Humidity Sensors: Capacitive vs. Resistive

Posted by Seta Davidian on Oct 25, 2018 3:17:57 PM

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.

humidity sensor

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

Humidity-Sensor-Guide

Download Our Humidity Sensor Selection Guide

Topics: Humidity Sensors

New Line of MEMS Vision Digital Humidity Sensors

Posted by Seta Davidian on Apr 12, 2018 9:59:32 AM

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.

mvh3200d Humidity SensorOur 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) 
mvh3200d

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.”

 

Contact Us

Topics: Humidity Sensors

1 Sensor Measures Pressure, Humidity & Temperature!

Posted by Seta Davidian on Aug 19, 2015 11:09:00 AM

pressure humidity temperature sensorSensors are rapidly changing with increased functionality in MEMs technologies.  The new MS8607-02BA01 exemplifies how new technology is creating amazing new sensors.

The MS8607 measures pressure, humidity and temperature in a small QFN package measuring only 5 mm3 x 3 mm3 x 1 mm3. Inside this small package is a piezoresistive sensor providing pressure and temperature and a capacitive-type sensor for measuring relative humidity.  The measured signals are converted into a 24-bit digital value for pressure and temperature and a 12-bit digital value for relative humidity measurement.

The sensor requires 8 pads for operation, uses I2C communication and operates with a very low 1.8 to 3.6  supply voltage. With an operating pressure range of 10 to 2000 mbar, it has a pressure accuracy of ±2.0 mBar and pressure resolution of 0.016 mBar. For humidity, the measuring range is 0-100% rH with an accuracy of ±3% rH and a resolution of 0.04% rH. Finally, for temperature, the operating range is -40°C to +85°C with a temperature accuracy of ±2°C and resolution of 0.01°C.

The MS8607 is ideal for applications in the consumer and industrial marketplace, including smartphones, tablets, printers, HVAC applications, weather stations, home appliances, humidifiers and much more.

Learn more about the MS8607.

Get budgetary pricing for the MS8607 and other barometric pressure sensors offered by Servoflo.

Download Barometric  Product & Pricing Guide

Topics: Humidity Sensors, Barometric Pressure Sensors

Why We Love the HTU20/21 Humidity Sensor Chips

Posted by Seta Davidian on Aug 4, 2015 12:40:35 PM

digital humidity sensor with PTFE filterThe HTU20/21 are tiny humidity and temperature sensors in a 3 mm x 3 mm x 0.9 mm DFN package. This tiny sensor packs a punch due to its:

  • Humidity operating range of 0-100%
  • Temperature range of -40°C to +125°C
  • Supply voltage of 0.3 to 3.6 VDC
  • Optional PTFE filter (F) option (shown in image on right)
  • No calibration required in standard conditions, allowing for full interchangeability
  • Instantaneous desaturation after long periods in saturation phase

Every sensor is individually calibrated and tested. The lot ID is printed on the sensor and an electronic ID is stored in the chip. Resolution can be changed by command from 8/12 bit up to 12/14 bit. A fast response time of 2 ms (using 8 bit resolution) up to 14 ms (using 12 bit resolution) gives designers flexibility in managing their humidity measurement.

HTU21D digital humidity sensor without filterFor temperature measurement, the accuracy is ±0.3°C at 25°C. The resolution is 0.01°C at 14 bit resolution and 0.04°C at 12 bit resolution.

The HTU20 has an accuracy of ±5% from 20-80% rH while the HTU21 has an accuracy of ±3% in that same humidity range. There are 2 output choices in each family: The P version has a pwm output while the D version has I2C. 

Best of all, the price of the HTU humidity sensors is extremely competitive. At 5,000 pieces, the price is between $1.46 to $1.95 each depending on the model.

Applications for the HTU20/21 family include medical, home appliances, printers, humidifiers, smart phones/tablets, indoor air quality and more.

Get the complete specification for HTU20/21.

Is this not the humidity sensor you are looking for? Then check out our complete line of analog and digital humidity sensors and transducers. We also have a product & pricing guide for your review.

Download Humidity  Product & Pricing Guide

 

Topics: Humidity Sensors

The Importance of Humidity Sensor Element Accuracy

Posted by Seta Davidian on Feb 6, 2012 12:04:00 PM

hyt 271 header 2Sensor technology has changed dramatically over the past few years. Previously, customers purchased the sensor elements and electronics and calibrated a sensor themselves. The development of improved electronics, MEMs technology and efficient manufacturing technology has created a new humidity sensor market - fully calibrated humidity sensors with an I2C output. Many companies are offering models with similar features.

Yet, price and performance does vary significantly between models, making it important for users to understand the the performance of a humidity sensor over the entire range. This data is often well hidden in fine print in data sheets.

IST, the supplier of our HYT digital humidity elements and the new sensor elements P14, tested 4 different humidity sensors at 85% rH @ 30C for 65 hours. 2 competitors, the HYT271, and the P14 humidity element were tested. The 2 competitors units showed a 1.25% and 2.5% deviation in readings compared to only 0.17% for the HYT271 and 0.09% for the P14.

What does this mean for designers trying to choose a humidity sensor? The humidity sensor element (such as P14) plays a critical role in the performance of a fully integrated and compensated humidity sensor. Electronics is limited in compensating for poor signals a sensor element sends. The combination of good sensor elements and electronics is the key to sensor design.

The integration of a sensor element and electronics is fairly straightforward. However, if performance over time and at extreme conditions is critical for your application, take the time to research the quality and stability of the sensor element used. Saving a little in upfront component cost could end up costing you much more in the long run!

Click me

Topics: Humidity Sensors

Digital Humidity Sensor White Paper in Design News

Posted by Seta Davidian on Sep 26, 2011 1:31:00 PM

digital humidity sensor with I2C outputRecently an article was published in Design News about digital humidity sensors offered by Servoflo.

Typical problems of traditional integrated sensor solutions include poor accuracy, unstable behavior around the measuring range limits and unsatisfactory chemical resistance against contaminants. Additional limitations are lack of dew formation resistance, inadequate long-term stability and failure during load spikes.

This article provides technical details about how these problems are solved with new digital humidity sensor technology. In depth details about design features and manufacturing techniques are discussed. Topics include ASIC functionality and design, construction, and what this means for the functionality of the humidity sensor.

Anyone who is considering designing in a digital humidity element should take a quick look at this topic. Please feel free to post a comment or question.

Read the complete article here.

Topics: Humidity Sensors