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inductor.

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allegro

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I read that traffic lights detect a car by measuring the inductance of an inductor that is placed on the road.

I wonder why would the inductance of the inductor change if the car doesnt get inside the loop's area?
 
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The magnetic fields surrounding an inductor extend to some degree in all directions, but are most intense in the plane of the coil. So even if you move metal nearby but not inside the coil itself you get some change in inductance.
 
The magnetic fields surrounding an inductor extend to some degree in all directions, but are most intense in the plane of the coil. So even if you move metal nearby but not inside the coil itself you get some change in inductance.

Thanks.
So besides measuring the inductor's inductance, the traffic light also applies current on the coil, in order to create a magnetic field?

Without applying current on coil, its inductance would change only if the car was really inside the coil?
 
So thats why my friends plastic P.O.S. car does not get the green light on the left turn lane sometimes! :p That inductance sensor is set to low. neat!

So will the street dept get pissy if I park an EMP generator on them and fire?:eek::rolleyes:
 
So will the street dept get pissy if I park an EMP generator on them and fire?:eek::rolleyes:
So, you have some vendetta against traffic lights?
 
So thats why my friends plastic P.O.S. car does not get the green light on the left turn lane sometimes! :p That inductance sensor is set to low. neat!

So will the street dept get pissy if I park an EMP generator on them and fire?:eek::rolleyes:

I didn't think they needed traffic lights in North Dakota. You got that many cars??? LOL
 
The worst thing about traffic lights are the pinheads that program them. You should see the traffic lights in Poplar Bluff, Missouri. We have around 15 right now with a new one being installed within the next few months and no two have similar programming, so a vistor has no idea what's going to happen next. Needless to say, it isn't the biggest town! The next-largest town south of us has one light.

Dean
 
Dean! has your town been stealing engineers from our town? We have a traffic light infestation. Minot North Dakota puts traffic lights on the top of everyone of our F- up 3/4 clover leaf overpasses. We even had a traffic light some years ago right in the middle of a street that no longer had an intersection! It still cycled like there was one though!
Got one of my first warning ticket for running it!
Cop said I ran a red light. I said I know. He said you could get killed or kill someone doing that! I said dont I need cross traffic first?
I Got off with a warning, And a good story to tell!
Your town must have hacked our highway depts computer and stoll a copy of our traffic light programs! No rime or reason here either!
 
In ressponse to ALLVol. We spend hunderds on street design and maintenace every year! and millions on street lights! come check us out some time. Theres a reason why we are rural people. Going to town and stopping for a poorly programed street light every block on the primary streets keeps city population down.
Use Google earth and do the street view mode for Minot North Dakota. Start at Wal-mart on the south end of town. Go up Broadway untill you get to the far north side.
Count how many street light there are. Pay attention to the first overpass as you head north. Four stop lights within one block! one at the end of both sides of the overpass itself and one a quarter block north from there and another a quarter block from the south end!
honest truth! On a busy traffic day one or more will back up traffic over the one behind it and block cross traffic. Happens all the time!
 
Thanks.
So besides measuring the inductor's inductance, the traffic light also applies current on the coil, in order to create a magnetic field?

Without applying current on coil, its inductance would change only if the car was really inside the coil?

The traffic light applies current to the coil in order to measure inductance. The two go together.

The ability of the system to measure a change in inductance when the car passes over comes from how sensitive it is at measuring change of inductance. They have designed it so that it is sensitive enough to work effectively when the car passes over it with the amount of current they pass through it. The intensity of magnetic field is a function of the current in the coil, this is true, but the field always surrounds the coil to varying degrees in all directions no matter how much current is passing through it. The field is never constrained to be completely inside just the loop itself.
 
The traffic light applies current to the coil in order to measure inductance. The two go together.

The ability of the system to measure a change in inductance when the car passes over comes from how sensitive it is at measuring change of inductance. They have designed it so that it is sensitive enough to work effectively when the car passes over it with the amount of current they pass through it. The intensity of magnetic field is a function of the current in the coil, this is true, but the field always surrounds the coil to varying degrees in all directions no matter how much current is passing through it. The field is never constrained to be completely inside just the loop itself.

