| 摘要 |
To monitor the amplitude of alternating voltages, particularly of track voltages in railway safety systems, a circuit arrangement is used in which a transistor ring core circuit, in connection with two Zener diodes (Z1, Z2), evaluates the supplied alternating voltage. In this arrangement, the ring core (RN) does not form a trigger threshold in connection with a premagnetisation of the ring core (RN) as is usual but acts as active monitoring element for ensuring that the switching threshold is failsafe. This threshold is formed with the aid of a Zener diode (Z2) located in the emitter circuit of the transistor (TR), which diode is connected to the other Zener diode (Z1) which has a smaller Zener voltage. The premagnetisation current through a winding (W1) of the ring core (RN) results from the difference between the Zener voltages of the two Zener diodes (Z1 and Z2) and the value of a resistor (R2) which is connected in series with the Zener diode (Z1). The special feature of this circuit lies in that the ring core (RN) does not need to be specially selected in any way. In addition, component failures in this circuit have such an effect that no signals which may be hazardous will be output. <IMAGE>
|
