Command Scan Items; Service Messages; Priority Agent - Honeywell CIU 888 Migration Manual

B - 2
B.4 Command scan items
When gauge commands are issued from the Host system, gauge
command scan items are added to the scan items pool. Gauge
commands scan items are scheduled with a higher priority ((i.e) less
minimum and maximum scan period) than configured foreground and
background items.
B.5 Service Messages
When service messages are issued from Service tools like Engauge,
service messages are added to the scan items pool. Service messages
are scheduled with a higher priority ((i.e) less minimum and maximum
scan period) than configured foreground and background items.
Adaptive scanning based on field device communication failures:
1. Field device retries are made smarter and spread rather than
configured consecutive retries.
2. If the communication errors are received for the configured number
of retries for a field device, the priority of all the scan items for that
field device will be reduced and retries are skipped until a valid
response is received for that field device.
3. On receiving a valid response from the field, the priority of the field
device is moved to the appropriate level and retry mechanism is
restored.
B.6 Priority Agent
CIU 888 also incorporates a Priority Agent which monitors the product
movement and product level close to Tank High limit and relatively
prioritizes the scan items by modifying the minimum and maximum scan
periods of the scan items so that critical parameters are scanned at a
faster rate compared to the less critical parameters. Priority agent can
be enabled / disabled with a configuration option.
Priority Agent is disabled - CIU 888 scans the field using a static time
based scanning algorithm for foreground and background scan items.
No priority changes happen based on Product movement and Tank
High Monitoring Limit.
Priority Agent is enabled - CIU 888 scans the field using a dynamic time
scanning algorithm based on the Product movement and Tank High
monitoring limit. Scan item's priority changes happen based on Product
movement and Tank High Monitoring Limit. That is, a relative
prioritization is done between static tanks (tanks with no product
movement), dynamic tanks (tanks with product movement), dynamic
tanks in which product level is beyond the configured Tank high
monitoring limit.
Ensite Pro to CIU 888 Migration Manual
CIU 888
Part No.: 4417593_Rev09