Pressure Sensors and Their Use in Aquatic and Underwater Applications

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

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Implementing Pressure Sensors into HVAC Systems

HVAC systems are vital when it comes to ensuring indoor air quality, health, and inhabitant comfort management.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

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Electric Vehicle Cooling Systems and the Role of Pressure Sensors

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.htmlhttps://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

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.

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