The Principle of Balancing the Temperature inside the Test Chamber by the Air Valve
Sep 22, 2025
Its core principle is a closed-loop negative feedback system of "heating - measurement - control". In simple terms, it is to precisely control the power of the heating elements inside the box to counteract the heat dissipation caused by the external environment, thereby maintaining a constant test temperature that is higher than the ambient temperature. The process by which the air valve stabilizes the temperature is a dynamic and continuously adjusting closed loop:
First, set a target temperature. The temperature sensor measures the actual temperature inside the box in real time and transmits the signal to the PID controller.
When the PID controller calculates the error value, it calculates the heating power that needs to be adjusted based on the error value through the PID algorithm. The algorithm will take into account three factors
P (proportion) : How large is the current error? The greater the error, the greater the adjustment range of the heating power.
I (integral) : The accumulation of errors over a certain period of time. It is used to eliminate static errors (for example, if there is always a slight deviation, the integration term will gradually increase the power to completely eliminate it).
D (differential) : The rate of change of the current error. If the temperature is rapidly approaching the target, it will reduce the heating power in advance to prevent "overshoot".
3. The PID controller sends the calculated signal to the power controller of the heating element (such as a solid-state relay SSR), precisely regulating the voltage or current applied to the heating wire, thereby controlling its heat generation.
4. The circulating fan works continuously to ensure that the heat generated by heating is distributed rapidly and evenly. At the same time, it also quickly feeds back the signal changes of the temperature sensor to the controller, making the system response more timely.
The air valve balancer measures air volume, while the density of air varies with temperature. Under the same differential pressure value, the mass flow rate or volume flow rate corresponding to air of different densities is different. Therefore, the temperature must be stabilized at a known fixed value so that the microprocessor inside the instrument can accurately calculate the air volume value under standard conditions based on the measured differential pressure value using the preset formula. If the temperature is unstable, the measurement results will be unreliable.
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