User`s guide

Copyright © 2004 EIM COMPANY, INC. • 13840 PIKE ROAD • MISSOURI CITY, TX. 77489
Page 22
Controlinc 1746-C (Version 5.21) Network Master Users Guide (2004-11-18)
4.2.2. Operation: The Network Communication Diagnostic Scan
After a predetermined number of loops through the network scanning the actuators (the “scan period”),
the 1746-C performs a communication diagnostic scan to determine if any “off-line” actuators can come
back on line. If there are any that are ready, the 1746-C will bring them back on line without human
intervention. This is the only time an off-line system can come back on-line.
The number of loops around the network is determined by the “scan period
” value. The PLC adjusts
this value to accommodate site requirements and current operating environments.
Unlike the other operations that access the actuators on the network, the diagnostic scan checks both
ports when communicating with the actuators. Because of this, it also always takes longer to execute
than standard data gathering scans. However, normal data is still gathered during a diagnostic scan.
The only major difference in data gathering between a standard scan and a diagnostic scan is
• In the diagnostic scan, the 1746-C determines actuator system type and actuator firmware
version ID (tables [18 & 19]).
• Both ports are explicitly tested when getting the system type information.
• The diagnostic scan ensures that the hardware ports are set correctly … 9600 - 8N1.
Otherwise, all other data gathering activities are the same as in a normal network scan.
Communication error indications may only be cleared during this scan.
The “scan loop counter
” is always zero (0) during a diagnostic scan … the diagnostic scan does not
count as part of the scans in the scan period. This is the only time the loop counter is zero … during
the diagnostic scan.
The diagnostic scan time increases as you increase the discrepancy between the
(number of valves actually on line and talking
) VS (the number of valves configured to be on line)
Below shows a sample of diagnostic scan times empirically taken on a network when there was no
network “writes to the actuators” (Table [0] was configured for 60 valves). As you can see, as you
increase the number of “off line” units, you increase the diagnostic scan time.
# Nodes “Talking” … On-Line
Version 5.21
Diagnostic Scan Times (secs)
60 of 60 (#1 – 60) 15
54 of 60 (#7 – 60) 16
48 of 60 (#13 – 60) 17
42 of 60 (#19 – 60) 18
36 of 60 (#25 – 60) 19
30 of 60 (#31 – 60) 20
24 of 60 (#37 – 60) 21
12 of 60 (#49 – 60) 23
6 of 60 (#55 – 60) 23
3 of 60 (#58 – 60) 24
2 of 60 (#59 – 60) 25
1 of 60 (#60) 25
The values in this table
“rounded values” and
have a precision of (+/-) 1
second.
Because of this, these
numbers are only
appropriate for estimates
and trend analysis.