Simple Sequence

Control system with step-by-step operation were switching on

from one step to another is dependent upon certain conditions
being fulfilled.
S1 S2 S3 S4

A B

Sequence example: A+ B+ A- B-
- First look at the last step, which is(B-). This is the initial
condition for the sequence to begin.
- B- means cylinder B is retracted, hence S3 is triggered
A+ B+ A- B-

S3 S2 S4 S1
S3

• S1 S2 S3 S4 à use 3/2-way valve micro switches.

• Use mechanically activated roller for the 3/2-way valve.
• If S3 is not functioning, A will not extend à process will not
start.
• Suppose everything is going well, then A- fails suddenly.
Then, S4 will have an issue. That is because S4 is the
condition required for A-.
• The sequence 1A+ 2A+ 1A- 2A- is to be read as follows:
 Cylinder 1A advances, cylinder 2A advances, cylinder 1A
retracts, cylinder 2A retracts. Sequential movements are
written consecutively.
• The sequence 1A+ 2A+ 1A- is to be read as:
2A-
Cylinder 1A advances, cylinder 2A advances and cylinder 1A
retracts, cylinder 2A retracts. Simultaneous movements are
written vertically.

1. Positional sketch: pictorial representation

2. Schematic or circuit diagram
3. S7 graph representation
4. Displacement-step diagram with signal lines

5. Displacement-time diagram: When time is lessà speed is

high and vice versa.

6. Control chart: represents all states of all components in a

circuit.
7. Function diagram: combination of all diagrams and chart
Complex sequence
To do A+ B+ B- A-, putting all rollers will
make a problem.
Using idle roller will solve the problem Partially.
Idle roller à choose actuation direction.

Actuate when extended

Actuate when retracted

Best solution:
When there two similar letters with different signs following
each other, there should be a separation of lines between them.

A+ B+G2 L2B- A-
G1 L1

S4(switch from L1 à L2)

S1(switch from L2 à
L1)

- These two lines L1 & L2 should be connected to the same

compressor.
- N=G-1 à eq. to find number of switching devices needed
- Suitable switching device: 4/2-way valve double pilot
pneumatically operated.
- Switching devices are connected in series.
- For example, S1(L2 to L1) à S1 makes L1 effective.

A+ B+ B- A-

B1(L1
à L2)
A0(L2
à L1)

How to do the connection for A+ B+ B- A-?

- 2 cylinders A & B will be connected directly to the 5/2-way
valve double pilot.
- First letter in the G# is connected directly to its L#
- For remaining letters, 3/2-way valve with roller and spring
return will be needed.
These valves’ input port 1 will be connected to their
respective lines.
- N=2-1 one switching device is needed to toggle between L1 &
L2.
- Connect output ports of the switching device to L1 & L2.
- Two more 3/2 valves will be connected with the switching
device.
- Connect input and output ports of these valves to their
respective lines. Ex: B1(L1 à L2)
- Put the limit switches accordingly to the given sequence.

How the circuit works?

This type of pneumatic circuit sequence needs 1 switching
device because it has 2 groups only. It can be observed that B1
switches L1 to L2 and A0 switches L2 to L1.
In order for the sequence to begin (A+), cylinder A should be
retracted (A-). This is sensed by limit switch A0. Once A0 is
triggered, L1 will be effective via switching valve, and signal
will flow through the double pilot pneumatically operated 5/2-
way valve. Therefore, connecting port 1 to 4 and allowing the
cylinder to extend (A+). The extended position will trigger limit
switch A1 which will activate the 3/2-way valve. As L1 is still
effective, the signal will travel through the 5/2-way valve and
make cylinder B extend (B+). This will trigger B1, which will
make L2 effective via the switching device. Now, cylinder B
will retract (B-) since there is a direct flow of air to the 5/2-way
valve. The rear end position of cylinder B will activate limit
switch B0, which will allow cylinder A to retract (A-). Once
again A0 will be triggered and the whole sequence will keep
repeating in the same manner.
A+ B+ B- C+ C- A-
A-
S4(L1
à L2) S6(L2
à L3)
S1 (L3
à L1)

How to do the connection for A+ B+ B- C+ C- A-?

- 3 cylinders A, B & C will be connected directly to the 5/2-way
valve double pilot.
- First letter in the G# is connected directly to its L#
- For remaining letters, 3/2-way valve with roller and spring
return will be needed. These valves’ input port 1 will
be connected to their respective lines.
- N=3-1, two switching device is needed to toggle between L1 &
 L2 / L2 & L3/ L3 & L1.
- Connect output ports of switching device#1 to switching
device #2 and the last effective line.
- Connect output ports switching device #2 to L1 and L2.
- Three more 3/2 valves will be connected with the switching
devices.
- Connect input and output ports of these valves to their
respective lines. Ex: S4(L1 à L2)
- Put the limit switches accordingly to the given sequence.

How the circuit works?

First of all, it can be seen that S4 connects L1 to L2, S6 connects
L2 to L3, and S1 connects L3 to L1.In order for the sequence to
begin, cylinder A should be retracted (A-). This is sensed by S1.
Input of S1 which is L3 will connect to its output which is L1
through the first switching device. Once L1 is effective, cylinder
A will extend (A+). This will trigger S2, and cylinder B will
extend (B+) activating S4.

