GEMTEQ I/O Appendix E. GEMCAN I/O Scanner Firmware Upgrade
APPENDIX C NODE GUARD PERIOD AND MASTER CHANGEOVER TIME
Master Change-over time
In a change over system it is good practice to set the change-over time to at least twice the
selected Node Guard Period Time (NGPT).
Consider the following:-
At 250K Baud the default NGPT is 80mS, setting the change-over time in each controller to
100mS may cause the system to momentarily swap to the "off-line" controller should any
changes be made to it's operational state e.g. Power Cycle or recompile.
To prevent the above, reduce the Node Guard Period or increase the change-over time as
required.
Freeze Fallback
A slave GEMTEQ output module has a default Freeze / Fallback delay time of 500ms.
At the selected Node Guard Period Time (NGPT), the GEMTEQ master sends a node guard
message to the first node and the second master (if fitted). The next Node Guard Period Time
(NGPT), a node guard message is sent to the second node + the second master (if fitted).
This continues for each node configured (C/D Reference in ladder) before it starts again.
Assume a Node Guard Period Time of 80mS and eight nodes have been configured in the
ladder.
Note: The node ID’s do not have to be sequential, the system only sends a node guard to
nodes referred to in the ladder program.
Each node is sent a unique Node Guard Message and as such it will take 640mS to service
each node.
Number of Nodes (8) x Node Guard Period (80mS) = 640mS
It can be seen that with a default Fallback delay (500mS) the modules will go to the fallback
state
To prevent the above, reduce the Node Guard Period or increase the Fallback delay as required.
GEMTEQ I/O Technical Manual (T2031En) Page E-1
Rev.02 (10/10)
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