To allow the device to be used regardless of three types of auxiliary machines and to secure sufficient operational safety in all cases, by comparing a first voltage with first and second individual projection thresholds and a drop-out threshold when the first voltage reaches one of the projection thresholds.
A control circuit 14 is provided with a microprocessor for comparing holding phases of signals supplied to input terminals E1-E3 with a set value in a projection phase. The control circuit 14 uses two individual projection thresholds and a drop-out threshold. The microprocessor of the control circuit 14 instructs a changeover to the projection phase of a preset period just after a first voltage U2 reaches one of the projection thresholds. In this case, the first voltage U2 is compared with the first and second individual projection thresholds and the drop-out threshold. The first projection threshold represents voltage of about 40%-50% of a rated power supply voltage of an electromagnet, and the second projection threshold represents 70%-85% of this voltage.
CHELLOUG MUSTAPHA
NEREAU JEAN-PIERRE
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