DC voltage pulses without or with very small residual ripple are, for example, taken from a battery, DC generator, electronically stabilised power supply, according to the circuit above.
These pulses are most suitable for the maximum possible frequencies due to their ideal square shape. If only AC voltage is available it must be rectified.
Therefore, according to count speed, a more or less greater degree of residual ripple has to be put up with.
A simple bridge-rectifier will give a residual ripple of approx. 50%, and the following relationship is applicable:
AC voltage (effective value) 12 24 48 60 110 220 V
DC voltage (arithm. mean value) 8,5 19,5 40 49 91 185 V
Two types of switching circuits can be used to drive the counters.
a) Pulse contact in AC circuit Model a0 or a
This circuit is mostly used when the count speed is ≤ 18 Imp/sec.
No spark required; contact bounces have no negative effect because the rectifier acts as spark quenching and provides inductive drop-out time lag.
Count speed only possible up to max. 18 Imp/sec.
b) Pulse contact in DC circuit version b
High count speed = 25 /cps, only one rectifier is necessary when driving several counters.
More sensitive to contact bounce, spark quenching is required.
4 connection points required is rectifier is built into counter
With pulse speeds 30 Imp/sec smoothed DC must be used. The residual ripple (smoothing degree) is determined by the count speed and is stated in the technical specification.
Simple bridge circuit smoothing by capacitor.
3 phase AC bridge circuit capacitor not required . Residual ripple 4.2 %
If the rectifiers are connected directly to AC mains they are often damaged through the contamination of the high peak voltages.
These peak voltages are caused by the switching of transformers, spot welding machines, switching motors on and off etc; they often exceed the mains voltage by many times. Therefore it is essential to use a heavy duty rectifier or one with suppressor circuit, so that these peak voltages will not have any destructive effects in the long run.
This is particularly important in the case of silicon rectifiers which are very sensitive to short period excess voltages. It is advisable to use controlled avalanche silicon rectifiers for this purpose. Rectifiers which we build in or attach to our pulse counters have to a large extent, a high dielectric strength, and an over voltage protection is provided, if required.
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