Ionization detector

This patent concerns an ionization detector specially designed for use in fire-detection systems. It comprises structures limiting a first chamber containing a first electrode, and a second chamber into which gases can be introduced from the surroundings, and which contains a second electrode. The chambers are separated from each other by a common electrode, in addition to which at least the second chamber contains a radioactive β-source for establishing an ionization current between the electrodes, the common electrode being connected to an alarm-activated circuit that reacts to changes in the ionization current. The first electrode in the first chamber limits a third chamber, and it is at least partly open to achieve an ionization track between the first and the third chamber. This detector, which comprises a variable electrode that reaches at least partly into the chamber structure to regulate the ionization current, is characterized by the fact that the first electrode has an aperture, through which the variable electrode can be introduced into the third chamber. (author)