRENA. Hydrogen: Overview. Available at: https://www.irena.org/Energy-Transition/Technology/Hydrogen (Accessed on 31 August 2023).
  6. IEA. CEM Hydrogen Initiative. Available at: https://www.iea.org/programmes/cem-hydrogen-initiative (Accessed on 31 August 2023).
  7. Qian, JY., et al. (2019) Hydrogen decompression analysis by multi-stage Tesla valves for hydrogen fuel cell. International Journal of Hydrogen Energy. doi.org/10.1016/j.ijhydene.2019.03.235.
  8. Ahn, J-W., et al. (2008) Coolant controls of a PEM fuel cell system. Journal of Power Sources. doi.org/10.1016/j.jpowsour.2007.12.066
  9. Vehicle Service Pros. Hybrid and EV cooling system service. Available at: https://www.vehicleservicepros.com/service-repair/battery-and-electrical/article/21197978/hybrid-and-ev-cooling-system-service (Accessed on 31 August 2023).
  10. Merit Sensor. TRVF-Series: Available Now! Available at: https://meritsensor.com/products/trvf-series/ (Accessed on 31 August 2023).

View this article on AzoSensors.com

Creating Accurate Blood Pressure Sensors for Medical Equipment

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In the medical industry, blood pressure monitoring is essential. Readings are used to evaluate general health and diagnose diseases. High blood pressure, otherwise known as hypertension, is a serious health risk and can also be indicative of other health problems.1

Thus, accurate and reliable blood pressure monitoring data is essential to ensure positive health outcomes for patients. Blood pressure monitoring is not only necessary for standard use but is critical when it comes to monitoring a patient’s condition online during critical surgical operations.

Extracorporeal membrane oxygenation (ECMO) is a crucial medical application that necessitates precise online monitoring. ECMO is used throughout certain surgical procedures where the patient’s heart and lung functions are compromised or for critically ill patients.

In an ECMO machine, blood is pumped outside the body for carbon dioxide removal and reoxygenation before returning it to the patient.2  ECMO is a feasible substitute for mechanical ventilation as it is able to reduce lung damage invoked by the positive pressure used in these methods.

Blood pressure monitoring equipment is essential when it comes to monitoring a patient’s condition and the ECMO machine itself.3 A typical healthy blood pressure level is traditionally lower than 120/80 mmHg. However, low blood pressure can be seen to fall as low as 90/60 mmHg.

In applications such as ECMO, blood pressure monitors with an extended reading range can be highly beneficial.

ECMO Machine featuring the BP Series extended range pressure sensor.

Merit Sensor Systems

Merit Sensor Systems is a globally renowned, industry-leading company with experience designing and producing highly accurate, piezoresistive technology-based pressure sensors. The company provides pressure sensors for blood pressure monitoring applications and a range of medical equipment.

The patient’s blood pressure measurements can be significantly impacted by the resting environment. One way in which data quality can be improved is by ambulatory blood pressure testing, in which portable devices are used to record blood pressure measurements throughout the day.4

MEMS piezoresistive sensors and assemblies, such as the BP Series, are ideally suited for portable blood pressure monitoring applications due to their compact sensor footprints.

Merit Sensor has a variety of sensors available for blood pressure monitoring applications. These include the BP Series, which operates in normal pressure ranges, and an extended range version suited for applications such as ECMO, where measurements must be taken over a wide range of -500 – 1000 mmHg.

The BP + T is designed for ultra-compact applications which additionally measure temperature ranges.

BP Series Sensors

Blood pressure monitoring sensors from Merit Sensor are ideal for invasive blood pressure monitoring applications and measurements, such as ECMO.

The standard BP Series configuration BP0001 covers the pressure range of -30 to 300 mmHg, providing a reliable signal that does not need any temperature correction (operating temperature 15-40 °C).

An ultra-compact sensor with an extremely robust design, the sensor is suitable for burst pressure readings up to 800 psi. Additionally, it is compliant with AAMI BP22 and RoHS standards.

Sensors provided by Merit Sensor Systems can be easily integrated into a range of medical devices, with standard solder pads providing connectivity. The standard seal diameter is 4.8 mm (BP0001), and a smaller seal diameter of 3.2 mm (BP0002), which minimizes the device’s overall footprint.

The small seal diameter in the sensors lowers the amount of blood in contact with the sensor, minimizing the risk of clotting or coagulation, which can decrease overall blood flow and cause problems with readings.

Alongside the sensor, a media-compatible medical dielectric gel is utilized for medical applications. The BP Series also includes an IMDS file for rapid and easy media compatibility verification, minimizing the time required to develop device prototypes.

       

BP Series 4.8mm Standard Seal Diameter               BP Series 3.2mm Small Seal Diameter

Extended Range

The BP Series Extended configuration provides measurements in the range of -500-1000 mmHg and can be used in applications such as ECMO. The system operates at a broader pressure range than the standard configuration.

The blood pressure monitoring sensors from Merit Sensor Systems are designed to handle high-pressure conditions and provide accurate readings over their entire operational range.

With an extended product shelf life of up to three years, the solutions offered by Merit Sensor Systems extend the lifespan of medical devices and ensure that pressure monitors remain functional, whether they are used as short-term or long-term solutions.

BP Series Extended Pressure Range Statistics

The graph below shows the over-pressure specifications limits for the BP Series Extended between -500 to 1000 mmHg. The test results are available in the Overpressure/Accuracy Report.

The BP + T sensor, which integrates pressure and temperature measurements in one device, is available as an upgrade option. The BP + T sensor is a direct in-flow measurement sensor that can monitor pressure and temperature at a single location.

