If the pulse contact is within the DC circuit of the counter, spark quenching is necessary in order to avoid any contact disturbance from the inductive breaking voltage.
Unfortunately, however, a more or less strong dropout delay is produced by the spark quenching and it should be checked in any case whether this will cause disturbance.
Spark Quenching with RC element
This spark quenching produces practically no disturbing dropout delay and is, therefore most suitable for all count speeds. It should preferably be used at very high count speeds. In general the RC element is located in parallel with the contact in order to produce high frequency interference suppression at the same time. However, it can also be connected in parallel with the coil.
Spark quenching with Diodes
Considerable dropout delay, therefore only suitable for low count speeds up to 10 cps. Particular attention should be paid to the correct polarity on connecting. The small fitting size is an advantage: e.g. this type of spark quenching can be used for resetting coils.
Spark Quenching with Zener Diodes
Low dropout delay, therefore suitable for higher count speeds because the diode only passes the inductive breaking current when the Zener voltage is achieved. It is also suitable for the protection of transistor circuits, where correct polarity must be observed.
Spark Quenching with Varistors
Varistors are voltage dependent resistors whose resistance decreases inertialessly and exponentially with rising voltage. They are therefore, suitable for spark quenching, the varistor ideally being connected in parallel with the coil. It is rated for the current to be approx. 1/10 of the coil current at nominal voltage.
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