Project report of programmable logic controller

A PROJECT REPORT ON “APPLICATION LOGIC FOR MAIN AND EMERGENCY AIRLOCKS USING PROGRAMMABLE LOGC ONTROLLER”

BY

K.SRINATH

WHAT IS A PLC

Def of PLC: Defined by NEMA( National Electrical Manufacturer Association) as a “digital electronic device that uses a programmable memory to store instructions and to implement specific functions such as logic, sequence, timing, counting and arithmetic to control machines and processes”.

# A PLC ( I.e., programmable logic controller) is a device that was invented to replace the necessary sequential relay circuits for machine control.

Evaluation to the present PLC:

Advantages of the PLC

Disadvantages of the PLC

PLC is a open loop control system

System Specifications:

General Specifications

Functional Specifications

Relay is an electro magnetic switch apply a voltage to the coil and a magnetic field generated. This magnetic field sucks the contacts of the relay in causing them to make a connection. This contacts can be considered to be a switch they allow current to flow between two points thereby closing the circuit.

Eg:- A relay is used to turn on a bell whenever a switch is closed.

Here we are using a dc relay to control an AC circuit.

Before PLC, use of relays

Example of bell using a relay

Typical industrial relay

PLC panel

Dc power supply Dc power supplies

Input cards Output cards

Logc o/p cards

Logic I/p cards

Cabinet Description:Structural Details

Fan Modules

Cards of the PLC systemCPU RT-20 BOARD

TBC-VME BOARD

VME I/O INTERFACE BOARD

VME BUS MOTHER BOARD

WATCHDOG TIMER

MODEM CARD

LOGIC I/O BIN

I/O BUS INTERFACE BOARD

LOGIC INPUT BOARDS

LOGIC OUT PUT BOARD

LOGIC MOTHER BOARD

FIELD INPUT INTERFACE BOARD

FIELD OUTPUT INTERFACE BOARD

FIELD MOTHER BOARD

BLOCK DIAGRAM OF PLC        

Logic I/O bin Control bin I/O bin Power Supply System 

PLC 

LogicInputCards 

I/O Businterface

Logic Output cards 

Field Input cards

Field Output Cards 

CPU VME I/O TBC VME WDT CARD MODEM

CPU sub system power supply

Logic I/O power supply Field contact interrogation 

PLC Input Module layout

sensor converter Optoisolator output Dc to cpu

Sensor

Converter

Isolator Opto isolator

Output

Output Modules: The output module operates in the

opposite manners on the input module. A DC from the CPU is converted through each module section to a usable output voltage, either AC (or) DC

How the inputs circuits of PLC work

How the DC Input work: DC input modules allow us to connect either PNP(sourcing) or NPN(sinking) transistor type devices to them.

Here we are using a sensor, we have to verify it is PNP or NPN output configuration.

An NPN type transistor has a load switched to ground where as a PNP device has the load switched +ve voltage.

On the NPN transistor we connect one output to the PLCs input and the other output to the power supply ground.

NPN (SINKING) SENSOR

On the PNP Sensor we connect one output to positive voltage and the other output to the PLCs

input.

PNP (SOURCING) SENSOR

How the AC input works

An AC voltage is non-polarized means that there is no +ve to “worry about”.

AC Voltage can be quite dangerous to work with if we are careless.

AC Input modules are less common these days than dc input modules. The reason being that today’s sensors typically have transistor outputs. A transistor will not work with an ac voltage.

The photo couplers are used to isolate the PLCs internal circuit from the inputs. This eliminates the change of any electrical noise entering the internal circuitry. They work by converting the electrical input signal to light and then by converting the light back to an electrical signal to be processed by the internal circuit.

Engineers Console SubsystemEngineer’s console is the man machine interface to program

programmable logic controllers. It’s main function is for programming the PLCs and monitoring the I/O status of the plant. In addition to this, it also has the following features:

i. Entering new rungsii. Editing of the existing rungsiii. Monitoring the rungsiv. Retrieving data from PLCv. Backup operationsvi. Storing the user logicvii. Display of diagnostics messagesviii. Hardcopy facilityix. Communication with PLCs

Mode of Operations

•Redundant mode

I. Active Mode

II. Stand by Mode

•Non-Redundant mode

The PLC system shall provide a mechanism for:

Switchover from Redundant to Non-Redundant mode on detection of a fault in the ‘Active’ or Standby’ CPU sub-system

Recovery from Non-Redundant mode to Redundant mode

•Hot Repair Mode

LADDER GRAPHIC LANGUAGE

The present Engineer Console software allows the user to program only the digital capability of the existing PLC. The programming language for the PLC is called ladder graphic language(LGL). It comprises of Boolean like statements AND, OR, NOT and its symbols are shown below:

Normally open contact

Normally closed contact

Output Coil --( )—

LGL STATEMENTS AND RUNGS

APPLICATION AND BENEFITS OF PLC

CHEMICAL / PETRO CHEMICAL

MINING

PULP / PAPERS / LUMBERS

MANUFACTURING / MATCHING

METALS

POWER

GLASS / FILM PROCESS

BENEFITS:

High reliability

Flexible control

Higher level of performance

Communication capability

Signal power operation

REACTOR BUILDING AIRLOCKS LOGIC CONTROL PANEL

Role of the system:

The Reactor Building Airlocks are provided to facilitate a restricted movement of the personnel and equipment to and from the Reactor Building and to various areas inside the Reactor Building during normal operating and shutdown conditions of the Reactor. Two Airlocks, namely Main Airlock(MAL) and Emergency Airlock(EAL) are provided for the entry/exit of the personnel and equipment into/from the reactor building, while maintaining the containment integrity.