The temperature reading is directly proportional to the Ohmic reading of the embedded thermistor, which is coated with a media-compatible substance. Two additional pads provide the temperature-measuring electrical connection (Kelvin-Point).

The BP + T sensor is also geometrically compatible with the BP0001 and overall BP Series configurations. The 3D-Model files are available for the verification of this integration capability.

Blood Pressure + Temperature Series

Applications

Merit Sensor’s devices are currently used in several novel lung support therapies and blood pressure sensors as part of lightweight and portable emergency response cardiopulmonary support systems.

The blood pressure sensors from Merit Sensor Systems are high quality and can handle the pressure peaks encountered in ECMO applications. Additionally, the sensors are cost-effective, even for disposable medical devices.

Contact Merit Sensor to find out which of its pressure sensors is the best option for your blood pressure monitoring application and how to benefit from its technical expertise and support.

Merit Sensor’s robust, reliable sensors offer clinical experts the highest quality assurance for medical applications.

References and Further Reading

  1. Elliott, W. J. (2003). The Economic Impact of Hypertension. The Journal of Clinical Hypertension, 5(3), 3–13. https://doi.org/10.1111/j.1524-6175.2003.02463.x
  2. Patel, A. R., Patel, A. R., Singh, S., Singh, S., & Khawaja, I. (2019). Applied Uses of Extracorporeal Membrane Oxygenation Therapy Different modes of ECMO therapy. Cureus, 11(7), e5163. https://doi.org/10.7759/cureus.5163
  3. Mossadegh, C. (2017). Monitoring the ECMO. In: Mossadegh, C., Combes, A. (eds) Nursing Care and ECMO. Springer, Cham. https://doi.org/10.1007/978-3-319-20101-6_5
  4. Turner, J. R., Viera, A. J., & Shimbo, D. (2015). Ambulatory Blood Pressure Monitoring in Clinical Practice: A Review. The American Journal of Medicine, 128(1), 14–20. https://doi.org/10.1016/j.amjmed.2014.07.021

Enhancing Pressure Transducer Performance with the S-Series Die

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A pressure transducer is capable of accurately measuring pressure. It converts applied pressure into an electric signal and can be classified as an active or passive pressure measurement device.

Various designs of pressure transducers are available depending on whether absolute or relative pressure measurements are required.

Originally developed to measure minimal pressure changes, pressure transducers gained widespread commercial adoption in the 1960s and 70s by introducing thin film, silicon, and quartz-based devices. This made them a popular choice for measuring both low and high pressures.1

A pressure transducer comprises two main components: a pressure-sensitive device and a transduction element that converts device changes into an electrical signal.

Multiple designs exist for pressure transducers, utilizing methods such as strain gauge displacement or membrane movement. The design choice depends on the pressure ranges that need to be measured.

How Do Pressure Transducers Work?

Pressure transducers measure static or dynamic pressures, depending on whether the measured object is stationary or subject to an applied force.2

Piezoresistive strain gauges are commonly employed to measure static pressures.

These gauges are attached to a diaphragm that deforms under pressure, leading to a change in resistance which provides a measurable electric signal. This change in resistance is converted into a measurable voltage using circuit configuration.

In the case of high-compact pressure transducers, a microelectrochemical system (MEMS) device is used.

MEMS-based pressure transducers operate on similar principles as their larger counterparts, where deformation in the sensing medium generates an electrical signal. However, MEMS devices are much smaller and more responsive to even minor pressure changes.3

For remote applications like environmental monitoring in unmanned aerial vehicles (UAVs), MEMS sensors offer advantages such as low power consumption and lightweight construction.4

Merit Sensor S-Series

The S-Series, developed by Merit Sensor, is a remarkable sensor development and manufacturing achievement. These MEMS silicon pressure dies utilize a thin, flexible diaphragm as their sensing medium.

The diaphragm’s deflection, caused by pressure, alters the capacitance between two plates. This alteration can be converted into an electrical signal to provide pressure readings.

To deliver unparalleled performance, accuracy, and reliability in pressure sensing, the S-Series leverages Merit Sensor’s cutting-edge MeritUltra™ technology. These dies are designed to operate effectively across various pressures, from 5 to 300 psi, making them suitable for diverse applications.

By incorporating the MeritUltra™ technology, the S-Series dies offer an impressive temperature operating range of 40 °C to 150 °C without compromising performance.

The exceptional accuracy of the S-Series dies enables designers to achieve accuracies better than 0.1% of the full scale, making them suitable for even the most demanding high-precision applications. The S-Series is available with and without glass.

Merit Sensor's S Series MEMS Sensing Element JPG file

Unbeatable Accuracy and Reliability

High-quality calibration is a critical factor in pressure sensing. Precisely translating the movement of the diaphragm into meaningful pressure values necessitates a thorough characterization of the resistance change in response to applied pressure.

To ensure this, every S-Series die undergoes electrical testing at the wafer level when constructed at Merit Sensor Systems’ wafer fab in South Jordan, Utah, USA. The dies can be packaged by mounting them onto a circuit board and incorporating the necessary signal amplification electronics.

Extensive and rigorous testing and calibration procedures are employed, ensuring the dies are ready to provide reliable measurements immediately.

The S-Series dies’ robustness, reliability, and outstanding technical performance make them the preferred choice for many engineers when building pressure transducers.

Their compatibility with a wide range of environmental conditions, excellent sensitivity, and compact footprint make them ideal for numerous applications, including industrial, automotive, and medical sectors, where components must meet additional regulatory requirements regarding reliability and performance.

Whether clients require pressure transducers for aerospace, automotive, medical device engineering, or any other application, reaching out to Merit Sensor Systems will enable them to explore the benefits of incorporating its state-of-the-art pressure dies into their devices, leading to improved reliability and performance.