Input of S4 which is L1 will connect to its output L2 through the

second switching device. Once L2 is effective, cylinder B will
retract (B-). This will trigger S3, and cylinder C will extend
(C+) activating S6.

Input of S6 which is L2 connects to its output L3 through the

first switching device. Once L3 is effective, cylinder C will
retract (C-). This will trigger S5, and cylinder A will retract (A-)
activating S1 which again will connect L3 to L1, hence
repeating the sequence.
S3(L3 à L1)

A+ A- B+
B-
 S2(L1 à
L2)

S4(L2
àL3)

How to do the connection for A+ A- B+ B- ?

- 2 cylinders A & B will be connected directly to the 5/2-way
valve double pilot.
- First letter in the G# is connected directly to its L#
- For remaining letters, 3/2-way valve with roller and spring
return will be needed. These valves’ input port 1 will
be connected to their respective lines.
- N=3-1, two switching device is needed to toggle between L1 &
L2 / L2 & L3/ L3 & L1.
- Connect output ports of switching device#1 to switching
device #2 and the last effective line.
- Connect output ports switching device #2 to L1 and L2.
- Three more 3/2 valves will be connected with the switching
devices.
- Connect input and output ports of these valves to their
respective lines. Ex: S2(L1 à L2)
- Put the limit switches accordingly to the given sequence.
A+ should be connected directly to L1
A- should be connected directly to L2
B- should be connected directly to L3
Now put 3/2-way valve for B+ and for switching between lines
The input of 3/2 valve should be connected to the respective line
• To put the limit switch:
S3(L3 to L1), S3 is for L3, so put S3 on the limit switch
which is connected to line 3
S2(L1 to L2), S2 is for L1, so put S2 on the limit switch
which is connected to line 1
S4(L2 to L3), S4 is for L2, so put S4 on the limit switch
which is connected to line 2
S1 is connected directly to 3/2-way valve for B
Electro-Pneumatics

solenoid relay
- Electric device - Electromagnetic switch
- Current à magnetic field is induced - Voltage à electromagnetic field is induced
- Has coil and contacts
- Contacts: NO, NC and change over
- Voltage is applied at the coil
- Usually drawn when deenergized in the circuit

• Latching connection à makes the relay stay connected.

• Most of electro-pneumatic works on 24V
• Indirect control à not sending voltage directlyà through relay
• In electronics, relay is used
• In electrical, contactor is used because it handles large currents
• For a good design, electricity shouldn’t be there
• Manual switch à operated by an operator
• Minimize the no. of relays in sequence
• More relays à low reliability
• Relays decarbonate over time and usage (layer of C on contacts), it is one of the
worst faults to happen.
 Electric Sensors

Push button switch limit switch Proximity

switch pressure switch
1. Normally open - Measures - Measures
1. Pressure switch
- Usually, to start displacement displacement
with mechanical
process - Contactless
contact (binary
- Long service life
output signal)
- High reliability
- 3 terminals
3 4 (+), (-), signal
2. Pressure switch
with electronic
1. Reed switch
switching
(binary output
2. Inductive
signal)
proximity
switch

3. Capacitive
3. Electronic
12. Normally
2 closed proximity
pressure sensor
- Usually, to stop switch
(Analogue output
process
signal)
4. Optical
proximity 2 4
 switch

1 2

4
2 4
Proximity Switch

Reed Inductive
3. Change over Capacitive Optical
- Usually, positive
Switch proximity switch
power supplyproximity
is switch proximity switch
connected to 1
- Magnetically - Electronic - Electronic - Electronic
operated sensor sensor sensor

- The field of a
magnet - Senses only - Senses all - uses optical
causes the electrical materials means for
two reeds to conductors and object
close, metals in a detection. Red
allowing short distance. - The operation light or
current to principle is infrared light.
flow. - The operation based on
principle is changes of the - Does not sense
- Interference based on capacitance of transparent
from other changes to the the capacitor materials.
magnetic alternating inside the
fields must be magnetic field sensor. - Has transmitter
avoided. generated by and receiver.
the sensor.
- Max. current - - Receiver:
Photodiodes or
must be phototransistors.
avoided to not
burn the - Sensing
contacts distance
depends on
colour and
reflective
nature of the
surface

- Not suitable for

dirty
Direct control environments.

