Basic Pneumatics
Module 10: Sequence control systems
PREPARED BY
Academic Services
April 2012
© Applied Technology High Schools, 2012
ATM 1132 – Basic Pneumatics
Module 10: Sequence control systems
Module Objectives
After the completion of this module, the student will be able to:
 Explain the the main types of displacement diagrams.
 Use a 3/2 way roller lever valve in sequence control systems to
eliminate signal overlap.
 Draw a displacement step diagram for a given sequence of
operation.
 Draw a circuit diagram from a given sequence of operation.
 Explain the difference between the displacement step diagram and
displacement time diagram.
Module Contents
Topic
Page No.
1
Introduction to sequence control system
3
2
Types of Sequence control
3
3
Control of multiple actuators
3
4
Displacement step diagram
4
5
Worksheet
7
2
Module 10: Sequence control systems
ATM 1132 – Basic Pneumatics
1- Introduction to sequence control system
A control system with compulsory stepped operation where switching
from one step to the next in the program is dependent upon certain
conditions being satisfied. In particular, the programming of jumps,
loops, branching, etc. is possible.
2- Sequence control is divided into two subgroups:
 Time-dependent sequence control system
A sequence control where the switching conditions are dependent
only on time. Step enabling conditions are generated via timers, or
cam-shaft controllers with constant speed.
 Process dependent
A sequence control system where the switching conditions are
dependent only on signals from the system being controlled. Stepdiagram control is a form of process-dependent sequence control;
the step enabling conditions depend purely on the stroke-dependent
signals of the controlled system.
3- Control of multiple actuators
In the case of multiple cylinder circuits, a clear definition of the problem
is important. The representation of the desired motion of all actuators
is
described
using
the
displacement-step
diagram.
The
special
conditions for the start of the sequence must also be defined.
If the motion diagram and auxiliary conditions have been clearly
defined, drawing of the circuit diagram can commence. The circuit
diagram should be designed according to the guidelines, in order for a
circuit to operate, it is essential to avoid overlapping signals.
By an overlapping signal, we understand signals applied simultaneously
at the two control ports of a double pilot valve. The following valves can
be used to eliminate signal overlap: roller lever valves with idle return
or toggle lever valves, time delay valves, reversing valves or
sequencers.
Module 10: Sequence control systems
3
ATM 1132 – Basic Pneumatics
4- Displacement-step diagram
The displacement step diagram and the
displacement-time diagram represents the
operating sequence of the actuators, the
displacement is recorded in relation to the
sequence step.
(a)
Positional sketch
If a control system incorporates a number of
actuators, they are shown in the same way
and are drawn one below the other. Their
interrelation can be seen by comparing the
steps as shown in (Fig. 10.1.b). There are
two cylinders 1A and 2A. In step 1 cylinder
1A extends and then cylinder 2A extends in
step 2. In step 3 cylinder 1A retracts and in
(b)
Displacement step
diagram
step 4 cylinder 2A retracts. Step number 5
is equivalent to step 1.
In
the
case
of
a
displacement-time
diagram, the displacement is plotted in
relation to the time as shown in (Fig.
10.1.c)
(c) Displacement time
diagram
Fig. 10.1
4
Module 10: Sequence control systems
ATM 1132 – Basic Pneumatics
Example (1)
Find the sequence of operation for the given displacement step diagram
Solution:
__________________________________________________________
Example (2)
Draw the displacement step diagram for the following sequence of
operation
A+B+B-A-C+C-
Solution:
Module 10: Sequence control systems
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ATM 1132 – Basic Pneumatics
Student’s notes
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Module 10: Sequence control systems
ATM 1132 – Basic Pneumatics
Work sheet
Draw the displacement step diagram for the given sequence of operation:
A+ B+ B- A- C+ C…………………………………………………………………………………………………………………………
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Draw a circuit diagram for the given sequence of operation:
A+ B+ A- B…………………………………………………………………………………………………………………………
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Module 10: Sequence control systems
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