This FAQ applies only to the SINAMICS G120/G120D Control Units without “-2” in the product name and MICROMASTER 4 inverters.
EMC correct installation
This is very important to prevent noise causing communications failures and damage to USS drivers.
Unlike PROFIBUS, the USS com port is not optically isolated, so much more care has to be taken to ensure that the installation practices do not lead to communication failures or damage to USS drivers.
The minimum measures that should be adopted are:
1) Motor cables to be screened - the screen to be correctly earthed at both ends. Typically and EMC gland making 360 degree contact with the screen is used at the motor, and a brass or copper P clip on the cubicle backplate at the drive. Try to avoid joins in the cable - if this is not possible then care must be taken to ensure EMC correct continuity of the screen at the join.
2) All nodes are to be well earthed (EMC earth).
3) All relay coils etc to be suppressed.
4) Pay attention to cable segregation - keep USS-communication-cables away from other cables, particularly motor cables.
5) Ensure the screens of USS-communication-cables are correctly earthed.
Can be found in MICROMASTER 4: EMC Design Guidelines; Entry-ID: 18162267
Bus termination and biasing
The bus must be correctly terminated at both ends, and biased too.
If a MICROMASTER 4 is the first or last node on the bus, the supplied USS termination/ biasing network (A5E00151017) must be fitted (refer to Fig. 1).
Fig. 1 – USS termination/biasing network for MM4
More information you will find in the operating instructions for MICROMASTER 4:
- Operating Instructions: MICROMASTER 440 0,12 kW - 250 kW, Chapter 220.127.116.11 USS bus configuration via COM link (RS485); Entry-ID: 24294529
- Operating Instructions: MICROMASTER 420 0,12 kW - 11 kW, Chapter 18.104.22.168 USS bus configuration via COM link (RS485); Entry-ID: 24523400
SINAMICS G110 and G120
If a SINAMICS G110 or a SINAMICS G120 with a Control Unit CU240S or CU240E is the first or last node on the bus, the build in the drive / control unit bus termination resistor must be used for bus termination.
This is achieved by setting the Bus Termination DIP switches on the front of the inverter to the ‘Bus Termination’ position (refer to Fig. 2). It is important that both DIP switches (2 and 3) are set to the ‘Bus Termination’ position (not in the OFF position). A small screwdriver will be required to change the position of the DIP switches.
Fig. 2 – DIP switches for bus termination on G110
More information you will find in the Operating instructions: SINAMICS G110, Chapter 3.3 Basic Commissioning; Entr-ID: 22102965
On the CU240S the USS termination can be activated via the Bus Termination Switch on the right side of the housing of the Control Unit (refer to Fig. 3). The switch is set in the position “ON”
Fig. 3 – DIP switch for bus termination on CU240S
More information you will find in the Operating Instructions: Control Unit CU240S, CU240S DP, CU240S DP-F, CU240S PN, CU240S PN-F, Chapter 4.3 Connecting a CU240S via USS on RS485; Entry-ID: 27864729
On the CU240E the USS termination can be activated via the Bus Termination Switch on the front side of the housing of the Control Unit (refer to Fig. 4). The switch is set in the position “ON”.
Fig. 4 – DIP switch for bus termination on CU240E