Duplex ionization-type fire sensor

Claim 1

Ionization-type fire sensor to supervise a predetermined space for the presence of fire or smoke therein comprising means forming a first, bipolar ionization chamber (B) which changes its electrical resistance upon change of concentration of smoke or fire aerosols in the atmosphere in said space, having a first pair of spaced electrodes and bipolar ion generating means in said chamber to ionize the atmosphere in said space which penetrates said chamber, said bipolar ion generating means being positioned with respect to said first electrode pair to result in ions of both positive and negative polarity in essentially the entire space between said first pair of electrodes to provide an ion current flow between the electrodes of the pair generated essentially by ions of both said polarities upon application of a potential between said first pair of electrodes said means defining the chamber forming a baffle means (15, 25) to prevent direct flow of stream of atmosphere in said space through said chamber and to slow or brake such flow there across; means forming a second unipolar ion chamber (U) changing its electrical resistance upon change of concentration of smoke or first aerosols in the atmosphere in said space having a second pair of spaced electrodes and unipolar ion generating means in said chamber to ionize atmosphere in said space penetrating said chamber, said unipolar ion generating means being positioned with respect to said second spaced pair of electrodes to result in ions of only one polarity in at least a portion of the space between said second pair of electrodes to provide for ion current flow between the electrodes of said second pair of electrodes essentially generated by ions of a single polarity upon application of a potential between said second pair of electrodes, said means defining said second, unipolar chamber being formed with apertures (16, 26) to permit direct flow or stream of atmosphere into and through the space defined by said chamber; a reference ionization chamber means (R) having two separate inputs, each input being connected to a respective ionization chamber (U, B); a common support (11, 21) for said first, bipolar ionization chamber (B), said second, unipolar ionization chamber (U) and said reference ionization chamber means (R); and a utilization sensing and threshold circuit means comprising two threshold circuits, each threshold circuit being connected to a respective junction between the respective ionization chamber and the respective reference ionization chamber, the threshold circuits sensing change in resistance of either, or both said chambers and providing an output signal when the resistance of at least one of said chambers rises above a predetermined threshhold level.