MicroE Mercury II 5000 - Manual (Page 34)

Appendix
IM-Mercury_II_5000_Series Rev. 1 Page 33 ©2014 MicroE Systems
Mercury II 5000 Series Encoders
Installation Manual and Reference Guide
MII5800Si/Pa
Controller Sample Rate and Maximum Encoder Speed for MII5800Si/Pa Index:
The Index Window is part of the MII5 800Si’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 5µm to 30µm. It is typically 20µm
after calibration. To ensure reliable index sampling, a value of 5µm can be used in the
above equation for all systems.
The maximum position sample rate is 4.4µs; there is no minimum sample rate.
For example:

Index Window width = 5µm.

Speed = up to 1.1m/s.

Index Window duration = 4.55µs.
 Therefore, the controller’s position sample rate must be 4.55µs or faster to read the Index
Window (at least one position word with the IW bit high).
6.7 RS-422 Compliance
The Mercury II 5000 Series Encoders are RS- 422 compatible. Encoder signals are “sending end
terminated.” Therefore, customer receiving terminations are not required. For more details, see
the Proper Signal Termination of 422 Data Transmission Signals Tech Note located at
http://www.microesys.com/products/technical-notes-and-white-papers .
Optional RS-422 compliant circuitry for long cable runs in harsh electronic environments is
illustrated below: