Self-regulating rod glow plugs

Self-regulating rod glow plugs (also called SRM = "Self Regulating Metal") have a heating coil and a control coil. They reach 900 °C in 4 seconds and have a long service life.
Self-regulating rod glow plugs from NGK

Self-regulating rod glow plugs (also called "SRM rod glow plug" for "Self Regulating Metal") are especially well suited for engine designs which require after-glowing.

There is a heating coil and a control coil inside a self-regulating rod glow plug. Its heating coil heats up very quickly. The control coil increases the resistance as the temperature increases and thereby minimises the current flow to the heating coil.

Such glow plugs reach 900 °C in only 4 seconds. As a result, the control coil, which is made of special material, enables a long service life for the SRM models.