Thank you!

When you dont apply current on the coil, then there's no magnetic feild inside and around the coil.
1. My question is, if you do not apply current on the coil, but you place a car above the coil, would its inductance change?

2. Now, if you place a car inside the (huge) coil, and still dont apply current on coil, would its inductance change?
 
"inductance" is meaningless if you aren't moving electrons. It's like asking what a hand-shadow would look like if you didn't turn the light on.


You guys with the traffic lights are lucky. Up here they have been installing goddamn ROUNDABOUTS all over the place. They even have them in front of strip malls. A year ago I could just drive straight down the road - in front of the mall there was a separate lane for cars turning left to the mall. No problem.

Now there's a roundy-go-bullsh!t in front of it. So you have to slow down to a crawl in case some of the oncoming traffic decides to do a one-eighty.

Another one is next to a railroad crossing. Train comes, roundabout gets choked with cars, nobody moves in either direction.

And they plant trees and bushes and crap on them, of course. So you can't even see the big ugly SUV whipping round the turn until it nearly smacks into you.
 
"inductance" is meaningless if you aren't moving electrons. It's like asking what a hand-shadow would look like if you didn't turn the light on.


You guys with the traffic lights are lucky. Up here they have been installing goddamn ROUNDABOUTS all over the place. They even have them in front of strip malls. A year ago I could just drive straight down the road - in front of the mall there was a separate lane for cars turning left to the mall. No problem.

Now there's a roundy-go-bullsh!t in front of it. So you have to slow down to a crawl in case some of the oncoming traffic decides to do a one-eighty.

Another one is next to a railroad crossing. Train comes, roundabout gets choked with cars, nobody moves in either direction.

And they plant trees and bushes and crap on them, of course. So you can't even see the big ugly SUV whipping round the turn until it nearly smacks into you.

San Antonio Tx was like that. I went to visit my dad, and them damn roundabouts was the only way to get somewhere. Took for freakin ever.
Confusing as heck too, when I was going to the airport there, I could see the airport but, I missed the right roundabout and about ended up driving to Dallas ...
 
Sorry to hear that. I like San Antone, used to go to conventions there, would stay at the Menger Hotel (great ice cream), visit the Alamo, go to that cool river area thing.

Roundabouts seem to be part of this deal where they think it's somehow cooler to make everything European. Have you seen all these stupid signs cropping up using spelling conventions like "Village Centre" - ? FFS, that's not pronounced "sen-ter", it's "sen-treh"! I don't care how the French spell it.
 
"inductance" is meaningless if you aren't moving electrons. It's like asking what a hand-shadow would look like if you didn't turn the light on.


You guys with the traffic lights are lucky. Up here they have been installing goddamn ROUNDABOUTS all over the place. They even have them in front of strip malls. A year ago I could just drive straight down the road - in front of the mall there was a separate lane for cars turning left to the mall. No problem.

Now there's a roundy-go-bullsh!t in front of it. So you have to slow down to a crawl in case some of the oncoming traffic decides to do a one-eighty.

Another one is next to a railroad crossing. Train comes, roundabout gets choked with cars, nobody moves in either direction.

And they plant trees and bushes and crap on them, of course. So you can't even see the big ugly SUV whipping round the turn until it nearly smacks into you.

But there is a formula for inductance, that doesnt depend on electrons movement:
H = (4 * Pi * #Turns * #Turns * coil Area * mu) / (coil Length * 10,000,000)

So how come you say that the inductance depends on electrons movement or on magnetic field?
 
get yourself a core and some mag wire. wind an inductor and then put it down on your bench. what it is? of course it's an inductor - but without it being in a circuit that has current flowing, its about as useful as a paperweight.

The formulas are for construction of an inductor and will tell you how you can expect the part to work in a circuit. BTW, it's not going to be the same for all frequencies and current levels, either.
 
I'm interested knowing whats right, not only whats useful.

If i place a steel inside a coil (no current applied), would its inductance grow?
 
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analyze your statement and you should be able to answer it yourself...

How is inductance affected by an external element? It affects the inductance by altering the magnetic field. If there is no current, there is no magnetic field. If there is no magnetic field, there is no change to anything.
 
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