2014 IEEE Students' Conference on Electrical, Electronics and Computer Science

Effect of PLC and SCADA in Boosting the

Working of Elevator System

Saru SehgaJ ECE Department, BMIET,

Sonepat, India sarusehgal1987@gmail.com

Abstract- Elevators are used as main connectivity unit

of the floors, in malls, offices, industries and, buildings

of the hospital. Generally, the chip based controllers are

used to control the working of the elevator system.

These controllers have some sharp specifications which

cannot be maintained at all the time and, that's why

faults occur from time to time. So, Programmable Logic

Controller (PLC) is implemented in place of embedded

system. PLC can easily withstand the faulty situation

occurred in industrial environment and easily maintain

all the specific requirement of the elevator system. In

the present work, the ladder programming is used for

PLC. It has very simple and handy programming, i.e., if

we want to increase, decrease or skip any floor then

program can change as per our requirements.

Supervisory Control and Data Acquisition (SCADA) is

also used to supervise and control the working of the

elevator. If somehow any fault occurs then SCADA

itself identifies the fault position and generates an

alarm. The response on the fault can be taken within

no time by interfacing PLC and SCADA with the

elevator system.

Index Terms - Programmable Logical Controller

(PLC), Supervisory Control and Data Acquisition

(SCADA), Elevator System (ES).

Notations - Normally open (NO), Normally Close (NC),

Ladder (LAD), Infrared sensor (IR), Force (F),

Magnetic Flux Density (B), Current (I), Length of the

Conductor (L).

I. INTRODUCTION

Now-a-days, elevator becomes the most important part of the human comfort in the offices, malls, hospitals and industries to move across the different floors. Earlier, the chip based controller circuit boards are used to control the working of the elevator but as they are not withstanding the harsh conditions of industries and hospitals due to their slow processor speed [1] that's why we need to move on the best controller, i.e., Programming Logic Controller which is widely used in the industrial environment for providing the automation and has the ability to overcome the faulty situation.

978-1-4799-2526-1/14/$31.00 ©2014 IEEE

Vikas Acharya MAE Department, MAlT,

Delhi, India vikas _ acharya@rediff.com

PLC has the similar structure as that of a digital computer, as shown in the Fig. 1. It has an input and output module, CPU, memory card and, power supply.

Power

Supply

U Input Central Output

� > Processing � � Module Module

H Memory

Unit

Fig. I. PLC Block Diagram [2]

Fig. 2 shows the working of PLC in which it scans all the inputs continuously and energies the output coil according to the program. Housekeeping program stores the entire status bit which is used in the future and, required for the continuity.

"'OlJltlHt Q.xDUiiolt

Fig. 2. PLC Working Cycle [2]

Due to this functional programming, PLC has many advantages over the embedded system which are as follows: smaller physical size than hardwire solutions, more flexibility, also have integrated diagnostics and, override functions [1]. Diagnostics are centrally available and applications can be immediately documented and duplicated in it whereas, SCADA is used to supervise and control the working of the elevator system due to its ability of data acquisition. It, also, generates solutions for the upcoming problems and fault which may affect in the programming related to floor skipping, door open at the middle floor and, loading efficiency [3].

11. HARDWARE AND SOFTWARE

Some hardware components like Siemens S7-200, DC motor, etc. and, Siemens software are implemented in the elevator system to achieve the rejection of faulty alarms occur in the chip controller. The main components used in this project are:

A. HARDWARE

1) Siemens S7-200: With the vast choice of equipments now available, the engineers can usually obtain similar systems from Original Equipment Manufacturers (OEM). These manufactures provides different ratings of input/output devices and, certain types of controller functions [4]. So, it is possible that one system from a single manufacturer standing out as more superior or cost effective than the other; but normally this is rarely the case. To determine the most suitable PLC to be used in the automation task, there are several basic considerations to be made:

• Necessary input/output capacity; • Types of I/O required; • Size of memory required; • Speed and power required of the CPU and

instruction set • Manufacturer's support and backup.

