Specifications

About Controllers and Channels
PlantScape Server and Client Configuration Guide 99
Monitoring Communications
Before you start defining controllers and channels, it is useful to understand a
number of concepts that are used in PlantScape to flag communications failures
and help you to monitor the state of your system.
After the connections between the server and the controllers have been
physically set up, defined, and enabled, the server starts to record channel and
controller communications statistics. These statistics can be viewed using the
channel and controller communications displays at a Station.
The server maintains the following communications statistics for each channel. If
there is more than one controller on a channel, the channel values represent the
sum of all of the controllers on that channel.
Total requests
Indicates the number of requests for data that have been sent to the channel
or controller.
Total errors
Indicates the number of times the controller did not respond or the
response was incorrect (for example, due to a bad checksum).
Barometer
Indicates the condition of the channel or controller. Every time an error
occurs, the barometer is incremented by 2 or more, depending on the error.
Every time a good call is made it is decremented by 1. If the number of
errors is relatively large, the barometer value will tend to increase. The
minimum value of the barometer is zero.
Marginal and Fail Limit Alarms
You can specify a “marginal” and a “fail” barometer limit for channels and
controllers. These barometer limits work as follows.
When the barometer reaches the marginal limit, an alarm is generated and the
channel or controller communication is declared to be “marginal.” If the
barometer continues to increase and the “fail” limit is reached, an alarm is
generated, the channel or controller communication is declared to be “failed,”
and scanning of points on that channel or controller ceases. You can specify the
priority of the alarms generated using the Alarm Priority tab of the Alarm & Point
Processing display.
For most types of controllers, the server will try to re-establish communications
every 60 seconds, using a diagnostic scan.
plscpcg.book Page 99 Monday, May 28, 2001 10:11 AM