ABB DSCS131MFB 57310001-LM bus controller
The LEDs assigned to lines A, B and M on the front panel are used to indicate busactivity (Act) and possible errors (Err) on the PROFIBUS lines. The monitoring
logic in RLM 01 assumes that lines A & B are used for communication during
operation. If it is subsequently possible to receive data over only one of the two
lines, the non-available line is reported as faulty. If the redundant (second) line also
fails, the same state results for the monitoring logic as for a redundant PROFIBUS
link A AND B that is not in operation at all. Since the logic has no criterion for
making a distinction, no error message is generated by RLM 01. The alarm contact
remains closed and the two Act and Err LEDs are unlit. But the condition just
described does not go undetected. In this case the PROFIBUS master generates the
error message, since it cannot access the slaves either via line A or line B.
An Err LED flashing at an undefined pulse/pause ratio indicates that the line in
question has failed AND that there is only sporadic data traffic on the redundantline.
The monitoring logic can only indicate operating and error states correctly if the
baud rate is set correctly.
RLM 01 also tests whether the supply voltage is present at inputs L1+ and L2+. A
single power supply with L1+ alone always requires a cable jumper from L1+ to
L2+ (see Chapter 3). This prevents an unwanted error message.
The monitoring logic in RLM 01 indicates operating and possible error states via
LEDs on the front panel. In normal operation, all yellow Act LEDs (flashing or
continuous) and the green Pwr LED are lit. The two red Err LEDs are unlit. Any
signalling configuration other than this indicates a communication or power supply
The text (yellow, red, green) in the two following tables means that the
corresponding LED is lit, thus displaying an operating or error state.

Act/Err LEDs Alarm contact Meaning
Yellow -/- Closed Data reception via all three wires (unin terrupted operating status) Yellow Yellow
Unlit Unlit
Yellow -/- Open Data reception via line A / M but not via
line B Yellow Unlit
Unlit Red
Yellow -/- Open Data reception via line B / M but not via
line A Unlit Yellow
Red Unlit
Unlit -/- Closed Data reception via line A / B but not via
line M Yellow Yellow
Unlit Unlit
Yellow -/- Open Data reception via line A / M and con tinuous transmitter on line B Yellow Yellow
Unlit Red
Yellow -/- Open Data reception via line B / M and con tinuous transmitter on line A Yellow Yellow
Red Unlit
Unlit -/- Closed No data reception via lines A / B and M
Unlit Unlit
Unlit Unlit
Redundant power supply
Pwr LED Act/Err LED's Alarm contact Meaning
Green Depending on status Closed RLM 01 is supplied with
L1+ and L2+
Unlit Depending on status Open L1+ or L2+ missing
Unlit All unlit Open L1+ and L2+ missing
Simple power supply
Pwr LED Act/Err LED's Alarm contact Meaning
Green Depending on status Closed RLM 01 is supplied with
L1+
Unlit Depending on status Open Wire jumper to L2+ miss ing
Unlit All unlit Open L1+ missing