Ionic current measuring glow plug and process and circuit for its activation

Ionic current measuring glow plug comprising:

• a plug housing electrically grounded to an engine block;
• a glow tube located in said plug housing;
• a heating element which is located in said glow tube and is electrically insulated relative thereto;
• and
• a control element located in a terminal-end area of the plug between the glow plug body and a series circuit comprised of the glow tube and the heating element for making and breaking an electrical connection between the series circuit and the engine block,
• wherein said control element is a semiconductor switch with a voltage evaluation circuit, the switch being adapted to break said electrical connection by being tripped by the voltage evaluation circuit only when a glow plug voltage UGK>0 V, and
• wherein the glow plug is adapted to operate with a vehicle electrical system voltage UB for producing glowing of the plug and an auxiliary voltage UH for producing measurement of ionic current applied with reverse polarity in accordance with one of the relationships:
• UB>0 V/UH<0 V
• and
• UB<0 V/UH>0 V.