The electronic solenoid has the label Y1 as it is related to the pneumatic

a. Diffuse optical
solenoid, the same is for Y2. switch:
pressing the manual NO switch 1 will send signal to Y1 andreacts cylinder
on the
will extend. reflection of
Pressing the manual NC switch 2 will send signal to Y2 and the cylinder
the detected
will retract
However, pressing both switched simultaneously will not have workpiece.
any
effect on the cylinder just like the pilot signals.
 Direct control
The electronic solenoid has the label Y1 as it is related to the pneumatic
solenoid, the same is for Y2. There are also two limit switches related to
the other pneumatic limit switches.
Initially cylinder is retracted and S1 is triggered, which will send signal
to Y1, and cylinder will extend.
Once the cylinder gets fully extended, S2 will be triggered which will
send signal to Y2 and the cylinder will retract

Indirect control
The electronic solenoid has the label Y1 as it is related to the pneumatic solenoid,
the same is for Y2. There are also two limit switches related to the other pneumatic
limit switches.
Initially cylinder is retracted and S1 is triggered which will energize relay K1
hence activating switch K1 on branch 2 and making it NC. This will send signal to
Y1, and the cylinder will extend.
Once the cylinder gets fully extended, S2 will be triggered which will energize
relay K2 (relay with switch-on delay), the cylinder will stay extended and not start
retraction until the timer reaches zero. Upon reaching zero switch K2 on branch 4
will be activated. This will send signal to Y2, and the cylinder will retract.

Indirect control
The electronic solenoid has the label Y1 as it is related to the pneumatic solenoid,
the same is for Y2. There are also two limit switches related to the other pneumatic
limit switches.
Initially cylinder is retracted and S1 is triggered which will energize relay K1(relay
with switch-off delay) hence activating switch K1 on branch 2 and making it NC.
This will send signal to Y1, and the cylinder will extend.
Once the cylinder gets fully extended, S2 will be triggered [however, there still is
signal at branch 2 because K1 did not reach zero] which will energize relay K2
(relay with switch-on delay), the cylinder will not start retraction until the timer
reaches zero. Upon reaching zero switch K2 on branch 4 will be activated. This
will send signal to Y2, and the cylinder will retract.
When cylinder is extended, S2 is triggered
Put NC switch, it’s like latching connection
but there is no signal at its branch

In the second pic, when we put the latching connection. S1 is actuated because
cylinder is initially retracted, K1 will get triggered, which will trigger the K1
contact and the changeover also. 1 will connect to 4 and signal will be sent to Y1
so that cylinder extends. Once reaching the end position, S2 will actuated hence the
limit switch will turn from NC to NO. this will remove signal from K1, and the
changeover will return to its initial position NO (1 to 2) and signal will be sent to
Y2 and the cylinder will retract.

Simple sequence
A+ B+ A- B-
Direct control
 Simple sequence
A+ B+ A- B-
Indirect control

Using relays

Always try to minimize the number of relays

 Hydraulics
Fluid power is the method of using pressurized fluid to transmit
energy.
Air is Compressible
liquid is Incompressibleà volume can’t be reduced

Power input Pump: pumps oil from the reservoir/tank to provide power.
device: Motor: The pump’s shaft is rotated by an external force

Hydraulic
systems
components
Control Valves: control the direction, pressure, and flow of the
device hydraulic fluid from the pump to the actuator/cylinder.
Power output Conversion of hydraulic into mechanical
device Cylinder: produces linear motion or motor: produces rotary
motion.
Liquid the medium used in hydraulic systems to transmit power

Conductors pipes or hoses needed to transmit the oil

power pack Pump + motor + tank+ Filters and commonly a Relief Valve
provides the energy required for the hydraulic system +
protection
local (near) to the machine that is using it.
One method of port designation:
P (pressure port), T (return port), A/B (power ports), and L (leakage oil port).
The other method of port designation is to label ports alphabetically
• Pressure valves are divided into pressure relief valves and pressure regulators

Pumps create flow, and pressure is created when flow is restricted

Hydraulics Pneumatics
• Uses pump (l/m) • Uses compressor (m3/h)
• Is Infinitely Controllable •
• Produces Extremely Large Forces • Does not produce large forces
• Requires High Pressures • Does not require high Pressures
• Requires Heavy Duty Components • Requires light Duty Components
• for relatively light moving, Clamping • earth moving equipment, heavy cutting,
and Process operations. Pressing and Clamping
• Bernoulli’s and other Fluid Flow Laws • Gas laws such as Boyle’s and Charles’s
• Expensive for Individual components • Inexpensive for Individual components
• Chances of fire hazard • Clean/low chances of fire
• Power pack is local to the machine that • Power pack is remote to the machine
 is using it. that is using it.
• Hoses and connectors are heavily • Pipes and push Fittings are of light
constructed. construction.
• Rubber hoses are steel Reinforced • Pipe is made from nylon
(Braided) to Strengthen them. • Fast
• Intrinsically Safe
• Overload Safe

hydraulic filters can be either Suction Strainers (suction side of the pump),
Pressure Filter (pressure side of the pump) or Return Filter (in the return to tank
line).
Electro-Hydraulics
• Both systems would use Solenoid actuated valves, either Directly Actuated or
Indirectly Actuated.
• An Electrical system would commonly incorporate Push Button Switches (for
human input), Reed Switches (to detect cylinder position), Proximity Sensors
and Photocells (to detect machine/component position).
• An Electrical system would also commonly incorporate Relays and computer-
controlled systems such as Programmable Logic Controllers.
Pressure here will read zero, because
whatever is pumped, is going back to the
tank directly. Working without blockage.

Pressure of pump is 6, pressure of relief

valve is 4, so the measured output

pressure will be 4.
Changing its value, will change
the output pressure