Siemens SINAMICS S120 Commissioning Manual page 426

Appendix
A.6 Overview of measuring systems / encoders
Parameterizing the protocol
For the protocol, define the "Position length", "Bit before position" and "Bit after position"
parameters:
1. Enter a value for the "Position length in bits" (p0447). Refer to the encoder data sheet to
identify which value is suitable for your encoder. For a singleturn encoder, 13 bits are
used for the position information, for a multiturn encoder, 25 bits (this contains 13 bits of
singleturn information).
Also observe the count direction for the position bit. For the examples shown here, the
protocols start with "0" (ascending from left to right). However, there are also
manufacturers, whose encoders use a count direction starting from the MSB counting
downward from left to right. Therefore, compare the setting with the data in the encoder
data sheet.
2. Enter a value for the "Bits before the position" (p0446); see the diagram above.
3. Enter a value for the "Bits after the position" (p0448); see the diagram above.
Bit functions in the SSI protocol
If alarm bits, error bits, or parity bits signal errors during data transmission, these alarms or
faults are output in the commissioning tool.
Alarm bit - only when supported by the encoder
If the encoder manufacturer has added alarm bits to the position value, you should certainly
evaluate these because they provide the only possibility to output alarms regarding the
position value. For example, the encoder may be soiled.
The alarm bit triggers an alarm on the SINAMICS device (A3x412, with x=1,2,3 for encoder
1, 2, 3). You can set the position and state (high or low active).
1. At "Bit activation", activate the alarm bit.
2. At "Bit position", enter the position of the bit in the SSI protocol.
3. At "Logical state", select at which level (high active or low active) the alarm bit should be
output. For high active, the alarm bit is set if the signal is received.
Error bits - only when supported by the encoder
If the encoder manufacturer has added error bits to the position value, you must also
evaluate them because they allow you to determine the validity of the position value.
Error bits trigger a fault on the SINAMICS device (F3x112, with x=1,2,3 for encoder 1, 2, 3).
You can set the position and state (high or low active).
1. At "Bit activation", select the bit number for the error bit. You can parameterize several
error bits (see Startdrive online help for the parameter).
2. At "Bit position", enter the position of the bit in the SSI protocol.
3. At "Logical state", select at which level (high active or low active) the error bit should be
output. For high active, the error bit is set if the signal is received.
426
Commissioning with Startdrive
Commissioning Manual, 11/2017, 6SL3097-4AA10-0BP1