Servoflo distributes a variety of capacitive and resistive humidity sensors for medical, HVAC, instrumentation, critical containment and other applications.  Some situations need precise and highly accuracy relative humidity (rH) measurement to maintain narrow, specific environmental conditions while others have a broad temperature range with wider tolerance ranges for rH measurement. This blog post explains the differences between capacitive and resistive relative humidity sensors and why to choose one type over the other.

Capacitive Sensors

Humidity and dew sensors, also called hygrometers, are necessary when consistent environmental conditions are required to be maintained.  A capacitive humidity sensor is so named because it uses capacitive measurement, which relies on electrical capacitance. These are a common type of humidity sensors.

The capacitive sensor is composed of two metal plates, or electrodes, separated by a thin layer of non-conductive polymer film.  The film attracts moisture from the air and when the moisture makes contact with the metal plates it creates a voltage change.  The output voltage measurement is captured and can be displayed via an analog dial, output into another system, or converted into a digital reading that indicates the amount of moisture in the air.

The capacitive sensor is contained in a hygrometer to measure relative humidity. The sensor is one part of the system that also contains a probe, cable, electronics, and an output signal.  Together they function to accurately measure the entire humidity range from 0% to 100%.

Resistive Sensors

Resistive sensors work on a similar principle to capacitive sensors, where electrical change is measured to produce a value for relative humidity. However, the mechanism in this system is different. Although resistive sensors use a hygroscopic (moisture-absorbing) material similar to the capacitive system, the difference is that the measurement is of the resistance change in the material rather than the capacitance. 

In this case, the output voltage has an inverse exponential relationship to relative humidity. As with capacitive sensors, the data regarding the output voltage can be captured, stored, or converted. These sensors use cost-effective, scalable dielectrophoresis, in which a free-standing structure is created to house pre-patterned electrodes that are separated by a single crystalline zinc oxide nanowire (ZnO NWs).

The benefit of a resistive sensor is the high surface-volume ratio, which allows it to measure humidity changes in the environment up to 90% relative humidity at room temperature. These systems do have limitations, and as such are not optimal for measuring values below 5% RH.  Applications that favor a resistive sensor include automotive, smart food packaging, and relative humidity sensor networks.

Selecting a Humidity Sensor

Although the capacitive sensor and resistive sensor have the same goal in measuring humidity, they differ in their methods.  Capacitive sensors are considered to be more accurate and stable while producing repeatable results—however, their cost can be prohibitive, making them more suitable for medical type applications where precision is paramount.  The less expensive resistive sensors are more practical for situations where frequent measurements are taken that do not require extremely precise data.

For more detailed information about selecting a humidity sensor and the applications and industries these are frequently used in, download our eBook.  You can check out our full line of digital humidity sensors on our website here. 

Industry professionals employ pressure sensors in a variety of applications, ranging from aerospace to oil and gas to utilities. In many cases, they are subjected to harsh operating and environmental conditions, such as high pressures, corrosive compounds, and temperature extremes. For use in these circumstances, ceramic pressure sensors are a suitable option.

Pressure sensors are often employed to handle extreme conditions such as high pressures, corrosive atmospheres, and high temperature processes. Ceramic pressure sensors are an ideal alternative to conventional oil-filled pressure sensors under such circumstances.

Because of their unique construction and ceramic’s chemically inert nature, ceramic pressure sensors can withstand harsh atmospheric conditions without sacrificing performance. Robust, reliable, and washable, they are a durable and cost-effective solution to a variety of demanding applications.

The following blog post provides an overview of ceramic pressure sensors, outlining the benefits, types available, and applications.

Benefits of Ceramic Pressure Sensors

Ceramic pressure sensors offer several benefits, including:

• Greater strength and durability. Compared to their stainless steel counterparts, sensing diaphragms made of ceramic are 10x stronger. This quality results in greater durability and longevity. Ceramic’s superior resistance to abrasion further enhances these characteristics.
• Lower cost. Ceramic diaphragms are less expensive to manufacture than stainless steel ones. This quality, coupled with longer service life, can result in significantly lower equipment costs.
• Better corrosion and chemical resistance. Ceramic is chemically inert and corrosion resistant, making it highly compatible with most process materials.
• Smaller environmental risk. Ceramic sensors do not contain oil, reducing their risk of negatively impacting the surrounding environment due to fluid leaks.
• Higher temperature and pressure operating capacities. Ceramic is capable of withstanding greater pressures and temperatures than stainless steel. It also displays a broader range of sensitivity, with the ability to simultaneously measure low pressure while withstanding high overpressure.

