PURPOSE:To allow screening with high accuracy by receiving the signal from an electronic balance, subtracting the tare weight value stored in a tare weight value memory circuit from this signal to calculate the net weight value and deciding the corresponding class of the material to be screened from the net weight value. CONSTITUTION:An arithmetic unit 12 calculates the net weight value by subtracting the tare weight value stored in an empty bucket weight value memory circuit 17 from the pulse signal which is sent from the electronic balance 5 via an amplifier 11 and corresponds to the total weight of a bucket 3 and the material 6 to be screened on the bucket 3 by an arithmetic decision circuit 15. The arithmetic unit compares the calculated weight value with the screening segment weight value set in a screening segment weight value setting circuit 14 and decides the corresponding class of the material 6 to be screened. The class signal is sent to a shift circuit 15 which transmits a discharge command signal 21 to a discharge device 8 corresponding to the position of this class to operate the discharge device, by which the material 6 to be screened is classified by classes.
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