IR Sensors: Analog

Introduction:

Welcome to smarter with sensors. Our video series that explains the latest sensor technologies, from TE Connectivity.

Today in SMARTER WITH SENSORS we’ll introduce the HTU31 humidity temperature sensor.

1. Humidity, what is it and why is it important?

Humidity is defined as some measure of the water vapor content of air (or other gas).

The term “humidity” is a general term to quantify the amount of water vapor in the gas or atmosphere.

Water vapor plays a critical role in maintaining quality and efficacy for products and technologies, that are used every day, as well as being essential for human existence.

It is essential for manufacturers, in a variety of industries to understand how accurate humidity measurements work, and the roles sensor products play.

2. How is it measured?

Humidity is the amount of water vapor in the air and can be measured in both absolute and relative terms. Absolute humidity is the mass of water (MW) in a volume of air and is expressed commonly in units of g/m3. Most people are more familiar with relative humidity, which is defined as the amount of water vapor in the air relative to the maximum amount of water vapor the air can hold at a given temperature and is expressed as a simple percentage from 0 to 100%.

3. What is dew point

The other term that many are familiar with thanks to the local weatherman is the term dew point, and that is defined as the atmospheric temperature (varying according to pressure and humidity), below which water droplets begin to condense and dew can form.

4. Why is humidity important?

The humidity in industrial and residential environments is critical to the long-term health and well-being of people – whether they are at work or at home. Humidity sensing and control is also important for many materials and processes in the manufacturing environment as well as for the safety of equipment and employees.

5. What are some issues associated with high humidity?

Most people are at least somewhat familiar with the issues from high indoor humidity levels. These issues can include poor indoor air quality, mold and mildew growth, lower productivity in industrial settings and lower quality sleep in residential settings, increased asthma and allergy symptoms, warped hardwood and furniture, strained HVAC systems and higher utility bills.

On the other hand, there are many problems associated with dry air or low indoor humidity levels and, these issues are generally less well known and understood. These issues include things like processing and handling of many materials in factories and industrial environments, electro-static discharge as well as human health and comfort.

6. Product description

TE Connectivity’s (TE) HTU31 series of humidity temperature sensors are designed to provide very accurate humidity and temperature measurements in a miniature 6-pin DFN surface mount package with very low power requirements.  These sensors are factory calibrated and are available with either an I²C digital output or a 0.5V to 4.5V analog output and operate over a wide temperature range from -40°C to +125°C.  They work over a wide voltage range and a programmable I²C address allows multiple HTU31 sensors to operate on the same I²C bus.  16 bits of resolution and an accuracy of ±2% for humidity and ±0.2°C for temperature.  With a miniature footprint of only 2.5 x 2.5 x 0.9mm, the HTU31 is one of the smallest and most accurate temperature and humidity sensors on the market today.

7. How it works

The HTU31 consists of a humidity sensing dielectric layer along with a porous upper electrode, an ultra-thin polymer layer and a lower electrode that converts humidity into a capacitive signal.

That capacitive signal is processed by a custom ASIC that outputs the humidity information into a digital format.  Temperature is also read by the HTU31 and temperature information is available in a digital format or as an analog output.  For temperatures other than 25 degrees celsius, the temperature information can be used to provide a more accurate humidity value.

Here are the components that make up the HTU31 sensor

-The lower gold electrode is designed to be very robust and to protect the sensing element from harsh environments

-The ultra-thin polyimide layer is used to improve the polymer-to-substrate integrity

-The polymer layer has been optimized for maximum sensitivity to humidity

-The thick porous material of the upper electrode is designed to provide a fast time response as well as a fast recovery time from condensation

Here is how it works - 1) air containing water molecules surround the HTU31 sensor

2) That humid air passes into the conductive porous electrode

3) Water molecules in the air permeate the humidity sensing dielectric

4) The dielectric constant changes in proportion to the water concentration

5) That changes the capacitance of the sensing element

6) The ASIC measures the capacitance of the sensing element and then converts that  capacitance reading into digital data

