7_flow chart design ppsx

Higher Engineering Education Alliance Program
Flowchart Design
Prepared by: Ngo Van Thuyen
Topics and Objectives

Topics:

Describing process control using flowcharts

Conversion of flowcharts to ladder logic

Objectives:

Be able to describe a process with a
flowchart.

Be able to convert a flowchart to ladder logic.
Flowchart symbols
Example
Flowchart construction

The general method for constructing flowcharts is:
1. Understand the process.
2. Determine the major actions, these are drawn as
blocks.
3. Determine the sequences of operations, these
are drawn with arrows.
4. When the sequence may change use decision
blocks for branching.

Once a flowchart has been created ladder logic can

be written. Two basic techniques: blocks of ladder
logic code, and normal ladder logic.
Block Logic

Step 1: Name each block in the flow
chart

Each block in the flowchart will be converted
to a block of ladder logic

Using MCR instruction. Pay attention to a
normal output in the MCR block

Step 2: write ladder logic to force PLC
into the first state

Step 3: write ladder logic for each
function in the flowchart
Block logic example
Block logic example

Note of
the
latch of
F1
Block logic example
Block logic example
Block logic example
Block logic example
Sequence bits

•
Methods used MCR statements of latches
are not preferred
•
Sequence bits can be used instead of MCR
•
Connecting arrows (transitions) are
labeled
•
Transitions indicate when another function
block will be activated
Sequence Bits

All of the logic
for the
transitions
should be kept
together, and
appear before
the state logic
that follows
Sequence bits
Summary