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Figure 1-1 shows two standard humidity sensor components whose sensing elements are exposed on the top (HDC2080) and on the bottom (HDC2010). These sensors have integrated ADCs and are designed to accurately and reliably measure and output the percentage relative humidity (%RH) and temperature data on an I2C-bus.
The capacitive sensing element is composed of a moisture-sensitive polymer as a dielectric and comb metal structure as the capacitance’s electrodes. A change in humidity correlates with the capacitance change with the entire sensing element structure is integrated on a top layer of a standard CMOS technology process. The capacitance value is converted to analog output voltage that is fed to the ADC and the proprietary linearization engine, and as a result, the percent RH value is computed and output is consistent, predictable, and accurate.
The sensor dielectric’s polymer is generally dust resistant and excellent for any normal environmental sensing application imaginable. As always with an exposed cavity, care must be taken during the assembly process because the polymer can be damaged by chemical or assembly cleaning and the scrubbing process.
Humidity sensors require additional storage and handling guidelines that must be followed. More information is available in our HDC20xx Silicon User's Guide.
A removable protective cover is a thin polyimide tape that covers over the entire surface of the humidity sensing component. It is a shield for temporary protection of the sensing element from contaminants, and should be removed before being used. This cover can protect against pollution during the PCB cleaning and scrubbing process, hence allowing this component to go through a normal PCB wash process without damaging the sensor.
This protective cover also protects the sensor during a conformal coating or potting for such application as a humidity module where other components and PCB solder joints need to be shielded from long term harsh environmental exposure. The protective cover is robust and designed to withstand multiple reflow soldering cycles. It comes with an adhesive-free tab that is easily peeled off at the end of the assembly process, by either using tweezers or another piece of polyimide tape. Figure 1-4 depicts a humidity sensor with a removable protective cover, the HDC2021, which is pin- and software- compatible with the HDC2080.
A permanent cover is made of hydrophobic microporous PTFE membrane to protect against water and dust according to IP67 specification, and is designed to stay on the package over the product lifetime. This protective cover has a filtration of up to 99.99% efficiency filtering particle sizes down to 100nm. In addition to being water and dust proof per IP67, this PTFE material has extremely high-durability and low-friction to repel water, condensation droplets and debris, while maintaining sensor response time, making it most suitable for outdoor use and rugged environment applications. Figure 1-5 depicts a humidity sensor with a permanent protective cover, the HDC2022, which is pin- and software- compatible with HDC2080 and HDC2021.
Most applications can use non-protective cover humidity sensors because of its robust polymer sensing element. Also, all these sensors are based on the same core and inherently offer some of the lowest power consumption with high and consistent accuracy in the market. If an assembly line cannot provide special flow for standard humidity sensors or a sealed humidity sensing module is desired, then a removable protective cover humidity sensor, like the HDC2021 would be an excellent option. For outdoor use or harsh environment usage, where condensation is likely to occur or volatile organic compounds (VOCs) may be present, the HDC2022 would be the best choice.
Humidity sensors require additional storage and handling guidelines that must be followed. More information is available in our HDC20xx Silicon User's Guide.