DTH reserve regulator is a unit of DDZ-Ⅲ series of regulating unit which completed with industrial control computer in process of industrial auto-control. It is used to control all kinds of controlled object when series connect with computer. When the computer is working, the control-object accept control signal by reserve regulator. The DDC reserve regulators which in the “reserve” status do not do any regulation but track and measure output signal. When the computer is broken, it will send a fault signal and the DDC reserve regulator will switch to PID regulating status automatically to control the object and to ensure the controlled object to work stably and reliably.