Rockwell Automation 1771-DE Absolute Encoder Module User Manual - Manual (Page 32)

Chapter
5
5Ć1
Offset Feature
Offset is a new feature of the Absolute Encoder Module (cat. no.
1771-DE, revision B). Revision A modules do not have this feature.
Offset is the difference between the 0 position of the absolute encoder and
the 0 position of the machine shaft to which the encoder is connected.
You can program this value to compensate for such factors as machine
wear or improper mechanical setup. You do not have to disconnect your
equipment to realign the 0 position of the machine shaft with the 0
position of the absolute encoder.
Determining the Offset Value
You can find the offset value using either of two equations, depending on
whether you use the 0 machine position or the 0 encoder position as your
reference.
To calculate an offset value from a 0 encoder position, use this equation:
N -M = S
where N = number of encoder positions, M = machine position at encoder
0, and S = offset.
To calculate an offset value from a 0 machine position, use this equation:
E - N = S
where E = encoder position at machine 0, N = number of encoder
positions, and S = offset.
Let’s look at an example finding the offset value with reference to 0
encoder position and 0 machine position. Assume the following:
You have a 0 to 4,095-position encoder (4,096 positions)
The machine shaft is at position 512 when the encoder is at position 0
The encoder is at position 3,584 when the machine is at position 0
Offset Feature