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temperature control Setting PID (three mode) controller
Jan 24, 2020

Setting the temperature controller involves setting the proportional, integral and differential values to obtain the best possible control for a particular process. If the controller does not include an automatic setting algorithm, or the automatic setting algorithm does not provide sufficient control for a specific application, then the device must be adjusted by trial and error method.

The following is the standard setting procedure for the temperature controller. Other setting steps can also be used, but similar trial and error methods are used. Note that if the controller uses a mechanical relay instead of a solid-state relay, a longer cycle time (20 seconds) should be used at the beginning.

The following definitions may be required:

Cycle time - also known as the duty cycle, is the total length of time that the controller takes to complete an on-off cycle. Example: for a cycle time of 20 seconds, the 10 second on time and 10 second off time represent 50% of the power output. When in the proportional band, the controller will cycle on and off.

Proportional band - the temperature range in% or degrees of full scale in which the proportional action of the controller occurs. The wider the scale band, the larger the area around the set value in which the scaling takes place. Sometimes it is also expressed as gain, which is the reciprocal of the proportional band.

Integration, also known as reset, is a function of adjusting the proportional bandwidth according to the set value to compensate for the offset (fixed deviation) from the set value, that is, it adjusts the control temperature to the set value after the system is stable.

Differential, also known as rate, senses the rate at which the system temperature rises or falls, and automatically adjusts the proportional band to minimize undershoot or overshoot.

If the PID (three mode) controller is properly set and used, it has excellent control stability. By following these instructions carefully, the operator can achieve the fastest response time and the smallest overshoot. Tuning the information of this three mode controller may be different from other controller tuning steps. For the main output, the self-tuning function is usually used to eliminate the need of using this manual setting step. However, the self-tuning value can be adjusted when necessary