Linear constant temperature and humidity test chamberIt is a core equipment in the field of environmental reliability testing, used to simulate the long-term performance of products under specific temperature (such as -70 ℃~150 ℃) and humidity (such as 10% RH~98% RH) conditions. Its high-precision control capability (temperature fluctuation ± 0.1 ℃, humidity fluctuation ± 1% RH) directly determines the reliability of test data. The core of achieving this accuracy lies in the closed-loop system collaboration of "precise perception intelligent regulation stable execution". The principle is analyzed from four key modules as follows:
1、 Temperature control:
The core of temperature accuracy is the precise matching of heating and cooling systems. The test chamber collects real-time temperature data through high-precision temperature sensors (such as platinum resistance PT100, accuracy ± 0.05 ℃), and the controller (PLC or industrial computer) compares the real-time value with the set value. The PID (proportional integral derivative) algorithm is used to dynamically adjust the output power of the heater (such as nickel chromium alloy electric heating tube) and the refrigeration unit (such as compressor+condenser).
Heating module: adopts graded control (multiple sets of heating tubes start and stop independently) to avoid temperature overshoot caused by excessive power of a single heater; When the temperature is lower than the set value, the PID algorithm increases the heating power (proportional term) proportionally according to the deviation value, and accumulates the historical deviation correction integral term (to avoid long-term small deviation accumulation), and adjusts the temperature change trend in advance through the differential term prediction.
• Refrigeration module: Adjust the cooling capacity through a variable frequency compressor (traditional fixed frequency compressors can only be fully turned on/off, while variable frequency technology can achieve 0%~100% stepless adjustment), and use an electronic expansion valve to accurately control the refrigerant flow rate (flow deviation ≤ 0.1L/min), quickly reducing the temperature inside the box and avoiding overcooling.
2、 Humidity control:
The difficulty of humidity accuracy lies in the precise generation and removal of water vapor. When humidification is required, the test chamber converts pure distilled water into steam and injects it into the chamber through an electrode humidifier (heating water to boiling to produce steam) or an ultrasonic humidifier (high-frequency vibration atomization of water molecules); The humidification amount is dynamically adjusted by the PID algorithm based on the deviation between the real-time humidity (detected by a capacitive humidity sensor with an accuracy of ± 1% RH) and the set value - increasing the steam flow rate when the deviation is large and decreasing the flow rate when it approaches the set value to avoid supersaturation.
Dehumidification is achieved through a refrigeration system: when the humidity is higher than the set value, the air inside the box flows through a low-temperature evaporator (with a temperature lower than the dew point temperature), and the water vapor condenses into water droplets and is discharged through a drainage pipe. At the same time, the PID algorithm controls the compressor power to avoid temperature fluctuations caused by excessive dehumidification (such as synchronously adjusting the heating power to compensate for temperature losses during dehumidification).
3、 Air circulation:
The uniformity of temperature and humidity depends on forced convection systems. Install a centrifugal fan at the top or bottom of the test chamber to draw air into the air duct. After being treated by heating/cooling/humidification/dehumidification modules, the air is evenly sent back to the inside of the chamber through a porous uniform flow plate. The wind speed (usually 0.5-1.5m/s) and direction have been optimized through design (such as avoiding direct blowing of sensors or samples) to ensure that the temperature difference between any two points inside the box is ≤ 0.3 ℃ and the humidity difference is ≤ 2% RH (standard requirements).
4、 Sensors and feedback: the 'nerve endings' for precise perception
High precision control relies on a multi redundant sensor network: temperature detection uses dual PT100 sensors (real-time comparison between primary and secondary sensors, triggering an alarm when deviation>0.2 ℃), and humidity detection uses capacitive polymer film sensors (response time<10 seconds, anti condensation interference). The sensor data is uploaded to the controller every second, and instantaneous interference is eliminated through digital filtering algorithms (such as sliding average filtering) to ensure the authenticity of the feedback signal.
Linear constant temperature and humidity test chamberThrough closed-loop control of "precise perception intelligent algorithm dynamic execution uniform delivery", millimeter level accuracy of temperature and humidity has been achieved, providing a "standard environment" for reliability verification in fields such as electronic components, aerospace materials, and biomedicine.