1. INTRODUCTION Programmable logic controllers provide dependable, high speed control and monitoring demanded by a wide variety of automated applications. Before the automotive industry discovered the advantages of PLC, the process of modifying relay circuitry was a difficult. In the past, annual car model changes forced plant engineers to constantly modify production equipment managed by relay circuitry. In some cases, the engineers had to scrap entire relay controlled panels and replace them with completely redesigned systems. Now, PLC’s allow engineers to implement numerous manufacturing changes with relative ease, which reduces changeover costs and downtime. Basically, it's a solid-state, programmable electrical/electronic interface that can manipulate, execute, and/or monitor, at a very fast rate, the state of a process or communication system. It operates on the basis of programmable data contained in an integral microprocessor based system. A PLC is able to receive (input) and transmit (output) various types of electrical and electronic signals and can control and monitor practically any kind of mechanical and/or electrical system. Therefore, it has enormous flexibility in interfacing with computers, machines, and many other peripheral systems or devices. It's usually programmed in
Transcript
1. INTRODUCTION
Programmable logic controllers provide dependable, high speed control and
monitoring demanded by a wide variety of automated applications. Before the
automotive industry discovered the advantages of PLC, the process of modifying relay
circuitry was a difficult. In the past, annual car model changes forced plant engineers to
constantly modify production equipment managed by relay circuitry. In some cases, the
engineers had to scrap entire relay controlled panels and replace them with completely
redesigned systems. Now, PLC’s allow engineers to implement numerous manufacturing
changes with relative ease, which reduces changeover costs and downtime.
Basically, it's a solid-state, programmable electrical/electronic interface that can
manipulate, execute, and/or monitor, at a very fast rate, the state of a process or
communication system. It operates on the basis of programmable data contained in an
integral microprocessor based system. A PLC is able to receive (input) and transmit
(output) various types of electrical and electronic signals and can control and monitor
practically any kind of mechanical and/or electrical system. Therefore, it has enormous
flexibility in interfacing with computers, machines, and many other peripheral systems
or devices. It's usually programmed in relay ladder logic and is designed to operate in an
industrial environment.
To know how the PLC works, it is essential that we have an understanding of its
central processing unit's (CPU's) scan sequence. The methodology basically is the same
for all PLC’s. However, as special hardware modules are added into the system,
additional scanning cycles are required.
2) OBJECTIVE
The objective of this project is to:
1. Understand PLC’s terminology, configuration, I/O modules addressing and types
of PLC memory devices,
2. Program instructions that perform logical operations and ladder logic programs,
3. Program the control of outputs using the timer instruction control bits,
4. Apply the PLC counter function and associated circuitry to control systems,
5. Install hardware components used in PLC systems.
6. Understand, design and develop PLC program.
7. Assemble and test run the correct components, circuits and program in PLC
system.
8. Safety practices in PLC laboratory; PLC components and functions;
Programming language; Step displacement diagrams; Circuit assembly for
pneumatics and electric for single and sequence actuation; Timer and counter.
3) SCOPE
In the end of this experiment we found that:
Student able to draw a basic electro-pneumatic circuit with PLC, install and test
run it to move an actuator.
Student able to design, construct, and troubleshoot of this PLC circuits.
Student able to identify and operate a few types of electro pneumatic
components including relay and its contactors.
4) SAFETY PRECAUTION
1. Never disconnect electro pneumatic lines or disassemble electro pneumatic
equipment when the pneumatic system power motor is running.
2. Make sure I/O and extension connector are installed correctly.
3. Use the PLC in an environment that meets the general specification contained in
this manual.
4. Make sure all external load connected to output does NOT exceed the rating of
output module.
5. Install a safety circuit external to the PLC that keeps the entire system safe even
when there are problems with the external power supply or PLC module.
Otherwise, serious trouble could result from erroneous output or erroneous
operation.
6. Never manually actuate switches, solenoids, relays, or valves on pneumatic
systems under pressure unless you are competent and qualified to perform these
actions.
7. All personnel taking part in and observing operation of power equipment must
remain alert, keep clear of moving parts, and be thoroughly familiar with the
safety precautions applicable to that equipment. At no time should skylarking be
allowed in the vicinity of operating power equipment.
8. Never use electrical or electronic equipment known to be in poor condition.
9. Use the right voltage. Most pneumatic devices are powered by air and
controlled with an electronic control valve.
10. Check and secure all of the mountings, fittings, piping, tubing, connectors and
connections before connecting any electro pneumatic components or systems to a
power supply.
5) METHOD AND STANDARD OPERATION PROCEDURE (S.O.P)
Task: Operating a Charge and Discharge Process
Charge and discharge of a reservoir is a common process in industry as well as a
need for mixing two or more substances. By using automated valves, this process can be
completely automated. Let us say that fluid used in the example is water, and that a
reservoir has to be filled up and emptied four times.
When you push T1 on the operating panel, valve V1 opens and a reservoir starts
filling up with water. At the same time, motor M of the mixer starts working. When the
reservoir fills up, water level goes up and reaches the level set by a sensor S1. V1 valve
closes and motor of the mixer stops. Valve V2 opens then and a reservoir start emptying.
When water level falls below the level set by a sensor S2, valve V2 closes. By repeating
the same cycle four times, lamp that indicates end of a cycle is activated. Pressing T1
key will start a new cycle.
Both types of differentiators are used in this example. You can get an idea of
what their role is from picture below. Level S1 and S2 sensors provide information on
whether fluid level goes beyond a specified value. This type of information is not
important when you wish to know whether fluid level goes up or down in a certain
sequence. Mainly, event of approaching the upper level, or a moment when fluid that
fills up a reservoir goes beyond upper level and activates sensor S1 is detected in
segment 3 of a ladder diagram. Brief activation of IR200.02 output has a consequence a
turn off of an output V1 (valve for water, prevents further flow of water but also motor
operation in the mixer). Moment prior to this (segment 5) valve V2 turns on which
marks a beginning of fluid outflow. Other two differentiators (in segments 6 and 7) have
a task of registering events such as closing a valve MV2 and drop in fluid level below
