Remember the resistance

Remember the resistance reading is Ohms X 1000, so you are showing about a million Ohms of resistance there. 

Are you cleaning your work with alcohol after soldering?  If not get some 100% isopropyl alcohol and a small, stiff brush.  Scrub all the solder joints and ties with the alcohol after soldering and let it dry.  You may be getting a tiny bit of conductivity across the gap from a thin layer of melted flux, from oil from your fingers handling the ties, maybe even from the sharpie ink.

Your hand

If, while you are measuring resistance/conductivity, and your fingers are in contact with the ohmeter probes, you are also measuring the circuit through yourself.  For me, that's in the 400,000 Ohm range +/- a couple hundred thousand, and everyone is different.   Your readings on the X1000 range would be consistent with a circuit through you.  Put a piece of dry paper, or some other insulator between you and the probe, then measure.  I hope that's your problem.

The only other possibility I can think of is that you have fine copper particles in the gap, forming a conductive path.

Simple ...

The answer's simple ... you're touching the metal part of the probes and the tester is adding you to the circuit. Your body is also a conductor, albeit a poor one. Keep your fingers off the business part of the probes, or wear rubber gloves (like the heavy diswashing gloves) - and then see what you get.

If you have a short, the resistance will be near zero 99% of the time. Anything else will be a high resistance connection between the two rails and is extremely rare.

The way a resistance tester works is to run a small current from a battery through the circuit and measure the drop. If you touch the metal parts of the probes, then there's a small current flowing through you, hence the high resistance reading.

Keep your fingers off when measuring resistance or it will skew the reading!

It's true!

In fact, with a good meter I have measured different body resistances based on pressure, perspiration and proximity.

I have to agree you are likely the high impedance short circuit your meter is detecting.

Zeus' brother Billy

Sorry about the confusion, I should have used the other pic, I don't normally test with my fingers, just did that to take the shot.  It's just the contacts and the metal, no fingers used in the 6hrs of filing and testing.  My meter isn't that sensitive, $9 home depot. The readings only happed after soldering so; heat, solder, flux, copper flakes or something gets active throughout the pcb because the copper is cut, from the first test.  The minuscule current is there, where it wasn't and shouldn't be. (I have come to the conclusion that it is microscopic electro mites hand carrying the current in buckets)

At this point, I just want to know what is the limit for DCC interfernce, because at 60 DC ignores it.  If it's safe to put in the additional 6 hours of construction to finish the switch and be satisfied that it will work on the layout then I can move on having discovered proof of an afterlife.

Shorts !!

I have a suspicion that your multimeter may be the problem. If you access to a good digital multimeter it would be worthwhile rechecking the readings with it. I went and rechecked my own fasttracks turnouts just to see if there was any reading using the highest and lowest range on my meter (20meg, 200ohms) and there was no reading whatsoever and then borrowed a $2.00 shop analog meter and bingo had a minor reading where previously there was none. Hope this helps

Meter check

If I may add my 2 cents, irrespective of the quality or sensitivity of your meter you will always get an infinite reading if there is no conductive path somewhere in the circuit. The resistance of air, even very humid air, is so high your meter can't measure it and assuming your fingers are not in contact with the probes then there must be a conductive path through your assembly else you would get no needle movement. If the short is due to a copper foil path then the resistance would not be a million ohms as your meter shows. Rather it would be relatively low probably a few ohms at most. The meter passes only a very small amount of current through the path to make the measurement so even the smallest of foil shorts will not cause much resistance. Therefore your culprit is more likely to be oils, flux, or some other coating on the PCB ties. Try cleaning the assembly with alcohol as mentioned earlier or a stronger solvent such as lacquer thinner if you have some. Also, check the resistance of the piece of pine you are using as a work surface. If the wood has a high moisture content it could have a resistance of a million ohms across a short distance. I seriously doubt the paper or ink of the template print would be conductive but would still remove it to elliminate one more variable. Lastly, if all else fails, try passing a large current (amp or two) through the assembly. If in fact your short is a microscopically small foil path then it will blow like a fuse when the current passes through.

Best of luck to you,

-a

Current

If your reading of 60-120kOhm is correct, that will give a current from one rail to the other of 0.0009A, hardly a short. You can have 1111 of those before you reach 1A.

