The picture and diagram above show a relay that controls its own electromagnet! The square of wire that takes electricity from the key of the relay to the electromagnet of the same relay is called a 'loop.'
No electricity can get from the top of the battery to the electromagnet because the key is up. However, if someone presses the key, then electricity can get to the electromagnet. Then, the electromagnet will hold the key down - even if the person lets go of the key! So we say that the loop remembers that the key was pressed. Remember that the key normally springs up because it is springy and bent upward.
Similarly, if someone then lifts up the key (A person is much stronger than a little electromagnet.), then no electricity will reach the electromagnet and the key will remain up even after the person releases the key. So we say that the loop remembers that the key was lifted up.
Most relays in a computer are used to make loops, or connect the loops together.
The picture and diagram above show a loop that controls a light bulb. A light bulb that is controlled by a loop is called a 'pixel.'
In a diagram, where a horizontal wire and a vertical wire meet, without crossing, there is a connection of the two wires.
Therefore, when the key is pressed, electricity can flow from the top of the battery, through the key, to both the light and the electromagnet. When the key is down and the light bulb is glowing, one says that the loop has value '1' and the pixel is 'on.' The loop has value '1' even if there is not a light bulb, just so the loop wire has electricity going through it, to the electromagnet, because the key is down.
When the key is up and the light bulb is not glowing, one says that the loop has value '0' and the pixel is 'off.' The loop has value '0' even if there is not a light bulb - just so the loop wire does not have electricity going through it (because the key is up).
Normally Closed Key
Normally Closed Key Diagram
The picture and diagram above show the top of a battery connected by a wire to a normally closed key, that is connected by another wire to a light bulb.
A diagram of an electrical machine is called a circuit diagram, a diagram, a schematic (pronounced ske-ma'-tic) diagram, or just a schematic.
The normally closed key is different from the keys described previously. The normally closed key is also a springy piece of steel, but is bent so that it normally is connected to the right wire. Therefore, the light bulb in the circuit above is normally on. However, if you push down on the normally closed key, the light bulb becomes disconnected from the 'power wire' and the light goes out.
A key is called 'closed' when electricity can flow through it from a wire on its left to a wire on its right. A key is called 'open' when electricity can not flow through it from a wire on the left to a wire on the right.
A normally closed key is normally closed, but is open when you push it down. A normally open key is normally open, but is closed when you push it down.
A relay is called closed if its key is closed. A relay is called open if its key is open.
An electromagnet is called 'powered' if the electromagnet is connected to the top of a battery, even if that electromagnet is connected to the top of the battery through a series of closed keys. In fact, any piece of wire is called 'powered' if that piece of wire is connected to the top of a battery, even if that piece of wire is connected to the top of the battery through a series of closed keys.
Any piece of wire that is powered is said to have value '1.' Any piece of wire that is not powered is said to have value '0.'
The values of the wire in a loop as described previously are a special case of these rules for assigning values to wires.
Normally Closed Relay
Normally Closed Relay Diagram
The preceding picture and diagram show a bottom key that controls an electromagnet. The electromagnet, in turn, controls the top, normally closed key. A normally closed key and the electromagnet that controls it are, together, called a normally closed relay.
When the bottom key is pressed, the electromagnet is powered and the electromagnet becomes magnetic. That makes the electromagnet attract the top, normally closed key and pull the top, normally closed key down, just like a finger can push a normally closed key down. A magnet (or a powered electromagnet) attracts the normally closed key because the normally closed key is made of steel. When the bottom key is pressed, the light turns off.
In other words, when the bottom key is pressed, the electromagnet energizes, disconnecting the top key.
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