KROHNE Summit 8800 Vol 2 - Manual (Page 174)

174 www.krohne.com 08/2013 - MA SUMMIT 8800 Vol2 R02 en
SUMMIT 8800 REDUNDANCY 14
14. Redundancy
Liquid Gas Steam
14 .1 Introduction
The SUMMIT has a health based redundancy feature. Its primary objective is to prevent down
time or failure that will affect the custody transfer of fluid.
Two SUMMIT flow computers can be put in redundancy mode, where both computers are run-
ning the same application in parallel with one assigned as the duty and one as the stand-by.
Both computers check the correct running of the other by two modbus interfaces between them.
Modbus master The main link to read the other computer’s status and the “loop-back” of its own
status.
Modbus slave: The link to write its own status to the other flow computer and to “loop-back” the
status read from the other flow computer.
If the information is not arriving a communication alarm will be given. At that moment the flow
computer will use the other link to get the other flow computers status including its time. If
the time deviates too much from the system time, than this is an indication that the other flow
computer failed.
See also volume 1 for the hardware connections and volume 3 for modbus coinfiguration..
On top of this each computer monitors its health and compares it with the heath of the other
flow computer. To determine the health, each alarm occurring in the flow computer or associ-
ated equipment can be associated with a penalty. An ideal running system is then 100% healty,
with alarms the health will go down.
Once the health of duty machine is lower than that of the standby machine the duty and standby
nominations will switch over. To prevent continuous switch-over score by a preset switch-over
value and a switch-over time is introduced.
14 .2 Global redundancy
Here the user enables the function and assigns the flow computer as either duty or standby. It is
assumed that a system consists of a duty and a standby flow computer that are in communica-
tion with each other.
Found under the general tab, this section allows a system redundancy to be set-up: