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Abstract

A counting device determines the number of similar articles, or parts, passing a detector. The device is especially useful in packaging small parts into containers, and in insuring that each package contains the correct number of parts. The counter is preferably of the type in which the parts interrupt a beam of light, changing the current through a photoelectric cell. When the current in the photoelectric cell falls below a predetermined threshold level, the device generates a pulse which indicates the presence of a part. The pulses are counted electronically. The device preferably includes a microprocessor which can efficiently control the counting, calibration, and diagnostic operations. The microprocessor stores information relating to the threshold current level, for a given type of part. The value of the threshold can be determined by a separate calibration procedure. The microprocessor is programmed to ignore pulses received for a predetermined time interval following the leading edge of a pulse, so as not to count the same part twice. The invention also includes circuitry for detecting faults in the system, such as an open-circuited or short-circuited photoelectric cell. The device also contains circuits for determining whether the wrong types of parts have been mixed into the batch being counted, and for determining whether more than one part has passed the photoelectric cell. The latter tests are based on a comparison of the observed level of current flowing through the detector with an expected level.

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