Solutions for Muffle Furnace Temperature Controller Overshooting Problem

Overheating is a common phenomenon / problem, which is offen happened on the temperature controller used on lab furnaces such as muffle furnace, tube furnaces etc at low temperatures especially temperature bellow 300°C).

OVERHEATING CHART
Overshooting/ overheating during the temperature rising

What is Overshooting or Overheating?

Overheating phenomenon refers to the temperature in the furnace chamber still rises after reaching the target value due to the residual temperature of the heating element; this is because the conduction of temperature relies on heat radiation, which causes the temperature received by the temperature sensor to have a certain hysteresis. This is a very critical point. While the temperature reached the set value, the sensor has not received the actual information and is still heating. Once received it, the heating system will stop working, but it may have exceeded. Because the surface temperature of the heating element is high, its heat radiation is continuing.

The following two steps can effectively relieve overshooting / overheating

1. Auto-tuning of PID parameters of the temperature controller

What is auto-tuning (AT)? The various artificial intelligence digital display regulators currently produced and sold generally have PID parameter auto-tuning functions. When using the auto-tuning function of the instrument for the first time, the instrument must be switched to display AT characters so that the instrument can determine the optimal P, I, D adjustment parameters of the system through auto-tuning, and realize ideal adjustment control. Before turning on the auto-tuning function, you should first set the SV value (set value) of the instrument to the value to be controlled, because the parameter values ​​tuned by the system under different set values ​​are not exactly the same. After starting the auto-tuning, the instrument will force the system to generate Disturbance, the auto-tuning state ends after 2~3 oscillation cycles. The instrument calculates the best adjustment parameters of the instrument by detecting the transition characteristics of the system from overshooting to the steady state (the measured value is consistent with the set value), and analyzing the period, amplitude and waveform of the oscillation. The most ideal adjustment effect is that the set value should be consistent with the measured value. The system adjustment quality can be evaluated from two aspects: dynamic (set value change or disturbance) and steady state (set value fixed). Tuning can meet most system requirements. Different systems have different auto-tuning time due to different inertia, ranging from a few minutes to a few hours.

2. Adjust the input power, the default power is 100, you can try a value of 40~100.

The above operation can effectively alleviate the flushing phenomenon, but it cannot completely solve it. After all, as mentioned above, the flushing phenomenon is normal, especially at low temperatures.

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