With the backing and expert support of the experienced professional teams at Merit Sensor, the client receives high measurement reliability, comprehensive pre-and post-sales support, and expert technical advice.

References and Further Reading

  1. Middelhoek, S. (2000). Celebration of the tenth transducers conference: The past, present and future of transducer research and development. Sensors and Actuators, 82, 2–23. https://doi.org/10.1016/S0924-4247(99)00395-7
  2. Bean, V. E. (1994). Dynamic Pressure Metrology. Metrologia, 30, 737. https://doi.org/10.1088/0026-1394/30/6/037
  3. Adams, T. M., & Layton, R. A. (2010). Introductory MEMS Fabrication and Applications. https://doi.org/10.1007/978-0-387-09511-0
  4. Jang, J. S., & Liccardo, D. (2006). Automation of Small UAVS using a low-cost MEMS Sensor and embedded computing platform. 2006 IEEE/AIAA 25TH Digital Avionics Systems Conference, 1–9. https://doi.org/10.1109/DASC.2006.313772

For more information, visit this article published on AZO Materials

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How Can Pressure Sensors Enhance Pneumatic Pressure Control in Robotics?

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As part of increased automation and Industry 4.0 developments, robots had to become ‘smarter.’1 Regarding automation, smarter robots are those with more advanced sensors that have the ability to be integrated with data analysis and feedback systems.

One of the most common robot types in the industry are robotic arms. They have many uses, from lifting and moving objects to highly precise manufacturing and welding processes.

As an articulated robot, the robotic arm can be designed with a range of motion to suit its designated task, allowing it to carry out any required movements.

Robotic arms provide significant efficiency savings due to their ability to move much faster than their human equivalents. They also maintain high accuracy on numerous repetitive tasks that are involved in manufacturing processes. For some tasks, it is feasible to simply install and program a robot arm to conduct the desired function.

However, for alternative tasks where the robotic arm is used in conjunction with machine vision or more advanced automation, the robot is required to be able to react to and understand changes in the surrounding environment.

One way to help a robot understand the world around them, and allow them to react to tasks in a way that does not simply require pre-programmed and hard-coded parameters, is the utilization of pressure sensors.

Developments in transducer-based sensors for robots have enabled the creation of highly sophisticated articulated robot hands which are able to hold delicate objects.2 The sensor information is communicated to actuators to avoid the use of excessive force.

Pressure Transducer

Achieving increasingly complex motion and degrees of automation demands even more sensors to be utilized. A highly articulated robot hand or arm necessitates a full suite of sensors, with considerations such as the sensor size becoming critical for the application.

The precision and accuracy of the sensors also become progressively important when complex sensor networks provide feedback systems for the robot.

If any sensor within the network begins behaving poorly, the resulting robotic motion will be incorrect and could cause problematic motions for the articulation of the robot or accidental breakages.

In addition to the greater degrees of automation and the utilization of data in manufacturing processes, another aspect of Industry 4.0 development is a bigger emphasis on sustainability.

Mobile robot arms must keep power consumption to a minimum to extend the lifetime of operation between charges. The avoidance of large power draw on sensors also helps minimize the robot operation costs and decrease excess energy consumption.

Pressure Monitoring

One of the most generic tasks for a robotic arm is to hold and pick up objects, some of which may be breakable. A pneumatic actuator converts energy, usually from compressed air, into motion, and such actuators make up the basis of many mobile robots.

Exertion of the appropriate amount of force on an object involves careful control of the volume of compressed air supplied to the actuator. This is generally achieved by measuring the vacuum pressure within the evacuated region, and pressure sensors are the perfect system for this.

In addition to the initial force applied to pick up the object with the actuator, pressure sensors may be utilized to continually monitor the vacuum pressure during holding to guarantee that a constant level of force is maintained.

Pressure sensors in pneumatic actuators are required to have a rapid response time to sudden changes in pressure, especially for robots where the physical motions must be fast. Sensors also must be highly sensitive and have the ability to measure in the vacuum pressure range.

Merit Sensor Systems

The advantages of pressure sensors in robotic arms are evident when creating dynamically responding robots that are capable of a wider range of more sophisticated tasks. The challenge is finding the correct pressure sensor for the task.

Merit Sensor Systems is an expert when it comes to the development of MEMS piezoresistive pressure sensors and provides a variety of different compact, low-power draw sensors.

Merit Sensors has the CMS Series, which is a fully compensated pressure-sensor package for smart robotics.

Based on a piezoresistive pressure sensor with an ASIC to calibrate and compensate for thermal and non-linearity, the CMS Series are highly compact sensors created to provide highly stable and long-term pressure readings.

CMS Series

With a footprint of only 6.8 mm x 6.8 mm, the CMS Series makes integrating numerous sensors into pneumatic robot systems easy.

The digital I2C and SPI output options allow the CMS sensors to be easily integrated into smart feedback systems and make responsive robotics. Where multiple sensors are required for an application, Merit Sensor is also able to create other I2C addresses upon request.

The incorporation of the proprietary Sentium® technology makes the performance of the CMS Series unique. This technology helps these sensors accomplish their wide compensated temperature range (0 to 50 °C or -15 to 85 °C) with best-in-class stability.

The CMS Series are extremely diverse sensors with an extensive operating pressure range of 2 to 150 PSI, with burst pressures from 2 to 100 times the maximum operating pressure.

For pneumatic robotics, this range, combined with the high accuracy and stability, means it is possible to create robots capable of the most delicate lifting tasks as well as more heavy-duty operations.

