Siemens SINAMICS DCM Operating Instructions Manual page 93

Arrangement at power interface C98043-A7109:
Arrangement of terminals XB
Notes:
In the diagrams above, switch S700 is shown in the state when shipped from the factory.
The disconnecting links for switch S700 must be soldered into the hooks to ensure the connection is secure.
Dimensioning current transformers, load resistors
The digital-to-analog converter circuit on the CUD can process voltages of up to ±3 V (peak
value). When dimensioning the current transformers and load resistors, it is important to
ensure the voltage at signals BUERDE_1 and BUERDE_2 (see "Current measurement"
figure) never exceeds this value, even at the highest expected overcurrent in the power unit.
On delivery, actual current value measurement on the SINAMICS DCM Control Module is
configured in such a way as to ensure an actual current value signal of 1 V at the rated
device current. The difference amplifier in the "Current measurement" figure can also be
used (with amplification of 0.1) to adjust the input voltage of existing measuring equipment
with different scaling.
It is better to dimension the current transformers and load resistors in such a way as to
ensure an average load voltage of no more than 1 V at the armature's rated DC current.
If an external load resistor is being used, ensure the wires between this resistor and
terminals XB-1 to XB-8 are twisted and kept as short as possible. To prevent measuring
errors, the external load resistor itself should be connected in accordance with the four-wire
method (potential tap) and have as little inductance as possible.
With the four-wire method, the current to be measured is routed through the resistor. The
resulting voltage (load voltage) is tapped at the connections at a distance specified by the
manufacturer. This ensures measurements are as accurate as possible.
Only load resistors with a maximum power loss of at least 0.5 W can be soldered in at the
soldering terminals parallel to the 10 Ω load resistors already installed. If 5 A current
transformers are already present, 5 A/ 0.1 A matching transformers should be used. In such
cases, the standard R701 and R708 load resistors can be used with 10 Ω each.
The maximum permissible current at input terminals XB1 to XB4, XB7, and XB8 is 1 A.
SINAMICS DCM Control Module
Operating Instructions, 06.2010, C98130-A7067-A1-02-7619
6.6 Measurement of the armature current
Arrangement of X_I_IST
Connecting
93