What's the difference between Fuzzy Logic and Auto-tune on the PUR-99?

Fuzzy logic block
Step changes in reaching the defined setpoint can be mitigated by the use of the fuzzy logic block, which utilises speed control as part of the setpoint change process. Using Fuzzy logic block, the user may dictate how quickly a fuzzy value reaches the target value in the process.

This feature is particularly useful in systems where a rapid change in the setpoint and the control signal could lead to unwanted behaviour or destruction of the product being manufactured. It is also possible to set the minimum difference between the setpoint, and the fuzzy setpoint, beyond which the controller step changes the fuzzy setpoint to the user setpoint. This is defined by the Hysteresis parameter. Both controllers use the same settings of the fuzzy logic block.

PUR-99 Fuzzy Logic explanation, on or off in PID controller

If the user does not know the dynamic parameters of the controlled system, and is unable to select the suitable controller coefficients or simply doesn’t have the time or patience, the controller auto-tuning system included in the device can be used instead.

Thanks to auto-tuning, the controlled system is identified and controller settings are selected using the Ziegler-Nichols method, which involves measuring the set oscillation parameters of the system. The auto-tuning process is divided into three phases, during which no device settings can be changed, and after completion the device automatically switches to operation in the PID mode. The duration of the auto-tuning process depends on the properties of the controlled system.