7) The ASIC also measures the temperature of the HTU31 sensing die and outputs that temperature information along with humidity data in either I²C or a analog output voltage

8. Health and comfort impacted by humidity

On the health side, the human body is about 65% water and the prevention of dehydration is critically important. Many human mechanisms exist to maintain the overall fluid balance in the body and health and comfort is significantly impacted by the humidity of the indoor air. Our skin, eyes and respiratory system all need proper humidity for optimal health and functionality. Research shows a link between low humidity and the likelihood of flu transmission. Studies show that higher humidity levels reduce the infectivity of the influenza virus.  Our body defenses are stronger at RH levels >30%, there is less infectious flu virus in the air at higher RH levels and the likelihood of flu infectivity.

9. Applications

There are a range of applications where the HTU31 is well suited including HVACR systems.  These systems require accurate humidity and temperature data in order to provide a comfortable environment for people in homes and workplaces.  The HTU31 is ideal as it provides accurate humidity and temperature data with no need for calibration and provides true plug and play operation as it connects directly to an I²C bus with a simple command set that streamlines programming or an optional analog version is available that supplies a 0.5 to +4.5 volt output.

The HTU31 allows for accurate and reliable control of indoor environments which is important not only from a comfort standpoint but also is important for controlling the spread of bacteria and viruses in the air. Humidity temperature sensors like the HTU31 can also play a pivotal role in a range of healthcare applications like CPAP and other breathing equipment.  Its small size and high accuracy provides accurate and reliable humidity and temperature information in a variety of medical applications.  The HTU31 provides data either in a direct digital format or a 0.5V to 4.5V output and combines a humidity sensing element, along with built-in temperature sensor to provide two sets of environmental data in a range of applications.

Many of the more sophisticated medical breathing systems include the ability to add humidity to the patient’s regulated airstream.  This addition of humidity can make the treatments not only more comfortable but, also more effective.

Another application that is well suited for the HTU31 is for appliances such as refrigerators, humidifiers and dehumidifier.  The tiny footprint of the HTU31 minimizes board real estate and its low power consumption and the ability to utilize sleep mode operation makes it suited for battery powered applications and anywhere, where power usage is important.  Also, its wide operating voltage from 3.0V to 5,5V makes it compatible with most typical appliance control circuits.

Another application that is well suited for HTU31 are printers and copiers. Humidity and temperature are critical parameters in the handling of paper as well as the dispensing of inks and toners and confirming the process is efficient and the results are professional. The high reliability and environmental robustness confirm that the HTU31 is suitable for a wide range of commercial, industrial and consumer printing applications.

Weather stations, both commercial and residential, are another area where the HTU31 can be utilized.  Its wide operating temperature range from -40C to +125 Celsius and high accuracy make it well suited for outdoor and cost critical applications.

Automotive comfort and control systems are another application area where the HTU31 is well suited.  The operating temperature range fits the needs of the automotive industry and its small size allows it to be integrated into tight spaces and respond quickly to changes in temperature. Humidity is important not only for passenger comfort but is critical for the monitoring and control for window and mirror defogging.

10. Summary

TE Connectivity has introduced a new surface mountable humidity and temperature digital output combination sensor, the HTU31, in a 2.5 x 2.5 x 0.9 mm package. These individually calibrated high accuracy sensors are serialized for traceability and provide a typical accuracy of ±2% for relative humidity and ±0.2°C for temperature.  They come in a compact 6-pin DFN package, provide a fast response time and have a typical power consumption of only 3.78μW. The sensors are available in both a digital I²C format with configurable addresses as well as an analog version with a 0.5-4.5V output.

Now that we’ve introduced you to our latest sensor technology today, it’s your turn to design the sensor into the products of tomorrow. Visit TE.com to learn more about this sensor and TE’s broad portfolio of sensor solutions.