Micromod MOD: 1800P - MOD 30ML Identity Module (Version 2) Algorithms, Tables and Sequential Logic Functions - Manual (Page 23)

Logic Functions - Book 2
EXPRESSION BLOCK
8-15
8.2.4 Expression Block Events
The event codes (and their suggested text messages) for the expression block are given
below. See the referenced database attributes (in brackets) for additional information. See
System Event Block, Logic Functions - Book 1, IB-23G600 for a description of event
transitions.
0 BLOCK STATE SET TO RUN
1 BLOCK STATE SET TO HOLD
2 BLOCK STATE SET TO OFF
3 BLOCK STATE SET TO DEBUG
4 CALCULATION ERROR (5)
8.2.5 Example 1: Using Expression Blocks to Store Trend Data
Expression blocks can be used for local data storage. You may want to do this for two
reasons: either to allow trend storage without tying up communication links to the host, or to
allow the MODCELL to accumulate data locally for later upload even if the communication line
(for example a modem) is disconnected for a period. For remote installations, another benefit
of trending using the expression block is portability. The data is stored in main memory, and
is therefore backed up onto the Memory Module. The trend data can therefore, be removed in
the Memory Module and taken elsewhere for analysis with a blank Memory Module left on the
MODCELL for another weeks or months data collection.
For analog variables, data is typically stored as period averages for a configured number of
periods (trend cycles). The application engineer must pick the number of variables to be
stored and the number of instantaneous values to store for the "fastest" trend period and
finally, the application engineer needs to specify how many averages to store for the slower
time periods. This is best done in table form as shown below.
Setup for Storing Trend Data Using Expression Blocks
Trend Cycle 1 Trend Cycle 2 Trend Cycle 3 Trend Cycle 4
Variable Scan Rate
(seconds)
(20)
Five Second
Samples
(30)
One Minute
Averages
(24)
Fifteen Minute
Averages
(24)
One Hour
Averages
FC-101 5
√
FC-102 5
√
FC-103 5
√ √
TC-100 5
√ √ √ √
TC-101 5
√ √ √ √