Absolute and gauge options are also offered if required, in addition to autozero and output averaging functions, making the CMS Series even simpler to use and integrate into any system.

The electrical connections are SMD solder pads with a 1.27 mm standard spacing, and the CMS products are compatible with a 2.7 to 5.5 V supply voltage range. The devices may be run in a low-power mode to maximize energy efficiency.

The CMS products are all RoHS compliant, with the reliability and accuracy of these sensors underpinned by a piezoresistive Wheatstone bridge that is designed to anodically bond the glass to a chemically etched silicon diaphragm.

Contact Merit Sensor Systems today to discover how the CMS Series could further the performance and accuracy of your pneumatic robots and the overall efficiency of your systems.

References

  1. Sartal, A., Bellas, R., Mejías, A. M., & García-Collado, A. (2020). The sustainable manufacturing concept, evolution and opportunities within Industry 4.0: A literature review. Advances in Mechanical Engineering, 12(5). https://doi.org/10.1177/1687814020925232
  2. Girão, P. S., Ramos, P. M. P., Postolache, O., & Miguel Dias Pereira, J. (2013). Tactile sensors for robotic applications. Measurement: Journal of the International Measurement Confederation, 46(3), pp. 1257–1271. https://doi.org/10.1016/j.measurement.2012.11.015

For more information, visit this article on AZOSensors.com

Pressure Sensors and Their Use in Aquatic and Underwater Applications

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Pressure sensors are essential safety and logistic equipment in a number of underwater applications. For scuba diving, a reliable depth gauge or diving watch is crucial to estimating diving depth and ensuring safe ascent and descent.

Historically, many dive watches and depth gauges have been analog designs. Digital pressure sensors have several advantages over analog sensors and can be easily interfaced with dive computers that combine information from multiple sensors.

A digital pressure sensor will consist of the sensing element; for pressure sensors, this is often a piezoresistive element and a transducer to convert the sensor response into a digital signal for processing. Digital sensors can be very compact, with no moving parts and can be used in harsh and corrosive environments, including in salt waters. Piezoresistive sensors are particularly well-suited for aquatic measurements as they have few restrictions on their operating depths.1

Common applications of such pressure sensors include sonar buoys, sometimes known as sonobuoys, tank and ocean depth measurements, dive watches and fishing.

MS Series inside Diving Watch

Merit Sensor Systems

Merit Sensor Systems is a leading expert in pressure sensors for a number of applications, including diving and freshwater work. Merit Sensor Systems offers several different sensing devices with incredibly small footprints and ultra-low power draw. The low power consumption is essential for many remote aquatic applications as devices must be battery operated and require a battery life of many hours.

For sonar buoys, deployable devices that use sonar signals to locate passing submarines and marine traffic or monitor tidal conditions, Merit Sensor Systems has developed pressure sensors that can replace the traditional wire/line technology. Normally, a buoy would be deployed with a spool of wire connecting the device to a float at the surface and the length of the wire is used to estimate the depth of the device. However, as the ocean is constantly moving, the wire displacement is often a bad measure of the depth due to lateral deflections of the device while it is in the water. A pressure sensor can instead provide more accurate depth measurements by measuring the local water pressure.

For sonar buoys, Merit Sensor Systems offers a range of suitable sensors, including the HTS 1510 Series, the TR series and, for more limited operating depths, the ultra low power MS series. All of these are highly compact, lightweight sensors that can be easily incorporated into a range of devices and provide many hours of continuous operation. The HTS series will also soon feature a Sleep mode so that the battery life can be further preserved.

All of the Merit Sensor Systems series are extremely media compatible with a range of water environments and conditions. The MS series is gel-filled for additional protection and its compact design footprint means it has been successfully used in dive watches. The MS series is an affordable option with excellent stability over an extensive temperature range and is also RoHS compliant.

HTS, TR, & MS Series in underwater applications.

Calculating Depth

Why do pressure sensors work so well for recovering depth information? As the density of water is constant in most environments, as is gravity, the underwater pressure is directly proportional to the submersion depth. With onboard electronics for the processing, a pressure sensor can rapidly convert these pressure readings into a measurement of submersion depth or even the local water level.

Diving computers can display and process a range of pressure information, from remaining gas levels in breathing tanks to diving depth. Some dive computers will use this to calculate the remaining safe time for a dive.

All of the Merit Sensor Systems pressure sensor series can be integrated as part of digital systems, but the HTS 1510 Series has the choice of providing digital or analog outputs.

Important for live depth calculations, all of the pressure sensors have 10 ms start up times in case devices need to be rebooted rapidly. Each pressure sensor is less than 2 g in mass, including any protective housing and mounts required, particularly for saltwater applications.

These pressure sensors are characterized by their potential to perform high accuracy measurements with only 0.5 % FS lifetime drifts, incredibly low pressure and temperature hysteresis. Whether you need a pressure sensor that can uphold the highest safety standards for manual diving, or a quick readout sensor for 24/7 online water tank monitoring, Merit Sensor Systems has something to offer.

The HTS 1510 Series, the TR series and the MS series each have different designs and housing to optimize them for particular tasks. The MS series is a surface-mounted, ceramic device. The fully-compensated TR series is a direct-media pressure monitor, designed to plug and play with existing devices. The HTS1510 series is a backside-pressure monitor which can be surface-mounted and integrated into existing control boards.

Contact Merit Sensor Systems today to find out how their state-of-the-art pressure sensors could be integrated into your underwater devices.

