| 摘要 |
The exciter coil (10), which generates a magnetic field in the tube of an inductive flow meter, is supplied by two electronic switches (11, 12) operated in push-pull, which are controlled by the output signal of a comparator (15). The switches (11, 12) are either opened or closed so that they have extremely low power dissipation. The exciter current is picked up from a current sensor (13) and supplied via a delay section (14) to the actual-value input of the comparator (15). At the setpoint input of the comparator (15), a setpoint signal of alternating positive and negative pulses is present. During a pulse of the setpoint signal, the switches (11, 12) are switched on and off numerous times because the operating threshold of the comparator (15) is exceeded in both directions. This produces an exciter current pulse on which a sawtooth is superimposed. The mean value of this pulse corresponds to the setpoint of the exciter current. The advantage lies in the low power consumption of the circuit and in being able to dispense with expensive cooling means. <IMAGE>
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