The Micro PLC SIMATIC S7-200 is used because of its compact, highly powerful real-time responses, fast features, great communication options and, easy-to-operate software and hardware capability making it user friendly technique for open loop control system. It also incorporates a compact modular design for customized solutions which aren't too large, but flexible enough to be expanded any time in the future.

Table T

S7-200 CPU Specifications [4]

CPU 222 Description Specification

Power Supply 85-264 VAC

24.4-28.8 VDC

Memory 4096 Byte

Backup (super cap) 50 Hours

Optional Battery 200 Days

Digital VO 8/6

Analog I/O None

Timer 256

Counter 256

The S7-200 Micro PLC shown in Fig. 3 (a) and figure 3 (b), is the smallest member of the SIMA TIC S7 family of programmable controllers. The central processing unit (CPU) is internal to the PLC, inputs and outputs (I/O) are the system control points where input monitor field devices, such as switches and sensors and output control other devices, such as motors and pumps. The programming port is the connection to the programming device. There are five S7-200 CPU types: CPU 221, CPU 222, CPU 243 and CPU 224, CPU 224XP, and CPU 226 and two power supply configurations for each type [5]. And we are here using the CPU 222 for our requirement.

Fig.3(a). S7-200[4]

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Fig. 3(b). S7-200[4]

2) DC Motor: DC Motor converts Direct Current (DC) electric power into mechanical power. It works on the principle that when a current carrying conductor is placed in a magnetic field, it experiences a m�chanical force whose direction is given by Flemmg Left-Hand Rule and magnitude is given by the equation 1

F = BIL new t cm

(1)

The DC motors have two basic parts: the rotating part, i.e., called armature and the stationary part that includes coils of wire called the field coils. The stator is stationary in space by defmition and therefore the current in the rotor is switched by the commutator which is also stationary in space. This is how the relative angle between the stator and rotor magnetic flux is maintained near 90 degree, which generates the maximum torque [6].

Fig. 4. DC Motor

In Fig. 4, different connections of the field and armature winding provide different inherent speed/torque regulation characteristics [6]. The speed of a DC motor can be controlled by changing the voltage applied to the armature or by changing the field current. The introduction of the variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often control by power electronics system called DC drivers.

B. SOFTWARE

1) Semantics S7 Micro Win: It is the programming software of the Siemens for the S7-200. It provides the ladder logic programming use for a Normally Open

. (NO) and Normally Closed (NC) contact logic,

the tuners and memory bit to make the program. La�der diagram is a graphic programming language denved from the circuit diagram of directly wired relay controls. It contains contact rails to the left and the right of the diagram; these contact rails are connected to switching elements (normally open / normally closed contacts) via current paths and coil elements. The LADDER (LAD) editor displays the program as a graphical representation similar to electrical wiring diagrams. A LAD program allow the program to emulate the

flow of electric current from a power source through a series of logical input conditions that in turn enable logical output conditions. It includes a left power rail that is energized. Contacts that are closed allow energy to flow through them to the next element, and contacts that are open block that energy flow [7]. The left vertical line of a ladder logic diagram represents the power or energized conductor. The output element or instruction represents the neutral or return path of the circuit. The right vertical line, which represents �he re�urn path on a hard-wired control line diagram, IS omItted. These diagrams are read from left-to-right, top-to-bottom. Rungs are sometimes referred to as networks and these networks may have several control elements, but only one output coil.

2) In touch: It is the SCADA software which is used to supervise the working of the elevator developed by the Rockwell Automation. It is used in the present work to see the change in the variables inside the elevator system and is also used to find out the fault location without any effort [4].

3) Software Process of Elevator System: The software process first check the status of the floors the up and down movements, the opening and shutting of the door, and the weight of persons to be carried on the elevator system by using sensors and

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then the LAD program is implemented in the system to control all the movements in time. The detailed system can be explained with the help of the process flowchart given in Fig. 5