References:

  1. Büttgenbach, S., Constantinou, I., Dietzel, A., & Leester-Schädel, M. (2020). Case Studies in Micromechatronics. In Case Studies in Micromechatronics. https://doi.org/10.1007/978-3-662-61320-7

For more information visit this article featured on AZOSensors.com

Implementing Pressure Sensors into HVAC Systems

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HVAC systems are vital when it comes to ensuring indoor air quality, health, and inhabitant comfort management.1 HVAC systems also have a central role in enhancing a building’s energy efficiency, as HVAC systems represent almost 50 % of the total energy consumption of buildings in the US and 20 % of all total energy consumption.2

Global temperatures and weather are likely to force an increased reliance on HVAC systems worldwide, meaning increased energy consumption which places utmost importance on finding ways to improve the efficiency of HVAC systems.3

One of the ways to achieve this is by using smart management systems for HVAC to do things like switch off unnecessary heating or ventilation in low or zero-occupancy buildings to ensure that no energy is wasted.4

The use of sensors lies at the core of smart HVAC systems. Sensors facilitate ‘machine vision’ for an automated system, delivering the information required to make intelligent decisions predicated on current demand and specified performance.

Sensors can also be incorporated into HVAC systems to enhance climate control and help send alerts when necessary maintenance to avoid needless work, which may also prevent system downtime.

Pressure Sensors in HVAC

Merit Sensor Systems is a global leader in the design and development of high-performance pressure sensors. Pressure sensors are one of the most important components in HVAC system technology for monitoring system performance, reviewing compressor conditions, and monitoring ducts to test the airflow through the ventilation systems.

Merit Sensor Systems has the services that help clients find the appropriate pressure sensors to make HVAC systems safer, more reliable, and cheaper to run.

HVAC systems are made of several components as a single system will need to have the capacity of cooling, warming, and providing air transport around the system and ventilation.

Continuous real-time pressure monitoring is suitable for checking if rooms or filters have pressure drops across them in order to check occupancy and performance. HVAC pressure sensors can also be installed to preserve pressure levels in key airways or those that necessitate positive pressures for safety reasons, including hospital laboratories.

LP Pressure Sensor

Compression

Conventional HVAC units typically contain a compressor that compresses a refrigerant vapor until it is transformed into a hot gas.

Pressure monitoring is crucial to check for leaks in this refrigerant application and the compressor performance, which is made possible with the TVC Series. Once the hot air is produced, it is cooled with ambient air that is subsequently heated by the transfer.

The gaseous refrigerant is pumped towards an evaporator as it cools, where it flows through a restrictor device to reduce the pressure of the refrigerant and evaporate it, cooling the air for recirculation.

There are various compressor designs, but the majority utilize the compression, evaporation, and cooling cycle to lower the air temperature.

TVC Pressure Sensor

Choosing Pressure Sensors

There are a number of different applications and a significant demand for pressure sensors in HVAC systems, but to be useful, pressure sensors need to have specific performance levels.

Some of the pressure changes in HVAC, including pressure drops across filters as a result of slight clogging, may be very small. Therefore, the pressure sensor needs to have a good limit of detection.

Small pressure changes and small overall pressures can also be observed in ventilation systems that require extremely sensitive pressure sensors. As smart HVAC systems are typically used to reduce energy consumption and waste, the pressure sensors that are installed in the system need to be completely reliable.

Errant and erroneous readings could lead to poor performance in the HVAC system or even damage components if maintenance warnings are not offered at the appropriate times.

The extremely compact LP Series pressure sensor is also part of Merit Sensor Systems’ portfolio and helps address all of these issues.

The LP Series pressure sensor has a low footprint and can be easily integrated into a circuit board design without resulting in extra bulk or weight to the finished product. The small footprint makes integration into nearly any application possible without the need for majorly redesigning components.

LP Pressure Sensor

LP and TVC Series Pressure Sensors

For HVAC applications, the LP Series pressure sensor has a detection capacity down to just 250 Pa with a resolution of more than 0.01 Pa. Initially designed with a sensitivity for the measurement of differential or gauge pressures, this pressure sensor requires just a 3.3- to 3.5 V supply to start supplying accurate and meaningful data.

The LP series pressure sensor contains two connectable (with tubing) pressure points. The sensor can then be connected via I2C or analog output for data monitoring in real-time as well as integration into smart building management systems.

The TVC Series is ideal for measuring refrigerant gas at higher pressures. It was developed to create a stable output, even at temperatures between –40 to 150 °C. The TVC is tasked with monitoring HVAC systems, water levels, water pressure and processes. It can also be used for air-conditioning and other refrigerant systems.

Inside the TVC Pressure Sensor

Inside the LP Pressure Sensor

Contact Merit Sensor Systems today to discover more and discover how the LP and TVC Series can revolutionize the efficiency of HVAC systems, with the sensitivity to determine exactly when the next maintenance cycle is due.

References and Further Reading

  1. Bearg, D. W. (2019). Indoor air quality and HVAC systems. Routledge. https://doi.org/10.1201/9780203751152
  2. Perez-Lombard, L., Ortiz, J., & Pout, C. (2008). A review on buildings energy consumption information ´. Energy and Buildings, 40, 394–398. https://doi.org/10.1016/j.enbuild.2007.03.007
  3. Wang, H., & Chen, Q. (2020). Impact of climate change heating and cooling energy use in buildings in the United States. Energy & Buildings, 82(2014), 428–436. https://doi.org/10.1016/j.enbuild.2014.07.034
  4. Wang, H., & Chen, Q. (2020). Impact of climate change heating and cooling energy use in buildings in the United States. Energy & Buildings, 82(2014), 428–436. https://doi.org/10.1016/j.enbuild.2014.07.034

For more information, visit this article on AZOSensors.com

Electric Vehicle Cooling Systems and the Role of Pressure Sensors

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The rise in popularity and uptake of electric vehicles cannot simply be put into words; one has to look at the data. Research carried out by the International Council on Clean Transportation (ICCT) in 2017 determined that global annual electric vehicle sales were increasing nearly at an exponential rate.1

TVC in an Electric Vehicle

By the end of 2020, more than 10 million electric cars were navigating roads across the world.2

Electric Vehicles are appealing to buyers for many reasons: they produce fewer emissions, can be operated at significantly lower costs and offer improved long-term prospects compared to gasoline-fueled cars.3–5

However, one of the greatest challenges in getting more people to convert to electric vehicles has long been the limited range that they can travel on a single charge.6 However, this obstacle is steadily being overcome.

