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SHT-series humidity sensors

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Accurate humidity measurement based on CMOSens® technology.

Sensirion landing

Nowadays, we are surrounded by all kinds of sensors. They can monitor various phenomena and conditions, including humidity. Such sensors are already common in offices, industrial buildings, but are also becoming increasingly popular in homes and cars. In companies associated with the electronics industry, who designate special areas known as cleanrooms, it is a common practice to monitor environmental conditions, so that the parameters of heating or ventilation systems can be adjusted in real time.

In order for environmental monitoring systems to work properly, they must be equipped with the right sensors, made with the highest quality in mind. The effectiveness of the entire system will depend on their accuracy and reliability. When choosing a sensor, it is worth taking interest in the offer of Sensirion, a company which designs components that are capable of measuring humidity and temperature levels.

Sensirion SHT2x series

\The SHT2x series of sensors includes three models: SHT20 (low-cost), SHT21 (standard) and SHT25 (highest performance version). All models are powered by 2.1V to 3.6V and feature a I2C, PWM & SDM communication interface.

It is also worth mentioning that every humidity sensor from the SHT2x series is individually calibrated and tested. A specific batch ID is physically printed on the sensor housing and is also electronically stored in the device memory, so that it can be retrieved at any time. Furthermore, the resolution of the sensor can also be changed from 8/12 bits to 12/14 bits (RH/T) using appropriate commands. The device also allows you to generate a checksum, which even improves its accuracy. The capabilities and features of specific sensor models can be seen in the table below.

SHT20

Temperature and humidity sensor: SHT20

Model SHT20 SHT21 SHT25
Power supply voltage 2.1-3.6V
Temperature measurement range -40 to +125°C (-40 to +257 °F)
Temperature measurement accuracy +/-0.3°C +/-0.3°C +/-0.2°C
Humidity measurement range -100% RH
Humidity measurement accuracy +/-3% +/-2% +/-1.8%
Communication interface I2C, PWM, SDM
Power consumption 3.2 µW (at 8 bits, 1 measurement /s)
RH response time 8 seconds (tau63%)
Dimensions (L,W,H) 3 x 3 x 1.1 (mm)

sensirion_sht2x (1)

sensirion_sht2x

Sensirion SHT3x series

\The SHT3x series, which is the successor to the SHT2x, also comes in three variants: SHT30 (low-cost), SHT31 (standard) and SHT35 (premium). They feature improved performance over the models of the previous series. The SHT3x sensors by Sensirion support the I2C interface and analogue outputs. Additionally, you can change the sensor’s address and set an alarm triggered at a specific temperature and humidity value. Moreover, these sensors can be powered with a wider voltage range – 2.15V to 5.5V. An interesting option is also a membrane filter or a protective cover, which can be found in some specific models in this series. Below are the most important features of the SHT3x-series sensors.

SHT30-ARP-B

Temperature and humidity sensor: SHT30-ARP-B

Model SHT30-ARP-B SHT30-DIS-B SHT30A-DIS SHT31-ARP-B SHT31-DIS-B SHT31-DIS-F STH31-DIS-P SHT31A-DIS SHT35-DIS-B SHT35-DIS-F SHT35A-DIS
Power supply voltage 2.4-5.5V 2.15-5.5V 2.4-5.5V 2.15-5.5V 2.4-5.5V 2.15-5.5V 2.4-5.5V
Temperature measurement range -40 to + 125°C (-40 to + 257°F)
Temperature measurement accuracy +/-0.3 at 0-65°C +/-0.2 at 0-65°C +/-0.3 at 0-65°C +/-0.3 at 0-90°C +/-0.2 at 0-90°C +/- 0.3 at -40-90°C +/-0.1 at 20-60° C +/- 0.2 at -40-90°C
Humidity measurement range -100% RH
Humidity measurement accuracy ± 3 at 10-90% RH ± 2 at 10-90% RH ± 3 at 10-90% RH ± 2 at 0-100% RH ± 1.5 at 0-80% RH ± 1.5 at 0-80% RH ± 1.5 at 0-80% RH
Communication interface Analogue output I2C Analogue output I2C
Power consumption 4.8 µW (at 2.4 V, low repeatability, 1 measurement / s)
RH response time 8 seconds (tau63%)
Dimensions (L.W.H) 2.5 x 2.5 x 0.9 (mm)

 

sensirion_sht3x (1)

sensirion_sht3x

Sensirion SHT4x-series humidity sensors

The SHT4x is already the fourth generation of sensors offered by Sensirion. Currently, the series includes only one SHT40 model, but the manufacturer reveals that we can expect the release of SHT41 and SHT45 sensors already this year. The sensors will offer an accuracy of ∆RH = +/-1.5% RH and ∆T = +/-0.1°C. The sensor is powered by voltage between 1.08V and 3.6V, which makes it ideal for small, battery-powered mobile devices. Here, too, the communication interface is based on the I2C standard. The sensor is housed in a DFN housing, which makes it possible to integrate the device into demanding designs and at the same time meet the highest reliability requirements, as demonstrated by JEDEC and JESD47 standards. In addition, as announced by the manufacturer, the device is expected to achieve IP67 protection class in the future thanks to an additional filter membrane. Parameters and features of the SHT40 model, the first of the SHT4x series, are listed in the table below.

 

SHT40

Temperature and humidity sensor: SHT40

Model SHT40
Power supply voltage 1.08-3.6V
Temperature measurement range -40 to + 125°C (-40 to + 257°F)
Temperature measurement accuracy ± 0.2°C
Humidity measurement range -100% RH
Humidity measurement accuracy +/-1.8% RH
Communication interface I2C
Power consumption 0.4 µA (at 1 Hz measurement frequency)
RH response time 6 seconds (tau63%)
Dimensions (L,W,H) 1.5 x 1.5 x 0.5 (mm)

sensirion_sht40 (1)

sensirion_sht40

How it works: CMOSens® technology

All Sensirion humidity sensors are based on CMOSens® technology. It involves the capacitive method of measuring humidity, which is one of the standards in the industry. According to its principle, the sensor is a kind of capacitor in which the dielectric material is made of a polymer that can absorb or release water in proportion to the relative humidity of the environment. Thanks to this process, the capacitance of the capacitor changes, and this change can already be electrically measured and, on this basis, the humidity level can be determined accurately.

However, the construction of sensors based on CMOSens® technology is somewhat more complex. The capacitor described in the previous example is in this case a system of electrodes, which – together with a polymer layer – form a capacitance that can be read and converted into an electrical signal. In addition, the module that is responsible for measuring temperature is placed right next to the RH module. Thanks to this, there is no possibility of measurement error resulting from the distance between the sensors. Each sensor is also equipped with a digital communication interface, thanks to which it can be easily operated and you can incorporate it into any system based on a microprocessor chip.

sensirion_technology_cmos

CMOSens

It is also worth mentioning that CMOSens® are not only humidity and temperature sensors. This technology is also employed in modules detecting the presence and flow of gases and liquids.

Text prepared by Transfer Multisort Elektronik Sp. z o.o.

The original source of text:tme.eu

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