The above qualities, among others, make ceramic pressure sensors well-suited for applications with harsh environments. Even when exposed to high pressures, extreme temperatures, corrosive compounds, or high levels of shock and vibration, they provide consistent and reliable performance.

Ceramic pressure sensors have many advantages over traditional stainless steel counterparts. Perhaps most importantly, they are significantly stronger than oil-filled diaphragms. Similarly, they can withstand high operating temperatures and pressures without losing sensitivity at low pressure values. They tolerate relatively high over pressures as well.

Since ceramic sensors do not rely on oil, the diaphragm can be thicker, and it does not carry the risk of a leak that could compromise an entire batch of sensors. Because they are sturdier, ceramic pressure sensors will not deviate from their calibrated setting even after multiple operating cycles, thus minimizing the risk of sensor drift. All these features make ceramic pressure sensors ideal for a large number of industrial applications, particularly if accuracy, dynamic range, and corrosion resistance are critical requirements.

Types of Ceramic Pressure Sensors

Ceramic pressure sensors are available in a wide range of designs, each suited for use in particular applications. Some of the most common ceramic pressure sensor variations include:

Flush Mount vs. Monolithic Sensors

The key difference between flush mount and monolithic ceramic pressure sensors lies in the surface design. While flush mount sensors provide a flat surface for exposure to the pressure media, monolithic sensors feature an indentation in the exposed side of the sensors. As flush mount sensors maintain a fixed reference, they are generally used for applications that require absolute or sealed gauge sensing.

Piezoresistive vs. Capacitive Sensors

Ceramic pressure sensors employ either piezoresistive or capacitive means to measure pressure. Piezoresistive sensors measure the changes in electrical current in direct correlation to changes in pressure on the diaphragm. Capacitive sensors measure pressure displacement by analyzing the difference in electrical frequency between two sensors. The latter type is preferable for applications that require the measurement of low-pressure values under high overpressure conditions.

Amplified vs. Unamplified Sensors

Pressure sensors come with several amplification options—including ratiometric, non-radiometric, current loop, and I2C—each of which can be calibrated as needed. For users who wish to perform their own amplification and calibration, unamplified ceramic sensors are also available.

Ratiometric vs. Non-Ratiometric Sensors

Ratiometric sensors take into account the power supply when converting sensor output, allowing for more accurate measurement without the interference of power supply variation. Non-ratiometric sensors are used when the measurements are against an absolute reference and not affected by fluctuation of the power source.

When to Use Ceramic Pressure Sensors

Ceramic pressure sensors are suited to a wide variety of industries. In the automotive industry, for example, they are often used to measure oil levels. Within the transportation industry, they are used to maintain hydraulic systems (which benefit from greater water resistance) and control emissions (where greater resistance to heat and corrosion may be necessary). They are also used to measure the flow rate of the working fluid in water reservoirs, wastewater treatment plants, and other chemical processing plants.

Due to their superior resistance to corrosion, high pressures, and extreme temperatures, ceramic pressure sensors find use in a variety of industrial applications with harsh environmental and operating conditions. Typical industries that employ these devices include:

• Automotive instrumentation
• Chemical
• Food and beverage 
• Heavy manufacturing
• HVAC
• Oil and gas
• Water and wastewater treatment  

The high strength of ceramic sensors makes them ideally suited for applications that feature a large number of pressure cycles. Because of ceramic’s chemically non-reactive nature, they can be used in HVAC systems to measure refrigerant levels and for flow measurement in the oil and gas industry. They are also inert enough for use in the food and beverage industry to monitor ingredient flow.

High-Quality Ceramic Pressure Sensors From Servoflo

For decades, Servoflo has served industries with quality pressure sensor support, optimization, and system design services. With customers from every major industry, ranging from aerospace to waste management, we have the knowledge and experience to provide ceramic pressure sensors that suit any requirement.

For the last 30 years, Servoflo has offered technical support, product optimization, and system design services to users of pressure sensors in every major industry. Trusted by companies of every size, our pressure sensors can handle difficult applications with accuracy and efficiency.

In particular, our ceramic sensors offer unmatched quality and reliability in industries ranging from aerospace to waste management. Regardless of your demands, Servoflo can help you meet any requirement.

If you’d like to learn more about Servoflo’s ceramic pressure sensors or discover how they can improve your business, download our “Ceramic Pressure Sensors 101: Why, When, and Where to Use Them” eBook today.

