CHAPTER 6

SELECTING, MAINTENANCE

AND TROUBLESHOOTING

OF PLC SYSTEM

COURSE LEARNING OUTCOMES (CLO)

Explain clearly blocks, parts, components and instructions found in the automation systems. (C2)

Handle the troubleshooting and maintenance of hardwired or PLC automation systems using appropriate equipment. (P3)

PLC SELECTION PROCEDURE

1. INPUT AND OUTPUT CAPACITY Input modules provide the interface between the

PLC and external input devices such as proximity sensors, push buttons, switches, and BCD thumbwheels.

Output modules provide the interface between the PLC and external output devices such as contactors, interposing relays, BCD displays and indicator lamps.

Capacity means the number of terminal connections on the input and output unit.

Table 1 show a few of input/output capacity.

Table 1: Input / Output Unit Specifications

INPUT UNIT

TYPE MODEL NO. CAPACITY

DC Input

CQM1-ID211 8 points

CQM1-ID212 16 points

CQM1-ID213 32 points

AC Input CQM1- IA121 8 points

CQM1-IA221 8 points

OUTPUT UNIT

TYPE MODEL NO. CAPACITY

Relay Output

Units

CQM1-OC211 8 points

CQM1-OC222 16 points

Transistor

Output Units

CQM1-OD211 8 points

CQM1-OD212 16 points

CQM1-OD213 32 points

CQM1-OD214 16 points

CQM1-OD215 8 points

AC Output Unit CQM1-OD221 8 points

The base I/O for the CPU ranges from 10, 20, 30, and 40 I/O points with maximum expansion to 100 I/O.

Specialized expansion modules include mixed analog I/O, temperature sensor inputs and serial communications.

Example: CPM1A I/O Capacity

Source: OMRON

CPM1A I/O Capacity

Source: OMRON

2. TYPES OF INPUT AND OUTPUT Before you use the PLC to control a job, you need to identify

the supply of which will be connected to the input unit either AC or DC.

Never connect AC supply to DC input unit and vice versa.

Input Device: Proximity Switches: use inductance, capacitance or light to detect

an object logically.

Switches: mechanical mechanisms will open or close electrical contacts for a logical signal.

LVDT (linear variable differential transformer): measures linear displacement continuously using magnetic coupling.

Output device Normal switching: use Relay

Fast switching: use TRANSISTOR

High-voltage switching: AC type (TRIACS)

3. MEMORY SIZE The memory system is the area in the PLCs CPU

where all of the sequences of instructions, or programs, are stored and executed by the processor to provide the desired control of field devices.

The memory sections that contain the control programs can be changed, or reprogrammed, to adapt to manufacturing line procedure changes or new system start-up requirements.

Memory size of a PLC is referring to the ability to save program in your PLC memory system.

Table 2 shows the number of memory size by CPU type.

Table 2: CPU Unit Specifications Example of memory: ROM,PROM, EPROM

No. Model Memory size

CQM1-CPU11-E 3.2 K-word Program Memory

1K-word Data Memory CQM1-CPU21-E

CQM1-CPU41-E

7.2 K-word Program Memory

6K-word Data Memory

CQM1-CPU42-E

CQM1-CPU43-E

CQM1-CPU44-E

Example: From datasheet

Omron CX-Programmer.

Syswin.

Mitsubishi. GX-Developer

Siemens. Simatic

STEPS 7

NAIS (Panasonic). Fpwin.

The best way to Designing Programming the PLC is using the PLC programming

software.

4. TYPES OF SOFTWARE

LANGUAGE

5. FUTURE SYSTEM EXPANSION

EXPANSION

Industrial control system is undergoing a transformation from traditional control to automated control.

PLC is a major agent of this automation system.

Many industries have implemented the automation-based control system, such as Flexible Manufacturing System (FMS) and Computer Integrated Manufacturing (CIM).

During PLC selection, future needs of the industry must be taken into account so that using PLC wont cause a drawback to the industry.

Several types of PLC are design to used the expansion unit to upgrade the number of I/O and application device (data logging, temperature unit and etc.).

Example(Omron CJ1W)

Example (Omron CPM)

6.SUPPORT AND BACKUP

Industrial automated control system requires support and backup unit.

Backup option is used where you must transfer the control of the process to a secondary system without interrupting the machine/process operation.

To guard against system shutdown, a backup system must provide: Equipment with exceptional reliability

Automatic fault isolation.

Minimal disturbance of the process when switching from the primary to the secondary system

There are requirement to setup support and backup system in control system.

Example :-

CJM-2M-CPU3(Omron) IP PORT( internet )

Serial Gateway.

Serial PLC link.

Fatal error detection.

Backup function.

Remote programming &

monitoring.

Requirement for support and backup system

CJM-2M-CPU3(Omron)

INSTALLATION TECHNIQUE

To reduce damage to the automation control systems, serious consideration should be given to the following during PLC installation and wiring :

Avoid installing PLC at places that has:

Direct exposure to sunlight.

Environment temperature exceeds range of 0C to 55C.

Relative humidity over range 10% to 90% RH.

Condensation occur due to sudden temperature change.

Contains flammable and poisonous gases .

Contains water, oil, chemical dust.

Vibration occurs easily.

1. SITE INSTALLATION CONDITION

CONSIDERATION

Operating Temperature :- Depend on speciation of manufacture.

Omron ( 5 40 C).

Sometimes front panel for plc application 10-15 C higher then ambient temperature of the room.

Used cooling system for ensure the temperature is low.

Method of cooling system :- Natural Cooling.

Controlled Ventilation.

Control Circulation.

Room Cooling System.

