Directional people counting arrangement

An arrangement for detecting the passage of living beings through a surveillance region into and out of a controlled-access space, comprising at least three pyroelectric detector devices arranged side-by-side with respect to one another above an entryway to be surveilled such that the surveillance regions of said detector devices transversely span said entryway, each of said detector devices including two detector elements situated in succession in the direction of passage into the controlled-access space and each having an active area directly exposed to thermal radiation from the surveillance region and operative for converting thermal radiation energy received thereby into an electrical signal, said detector elements being coupled in such a manner that said electrical signal has one polarity for one of the detector elements and the opposite polarity for the other detector element;

• means for so optically subdividing said surveillance region of each of said detector devices into two surveillance zones arranged in succession as considered in said direction that thermal radiation energy from a living being passing through the surveillance region reaches initially only one and subsequently only the other of said detector elements when such living being is entering, and initially only said other and subsequently only said one detector element when such living being is leaving, the controlled-access space, with attendant generation of said opposite polarity electrical signals by said detector device in one lead/lag time relationship for a living being entering, and in the opposite lead/lag relationship for a living being leaving, the controlled-access space through said surveillance region;
• means for evaluating said electrical signals of said detector devices to provide an indication of the entry and/or exit of a living being through the respective ones of said surveillance regions from the then existing lead/lag relationship of said opposite polarity electrical signals, including at least three generating means each associated with a different one of said detector devices and operative for generating a first output signal when one of said opposite polarity signals leads the other;
• and further comprising a combination circuit receiving said first signals from all of said generating means and issuing a single output signal when said first signal is present from said generating means associated with the central one but not from either one of said generating means associated with the lateral ones of said detector devices, or from one but not from the other of said generating means associated with said lateral detector devices, and two output signals when said first signal is present from said generating means associated with both of said lateral detector devices.