Electronic frequency monitoring of linear and rotary movements - using two retriggerable monostable multivibrators for machine or plant

The multivibrators (1.4), for the prodn. of different holding times, are operated by supply voltages (U1,U2,(9,8)) of different levels. The multivibrator (1) reached first by the square wave voltage is operated at a lower supply voltage (U1,9) than the second multivibrator (4). Both multivibrators (1,4) are wired with similar RC elements. The supply voltage for prodn,. of a hysteresis at the moment of the changeover of the charging current for the time determining capacitors (3,6), is lowered at increasing frequency and increased at reducing frequency. One of the multivibrators is logically connected to an AND-gate. The output of the multivibrator (4) as well as the output of the AND-gate (7) are connected to constant current sources (2,5) for attaining a lower current from the change-over point upon increasing frequency, or a higher current from the change-over point upon reducing frequency, and thus the formation of hysteresis. ADVANTAGE - Larger adjustment range for switching point.