Choosing a humidity sensor in a negative pressure environment is a professional issue that requires comprehensive consideration of technical parameters and practical application conditions. Negative pressure environment (pressure lower than atmospheric pressure) poses unique challenges for humidity measurement. When selecting sensors, the following points should be prioritized:

　　1. Pressure compatibility

Is the sensor principle affected by pressure? The dielectric constant of sensors based on certain principles, such as capacitive polymers, may vary with pressure, leading to reading drift.

Structural integrity: The sensor package and probe must be able to withstand pressure differentials to prevent deformation, leakage, or rupture. It is necessary to confirm its rated working pressure range (including vacuum degree).

　　2. Compatibility between pollution prevention and purification

Negative pressure environments (such as cleanrooms, biosafety laboratories, semiconductor process chambers) are commonly used to prevent the leakage of pollutants, but there may be chemical gases, particulate matter, or frequent sterilization required (such as high temperature and high pressure, VHP ethylene oxide) inside.

Sensors need to have the ability to resist pollution, chemical corrosion, cleanliness, or withstand sterilization cycles.

　　3. Sampling method - in-situ installation vs bypass sampling:

In situ installation: directly installed on the negative pressure chamber/pipeline wall. Ensure that the installation is sealed and the sensor can adapt to the airflow conditions.

Bypass sampling: Gas is led out to the sensor through a pipeline. Please note that the sampling pipeline may introduce measurement errors due to pressure differences (such as ambient air infiltration), and the compatibility of the sampling pump must be ensured. Maintaining pressure balance between the sampling circuit and the main environment is crucial.

　　4. Accuracy and response time

In dynamic negative pressure systems, fast response time is crucial for process control.

Clearly define the required accuracy (such as ± 1.5% RH) and measurement range (such as 0-100% RH).

　　5. Output signal and integration convenience

Consider compatibility with existing control systems (PLC, SCADA): analog output (4-20mA, 0-10V) or digital output (RS485, I2C, Ethernet).

　　Comparison of recommended humidity sensor technology types: