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Described is a method of employing the solenoid of an electromagnetic latch to serve a dual purpose as a filter inductance. Savings of component cost, space and power dissipation result.
English (United States)
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Latch Solenoid Used As a Filter Inductor
Described is a method of employing the solenoid of an electromagnetic latch
to serve a dual purpose as a filter inductance. Savings of component cost, space
and power dissipation result.
Removable equipment using electric motors driving high-speed rotating parts
that constitute a safety hazard to the operator are required to employ
electromagnetic locking latches to prevent access into the housing or removal
from a rack while the motor is rotating. Such equipment may also require a filter
inductor in series with one of its DC supplies and the motor drive electronics to
prevent interference to other sensitive circuits on the same DC supply by rapidly
switching high currents in the motor driver. The nature of the motor current
through the filter inductor and the requirements of the latch solenoid winding are
such that the inductor function can be provided by the solenoid.
The example chosen is a 12 V motor, speed controlled by chopped DC
pulses. Fig. 1 shows the solenoid winding incorporated as the inductor in the pi-
filter network between the +12 V DC supply and the motor drive electronics. Fig.
2 shows how the average current demanded by the motor changes from when it
starts to when it has reached the normal running condition. The variation in
absolute current levels given are what may be experienced over a large number
of units. During starting, the current is DC but during running it is pulse-width
modulated, as shown in Fig. 3, to give the lower average current. The chopping
frequency would be typically a few tens of kHz.
One of the major constraints on the solenoid winding is its resistance. This
must be of the order o...