IGBT Modules - Technologies, Driver and Application (Second Edition) - page 452

12.4 Measuring voltage
In the field of power electronics, it is often necessary tomeasure voltages at a verywide
range of locations, due to the design, or repair and maintenance work, or the need to
obtain measurement values to monitor the application while it is operating. For
measurements in the first of these instances, voltmeters or digital multimeters are
usually used. For measurement of changing voltages, an oscilloscope is used.
Depending on the voltage level and the reference potential, the voltage can be
measured either with the appropriate standard probe
) or with a differential
). For measurement with a standard probe, the
reference point for themeasurement has the same potential as the earth connection of
the oscilloscope. For measurement with a differential probe, however, the reference
point may be at a completely different potential from the earth connection of the
oscilloscope. Specialist manufacturers make probes for a range of voltage levels up to
several 1000V. The probes are usually compatible with other manufacturers' products,
but some have a special connection code that means they can be used only with
equipment madeby the samemanufacturer.
Fig. 12.24
A selectionof TektronixandProbeMaster probes
When using differential probes with an isolated potential, it is important to remember
that thismethod shows greater coupling capacitance, which can cause significant errors
in dynamic processes. The coupling capacitance is caused by the way the measuring
instruments are set up. Further, these measuring instruments should not be operated
with an external power supply, as this increases the coupling capacitance to the supply
mains, towhich the oscilloscope is also connected.
When measuring voltage within the application to determine the status, the measuring
circuit must be integrated in the electronics of the inverter. In many applications, there
are basically only two points at which voltage is determined, as shown in
This does not include measuring voltage to determine the current indirectly. One
example of this is the utilisation of shunt resistors, which are described inmore detail in
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