How to build a inductive gate loop

[J.P.]

I haven't messed with gate openers, garage doors much beyond supplying power. I was leaving a job recently and the fence/gate installer was out by the gate. I stopped and asked if he need the breaker turned on.

It turned out that he needed his keypad wired and programmed and the batteries hooked up and a gate loop put in. I had to set the gate limits and the remotes as well.

I had no clue and still don't have much of a clue about the gate loop. I thought it was a pre-made part that just got wired in to the operator.
In this case it was some #12 THHN....

I read a few differing opinions on installation. The boss's opinion is what counts though, he seemed pretty vague on details. But I still am curious.

Does the wire have to be twisted?
I have seen a few diagrams where they take a single strand from the operator make 3 turns around there trench or cut and head back to the operator. The only twisting was where the lead in wires were just to keep them neat.

The method I used was to make 100ft of twisted wire at 6 twist per foot and loop that around the trench once.

Could I have put it in pvc? Would it even work through pvc?

Would 12/2 urd work for this or is the separation of the wire inside the insulation to great?

I didn't get to test the loop because the loop detector module wasn't even ordered. I would really have liked to try out both methods before covering up the wire.

 

[hurk27]

The twisted part of the loop is only between the operator (electronics) and the start of the loop, the two conductors are not twisted once you get to the point where they are separated and run under the drive in the loop as each wire is run around the loop as a single wire.

The reason the feed in conductors are twisted between the loop and the electronics is to prevent any detection of metal between the loop and the operator, it does this by twisting the two lead in conductors this causes a 180? out of phase of the conductors at each reversal of the wires at each twist, back when we used to use twin lead in wires from an antenna we would twist the lead in wire to prevent the wire from acting as part of the antenna, this prevented unwanted signals such as noise from being picked up by the lead in wire where it might pass a source of electrical noise.

In the case of a detection loop under the drive you should only have one conductor run around the loop, it didn't have to be #12 as we used stranded 18 awg, once the wire reaches the edge of the drive we run out enough wire to return both sides of the loop back to the controller we cut the ends the same length and put then in a drill and run the drill to twist them, the last couple I have done I used 3/8 polyethylene tubing the same kind of tubing they use to connect a water line to the ice maker on a fridge, I did this so if the wires ever go bad they can be replaced without damaging the drive which is good when you have an expensive brick cobblestone drive.

If you have run both conductors around the loop and twisted them then they will not detect a vehicle as the twist will cancel out the pickup signal.

 

[GoldDigger]

Depending on how the twisted wires were run, you either have a double turn loop in which the twist is irrelevant, or some other things that may or may not work.

Think of the detector loop as a very large inductor and the car as the core or as a shorted turn depending on the type of detector.

There are also some choices as to the size, position and shape of the loop which will detemine the possible sensitivity pattern for cars, motorcycles and even bicycles.
I feel for your predicament in being thrown into this without any other help.
Putting the loop into PVC should not affect its performance in the least.
And as long as you wire the loop in the right direction, using one two or even three of the wires (the bare EGC can be used too with care.)

The key point is this:
If you call the two wires you twisted red and black, you should connect one red to the detector, the far end of the red to the NEAR end of the black and the far end of the black to the detector.
That will make a two turn loop.
If you connect the two ends of the red and black together and connect the paired ends to the detector. That will give you a one turn loop and waste wire.
Or you can connect one end of the black to the detector, the same end of the red to the other detector terminal. Then tie the other two ends together. That will give you a totally useless zero turn loop.
If you do the same thing but insulate the far ends, you will not have a loop at all.


Tapatalk!

 

[hurk27]

here is a You Tube video on installing loops, before I forgot to mention that most detector units require three loop turns as you will see in the video, but there are some that only require one turn, also the video has you just run the PVC conduit to the edge of the drive, I always put in a WP junction box so that if the wire to the controller ever has to be replaced or the loop gets damaged then you have a way to do it, like I said I use tubing to allow me to replace the loop under the drive without re sawing the drive, as they do go bad from time to time, but your method is up to you.

Heres the link to installing the loop: Installing a detection loop

 

[J.P.]

I saw that video. I drove a stake in each corner of my trench and wired my detector that way.

Unfortunately I didn't have the loop detector module and couldn't test it. If it had worked I would have left it that way and apparently been better off.......

After I called the office and said I had missing part I got the distinct impression that the boss man really wanted the wires twisted and he wasn't happy with how I had done it.
Since the trench was open it wasn't a big deal to change it.

From gold diggers description I have a one turn loop?

I took a single stand (200") of wire folded it half and twisted it in a drill. So my ends are at the controller. I did only make one turn around the hole. So I have a weak loop I guess?

 

[PetrosA]

I took a single stand (200") of wire folded it half and twisted it in a drill. So my ends are at the controller. I did only make one turn around the hole. So I have a weak loop I guess?

If you twisted the entire length of the wire (100') and put that in the ditch, it won't work at all.

