SNAA344 October 2020 HDC2080
In the ideal ambient temperature sensing system, a humidity or temperature sensor is enclosed in enough of a surrounding case to protect the sensing element, but still has sufficient airflow and layout space around the sensor to allow accurate temperature and humidity values. In general, the best and most reliable performance from an IC temperature or humidity sensor can be obtained by following correct design guidelines like those in detailed in Temperature sensors: PCB guidelines for surface mount devices, and Optimizing Placement and Routing for Humidity Sensors.
In some cases, due to restrictions on area or desire for condensation or particulate protection, system engineers may be forced to compromise on layout and case design. When working with ambient temperature and humidity sensing systems, suboptimal design primarily results in three conditions that designers will want to correct for:
Each of these can be corrected through a combination of system level characterization and a simple set of mathematical compensation techniques. All three of these manifest as increased system level inaccuracy in the output of the temperature and humidity sensor readings. Analogous to circuit analysis, these effects can be separately considered as steady state error, and transient error.
Section 2 and Section 3 discuss using temperature characterization of a system to correct for steady state inaccuracy in temperature and relative humidity readings. Section 4 discusses how to predict and correct for transient error in the temperature response of a system. This kind of compensation is best in systems where ambient temperature can change continuously, and where slow thermal response can negatively affect other elements of the control loop in the system. This makes thermal response compensation particularly suitable for HVAC systems. Additionally the temperature cycling times in HVAC can be on the order of minutes to hours, improving the tradeoff between processor overhead and compensation benefits.