Do you think splicing 100' of wire onto a GTO exit wand would work?
in [Repair]
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From: Elmo on 2 Feb 2010 01:02 On Mon, 01 Feb 2010 20:16:20 -0500, news(a)jecarter.us wrote: > Could be like the gate at a corporate site I occasionally visit - for > entry, you speak to a guard and show ID via a TV camera and the guard > opens the gate. A device like the one in this thread is used to allow > people to exit the gate. Yes. The "typical" gate setup is: 1a. Owner approaches gate and flips remote control to get in. 1b. Utility truck approaches gate and pushed their logged 4-digit combo on the digital keypad to get in (whether or not someone is home) 1c. Guest arrives and has to press the intercom button and can only be let in if someone inside the house provides them access. Guest then pushes a button on the keypad to open the gate. 2. In all cases above, the gate closes 25 seconds after it was opened. 3. In all cases above, when the owner/utility/guest leaves, the gate automatically opens for them via the exit want magnetic field disturbance sensor. At least that's how my gate is set up. Some are set up to open via cellphone but mine isn't fancy.
From: Jeff Liebermann on 2 Feb 2010 02:08 On Mon, 1 Feb 2010 15:15:51 +0000 (UTC), Elmo <dcdraftworks(a)Use-Author-Supplied-Address.invalid> wrote: >I bought too short of a driveway-gate exit wand (GTO FM139 = 50 feet); I >need 150 feet. > >Nobody told me (so I'm saying it here), one really needs about 150 feet if >they want the driveway gate to be open by the time the moving mass of metal >(i.e., automobile) reaches the gate. Lesson learned. I suppose it's too late to exchange the exit wand. >Researching the web, it appears GTO sells three wands: >http://www.gtopro.com/access_controls.htm >- FM139 = 50 feet wired (about $180) >- FM140 = 100 feet wired (about $200) >- FM141 = 150 feet wired (about $225) > >The instructions say you can not splice additional lengths >(http://www.gtopro.com/PDF/Flyers/Gate-Opener-Access-Control-FM139-vehicle-sensor.pdf Yep. For good reason. The contraption belches RF somewhere between 20Khz and 150Khz and is similar to the vehicle detectors used for traffic signal control. The mass of the vehicle detunes the coil resulting in an increase in oscillator gate(?) current. In other words, the whole mess, including the cable, is part of a resonant circuit. If you were able to rip apart the tube, you'll probably find an iron core, with a zillion turns of wires wrapped around it. There will also be a tuning capacitor, which is the key problem. Each length of cable will have a different tuning capacitor, where the difference in lengths is roughly equal to the difference in capacitance. These differences are compensated by the internal tuning cap. If you're lucky, they may have jumpers inside to select different cable lengths. If the designer is really cool, the capacitor might be inside the controller. You might be able to get some clues if there are any patent numbers of FCC ID numbers on the devices. I couldn't find anything registered to "Gates That Open". >Calling www.gtopro.com technical support at 800-543-4283, they say there is >no difference between the wands or the wire other than the length BUT if I >splice in a wire, it won't work. They may be right. 100ft of untwisted parallel cheezy wire is good for about 500pf or so. That's quite a bit and will seriously affect the resonant frequency of the wand. However, if the support droid is telling the truth, then there should be a jumper or adjustment inside the controller box for different lengths of cable. The manuals are useless. So, you get to rip it open. Learn By Destroying(tm). >The technical support guy was very helpful. He said the reason it won't >work is that the "sensitivity of the magnetic field" changes with the >splice. Baloney. Well, maybe 50% baloney. The resonant frequency will change, and therefore, so will the sensitivity. >I don't understand why (if I make a good splice) but maybe there is >something about magnetic fields I don't understand that you can elucidate >for me? The wire is 5 conductor 16awg multi-strand shielded. It's not the splice. It's the added capacitance wrecking the resonance. >What is it about a splice that destroys the magnetic field? Nope. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl(a)cruzio.com # http://www.LearnByDestroying.com AE6KS
From: Jeff Liebermann on 2 Feb 2010 02:21 On Mon, 01 Feb 2010 23:08:04 -0800, Jeff Liebermann <jeffl(a)cruzio.com> wrote: >>The instructions say you can not splice additional lengths >>(http://www.gtopro.com/PDF/Flyers/Gate-Opener-Access-Control-FM139-vehicle-sensor.pdf > >Yep. For good reason. The contraption belches RF somewhere between >20Khz and 150Khz and is similar to the vehicle detectors used for >traffic signal control. The mass of the vehicle detunes the coil >resulting in an increase in oscillator gate(?) current. In other >words, the whole mess, including the cable, is part of a resonant >circuit. Ok, I lied. It's not the added capacitance. It's the added inductance of the 100ft of feed cable. The destructions for a different type of loop at: <http://www.hooverfence.com/gtopro/manual/loopdt1-manual.pdf> show an inductance of 0.22 microhenries per foot for the connecting cable (presumably the same cable for both types of loops). That's quite a bit of added inductance. I'm guessing, but it looks like the target value for the loop and cable feed is about 100 microhenries. Either way, adding the 100ft of cable is not going to work. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl(a)cruzio.com # http://www.LearnByDestroying.com AE6KS
From: Jeff Liebermann on 2 Feb 2010 02:26 On Mon, 01 Feb 2010 23:21:31 -0800, Jeff Liebermann <jeffl(a)cruzio.com> wrote: >Ok, I lied. It's not the added capacitance. It's the added >inductance of the 100ft of feed cable. The destructions for a >different type of loop at: ><http://www.hooverfence.com/gtopro/manual/loopdt1-manual.pdf> >show an inductance of 0.22 microhenries per foot for the connecting >cable (presumably the same cable for both types of loops). That's >quite a bit of added inductance. I'm guessing, but it looks like the >target value for the loop and cable feed is about 100 microhenries. Looks like the oscillation frequency is dependent on the loop inductance. I (wrongly) assumed it was a fixed frequency (to make the FCC happy). That means you could probably extend the cable feed and all that will happen is that the oscillation frequency will be drastically lowered. I don't know if that's going to cause a problem with whatever they use for a detector, but it just might work. However, if the new lower frequency causes airplanes to fall out of sky, I suggest you instead purchase the correct exit sensor. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl(a)cruzio.com # http://www.LearnByDestroying.com AE6KS
From: PeterD on 2 Feb 2010 08:39
On Tue, 2 Feb 2010 05:56:54 +0000 (UTC), Elmo <dcdraftworks(a)Use-Author-Supplied-Address.invalid> wrote: >On Mon, 01 Feb 2010 17:53:54 GMT, GregS wrote: > >> Whats the connector look like ?? > >There is no connector. Each of the four 16 AWG multi-stranded wires arrives >from the factory stripped of about 1/4 inch at the ends and tinned solid. > >We just screw those four wires plus the shield into connections on the gate >opener motherboard. The simple answer is just try it! What do you loose, a few minutes of time? That said, just make sure your splice is absolutely waterproof. 3M makes underground splice kits that may work (used primarily for telco work). |