Incremental improvements in battery technology are on the rise, and the maximum range of electric vehicles is extended with each advance, making electric vehicle ownership a more viable option for a future generation of drivers.

The Importance of Cooling Systems in Electric Vehicles

Attempts at improving battery capacity, however, can present certain challenges. The main question is related to cooling. Batteries generate heat when they charge and discharge. Therefore, the more energy a battery stores and the more quickly it charges or discharges, the more heat it will tend to create.

Vehicles that are entirely electric are equipped with a cooling system that maintains particular temperature limits in the vehicle’s power electronics and battery packs. The main role of the cooling system is to ensure that the battery temperature remains within safe operating limits.

If the lithium-ion battery pack’s temperature in any given cell gets too hot, it can provoke a chain reaction known as thermal runaway, in which the complete battery pack experiences catastrophic exothermic decomposition.7

Preventing overheating and thermal runaway is, of course, critical. The majority of EV cooling systems aim to keep battery packs at their optimum operating temperature most of the time.

Usually, this means a close-to-uniform temperature distribution in the 15 – 35 °C range.8 If temperatures are allowed to significantly vary throughout the pack or fall outside this particular range, then charging times and efficiency can be negatively affected resulting in a reduction in the service life of the battery.

EV Cooling Technologies

Electric vehicles employ various cooling technologies to manage the temperature of power systems: air, fins and liquid cooling.

Fin cooling is a simple and economical passive cooling mechanism that has been demonstrated to be successful in the world of electronics.

Effectively, building power-intensive components to feature fins and ridges as opposed to flat faces increases their surface area, thereby improving the rate at which they can dissipate heat to their surroundings.

However, fins have limited application in electric vehicles as they can increase the weight of power systems significantly.

Air cooling, the circulation of relatively cool air across the surface of a hot object, is another comparatively simple technology as it will cool it down more rapidly.

Air cooling is typically cost-effective and has been employed in some electric car models (including early models of the Nissan Leaf). However, this system can be relatively energy-intensive, and cars that are dependent on air cooling can run into trouble in hot weather.8

Liquid cooling is the most efficient way of controlling the temperature of batteries and power systems in electric vehicles.

Piping liquid coolant throughout power systems facilitates effective heat removal and while it is comparatively expensive and complex, it offers more precise temperature control of electronic systems and battery packs in electric vehicles.

As manufacturers are driving towards installing increasingly higher capacity battery packs in electric vehicles, the demands that these cooling systems must be able to cope with are also increasing.

Liquid cooling systems are becoming more crucial and complex as charging rates and battery capacity increase.9,10 Liquid cooling systems in today’s electric vehicles may necessitate subdivision of the cooling system into several circuits and heat exchange between battery coolant and A/C system refrigerant.

The Role of Pressure Sensors in EV Cooling Systems

Pressure is a key parameter in an electric vehicle’s liquid cooling system. Pressure sensors are vital components both for feedback for cooling system regulation and optimization as well as being able to detect pressure loss that could suggest a leak.

As liquid cooling systems grow in complexity, the demand for accurate and robust pressure sensors for EV cooling systems is now greater than any time before.

Merit Sensor Systems designs and manufactures a wide range of high-performance pressure sensors appropriate for demanding EV applications. The TR series sensors have been developed to offer precise pressure measurements in harsh media such as gases, oils and refrigerants.

TR series pressure sensors incorporate a hermetically sealed die that is able to take pressure measurements from the backside, where the media only comes into contact with the ceramic substrate, glass and gold-tin eutectic solder.

TR series sensors also offer accurate, dependable and robust pressure sensing in complex EV fluid system applications while rated for temperatures from -40 °C to 150 °C.

TR-Series face sealing integration (MeriTrek starter Kit) into metal/plastic housing.

TVC series sensors have been optimized for measuring mid-to-high pressures in refrigerant gases up to 2,000 kPa.

Mounting the silicon die sensing element at the top of a ceramic pressure port means the TVC sensors have the capacity to measure backside pressure while separating the media from internal electronics, offering reliable and robust pressure (burst pressure 5x) measurements over a prolonged service life, even in harsh media.

TVC-Series easy integration in metal / plastic housing with radial sealing (o-ring).

With simple sealing and electrical connections, TR and TVC series pressure sensors have been engineered for seamless integration into complex fluid system pipelines and rapid connectors owing to reliable face and radial sealing.

To discover more, contact Merit Sensor Systems and find out how its pressure sensors offer a series of unparalleled advantages in EV systems.

