ASHWINI MUSALE
Department of electronics engineering,
Jawaharlal Nehru engineering college, Cidco, Aurangabad, India Email –id: [email protected]
Abstract:
The companies, manufacturing relays are bound to test their products for specifications and compatibility. The production line in a company manufactures exceeds thousands of relays each day. This fact necessitates rapid and accurate testing of relays. A single person can’t handle the work alone. Even if he manages to handle, the time consumption is more and a mistake may occur.
So, it is necessary to employ an automation system for the testing of relays. The use of automated system facilitates less time consumption with the least possibility of error as relays are most important part of the circuit and they can be used as automatic switches, we are developing simulator for relay. The project is capable of testing a relay (either SPDT or DPDT) along with generation of the relay testing report and its specifications on the desktop.
Keywords: Relays, simulation, microcontroller, Hardware, SPDT. 1. Introduction:
This project aims to design a system which will test the relay using relay test kit and display the data regarding the test. The relay testing system is common in many industries, to reduce the use of man power behind this work, minimize expenses and time consumption too. To increase the efficiency of the system and to reduce the cost, we use a computerized system which will also increase the speed of whole system. This system covers the knowledge of Electrical Engineering, Electronics Engineering, and Computer Science. In this project we are testing a relay with the help of relay testing kit
The system is used for the automatic relay testing pad, along with the generation of the data, describing the status of the relay under test. The circuit used in this project tests the coil of the relay and the normally open and normally closed contacts for the continuity of current. The microcontroller, connected to the test circuit interfaces the result generated from testing to the personal computer to display the result, whatever we have obtained.
2. Relays:
Fig1: Relays
2.1. Traditional methods of testing relays:
If the relay is not labeled, use an ohmmeter and check to see which pins are connected to each other. You should typically find an ohm value of approximately 50 to 120 ohms between two of the pins. This is the control circuit. If the coil is less than 50 ohms it could be suspect. The remaining two pins should read OL (infinite) if it's a normally open relay or 0 ohms (continuity) if it's a normally closed relay.
If the readings are correct, proceed to the next test. If none of the relay pins showed a coil value and all pins show OL or 0 ohms, the control is damaged and should be replaced
Fig2: Relay continuity checking
Once the pins have been identified, energize the control circuit by supplying B+ to pin 1 and a ground to pin 3. A faint "click" will be heard; although this "click" means the switch has moved (closed), it does not mean the relay is good. The load circuit switch contacts could still be faulty (high resistance), and further testing is required.
2.2. Problem of this system:
Testing relays with built in clamping diodes require a special procedure. These relays are polarity sensitive; placing B+ to the wrong pin (backwards) while performing a practical test will forward bias the diode and damage the diode, thus destroying the protective quality of the diode. To overcome this we are developing simulator for testing relays.
3. Hardware Interface:
3.1. Working principle:
As soon as power is supplied to system device starts working. As seen in figure device can test four relays at a time, each relay has its respective switch as soon as you press it, output whether relay is ok or faulty can be displayed on the screen. Here each relay is followed by optocoupler. Optocoupler here are used for isolation purpose after which signal is fed to microcontroller after which crystal is present. Crystal here is used for frequency stability. Also capacitors are present around microcontroller to remove noise. MAX232 is used to bring amplitude of signal to 5V. Here RS232 is used which is used to connect circuit to computer and finally output is displayed on screen
4. Functional Block Diagram :
Figure 4 shows the functional block diagram of simulation kit for testing relays
Fig4: Block diagram of simulation kit for testing relays
Here block diagram is divided into three main parts: 1. Electrical design of the circuit
2. Electronics design of the circuit 3. Software
4.1. Electrical design of the circuit:
Electrical part consists of power supply and relay test pad circuit. The power supply has the input of single phase 230 V, 50Hz AC supply and output of 12 V regulated DC
4.1.1Power
Supply:-The 230 V single phase AC is given to step down transformer which has secondary voltage of 12 V and 1 Amp current .The output of transformer is given to a bridge rectifier IC which will convert 12 V into 12 V pulsating DC. The capacitor C1 of 1000 microfarad is connected between +12 V and ground and serves as filter to remove all the AC components
4.1.2 Relay test pad:
4.1.2.1Relay under test:-
SPDT Relay: (Single Pole Double Throw Relay)
It is an electromagnetic switch, consist of a coil (terminals 85 and 86), one common terminal (30) ,one normally closed terminal (87a), and one normally open terminal (87). When the coil of relay is at rest (i.e. not energized), the common terminal (30) and the normally closed terminal (87a) have continuity. When the coil is energized, the common terminal (30) and normally open terminal (87) have continuity. The diagram below centre shows the relay at rest, with the coil not energized. The diagram below right shows the relay with the coil energized.
Fig5: SPDT Relay
When energizing the coil of a relay, polarity of the coil does not matter unless there is a diode across the coil. If a diode is not present, we can attach positive voltage to either terminal of the coil and negative voltage to the other.
4.2 Electronics design of the circuit:
Electronic part consists of AT89C51 Microcontroller. 4.2.1. Description of AT89C51 Microcontroller:
The AT89C51 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density non-volatile memory technology. It has following features:
1. 4K Bytes of In-System Programmable (ISP) Flash Memory 2. 4.0V to 5.5V Operating Range
3. 8-bit Internal RAM
4. 32 Programmable I/O Lines
5. Two 16-bit Timer/Counters
4.3. Software:
In this project we had used VB.NET software. However .net program consists of one main program and one sub-program. Sub programme is programme for port access. Microcontroller AT89C51 is interfaced with embedded C programming. The logic behind embedded C program is if else rule, which is simple conditional statement in C program.
5. Results:
[5] Mason, C. R. "Art & Science of Protective Relaying, Chapter 2, GE Consumer & Electrical". Retrieved October 9, 2011
[6] Terrell Croft and Wilford Summers (ed), American Electricans' Handbook, Eleventh Edition, McGraw Hill, New York (1987) ISBN 0-07-013932-6 page 7-124
[7] Ian Sinclair, Passive Components for Circuit Design, Newnes, 2000 ISBN 008051359X, page 170
[8] Neville Arjani: Examining the Trade-Off between Settlement Delay and Intraday Liquidity in Canada's LVTS: A Simulation Approach (Working Paper 2006-20, Bank of Canada) Simulation publications
[9] “Relay Specific Computer Aided Testing for Relays” by K.C.A. Dierks, Eskom, Republic of South Africa [10] Relays Application Guide 3rd Edition, GEC Alsthom Measurements Ltd. 1987, no ISBN, pages 9-10, 83-93 [11] Ian Sinclair, Passive Components for Circuit Design, Newnes, 2000 ISBN 008051359X, page 170 [12] Bob Beresh: Relay Functional Type Testing 04 .01.2012
[13] Gurevich, Vladimir (2005). Electrical Relays: Principles and Applications. London - New York: CRC Press.