 

[kwired]

That loop is a one turn coil, or could be a multi-turn coil if you run more than one turn around the loop. When you drive a vehicle over the loop the vehicle becomes a steel core and with the combination of the core and coil you have an inductor. When the loop sensor sees a change of current because of a change of inductance, it triggers the output of the loop sensor.

By twisting leads when they are not a part of the loop you are just trying to eliminate any non desired inductive interference that is not inside the intended loop from false triggering the loop sensor.

Traffic signals use similar setup for detecting if there is traffic in particular lanes of traffic to trigger operation of certain functions.

 

[GoldDigger]

Since modern vehicles may not contain much ferrous metal, some traffic loops detect instead the change in losses (Q) of the coil caused when any large mass of conductive metal is present.

The twisting of the connecting wires still serves the same purpose of limiting the active area of the detector.

Tapatalk!

 

[iceworm]

JP -
Why guess? Didn't this come with an installation manual?

ice

 

[J.P.]

The manual for the keypad was all I had. My helper looked up the operator on his phone, but it didn't have loop building instructions.

It did have a pre made strip part number.........

So My loop wont work at all right?

A. Because I twisted the whole thing?

B. Because I only have one turn in my trench?

C. Because it was like 11 degrees and windy while we were out there chipping away at the driveway and no sweat equity was involved?

D. Thanks. I wont be repeating this mistake.

 

[GoldDigger]

The manual for the keypad was all I had. My helper looked up the operator on his phone, but it didn't have loop building instructions.

It did have a pre made strip part number.........

So My loop wont work at all right?

A. Because I twisted the whole thing?

No. Because of the way you connected the ends of the two lengths of wire.

B. Because I only have one turn in my trench?

Actually, based on your description, you may actually only have zero turns.

C. Because it was like 11 degrees and windy while we were out there chipping away at the driveway and no sweat equity was involved?

That explanation works for me!

D. Thanks. I wont be repeating this mistake.

To help you get there from here, I have a bit of text graphics to try to clarify what we are looking at. If I do not cover what you did, come back with your description based on my "diagram".

Controller: 
T1
T2

Wires:

A-------------------------------B

C-------------------------------D

Did you connect A to T1, C to T2 and B to D? If so you have no loop at all, but you do have a connection from T1 to T2.
Did you connect A and B to T1 and C and D to T2? If so you have no loop and no connection between T1 and T2.
Did you connect A and C to T1 and B and D to T2? If so you have a one turn loop and it may or may not be sensitive enough to work. Depends....
Did you connect A to T1, B to C and D to T2? If so you have a two turn loop that might work.

The twisting of A-B and C-D will have no effect whatever on whether the loop part works. What counts is twisting the wire attached to T1 with the wire attached to T2 up to the point where the loop starts.

If you still have access to all four wire ends, you could still end up with a two turn loop without doing any additional digging. The twists will not hurt you in that case.

 

[J.P.]

Here is an " Artist " rendition of what I have wrought......

 

[kwired]

Here is an " Artist " rendition of what I have wrought......

What you had originally done will work, what you made with the twisted wire will not, you would need to twist a steel strand within the twists of that to make a change in inductive reactance. That would be kind of hard on the vehicles if you want to stretch them out and insert them within the twisted wires so they can be detected by the gate equipment.

 

[J.P.]

Ok. Thanks.
So what your saying is..........I need to somehow compress the vehicles in order to fit through the twist in my wire. Got it!

I'm printing this off as proof

 

[GoldDigger]

Ok. Thanks.
So what your saying is..........I need to somehow compress the vehicles in order to fit through the twist in my wire. Got it!

I'm printing this off as proof

But if you compress them that much, they could just fit through the gate while it was still closed.

And although your first idea would have worked just fine, if you had twisted just stretch of wire running from T1 and T2 to the corner of the loop, it would have been less sensitive to motorcycles or lawnmowers parked above that home run of wire. (Unless you squeezed them real thin too....)

 

[plumb bob]

Interesting thread and I certainly don't want to derail it, but I'm in the market for a humongous drill and wonder if JP has any advice? :lol:

 

[J.P.]

Are you by any chance a poorly drawn stick midget? If so....... Then I am the distribution point for all of your humongous drill needs!

We are now offering discounts to soulless gingers.

 

[Rampage_Rick]

After I called the office and said I had missing part I got the distinct impression that the boss man really wanted the wires twisted and he wasn't happy with how I had done it.
Since the trench was open it wasn't a big deal to change it.

The amusing part is that you did it correctly on your own, and only changed it after talking to the boss. I wonder how receptive he is to the inevitable finger pointing?

 

[J.P.]

The amusing part is that you did it correctly on your own, and only changed it after talking to the boss. I wonder how receptive he is to the inevitable finger pointing?

I'm not one for finger pointing. My boss is pretty honest, he'll remember the phone calls he got from me about this.

 

[boboelectric]

What will happen now that they are making all aluminum cars and trucks?