On-off control with one setpoint turns on and off the key output unit depending on Tset temperture setpoint andТ hysteresis (dead zone). There are two methods of On-Off control: with direct and reverse hysteresis.
If it is on-off control with direct hysteresis, an output device is switched on when Тmeas<Тset-T, and switched off when Тmeas>Тset+T. If it is on-off control with reverse hysteresis, an output device is switched on when Тmeas>Тset+T , and switched off when Тmeas>Тset-T. Typical applications are simple fast-response heating and cooling systems.
On-off control with two setpoints. An output device is switched on when Тmeas>Тset1 , and switched off when Тmeas>Тset2.
Three-position control might be used with both one key output and two key outputs.
Three-position control per one output operates as follows. The user sets three levels of output power of the only output device: "max heating" (for example, 100%), "nominal heating" (for example, 50%) and "minimum heating" (for example, 10%). The following parameters are entered: two set-points, PWM period in sec and hysteresis T. In this case, when Тmeas<Тset1, the device output generates maximum power of 100%, i.e. it is constantly switched on. When Тset1+T<Тmeas<Тset2-T, the device output generates nominal output power of 50%, i.e. PWM is swithed on half of the period, and half of the period it is switched off. When Тmeas>Тset2, device output generates minimum output power of 10%.
Three-position control per two outputs operates as follows. The first output device is a “heater”, the second is a "cooler". They are controlled according to the setpoint Tset and hysteresisТ. Three-posistion controller turns on the first output device when Тmeas<Тset-T and turns it off when Тmeas=Тset, then it turns on the second output device when Тmeas>Тset+ T and turns it off when Тmeas=Тset. Typical applications are high-speed temperature control systems.
Multi-zone control allows to change a temperature setpoint depending on time and event in a zone mode. Each output channel may contain up to 16 programs with 24 zones each. The following parameters can be set in each zone: setpoint temperature, acceleration time, retention time, control law. For each program user sets: number of program, number of zones, start time, hysteresis and control period. If the program contains PID control, it's necessary to start self-tuning PID control for all temperature setpoints. All program and device settings are stored in a nonvolatile memory.
Typical application of multi zone control is temperature processes ocurring in time.
See also "P, PI and PID Control.