Micromod MOD: 1800P - MOD 30ML Identity Module (Version 2) Algorithms, Tables and Sequential Logic Functions - Manual (Page 124)

Logic Functions - Book 2
SEQUENCE BLOCK
10-4
10.3.1 Input Processing
The block processes each input based on user configuration as follows:
•
The input is used in transition expressions.
•
The input is connected directly to one or more outputs.
•
The input is used for both the transition expressions and direct connection to outputs.
Inputs that are used in transition expressions affect the result of the expression evaluation,
and influence the control of the step sequence via the step determination logic. Inputs that are
directly connected to outputs bypass the step determination functions. The values of the
direct connected inputs are made available as block outputs on a sequential basis as a
function of the output configuration for each step. Any block input can be used in both ways
depending on the requirements of the batch control application.
10.3.2 Transition Expression Evaluation
A transition expression can be configured for each step in the sequence. The block evaluates
the expression for the current operating step, and the result of the evaluation is used by the
step determination logic in determining whether to change to a new step or remain on the
current step.
Transition expressions are entered by the user in algebraic format using ‘C‘ symbology for
operators and functions and assuming ‘C‘ like operator precedence. Transition expressions
use all the same operators and data types, and follow the same rules as the Expression block.
See Section 8.2 Expression Block (EX) for additional information.
10.3.3 Step Determination
During normal run operation in the automatic mode, the step determination logic controls the
step sequence, Figure 10-2. At the start of each block execution cycle the elapsed time in the
current step is updated, then the block checks for the presence of an external step source. If
there is no external step source, the block looks for a transition expression. If there is no
transition expression, the sequence remains on the current step.
When a transition expression is configured, the expression is evaluated and the sequence
either remains on the current step or changes to a new step depending on the results of the
evaluation. The result can be the next step or any other configured step as determined by the
expression.
If an external step source is present, and its value is other than zero, the sequence either
remains on the current step or changes to a new step depending on the step source value.
When the step source is zero the logic returns to the transition expression path.
When the block is switched from automatic to the semi-automatic mode, the block status
changes to Waiting upon entry into the next step in the sequence. The sequence progression
is suspended and the block waits for operator intervention. The sequence progression is
restarted by switching back to automatic and writing a run command to the block. When the
block is switched to the manual mode, the step transition logic is completely bypassed, and
the step sequence is entirely under the manual control of an operator.