User`s guide

Page 92

Controlinc 1746-C (Version 5.21) Network Master Users Guide (2004-11-18)

6.2. App Note: 1746-C Operation – Additional Detailed

Information

6.2.1. Scan Operation: Determining & Exiting “Network Down” Condition

If the 1746-C ever detects “network down” (no actuators communicating) then LED2 will come on and

the program enters the diagnostic scan mode and remains there until at least one actuator responds.

After scanning the “down” network, if any actuator responds and the number of actuators that

responded is not the same as the number configured in table [0], then the 1746-C will perform one

more network scan in the diagnostic mode to afford the opportunity to “simultaneously” bring as many

actuators on line as possible – as soon as possible – within the same scan and not have to wait an

entire scan period.

This scenario happens when “total power on a network is restored at once and the network master

happened to be in the middle of a scan period when power was restored” … which is the most common

scenario. In this case, the repeat diagnostic scan allows the network master the opportunity to bring

“as many systems as possible on line at one time as soon as possible” and not have to wait until the

end of the scan period for the next diagnostic scan.

In other words, without this feature of repeating the diagnostic scan, if the network went down and

came back up in the middle of a diagnostic scan (which was most probable), then the program would

usually detect only a portion of the network and would wait until the end of the scan period to check for

the rest. This is a relatively long time if we are considering the network "going up/down" due network

wiring and not actual powering of actuators (which was most common).

Therefore, to speed up getting most of the network on-line early, if the entire network goes down, the

program repeats the diagnostic scan one more time in an attempt to get more units "on-line".

LED2 will remain on until the diagnostic scan finishes and normal scan operations resume.