Higher Temperature malfunction the PLC/ damage

Cooling System

2. PANEL/CABINET INSTALLATION

CONSIDERATION.

Install the PLC in the panel / cabinet with the following characteristics:

Enough space for air circulation.

Cooling fan.

Device that produces heat is place under the PLC.

Not containing high voltage equipment.

Power line situated approximately 200 mm from the PLC.

For safety requirement all PLC must be installed with some distance from higher voltage source.

All panel must be grounded.

The input/output signal should be install separately from power cable (Figure A).

3. WIRING PRECAUTION CONSIDERATION

Figure A

If there are several group of cable in thesystem, install it in group (Figure B).

Figure B

Types of wiring method.

1. Handing Ducts Wiring Method

2. Floor Ducts Wiring Method

3. Conduit Wiring Method

Power Line

Follows the wiring instructions as shown below: Use the cable as short as possible. Use a single line and do not connect between cables to

extend it. Avoid making sharp curve on the cable. Distance control system space and control wiring from high

energy wiring. Separate input wiring, output wiring and other types of

wiring. Separate AC and DC wiring. Establish a good grounding for all components. Ensure the wire is the correct gauge and have proper size to

handle the maximum possible current. Each field wire and its termination point should be labeled

using a reliable labeling method. Use wire bundling technique to simplify the connections to

each I/O module. Input, power, and output bundles carrying the same type of signals should be kept in separate ducts, when possible, to avoid interference.

PLC contains many active components such as transistor and integrated circuit.

If surge voltage (resulting from lightning) occurred, the active components will burn.

This problem can be overcome by: Ensure that the ground terminal and PLC ground are

grounded by maximum of 100 W.

Make sure that the grounding cable is at least 2 mm2.

Grounding base and the green cable must end at the cable lug. Cable lug must be screwed and soldered.

Corrosion and paint coatings must be removed from the ground connection.

4. INSTABLE VOLTAGE AND VOLTAGE SPIKE

Output Inductive load

Noise filter for PLC power supply

Grounding

PLC MAINTENANCE AND TROUBLESHOOTING METHODS

Maintenance

Involves fixing any sort of mechanical or electrical device should it become out of order or broken (known as repair, unscheduled or casualty maintenance).

Preventive maintenance carry out normally for 1 year or 6 month for checking the PLC (I/O device).

Troubleshooting

Problem solving technique.

Applied to repair failed products or processes.

1. PLC EXTERNAL FAULTS

Input/output equipment damage (sensors and actuator)

Wiring damage Communication connection damage Power supply failure

INPUT/OUTPUT EQUIPMENT DAMAGE (Sensors and

Actuator) 60% - 80% damage in the automation control

system usually occurs due to the input and output devices faulty.

The possibility of this damage is caused by:

Sensor in the cylinder vary from the original position.

Sensor internal contact failure damage.

Sensor burns due to over current.

Motor coil or solenoid valve burns due to over current.

WIRING DAMAGE

Likely caused by: Conductor in the cable disconnected/fault.

Loosen screw; at input and output terminals.

Conductor oxidized.

COMMUNICATION CONNECTION DAMAGE Can be caused by:

Conductor in the communication cable disconnected/fault.

Terminal connection pin bent or broken.

Loose pin connection.

Interference occur in the communication cable caused by motor, coil, high voltage, sloppy soldering.

Short circuit occurs between conductors in the communication cable.

POWER SUPPLY FAILURE

Power failure occurred in the automation control

system when the supply voltage dropped below 85% of the rated value.

This situation will cause the PLC to stop immediately.

2. PLC INTERNAL FAULTS Can be caused by:

Relay or transistor in the PLC unit/output module burn.

Optocoupler at the unit/input module not working.

Fuse burnt .

Weak storage battery.

Micro-electronic component (microprocessor, RAM, ROM) burnt.

Programming error.

Off Line (using software or console)

ON line ( using mode monitor for OMRON).

3. METHODS TO MODIFY PROGRAMS

4. PROGRAMMING AND MONITORING METHODS.

PLC have a large number of ports for interacting with analogue systems, sensors, switches, motors, and various other systems needed to operate, monitor, and maintain a control system used in industrial automation applications.

Remote monitoring is used to monitor the system and to aid in the prevention of problems and to keep track of the operations of the equipment.

To perform remote monitoring, the software needs to communicate with the PLC used in the control systems.

The system can be monitored through the ladder logic programming language.

Each rung will be one of two things:

A switch that activates based on an internal variable or the status of an I/O port (input / output)

An action to take such as changing an internal variable or switching a motor on via an I/O port

Remote monitoring software retrieves the values for a range of memory addresses. The values returned by the PLC can be parsed and reveal the current status of the control system at the facility.

Example: The current electrical usage of a motor being stored in

memory range 0xf489 0xf48c.

To get the information from this memory range, the remote monitoring software would send a command packet to request this memory range from the PLC, listen for a valid response, and interpret/store the returned information as necessary.

5. PREVENTIVE MAINTENANCE PLC preventive maintenance can be made as follows: Making periodic inspections for screw tightness at the input

and output terminals. Ensure that all components are dust free. PLC cooling system

can not be executed if there is dust on its layer. Corrosion may occurred in some circumstances. Perform

periodic inspection at the connection terminal for corrosion. Printed circuit boards and connectors may have corrosion internally.

Spare parts equipment must be stored well for future use if any damage arise too the components. Users will suffer losses if there is no spare parts and they have to wait for a period of time.

Documentation for program operations and circuit wiring must be kept safe. It may be needed in case of emergency.

6. STEPS FOR TROUBLESHOOTING PLC SYSTEMS