References

  1. Lutsey, N. & Nicholas, M. Update on electric vehicle costs in the United States through 2030. (2019).
  2. Global EV Outlook 2021 – Analysis. IEA https://www.iea.org/reports/global-ev-outlook-2021.
  3. How green are electric cars? | Environment | The Guardian.
  4. Running Costs of EVs: How much it costs to buy and run an electric car | OVO Energy. https://www.ovoenergy.com/guides/energy-guides/how-much-does-it-cost-to-charge-and-run-an-electric-car.html, https://www.ovoenergy.com/guides/energy-guides/how-much-does-it-cost-to-charge-and-run-an-electric-car.html.
  5. How long before we run out of fossil fuels? Our World in Data https://ourworldindata.org/how-long-before-we-run-out-of-fossil-fuels.
  6. The real barriers to electric vehicle adoption. MIT Sloan https://mitsloan.mit.edu/ideas-made-to-matter/real-barriers-to-electric-vehicle-adoption.
  7. Feng, X., Ren, D., He, X. & Ouyang, M. Mitigating Thermal Runaway of Lithium-Ion Batteries. Joule 4, 743–770 (2020).
  8. Chen, D., Jiang, J., Kim, G.-H., Yang, C. & Pesaran, A. Comparison of different cooling methods for lithium ion battery cells. Applied Thermal Engineering 94, 846–854 (2016).
  1. Design of Direct and Indirect Liquid Cooling Systems for High-Capacity, High-Power Lithium-Ion Battery Packs on JSTOR. https://www.jstor.org/stable/26169002.

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Why a Pressure Sensor’s Packaging Matters

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System developers who require pressure sensing capabilities where the sensor will be exposed to harsh media and extended temperature should know that packaging is critical to improve the pressure sensor’s reliability. Pressure sensors are often exposed to harsh fluids, such as gas, oil, refrigerant, and other caustic solvents that can damage the sensor’s circuitry if the sensor is not properly packaged. Damaged pressure sensors can lead to sensing errors and ultimately product recalls and safety risks.

Aerospace and automotive specifications are particularly stringent. In these applications temperatures range between -40 and 150 °C. Furthermore, accuracy and reliability requirements in these applications tend to be demanding, as a component failure can result in safety risk and/or product recall.

Another thing to consider that is related to temperature is the thermal coefficients of expansion (TCE) between the MEMS sensing element, or die, and the substrate on which it is attached. Stainless steel might seem like a great substrate material, but its TCE is much higher than the TCE of silicon, of which the MEMS die is made. In short, the stainless steel expands and contracts much more than does the silicon. These differences in TCE cause the MEMS sensing element to react as it would with real pressure, therefore introducing sensing errors.

TR Series for a face seal and backside pressure

The media also has to be considered. Adhesives are often used to seal the MEMS die to the substrate and protect the sensor’s circuitry. However, adhesives do soften with extended exposure to harsh media. Medical applications, for example, do not expose the sensor to media as harsh as gasoline, but even saline can be corrosive after the sensor is exposed to it long enough. Furthermore, the cleaning and sterilization process typically requires repeated contact with caustic chemicals, such as bleach. When the adhesives soften and seals break, the circuitry can be damaged, and sensing errors can occur.

In addition to temperature and media, pressure must be considered. High enough pressures—around 300 psi—can cause the MEMS sensing element to detach from the substrate when adhesives are used for the MEMS die bond.

Another thing that degrades the bond strength of adhesives is humidity. Very few adhesives or epoxies can withstand long-term exposure to elevated temperatures with high humidity. And the specialty epoxies designed for this environment will exert a significant stress on the MEMS sensing element, again triggering sensing errors.

For a pressure sensor to perform well from -40 to 150 °C, even in harsh media and pressure above 300 psi, the right packaging is essential.

TR Series for an O-ring seal and backside pressure

We at Merit Sensor have ensured that our pressure sensors have been designed for harsh media and high temperature. We have innovative die bonds made of elements that are very resilient to harsh media. These die bonds are done on ceramic substrates, resulting in closely matched TCEs. This results in pressure sensor packages with high accuracy and reliability.

For more information, visit this article featured on AZOSensors.com

Pressure Sensor Platform for a Range of Harsh-Environments

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A compact MEMS device with integrated signal conditioning is needed by many pressure sensor applications; however, the challenge is to find an approach that is capable of supporting the application’s volume and cost requirements including flexibility in terms of pressure range. From industrial to medical applications, after-market to OEM automotive high-volume projects, the solution is considered to be a platform that can be adapted based on the pressure range, temperature range and media compatibility.

The Merit Sensor TVC sensing platform is a new approach that addresses applications that need lower pressure ranges integrated with a radial seal. Instead of a single-chip solution, which limits pressure range and output configuration changes, these applications are perfectly suited to a customizable sensor platform that incorporates the MEMS device and signal conditioning in a compact, cost-effective package.

Sensor Platform Meets Exact Application Needs

The customizable sensor platform incorporates a high-sensitivity MEMS device chosen from one of the globally leading, largest MEMS sensing element portfolios, which comprises of devices from the lowest range of 7 kPa up to 3.5 MPa absolute, along with an individual signal conditioning capability. This supports almost any application with readily available components, saving the investment in the production of a device for particular dimensions and ranges. The signal conditioning ASIC with the related electronics components is fixed on a harsh-media-compatible ceramic substrate. The MEMS sensor is fixed on a pre-molded, ferrule-type ceramic pressure port, thus preventing any additional potential leak paths.

The MEMS backside, the ceramic port and the attach material are the only elements exposed to the media. The populated ceramic substrate completely protects the components, and hence does not require the addition of dedicated media-compatible coatings. The components and the signal conditioning fulfill EMI/ESD protection norms, thus the all-in-one sensor platform minimizes the requirement for external components.

The two-component solution includes both signal conditioning and MEMS in separate mechanically attached subgroups. This enables Merit Sensor to choose both the exact MEMS pressure sensor and signal conditioning output (analog or SENT) required for the end user application. Keeping the two elements separated has a functional advantage and also provides a more cost-efficient solution by taking advantage of higher quantity MEMS unit cost, even if the signal conditioning needs change across applications.