Servoflo will be exhibiting at this year's Sensors Expo from June 26-28, 2018 in San Jose. We are pleased to offer free exhibit passes and $100 off the conference attendance to our customers and visitors (use code 232L when registering). Please see the information below on how to register. We will be there with all of our products!

Visit us at Booth 648!

Sensors Expo & Conference
Conference & Expo: June 26-28, 2018
Pre-Conference Symposia: June 25, 2018
McEnery Convention Center
San Jose, CA
www.sensorsexpo.com

Event Description
Sensors Expo & Conference is the only industry event in North America exclusively focused on sensors and sensor-integrated systems. For more than 30 years, Sensors Expo has brought technical innovation and thought leadership to engineers involved in the development and deployment of sensors and sensing systems. During this information packed, 3-day program, explore cutting-edge trends and applications through new products, technology pavilions, demos, and showcases of 300+ of the latest sensors. The featured technology displayed includes: Energy Harvesting & Power, Emerging Technologies, Flexible & Wearable Tech, IoT & Wireless, Measurement & Detection, MEMS & Sensors, Novel Sensor Applications, Optical Sensing & Detection, Sensors & Embedded Systems, and Sensor Data. New this year, the event will be co-located with the Medical Sensors Design Conference and an Autonomous Vehicle Sensors Conference. This educational, information-packed Sensors & Connectivity week provides the ideal place for technologists to find opportunities and engineers to innovate solutions.

For nearly 30 years, the team at Servoflo has been helping companies across a range of industries manage their unique measurement needs. Whether clients are working with standard pressure sensors, vacuum sensors, sensor signal conditioning solutions, oxygen sensors, or micropumps, we’ll work to find the ideal components for your specific measurement application.

Our vast inventory is always growing to meet shifting industry needs and incorporate the latest technologies, and we’re now proud to introduce a new line of digital humidity sensing products from MEMS Vision: smart sensors with unmatched accuracy and breakthrough manufacturing technology. 

Microelectromechanical Systems: Tiny Tech With Major Impact

Microelectromechanical systems, or MEMS, are generally comprised of components less than 100 micrometers in size, and a standard MEMS device typically measures between 20 micrometers and 1 millimeter.

Scientists and industry leaders have been aware of the high potential of micro machines since the 1950s; manufacturing technology simply needed to catch up. For example, today’s MEMS are built with modified semiconductor device fabrication technologies, such as wet etching, molding, plating, dry etching, and electro-discharge machining.

MEMS Vision Series MVH3200D: High-Performance Digital Humidity Sensors

The team at MEMS Vision specializes in innovative small devices and components, crafting some of the world’s leading nanotechnology. Their unique line of relative humidity and temperature (RH & T) products are made with breakthrough MoSiC™ micro/nanotechnology, and are designed to serve a wide range of original equipment manufacturer (OEM) applications. All sensors are backed by expert engineering techniques for optimal performance and minimal time to market. 

The MVH3200D line of miniaturized digital humidity sensors, in particular, is engineered for unparalleled accuracy. These smart sensors can be independently programmed for customized humidity and temperature resolutions, providing maximum flexibility alongside full calibration. MVH3200D sensors can also provide standard digital I2C outputs to enable plug-and-play integration.

The micro-Watt levels of power demanded by MVH3200D products make them an ideal choice for portable and remote applications, or any situation requiring minimal power consumption.

Available sensor models include:

• MVH3201D (10% to 90% RH range, ±1.5% RH accuracy)
• MVH3202D (10% to 90% RH range, ±2.0% RH accuracy)
• MVH3203D (20% to 80% RH range, ±2.5% RH accuracy)
• MVH3204D (20% to 80% RH range, ±3.5% RH accuracy) 

Key sensor features include:

• DFN-type package, 3 mm x 2.4 mm x 0.8 mm
• Relative humidity and temperature digital output, I2C interface
• Full calibration
• Self-diagnosis algorithms to ensure accurate and repeatable measurements
• Independent resolution settings for RH & T of 9, 10, 12, or 14 bits
• Voltage supply range of 1.8 V to 5.5 V
• Low-power consumptions: 1.0 µavg current at one RH & T measurement per second (at 8-bit resolution, 1.8 V supply)

Common Humidity Sensor Applications

MEMS sensors can be used in a huge range of applications, from smartphones to vehicles to residential temperature control systems. Offering highly reliable performance, these tiny sensors help keep countless everyday devices operating accurately and efficiently.

