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گروه آموزشی مکانیک خودرو استان یزد - نحوه عملکرد رله

نحوه عملکرد رله

پنجشنبه 21 مهر 1390 11:29 ق.ظنویسنده : گروه مکانیک خودرو

 

رله یا افتامات دارای به طور کلی 5 پایه دارد که دو پایه 85 و  86 به دو سر سیم پیچ متصل است که با جریان ضعیف می تواند تحریک شده و خاصیت اهنربایی پیدا کند در سمت دیگر سه پایه دیگر قرار داده شده است که به نامهای 30 - 87 و 87a نامگذاری میشود که در حالت عادی و قبل از تحریک سیم پیچ (پایه 85 و 86 ) دو پایه 30 و 87a به متصل هستند ولی هرگاه سیم پیچ بوبین شد پایه 30 از پایه 87 a جدا میشود و به پایه 87 متصل شده میشود و اگر ما در پایه 30 برق داشته باشیم این برق از پایه 87a قطع شده و پایه 87 وصل میکند 

به طور کلی افتامات یا رله دو کار مهم انجام میدهد 

1- کوتاه کردن مسیر سیم کشی در مدارات الکترونیکی برای رساندن برق به مصرف کننده از طریق پایه 30و 87

حفاظت از کلید برای اینکه جریان قوی از کلید عبور نکند و کلید فقط سیم پیچ را بوبین کند و برق فشار قوی از پایه 30و 87 عبور کند 

برای فهم بهتر  فایل فشرده انیمیشن های آموزشی رله  را دانلود کنید 


Basic Relay Operation


The Contacts

Before extending to the various types of relays, i will first explain what and how the basic relay operates. Each relay has two mechanical parts inside. The first one is the contact(s) of the relay. The contacts operates similarly to the contacts of a simple switch or pushbutton. You should consider the contacts as a pair of metals like the following diagram:



 

The two terminals operates as a switch. When the contacts are 'in contact' then the current flows from Terminal 1 to Terminal 2. There are two types of contacts: the NO and the NC. NO stands for Normal Open contact, while NC stands for Normal Closed contact. The Normal Open is a contact like the one showed in the previous illustration. When the contact is still, then no current flows through it (because it is an OPEN circuit). On the other hand, a Normal Closed contact allows the current to flow when the contact is still. Bellow i illustrate both of these contacts:



 

You may notice that the NC contact is turned upside-down compared to the NO contact. This is done in purpose. This way, both contacts (NO and NC) will change state if a force is applied to the left metal heading from UP to DOWN. The following animation shows how a NO contact operates by lighting a light bulb:



 

As for the NC contacts, it works exactly opposite as the NO contacts. Look the following animation:



 



A combination of contacts

A relay may have a combination of the above contacts. Look at the following illustration



 

In this case, there is a 3rd terminal called "COMMON". The NO and NC contacts are referred to the COMMON terminal. Between the NC and the NO contact, there is no contact at any time! The following animation shows how this pair operates:



 



And WHO defines the NORMAL state?

OK, we have the NORMAL open and NORMAL closed contact. But which state is considered as NORMAL? Going one step closer to the relay operation, we find the spring. This spring defines the NORMAL position of the COMMON contact. If you see the above 3 animations, you will notice that one time an F force is applied to the COMMON terminal, and the other time there is no force applied. Well, this is actually wrong. There is indeed another force that pulls the contact towards UP and this force is applied ALL the time. This force comes from the spring. Look the following image:



 

Now you can see who is pulling the COMMON terminal UP all the time. So the spring defines what is the NORMAL state, and thus defines which contact is the NORMAL OPEN and which the NORMAL CLOSED. In other words, the NORMAL state is defined as the state that there is NO other force applied to the COMMON terminal except the one from the spring.




The last part - WHO move the common contact of the relay?

This is the last part of the relay operation. The device that forces the terminal to move, is actually an electromagnet! A coil is placed right under the contact. When current is flown through this coil, a magnetism is created. This magnetism can overcome the force of the spring and can pull the contact towards it, thus it changes it's position! And due to the fact that the contact is usually a small piece of metal not capable to be pulled by the electromagnet, another piece of metal is attached to the common. This piece of metal is so called "Armature". Following is (at last) the complete illustration of the basic relay:



 

Now, imagine that someone wants to control a 220Volts 1 K-Watt load with a command that comes from a 5 Volts battery. A load-Relay should be used for this application. The Coil of the relay is driven with the 5 Volts. The contacts from this relay (NO) will be connected in series with the power supply of the load. Thus, the load will only operate when the relay is actuated. Our friend bellow will turn on an electric oven bare-handed!!!



 

Looking inside the relay

I used an octal-type relay. These relays are easy to open (either with screws or clips), and are big enough to have a clear view. So, here is the relay opened:



 

You can clearly see the common contact, the NO and NC contacts as well as the electromagnetic coil and the return-to-normal spring. The armature is the thick metal that the common contacts are fixed on it. The following two pictures shows how the common contacts are move with the armature, and how the relay changes state:


The common contacts are in the normal position I press the common contacts and the state of the relay is changed


The following video demonstrates how the common contacts are moved:


Biased Relays



A permanent magnet is attached to the armature

This is a variation of the neutral relays. These kind of relays have exactly the same coil as the neutral relays, but they carry a permanent magnet on the armature. The polarization of the magnetic field of the coil depends on the polarity of the supply. Therefore, the armature is actuated only if the polarity of the coils' magnetic field is opposite to the polarity of the permanent magnet's magnetic field. This way, the relay is actuated only if the coil is correctly biased.




برگرفته از سایت 
http://pcbheaven.com/wikipages/How_Relays_Work/?p=0
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