BRIEF OVERVIEW OF THE SYSTEM:

The Airlocks Logic Control Panel shall be identified as 62420-PL-1 The Control panel shall be consist of all the devices, modules, components and subassemblies to meet its functional requirements like operational Hand switches, Pushbuttons, indicating lamps(LED), engineering console, PLC units with its modules, Power supplies, Terminations and cabling/wiring. All the system operation hand switches/pushbuttons, Airlock doors/devices status indicating lamps and Engineering console shall be located on the from of the control panel. PLC units with its modules, power supplies, termination blocks and other components/devices shall be located inside the panel accessible from the rear side of the panel.

TYPICAL OPERATION SEQUENCE FOR PERSONNEL DOORS OF MAL

DOOR OPENING SEQUENCE FOR MAL PERSONNEL DOORS:

1. Open/being opened status of the doors of the MAL is checked. PEV closed status is checked for the operation of RB side door and middle door .If all other doors are closed /not being operated and PEV is closed &’Door Open’ command from Push Button is accepted and latched.

2. Closing operation of the door is terminated.

3. Solenoid valves provided on seal inflation lines are de-energised to cut-off air supply to inner and outer seals .

4. Solenoid valves provided on bleed air lines are energized to cut-off the bleed air supply to both (inner and outer) the seals.

5. Solenoid valves provided on seal deflation lines are energized to connect both the seals to vacuum tank for seal deflation. Both the seals are deflated by connecting the seals to vacuum tank and cam disc is unlocked.

6. Differential pressure across the door starts equalizing after deflation of the seals. A differential Pressure switch (DPS) is provided to sense the differential pressure across the door equalized condition. Check the contact status from the DPS for DP across door equalized condition.

7. After the differential pressure across the door is equalized (DPS contact is closed), Solenoid valve provided for cam rotation to unlock the door for opening is energized. A Limit Switch is mounted on the door to sense the door unlocked condition (i.e. locking pins fully retracted/disengaged ) .

8. After the door is unlocked (LS contact closes). SV provided for door rotation to open the door is energized for a specified period required for the opening of the door (normally door opening takes about 60 sec.. timer is adjustable from 1 to 180 sec. and is to be set during commissioning).

DOOR CLOSING SEQUENCE FOR MAL PERSONNEL DOORS

1. ‘Door Close’ command from push button is accepted and latched.

2. Opening operation of the door is terminated if being executed.

3. Solenoid valve provided for door rotation to close the door is energized if both the seals are in deflated condition ( as sensed by the pressure switches provided to monitor seal deflated conditions).

4. After door is fully closed as sensed by the Limit Switch provided on the door ,Solenoid valve provided for cam rotation to lock the door is energized to lock the door.

5. After the door is fully closed (as sensed by the limit Switches ) Solenoid valves on seal deflation lines are de-energised to isolate both the seals from vacuum tank.

6. After the door is locked as sensed by Limit Switch provided on the door (to sense fullyengaged condition of locking pins). Solenoid valves provided on seal inflation lines are energized to supply the air to both the seals for inflation.

7. After either the seals or both the seal are inflated as sensed by the respective pressure switches, closing operation is completed. Solenoid valves provided for seal inflation lines are de-energised to cut-off air supply to both the seals through seal inflation line.

8. When the door is fully closed and locked as sensed by the Limit switches provided on the door ,Solenoid valves provided on the bleed air lines are de-energised to supply the bleed air to both seals(size of this line is small compared to size of seal inflation line). Bleed air supply is continued to make up the air loss through leakages to maintain the seals inflated condition.

Force close operation of MAL doors :

A ‘Force Close’ push button is provided on each of the local field panels of MAL doors. Operation of ‘Force Close’ push button from any of the local field panel initiates closing all of the personnel doors of MAL and initiates inflation of the seals of all equipment doors as per closing sequence of respective doors.

CONCLUSION

A Programmable Logic Controller ( PLC ) is a device that was invented to replace the necessary sequential relay circuits for machine control. A person knowledgeable in relay logic systems can master the major PLC functions. These are used extensively in nuclear reactor building and security control system. It is a reliable compare to other control systems. These may be used to run a vibot. By using the PLC application logic we can control the airlocks logic control panel of reactor buildings. These PLCs are used in many “Real World” applications. So using these PLC’S nuclear reactor building doors namely Main Air Lock & Emergency Air Lock are con