Check the status of

the floor through

sensors

Check the status of

the press input in

the queue

Open the door,

and after a delay

close the door

desire level

Fig. 5. Process Flow Chart of Elevator System

Move

motor

reverse

upto desire

level

G

Ill. INTERFACING FOR ELEV ATOR SYSTEM

A. Interfacing of PLC and SCADA with Elevator

System

For the interfacing of PLC and SCADA with the elevator there are many steps towards it. Three switches are connected to the PLC through 24 V supply as well three floor position sensors are also connected to the PLC through the relays [8]. Another sensor for the door opening and closing is connected to the PLC. It is the job of PLC to drive the output devices in response to input signals present at its Input ports. It act as the master controller, on one hand it collects a variety of input

signals of the elevator system, including the location of the elevator, state of the signal of internal and external command button, the door lock signal, the door zone signal, forced to slow down the signal within the wells and, fIre signals. On the other hand, based on signals it has the elevator floor signal and speed signal, switch gate signal, the directional relay and brake relay which runs calculations to control the operation of the elevator system.

Conditional branches are usually used in elevator applications; the program is broken into several functional blocks.

On switching on the power, it starts its working cycle and scans for inputs and decides what to do base on the program burned into its memory.

111UAC PUSH BUIIOH

LED 1 1 3

11.1

Ii.l

11.1

11.3

II.�

11.1

11.6

DC COl

PLC QI.I 5irnen5 S7-m

QI.I

QI.1

QI.3

AC con'

AC con-

DC con

Fig. 6. Circuit Diagram of Elevator System [4]

According to all these inputs PLC generates output which is given to the motors through the 2 set of relays for their forward and reverse motion.

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Fig. 7. SCADA of Elevator System

SCADA is the computer software and is generated on the screen of the computer. A cable is connected to the PLC to the computer named as CP3. It gives all the data to the computer and so through the SCADA of Elevator System in figure 7 we can easily monitor them.

B. Application of PLC and SCADA in Elevator

System

1) PLC Application: PLC gives very same working as the other controllers provides. It's working principle and programming features provides the elevator to add many others extra features. We can provide an alarm through the PLC as well we can extend the number of floors and also decrease or skip as per our requirements. Programming language provides user to store the mUltiple inputs and execute them according to the first come first get method.

2) SCADA Application: SCADA provides a pictorial view of the working of the elevator. For the maintenance of elevator, the supervisor not need to go to the elevator but just check the status through the computer screen [9] and also he can control and command the elevator. Through SCADA faulty location easily fmd out and action can be taken in no time.

IV RESULT AND DISCUSSION

All the setup is made according to the circuit diagram in Fig. 6 and all the devices are, checked thoroughly. The elevator system comprises different cases which are given below:

Case 1: If the elevator is on the ground floor and a call button is pressed from the ground floor then motor will not acuate and the doors will open simply. But if the call button of the 1 st floor or 2nd floor is pushed then the motor actuate in forward direction and move to the desired floor and open the doors for a while as shown in the Fig. 8 and 9.

Fig. 8. Pictorial Back View of Elevator System

Case 2: If the elevator is on the first floor and a call button is pressed from first floor then motor will not acuate and the doors will open simply. But if the call button of the ground floor then motor moves in reverse direction or 2nd floor is pushed then the motor actuate in forward direction and move to the desired floor and open the doors for a while.

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Fig. 9. Pictorial Front View of Elevator System

Case 3: If the elevator is on the 2nd floor and a call button is pressed from 2nd floor then motor will not acuate and the doors will open simply. But if the call button of the 151 floor or ground floor is pushed then the motor actuate in reverse direction and move to the desired floor and open the doors for a while.

Case 4: While the door is closing and someone put his hand between the closing of the door then door reopen and after removing the obstructer it waits for the 10 sec. and, then recloses. This process will occur all the time.

V CONCLUSION

After implementation of the above, some conclusions are made as follows:

PLC can easily control the working of the elevator. It is observed that PLC based elevator works better than all other control system. It does not provide the enough power to produce the torque in the motor so we need to provide the internal power and we have to use contactors to provide the controlling through PLC and power through external source. It can be easily programmed and program can be changed online i.e. in process we can change program according to our requirement.

SCADA is providing the best superViSiOn of the working of elevator and also provide the supervision of the internal component. It also provides the close supervision on the variable changes in the elevator process and, provides alarm as well as comments so that fault can be alarmed and appropriate solution comments provided on the alarm.

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