The 5 characteristics of temperature and humidity sensors are as follows:

1) Accuracy and long-term stability:
The accuracy of temperature and humidity sensors should reach ± 2% to ± 5% RH. Without this level, it is difficult to use them as measuring instruments. It is quite difficult for temperature and humidity sensors to achieve an accuracy of ± 2% to ± 3% RH. Usually, the characteristics given in product information are measured at room temperature and in clean gases. In practical use, due to the influence of dust, oil, and harmful gases, aging and decreased accuracy will occur over time. The accuracy level of temperature and humidity sensors should be judged based on long-term stability. Generally speaking, long-term stability and service life are the top issues affecting the quality of temperature and humidity sensors. Products with annual drift controlled at 1% RH are rare, usually around ± 2% RH or even higher.

2) Temperature coefficient of temperature and humidity sensor:
Humidity sensitive components are not only sensitive to environmental humidity, but also to temperature. Their temperature coefficient is generally in the range of 0.2-0.8% RH/℃, and some humidity sensitive components have different temperature coefficients at different relative humidities. Temperature drift is nonlinear, which requires temperature compensation to be added to the circuit. The use of microcontroller software compensation or humidity sensors without temperature compensation cannot guarantee accuracy over the entire temperature range. The linearization of the temperature drift curve of the humidity sensor directly affects the compensation effect. Nonlinear temperature drift often cannot be compensated for well, and only by using hardware temperature tracking compensation can the true compensation effect be obtained. The temperature range within which temperature and humidity sensors operate is also an important parameter. Most humidity sensitive components are difficult to operate normally above 40 ℃.

3) Power supply for temperature and humidity sensors:
When direct current voltage is applied to humidity sensitive materials such as metal oxide ceramics, polymer materials, and lithium chloride, it can cause performance changes and even failure. Therefore, these temperature and humidity sensors cannot use direct current or alternating current voltage with direct current components. It must be powered by alternating current.

4) Interchangeability:
At present, there is a common problem of poor interchangeability in temperature and humidity sensors. Sensors of the same model cannot be interchanged, which seriously affects their effectiveness and adds difficulties to maintenance and debugging. Some manufacturers have made various efforts in this regard and achieved good results, but the interchangeability is still poor.

5) Humidity correction:
Humidity correction is much more difficult than temperature correction. Temperature calibration often requires a standard thermometer as the standard, while humidity calibration standards are difficult to achieve. Dry wet bulb hygrometers and some common pointer hygrometers cannot be used for calibration, and their accuracy cannot be guaranteed. In general, under suitable humidity conditions, when there is a lack of complete calibration equipment, a simple saturated salt solution calibration method is usually used.