The digital relative humidity sensor integrated circuit is precise, robust and so is the temperature

What you will learn:

  • Features of the new family of TI relative humidity sensors.
  • The dual capacity of the RH sensor to measure temperature.
  • Applications for the HDC302x family.

Temperature is the most widely measured environmental parameter, which is nothing new. But relative humidity (RH) is also an important parameter in the measurement scenario, often in conjunction with temperature.

The dilemma is that while it is possible, if necessary, to protect a temperature sensor from harsh environmental conditions while taking a measurement (after all, you are actually measuring thermal energy), in most cases a HR sensor must be “submerged, and therefore subject to its environment. The result is that HR sensors will face harsh conditions which often affect their reliability and long term performance. (Non-contact detection of RH can be performed indirectly using infrared devices or lasers – see The references below for two examples, but these solutions are complicated, bulky, expensive, and obviously impractical for many applications.)

Meeting the challenge of RH detection, Texas Instruments’ HDC302x offers high-precision, digitized humidity and temperature detection, low power consumption, as well as ultra-low drift. The company maintains that this device offers the highest reliability and accuracy in the industry and the lowest power consumption, as well as built-in protection of the sensing elements. (Fig. 1).

% {[ data-embed-type=”image” data-embed-id=”60f867c2af367119258b45a3″ data-embed-element=”span” data-embed-size=”640w” data-embed-alt=”1. The HDC302x family of humidity and temperature sensors includes the sensor itself, digitization, calibration, and an I2C interface, along with other functions and features.” data-embed-src=”https://img.electronicdesign.com/files/base/ebm/electronicdesign/image/2021/07/ED_humidity_sensor_NP_Fig1_web.60f867c25a39d.png?auto=format&fit=max&w=1440″ data-embed-caption=”1. The HDC302x family of humidity and temperature sensors includes the sensor itself, digitization, calibration, and an I2C interface, along with other functions and features.” ]}%

The design guarantees and preserves data integrity under stressful conditions. It is the first in the industry to provide integrated correction to accommodate drift caused by natural aging, environmental stress or interactions with ambient contaminants.

Applications include consumer appliances (washers, dryers, refrigerators, freezers), cold chain monitoring, HVAC and environmental control systems, humidifiers / dehumidifiers, and continuous positive pressure ventilation systems ( CPAP) and ventilation. In automotive designs, humidity readings are needed for cabin HVAC, cabin air quality, and even particle detection, as well as for battery management systems (BMS) and management of the on-board charger.

The sensor has a 0% to 100% RH operating range with a typical accuracy of ±1.5% and incorporates drift correction (a common occurrence with relative humidity sensors) to reduce offset and return the unit to its original accuracy specification. Long-term drift is only 0.21% RH / year, and the device includes protection against condensation (another common “disease” of RH sensors) via a built-in heater.

It is common and often necessary to also measure temperature as well as relative humidity. The series provides temperature readings over an operating range of 40 to +125°C with ±0.1°C typical accuracy. Temperature and humidity sensors are 100% tested and adjusted to a production setup traceable and verified by NIST with equipment calibrated to ISO / IEC 17025 standards.

The RH / temperature sensor uses an I2C interface operating up to 1 MHz with four selectable I’s2C addresses, plus command / data protection using CRC checksum. Average current requirements of this sensor, which operates from a supply of 1.62 to 5, – V and comes in a compact form of 2.5- × 2.5mm package, is a simple 0.7 µA.

An automatic measurement mode detects humidity at regular intervals to capture data while the rest of the system is on standby, thus preserving system battery life in applications such as data loggers in the system. cold chain ; wirelessly connected environmental sensors such as air quality monitors, smart homes or wireless sensor nodes in buildings; or IP network cameras. Additionally, an ALERT output provides hardware notification of ambient temperature and relative humidity measurements that violate any of four user-defined thresholds, with four programmable thresholds for temperature and relative humidity. (Fig. 2).

% {[ data-embed-type=”image” data-embed-id=”60f867db323355360e8b4682″ data-embed-element=”span” data-embed-size=”640w” data-embed-alt=”2. Users can program multiple humidity/temperature alarm thresholds into the HDC302x devices, reducing processor and I/O loading.” data-embed-src=”https://img.electronicdesign.com/files/base/ebm/electronicdesign/image/2021/07/ED_humidity_sensor_NP_Fig2_web.60f867dac9fdf.png?auto=format&fit=max&w=1440″ data-embed-caption=”2. Users can program multiple humidity/temperature alarm thresholds into the HDC302x devices, reducing processor and I/O loading.” ]}%

The HDC3020 is offered in an open cavity packaging without a protective cover. Two other device versions come with a cover option to protect the open cavity RH sensor: the HDC3021 with a removable protective tape to allow conformal coatings and PCB washing, and the HDC3022 with a membrane filter cover Permanent IP67 to protect against dust and water.

Covers provide dust and moisture protection for devices during assembly and system life and help maintain accuracy when the sensor is exposed to contaminants (a common and often unavoidable situation). There is also the HDC3020-Q1 car homologated version with its own technical sheet.

Pricing for the 8-pin WSON device starts at $ 1.65 (1,000 units). In addition to details 51 page datasheet for non-auto versions and additional ones 46 page datasheet for the self-qualified version, TI offers useful application support materials: “Why Consistent Long-Term Performance Is Important For Relative Humidity Sensors, “How the HDC3020 humidity sensor achieves the industry’s lowest drift, “and”User Guide: HDC3 Silicon”, Which provides storage and handling guidelines, software configuration examples, and pseudo-code.

The references

Bulk-Blog (Bulk solids handling), “Online humidity measurement: non-contact NIR humidity sensors in powdered and bulk solids.

In search of solutions, “Non-contact infrared ambient temperature and relative humidity sensors. “

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