Other signal modules
7.4 Position decoder module SM 338; POS-INPUT; (6ES7338-4BC01-0AB0)
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
503
7.4.3.3 Transferred encoder value and scaling
The transferred encoder value contains the encoder position of the absolute value encoder.
In addition to the encoder position, the encoder transfers additional bits located before and
after the encoder position, depending on the encoder used.
The SM 338 determines the encoder position based on the following settings:
● Scaling, places (0..12), or
● scaling, steps / revolution
Scaling, places
Scaling determines the position of the encoder value at the feedback interface.
● "Places" = 1, 2....12 indicates that appended irrelevant bits in the encoder value are
shifted out, and the encoder value is right-aligned in the address area (see the example
below.)
● "Places" = 0 determines that appended bits are retained and available for evaluation.
This may be useful when the absolute value encoder used transfers information in the
appended bits (see manufacturer specifications) which you want to evaluate. Refer also
to chapter "Gray code/binary code converter (Page 502)".
Steps per revolution parameter
Up to 13 bits are available for the steps per revolution parameter. The resultant number of
steps per revolution is displayed automatically according to the "Places" setting.
Example of encoder value scaling
You are using a single-turn encoder with
2
9
steps = 512 steps per revolution (resolution/360°.)
Your configuration in
STEP 7
:
● Absolute encoder: 13 bits
● Scaling: 4 places
● Steps per revolution: 512
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