Essential MEMS technology can be found in:

• Technical instrumentation, and logistics and safety monitoring solutions
• HVAC systems, thermostats, heating controls, and building automation
• Meteorology and weather monitoring
• Data logging and sensor nodes
• Consumer products and electronics, such as smartphones and tablets
• Household appliances, such as refrigerators and humidifiers
• Medical monitoring solutions, wearables, and health care support

MEMS Vision Sensors From Servoflo

The MEMS Vision line offers built-in, fully calibrated systems, ensuring high-accuracy measurements and linear behavior even in varying sensing environments. These sensors are known for their long-term stability and reliability, with a unique build that includes:

• Proprietary sensing structures
• Long-term protection technology
• Robust biasing circuitry
• Self-diagnosis algorithms to ensure accurate, repeatable measurements

Each sensor also features digital output capabilities, allowing for native interfacing with embedded system components, such as FPGAs, microcontrollers, and so on.

To learn more about MEMS Vision products and explore the full catalog of humidity and temperature sensor offerings from Servoflo, download a copy of our new “Humidity and Temperature Model Overview.”

To obtain accurate, precise flow measurements, it’s critical to select the proper MEMS mass flow sensor for the specific application at hand. When choosing a flow sensor, accuracy, sensitivity, and size should all be kept in mind, along with a range of other key factors.

Flow sensors play a crucial role in many different applications and industries, such as chemical and semiconductor manufacturing, medical device manufacturing, and natural gas metering.

Thermal mass flow sensors, in particular, offer numerous advantages, including:

• Small size
• Fast response time
• Low power consumption
• High sensitivity to low flow rates

Operating independently of density, pressure, and viscosity, these devices generally consist of upstream and downstream temperature sensors and a heater located between them.

When selecting a MEMS thermal flow sensor, the following measurement considerations should be kept in mind: mass flow rate vs. volumetric flow rate, mechanical flow channel diameter vs. flow rate, and the nominal operating flow rate of the products.

Mass Flow Rate vs. Volumetric Flow Rate

MEMS flow sensing products typically measure the mass flow rate, which is automatically compensated for changes in temperature and pressure. Mass flow rate always is referenced in relation to the standard condition of a specific temperature and pressure.

The reference pressure is typically 101.325 kPa, or 14.5 PSI; the standard temperature may vary, at 0°, 15°, or 20 °C. The manufacturer will specify the conditions in the user manual. The default reference temperature for current Siargo products, for instance, is 20 °C, which can be customized upon request.

Mechanical Flow Channel Diameter vs. Flow Rate

All flow measurement products are packaged with a flow channel to ensure optimal performance; therefore, it’s critical to select the proper flow channel for the desired flow rate measurement.

It’s generally not recommended that users measure a high flow rate in a small channel or a small flow rate in a large channel. Also, the product’s flow channel should not be connected to a different size system channel. However, if there is no option but to alter the flow channel size, the product’s flow channel size should always be smaller than that of the system channel.

Nominal Operating Flow Rate of the Products

Flow sensors normally have about a 20% margin for the specified full-scale flow rate. However, it’s recommended that users select a full-scale flow rate that falls within the application’s maximum flow rate in order to ensure optimal performance and reliability.

When dealing with low flow rate accuracy, sensor products have a default range of over 100:1, allowing them to meet most applications’ requirements. Most of today’s products do not offer a bidirectional flow rate measurement option, but this can be customized as needed.

Learn More

For further assistance in picking the right flow sensor for your specific application, and to learn about other key considerations to keep in mind during the selection process, download our free eBook, “MEMS Mass Flow Sensor Selection.”

When selecting a pressure sensor for a specific application, designers must first determine the total system accuracy required, as well as the performance requirements for the lifetime of the product.

Like a bathroom scale that is used day after day, a pressure sensor's output may vary over time. The amount of drift depends on the specification given by the manufacturer. Other factors, such as humidity and operating temperature range, can also affect the accuracy of a pressure sensor, regardless of which type of sensor you purchase.

In critical applications requiring optimal accuracy and minimal drift, designers will have to either calibrate or tweak the performance of the pressure sensor to meet the system accuracy requirements. Furthermore, some systems often require recalibration or resetting to zero to ensure optimal reliability after extended use. Back to our example, a good analogy is a mechanical scale, in which the zero point will drift over time and the user must adjust the zero point to maintain accurate weight measurements.