The MEMS sensing element is considered to be a key component for the platform. The TVC-Series can cover from 7 kPa to 3.5 MPa pressure applications along with the HM and J-Series. Both series have been designed for backside pressure measurements, and the HM-Series (harsh environment MEMS) covers the absolute configuration from 100 kPa to 3.5 MPa as well. The J-Series is the most sensitive element (5333 µV/V/ psi = 760 µV/V/kPa), employed as gage configuration (backside) and comprising of superior pressure (< 0.025% FS) and thermal hysteresis (< 0.1% FS) in order to deliver a stable signal to the signal conditioning via wide temperature ranges and low pressure.

Merit Sensor knowhow is applied to the MEMS geometry and configuration, mainly on the glass thickness, in order to ensure the correct mechanical decoupling for optimal thermal behavior and stability. The three die-attach processes provided within the platform address varied application requirements, thus combining the best MEMS thermal behavior with burst pressure along with the requested media compatibility. MEMS sensing elements are developed by Merit Sensor’s own fab, which provides direct and dynamic control of the different solutions.

Figure 1. The Merit Sensor TVC sensing module is highly customizable to meet specific application requirements in a cost-efficient, compact package.

Figure 2. Pressure sensing elements can be chosen from the world’s largest portfolio of MEMS pressure sensor devices.

Choose Appropriate Attach Process for Environment and Cost

The sensing platform is geometrically compact, and the cavity and pressure port have defined dimensions for air, fluids and gas. However, a vital element for accuracy and reliability is the choice of die-attach. Conventional adhesives that are used for creating the pressure seal and protecting the sensor die and related circuitry are considered to be a cost-effective approach for non-aggressive gases and air, but they eventually soften in harsh vapors or fluids. Once the seal breaks, the sensor circuitry is damaged, developing a common reliability failure that can be expensive if it leads to a product recall or demands regular maintenance and replacement of the sensing subsystem.

At the other end of the spectrum, a eutectic die bond using a gold-tin soldering alloy provides a hermetic seal even in harsh fluids, at extremely wide temperature ranges and at high pressure. While this gold-tin solder is a lot more expensive than adhesive, the cost difference is minute in comparison to the major improvement in prolonged reliability and maintenance costs.

The die-attach process using the glass-frit introduced with the TVC platform is considered to be a cost-efficient solution for high-burst pressure in terms of reliability, improved media-resistance compared to adhesive and more stability in medium/low pressure ranges thanks to the close-to-silicon TCE sealing material. The high temperature (> 300 °C) curing process during the MEMS-to-port assembly guarantees stability in wide temperature range applications.

Merit Sensor offers a wide range of MEMS attach processes on the Al2O3 ceramic pressure port in order to support sensor media and environment demands, and also cost and reliability requirements of each application (see Table 1). The MEMS backside pressure measurement, along with the dedicated die-attach process of the platform, ensures a safe burst pressure in every pressure range (Table 1).

Table 1. Comparison of die-attach approaches and appropriate media, along with trade-offs in cost and burst pressure.

Customizable Pressure Sensing Platform Addresses Full Range of Design Decisions

The Merit Sensor TVC sensing module addresses a variety of application-oriented requirements with a single solution. This covers the low-pressure, below 100 kPa exhaust gas measurement, up to 3.5 MPa air conditioning gas measurement in just the automotive domain. Both need a solid media compatibility, which involves in-depth knowledge in the MEMS die-attach, as well as matching the accurate components for application temperature and various other environmental requirements.

The sealing joint and choice of how to mechanically incorporate and electrically couple the sensor is majorly dependent on the type of application, pressure range and temperature. Standard electrical connection can be accomplished with lead-frames and pins or with pads without holes (see Figure 3 for example). Thick wire bonding can be used as a mechanical stress-free connection ideal for extremely large temperature ranges from -40 °C to +150 °C and low pressure. The sealing also needs attention to the material (media compatible) and tolerances (leak), as well as determining the pressure range without or with a vacuum, which would need the sensor to be fixed in order to avoid any movement by negative/positive pressure crossing.

 

Figure 3. 3D view of the TVC Merit Sensor compact module, 3D step file is available for a quick design-in into the end sensor housing.

The pressure port configuration, permitting the radial sealing and limiting the material in contact with the media (simplifying the design), expands and then fulfills the Merit Sensor packaged sensing modules solutions. The mechanical stress-free design enables the use of very sensitive MEMS elements, ideally supporting the low pressure needed for the most challenging applications that are currently available, and these include fuel vapor, exhaust gas and fuel pressure. The 14 x 10 x 4 mm compact geometry sensing module includes all essential components.

Comparison of sensor package type and design considerations.

The use of the modern ASIC to support analog or SENT output allows the setup and calibration from the three external pads, which indeed supports data programming (traceability) and customization (output values, parameters), even when the sensing module has previously been installed in the housing. The TVC-Series is supplied as temperature-and pressure-calibrated, attaining accuracy better than 2.5 %FS between -40 °C to+125 °C. The accuracy can vary based on the pressure range and MEMS attach technology.

Merit Sensor is completing the portfolio for high temperature, harsh environment applications with a solution that is capable of solving the mechanical stress and expands to the low pressure incorporating new MEMS (J-Series) and attach technology, for a cost-efficient solution.

Features

  • Customizable
  • Compact design
  • Limited requirements for external components
  • Wide range of pressures (7 kPa…3.5 MPa)
  • Reduced mechanical influence (housing integration)
  • All-in-one, ready-to-use sensing module (tested, calibrated)
  • Cost-efficient solution for media-compatible applications

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