Overshoot and undershoot caused since process temperature cycles below and above set point.

Since continuous power is fed to heaters to maintain temperature at constant level it will extend the heater life by avoiding thermal shock. This feature improves heater life.

Due to high-low cycling there is consistent stress on heaters

No moving parts are involved therefore no wearing out and maintenance problem.

Due to frequent switching, necessity of frequent contactor maintenance.

Isolation provided between power and control.

No isolation provision.