Appendix H - Point Quality Definition

H.1   General Description


This appendix defines the point quality flag states for analog I/O, digital I/O, and module bus I/O.


NOTE: The control module can be configured to trip or continue operation upon the loss of an I/O module.



H.2   Individual Analog Inputs


Each analog input is compared to a low value of -0.75 VDC and a high value of 5.25 VDC. If the input goes outside either limit, the value is held to the limit and the point quality flag indicates bad.



H.3   Group Analog Inputs

If an I/O module is not connected, all points in the group will have their point quality flag set to bad.



H.4   Group Analog Outputs

All outputs are read back by feedback input circuitry. If the feedback voltage signal does not match the requested software output value, the point quality is set to bad for that output.



H.5   Digital I/O

If the I/O definition block is configured to use an I/O module, but the I/O module is not installed, the point quality flag for the associated module I/O group will be set to bad, and the control module generates a problem report.



H.6   Peer-to-Peer and Module Bus I/O

If input data cannot be read for a period of 2.0 seconds (S2 of FC 90 = 0.250 sec.), the flag will be set to bad. A new attempt will be made to read the data at least every 20 seconds.


NOTE: After the point quality flag is set to indicate bad quality, the receiving module retains and uses the last good value that was obtained.


The Harmony controllers utilize a configurable retry period for determining bad quality. The base retry period is configured in the extended executive (function code 90) base periodic sample I/O period S2. This specification (S2) also determines the time resolution for all periodic sample I/O pole periods configured in the module. This includes the segment control (function code 82) periodic sample I/O period S13. All periodic sample I/O periods should be configured in multiples of function code 90, S2. To determine the typical time required to mark a periodic sample I/O point bad, multiply function code 90, S2 by eight.



function code 90, S2 = 0.250 sec.

0.250 sec. x 8.000 = 2.000 sec.


A point will not continue to retry at the function code 90, S2 period after being marked bad. The bad point retry is only performed once every 20 seconds.