Definition
A laboratory thermohygrometer is an instrument used to measure and display air temperature and relative humidity in an experimental environment. Its core function is to provide stable and traceable temperature and humidity data to ensure that experimental conditions meet the requirements of specific standards or operating specifications. These instruments typically integrate sensor components, signal processing circuits, and digital or analog display units, making them suitable for use in various controlled environments such as clean rooms, constant temperature and humidity rooms, and material testing rooms.
How it works:
The thermohygrometer is measured based on two separate but working together sensor systems. Resistive temperature detectors or thermocouples are often used for temperature measurement. For example, the resistance value of platinum resistors changes in one direction with the rise of temperature, and is converted into a voltage signal through the Wheatstone bridge circuit, and then the temperature value is obtained through analog-to-digital conversion. Relative humidity measurement mostly relies on capacitive or resistive polymer thin-film sensors. These sensors take advantage of the change in dielectric constant or conductivity of sensitive materials after adsorbing water molecules. When the air humidity changes, the sensor capacitance value changes accordingly, which is converted into a frequency signal through an oscillation circuit and finally converted to a relative humidity percentage. The typical relationship is:
Relative humidity RH is equal to the current partial pressure of water vapor divided by the saturated water vapor pressure at the same temperature and multiplied by one hundred percent.
Measurement method
Laboratory thermohygrometers mainly use two methods: static measurement and dynamic monitoring. Static measurement is suitable for single or timed readings of fixed points, and the instrument is placed in the center of the environment to be measured, avoiding heat sources, cold sources or vents, and recording after the reading is stable. Dynamic monitoring is continuously sampled at set intervals through data loggers or networked sensor arrays, which is suitable for long-term experiments that need to track temperature and humidity fluctuations. For high-precision scenarios, on-site comparison and calibration is often carried out with humidity generators or standard wet and dry bulb methods. Multichannel instruments can also measure multiple regions simultaneously for environmental uniformity assessment.
Influencing factors
Measurement accuracy is constrained by several factors. In terms of temperature, the sensor's self-heating effect can cause high readings, so it is necessary to ensure that the probe and the DUT achieve thermal equilibrium. In terms of humidity, sensors are sensitive to condensate, oil mist, or corrosive gases, and exposure to such environments can cause response shifts or failure. The airflow velocity also affects humidity measurement, and high flow velocity accelerates the evaporation of moisture on the sensor surface, resulting in a low-humidity phenomenon. In addition, electromagnetic interference can introduce signal noise, and long-term uncalibrated instruments can drift due to aging components. Improper placement, such as near doors, windows, or lighting fixtures, can also lead to non-representative data.
Application scenarios
Laboratory thermohygrometers are widely used in chemical analysis, material testing, reliability verification of electronic components, food storage stability assessment, building energy conservation research and other fields. In chemistry laboratories, precise temperature and humidity conditions are essential for reagent weighing, reaction rate control, and spectroscopy. Materials laboratories need to use a constant temperature and humidity environment to determine the dimensional stability or mechanical properties of samples. For precision instruments such as balances or interferometers, temperature and humidity fluctuations can directly interfere with measurement repeatability and require real-time monitoring. In addition, plant growth boxes, culture chambers and cultural relics repositories also rely on such instruments to maintain set parameters.
Key points of selection
When selecting a temperature and humidity meter, it is necessary to focus on the measurement range, accuracy, response time, long-term stability and environmental adaptability. For conventional laboratories, the temperature range should cover minus 10 degrees Celsius to 50 degrees Celsius, the humidity range should cover 10% to 95% relative humidity, and the accuracy level should be at least plus or minus 0.3 degrees Celsius and plus or minus 2% relative humidity. The response time should match the dynamic requirements of the experiment, the slow response is suitable for the steady-state chamber, and the fast response is suitable for a well-ventilated open environment. During the selection of the recording function, it is necessary to evaluate the built-in memory capacity, data export method and battery life. In terms of protection level, if there is condensation or dusty conditions, choose a model with an enclosure sealing level of IP65 or above. Finally, it is recommended to pay attention to the traceability of the calibration certificate to ensure that the data can be traced back to national or international standards.