A bill of materials, though intended to estimate project costs for production volumes, can actually distract from one of the most expensive aspects of a project — the labor required to inspect, install, and test different components. By focusing on the price tag of individual components themselves, manufacturers often overlook the additional costs of board space, sourcing from multiple distributors, calibration labor, stocking locations, and multiple purchase orders.

Alternatively, sourcing one complete sensor solution from one provider can alleviate all of these pain points while incurring lower service costs down the road. In particular, customers without explicit sensor design/calibration expertise can greatly benefit from an all-in-one solution, as it allows them to reduce both labor and overall bill of materials costs.

Partnering with the factories we represent,  Servoflo supports customers anywhere along the price/performance continuum from the most basic components to modified output sensors to completely customizable turnkey sensor solutions across a wide range of industries. Depending on the factory/partner, it could be possible to add a display unit, Wi-Fi, or Bluetooth capabilities.  Or,  adding flex to a sensor, creating packaging enclosures and custom flow paths, or integrating multiple parameters into a single sensor.  It is worth the time and effort to ask:  Who can best provide the required features:  factory or customer?

Throughout our nearly 30 years of experience providing efficient, reliable sensor related services, we’ve handled a diverse range of projects. Below are some examples of our past work and tailored solutions.

• Creating a pressure gauge with display and enclosure
• Integrating a pressure sensor and electronics in a hybrid circuit design for better protection in high-temperature and high-humidity environments
• Eliminating installation assembly and testing by adding a flex cable to a standard board level sensor
• Customizing sensor calibration and output to meet exact customer specifications
• Designing a custom flow path in a mass flow sensor for medical equipment
• Designing custom electronics to create pressure switches, mass flow switches, and other environmental sensors

As with all of our application-specific work, these solutions helped customers simplify their bill of materials and reduce downstream maintenance costs for maximum lifetime cost efficiency.

Optimize Your Sensor Solution with Servoflo

Servoflo is proud to be a one-stop shop for reliable, industry-leading solutions tailored to your unique system requirements. By dealing with one vendor, one point of contact, and one invoice, you can greatly simplify your bill of materials and reduce overall costs.

To discuss a custom sensor solution based on your specific needs, contact Servoflo today.

Come visit Servoflo at Booth 648 during Sensors Expo June 27-29 in San Jose, California! Here is a great from Sensors Expo:

"The Sensors Conference is where you'll find the best in the sensors industry, along with new and innovative ways to jump start your sensor solutions. It's North America's largest and most comprehensive educational program that brings together thousands of engineering professionals all under one roof.

With updated and expanded tracks, exciting and visionary Keynote Presentations, and new Pre-Conference Symposia, the Sensors 2017 Conference Program brings you the leading sensors content that you need to succeed from over 100 industry experts. Expanding the program to include interactive content, applications, demos, and hands-on components, the 2017 Conference will have you walking away with the sensors solutions you need."

Visitors to our booth who share their pressure sensor or mass flow sensor application is elible to enter our drawing for a $100 Amazon gift card!

Servoflo will be participating in the first ever Medical Sensors Design Conference taking place May 8-9, 2017 in Newton, MA. This event focuses on driving sensor development and innovation in medical applications. 

The conference is filled with various industry speakers from cutting-edge medical design companies and technologies. 

Key themes covered in the conference include:

• Artificial Intelligence
• Battery-powered Wearable Fitness
• Biometric assessment
• Biosensors
• Blood & Oxygen Meters
• Concussion assessment
• Critical Care Sensor Devices
• Data & Analytics
• Drug Delivery
• ECG & EEG
• Fluid Management
• Healthcare and Security
• Low-Power Sensors
• Medical Grade Wearables
• Metabolic Measurement
• Non-Contact Measurement
• Non-Vascular Therapies
• Patient Friendly Medical Products
• Patient Monitoring and Diagnostics
• Respirators
• Security
• Sensing and the Future of Healthcare
• Sensors in Clinical Trials
• Wearable Sensors

Sensors Magazine is offering a special code for $100 off your all-inclusive Attendee Pass. The code is SENSORSMAG.

Join us at this new, informative conference!

We have some specific pressure sensors on sale! Take a look at our clearance inventory for heavily discounted opportunities. These parts have never been used by customers. Check back frequently for updates.

Payment terms are prepayment via check or credit card only. No performance guarantees or warranties are in effect. The pdf data sheet is in the model number link. The quantity available is subject to change without notice.

Contact us or call us at 781-862-9572 to make an offer.