Appendix
IM-1004 | REV181127
Page 36
©2018 Celera Motion
Mercury II 6000 Series Encoders
Sensor Installation Manual and Reference Guide
MII6800Si/Pa
Controller Sample Rate and Maximum Encoder Speed for MII6800Si/Pa Index:
The Index Window is part of the MII6800Si’s serial word and does not latch. To detect the index
mark, the controller must issue a sample command while the sensor is over the index mark on the
scale. When this happens, the Index Window bit will be high. If the sensor is not over the index
mark, the IW bit will be low. Consequently, the sample rate must be at least as fast as the output
from the following equation to ensure that a sample command occurs when the sensor is over the
index mark:
Index Window duration (µs) = Index Window width (µm) / encoder speed (m/s)
The Index Window’s width can be in the range from 5 µm to 30 µm. It is typically 20 µm
after calibration. To ensure reliable index sampling, a value of 5 µm can be used in the
above equation for all systems.
The maximum position sample rate is 4.4 µs; there is no minimum sample rate.
For example:
Index Window width = 5 µm.
Speed = up to 1.1 m/s.
Index Window duration = 4.55 µs.
Therefore, the controller’s position sample rate must be 4.55 µs or faster to read the Index
Window (at least one position word with the IW bit high).
7.7 RS-422
Compliance
Mercury II 6000 Series Encoders are RS-422 compatible. Encoder signals are “sending end
terminated” and customer receiving terminations are not required.
For more details, see the following Tech Note:
Proper Termination of Digital Incremental Encoder Signals.
Optional RS-422 compliant circuitry for long cable runs in harsh electronic environments is
illustrated below:
