Current Measurement Via Terminal Block Xb-1 To Xb-4 With External Measuring Circuit - Siemens SINAMICS DCM Operating Instructions Manual

6.6.3 Current measurement via terminal block XB-1 to XB-4 with external measuring
circuit
6.6.3.1 External current transformers in V-circuit with +1 V at rated armature DC current
Principle of operation of the V-circuit
Two current transformers (CTs), a rectifier bridge and an external load resistor are
connected-up corresponding to the following diagram to measure the current.
It is important that the ends with the same name (lower case l) are connected together. This
is then followed by a 3-phase bridge rectifier with a load resistor. As a consequence, any
current can flow through the load resistor.
Advantage of the V-circuit
Due to the threshold voltage of the diodes, the CT (current transformer) is more quickly
demagnetized.
Disadvantage of the V-circuit
The demagnetization current of the CT is converted into an apparent armature current as a
result of the rectifier diodes (in spite of armature current = 0). This makes it more difficult to
identify a no-current interval to change the current flow direction. As a consequence, when
using this circuit, a longer torque-free pause must be maintained than when directly
measuring the armature current.
Connection
The output signal of the V-circuit is connected to terminals XB-1 (+) and XB-2 (-).
Terminals XB-3 and XB-4 are not used.
S700 switch positions:
Remove R701! The difference amplifier is not used.
SINAMICS DCM Control Module
Operating Instructions, 12/2018, A5E34888669A
6.6 Measurement of the armature current
2 – 3 connected
5 – 6 connected
8 – 9 connected
Connecting
101