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how does a traffic light detect that a car has pulled up and is waiting for the light to change?

by:ShenHao     2020-06-26
\"Know\" you have some exotic at the traffic lights there-
They changed as soon as you came up!
How do they find out about you?
Some lights don\'t have any detectors.
In a big city, for example, a traffic light may just operate on a timer. -
No matter what time of day, there will be a lot of traffic.
However, detectors are common on suburban and rural roads.
When a car reaches the intersection, they may find that there are too many cars piled up at the intersection (
Control the length of light)
Or when the car enters the turn lane (
To activate the arrow Light).
There are various technologies for detecting cars. -
Everything from lasers to rubber hoses full of air!
The most common technology so far is induction loops.
The induction coil is the coil embedded on the road surface.
To install the loop, they lay the asphalt and then come back and cut a groove on the asphalt with a saw.
The wire is placed in the groove and sealed with a rubber compound.
You can often see these large rectangular rings on the sidewalk because the compound is obvious.
The induction circuit works by detecting the change of the inductance.
To understand this process, let\'s first look at what an inductor is.
The illustrations on this page are very helpful.
What you see here is a battery, light bulb, coil around a piece of iron (yellow), and a switch.
The coil of the wire is an inductor.
If you have read how the magnet works, you will also realize that the inductor is an induction magnet.
If you take the inductor out of this circuit, then you have a normal flashlight.
If you turn off the switch, the light bulb will light up.
As shown in the figure, the behavior of the inductor in the circuit is completely different.
The bulb is a resistor (
The resistance generates heat, causing the filament in the bulb to glow).
The wire resistance in the coil is much lower (it\'s just wire)
, So when you turn on the switch, you expect the light bulb to emit a very dim light.
Most current should follow low current
Through the resistance path of the loop.
Instead, when you turn off the switch, the bulb burns brightly and then darkens.
When you turn on the switch, the light bulb burns very bright and then goes out very quickly.
The reason for this strange behavior is the inductor.
When the current starts to flow in the online circle for the first time, the coil wants to establish a magnetic field.
The coil inhibits current flow when the magnetic field is established.
Once the field is established, the current can flow through the wire normally.
When the switch is on, the magnetic field around the coil keeps the current flowing in the online circle until the magnetic field crashes.
Even if the switch is on, this current keeps the bulb lit for a while.
The capacity of the inductor is controlled by two factors: placing the iron in the core of the inductor will be more than air or any other non-
Magnetic core will.
There are some devices that can measure the inductance of the coil. The standard unit of measurement is Henry. So. . .
Let\'s say you take a coil that may be 5 feet in diameter with five or six wires inside.
You cut some grooves on the road and place the coil in the groove.
You attach an inductive meter to the coil to see what the inductance of the coil is.
Now you park your car on the coil and check the inductance again.
Due to the large steel objects placed in the magnetic field of the coil, the inductance will be much larger.
The car parked on the coil is like the core of the inductor, and its presence changes the inductance of the coil.
Traffic light sensors also use loops in the same way.
It constantly tests the inductance of the loop on the road, and when the inductance rises, it knows that there is a car waiting!
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