Image Processing Reference
In-Depth Information
and is suitable for most sensors and electrical actuators (like pneumatic valves) in discrete factory
automation.
28.5.1 “Magnetic Supply”: WISA-POWER
The basic principle of a magnetic field-induced power supply can be described by the well-known
transformer principle. A power supply unit feeds a primary winding, a large coil, which can be
arranged around a production cell. The secondary side consists of a practically unlimited number
of small receiver coils, see Figure .. Each receiver coil is equipped with a ferrite core to increase
the amount of flux collected by the coil and to minimize effects of external conductive materials.
For this type of “transformer,” magnetic coupling is very low
. (<.%).The receivable power is deter-
mined by the amplitude of the magnetic field at the location of the receiver (secondary) winding
and its size.
Although human operators will rarely work continuously inside such an automated production
cell, the strength of the magnetic field at all working positions (including within such a cell) complies
with international occupational regulations and recommendations []. WISA-POWER works at the
frequency of  kHz. The distance to be observed by a pace maker carrier to this setup would be
. m at the maximum current of the WPU ( A) according to strict German regulations
Energy losses in such a WISA-POWER system are surprisingly small and are mainly caused by
skin and eddy current effects in the coil itself and in nearby metal objects, especially steel. In many
different production cells in factory automation equipped with WISA-POWER, energy losses have
been measured to be around - W
(<
.%
)
m of supplied cell volume.
The principle does not depend on the frequency, but the chosen frequency is a good balance
between
/
Higher amplitudes needed at lower frequencies (higher ohmical losses)
High frequency losses in a realistic environment, where always metal will be present to a
certain degree (eddy current losses)
Semiconductor switching losses
Capacitive dielectric losses
Component size (larger at lower frequencies), which is especially an issue on the receiver
side, where you need to have small devices
As the receivers will typically be designed to consume just - mW (sensors-small actuators), the
above-mentioned losses will clearly dominate the power consumption. herefore, the amount of such
wireless devices is practically not limited, several hundreds or even  can be supplied.
28.5.2 Resonant, Medium-Frequency Power Supply
These unconventional transformers have to be operated in a “resonant” mode, to compensate for the
large leakage inductances of the transformer. he resonant principle allows the wireless power unit
(WPU) to stimulate the resonant circuit at relatively low voltages
.
heWPUhastohaveacontrolcircuitthatmustalsobeabletoaccommodate:
Changes over time in the environment, e.g., caused by the movement of large, metal
objectssuchasrobots.
Different “load” requirements, caused by differently sized and formed primary coils
(inductance values), and losses, caused by factors such as eddy currents in adjacent metal
objects.
Other nearby wireless supply systems, which may couple inductively.
(<
 V
)
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