What a combined temperature and humidity sensor measures
A combined temperature and humidity sensor measures air temperature and relative humidity at a defined point. Combining both measurements in one assembly can simplify integration, but it does not by itself guarantee representative readings or a particular accuracy. Probe placement, thermal gradients, airflow, the enclosure, sensor construction and the host controller all affect the result. Define the complete measurement requirement before selecting a sensor.
Account for the relationship between temperature and relative humidity
Relative humidity depends on both water vapor in the air and temperature. If the sensing element and the measured air are at different temperatures, the reported relative humidity may not represent the process conditions. Place the temperature and humidity sensing elements in the same representative environment, avoid unwanted heat transfer through a wall, mounting fitting or cable, and confirm the installation against the sensor manufacturer’s guidance. For guidance on humidity probe placement and temperature differences, see the Vaisala HMM170 mounting instructions.
Specify the installation environment
Document the measurement location, normal and excursion conditions, air movement, enclosure, exposure to dust or chemicals, cleaning method, moisture and possible condensation. A sensor exposed to condensation or direct wetting may require a specifically qualified construction and recovery procedure. Do not infer washdown protection, chemical resistance, operating limits or recovery time from the words “temperature and humidity sensor”; verify the exact product documentation. Keep the probe away from local heat sources and stagnant pockets unless those conditions are the measurement target.
Match the electrical interface and controller
Before release, identify the required output or communication interface, supply, wiring, cable length, connector and controller input. Confirm scaling, units, sampling or update needs, fault behavior, mounting constraints and how readings will be checked during commissioning. If the system will calculate dew point or drive a control action, define that function in the controller requirements and verify it at the system level; do not assume it is provided by the sensing element.
OEM selection and RFQ checklist
- Application, measurement point, target air conditions and required system-level performance.
- Probe placement, dimensions, mounting, airflow and thermal-gradient considerations.
- Condensation, dust, chemical exposure, cleaning and other environmental conditions.
- Output/interface, supply, wiring, connector, controller input and any enclosure needs.
- Required inspection, calibration evidence, sample validation, quantities and documentation.
For more selection considerations, read our humidity sensor guide and review the temperature and humidity sensor range. You can request an OEM review with an installation sketch and controller details. Confirm final suitability with the specific sensor documentation and a representative system validation.
Technical reference
See Vaisala’s probe mounting guide and Sensirion’s temperature and humidity sensor design guide for product-specific design-in considerations.