Altho it's strange that it shows up, I doubt it will be a problem.

Copper slivers...

When laying track with PC ties, its is EXTREMELY important that all slivers of copper, both at the edges of the ties and where gaps are filed in the upper foil surface, are COMPLETELY removed.

I habitually use 400 grit emery paper to 'polish' (well not quite polish...) the edges and surfaces of my ties. I thoroughly inspect all gaps for slivers or burrs.

Why?  Because at one time in the past, I put a turnout into operation that seemed to be working fine. The ohm meter said there were no shorts and rolling stock tracked through it without problem.

However, one day during an op session the dread words were spoken - "Hey, does anyone else smell smoke?"

Anyone else(s) did indeed. Track power was shut down and an olfactory search was performed. Eventually the smell of charred cork was traced to the turnout. As near as I can tell, a whisker/burr/sliver of copper foil had been left on the turnout near the points (that's where the charred cork was located).  Originally, it had made no contact with 'the other side' (that is the electrical other side) so there was no short.

Somehow though, that whisker/burr/sliver had gotten bent or shoved a bit so that it was ever so gently brushing against an adjoining PC foil area of opposite electrical polarity. Not enough to make a low impedence short which would have triggered the DCC booster crow-bar circuit and shut down power. Instead it was a high impendence 'short' which apparently allowed a couple of amps to flow. Not enough to trigger the crow-bar protection in the boosters, but plenty to get things really, really, hot.

So now, I use the 400 grit to smooth the edges of PC ties and an very careful about visual inspection of gaps with a magnifying aid looking for whiskers.  AND I try to never leave track power on unless someone is in the train room. I don't know what would have happened if nobody had been there to smell the smoke and shut off power, but I'm glad I didn't find out the hard way.

Charlie

High impedence 'shorts'

When you are measuring the impedence from rail to rail in the turnouts:

• is there *anything* else touch the tracks/rails?
• No equipment on the tracks (especially locos or passenger cars with lights)?
• The track isn't sitting on anything conductive (like an antistatic mat)?
• Does your ohm meter read 'infinity' if the probes are touching anything?
• Does the ohm meter have a reasonably fresh battery in it?
• Have you visually inspected all PC ties and gaps for foil whiskers/burrs/slivers?
• Have you visually inspected all rail gaps for whiskers/burrs/slivers of nickel-silver?
• Have you filled in your rail gaps with something?  If so what material did you use? Have you checked the resistance of this material?

I suspect you've probably done all this already. But thought I'd mention them just in case.

FWIW

Charlie

I agree with Charlie

I have had a faint reading ony ohmmeter (exact same as yours) after I swore up and down that I initially had no shorts. I personally think just handling the turnouts (taking them in and out of the jig, touching the ties etc) allows a tiny, tiny whisker of copper to bridge the gap.

I have found that you darn near need a microscope to see those short causing strands.

I have noticed that the larger the item is doing the shorting, the more it registers on the ohmmeter. The tiniest little copper shavings give a low, subtle result as you described.

Painting the turnout should prevent further strands from contaminating your gaps.

to the test track

Thanks for the confirmation, do you run DCC on your track?  I'm setting up the Digitrax 8amp and a little concerned about potential damage to my only working DCC engine though it sounds like I shouldn't be worried? 

my current stage in track laying (http://www.chicago-l.org/trains/gallery/images/5000mkII/cta5001a.jpg)

Next switch I am going to experiment with etching the copper on the pcb tie instead of filing. I could just mask copper for soldering and it might just pass for tie plates.  The foil on the bottom serves no real purpose other than as a backup.

If you etch your gaps, be

If you etch your gaps, be certain that ALL of the etchant is washed completely off or you will see greenish evidence of further corrosion.

If you just fold up a small piece of 400 grit sandpaper/emory cloth and run the ties through that before soldering them in place you'll drastically smooth the edges of the ties.  This pays two benefits: 1) the ties in the region of the points will have no rough edges to snag the rails as the points (attempt to) move back and forth (be sure to sand off any rough edges on the points, too). 2) And whiskers of foil on the edges of the ties will either be removed or made plain enough that you'll see them and remove them.

Filing gaps generally does not result in whiskers too fine to see if you have reasonable vision and are wearing a magnifying headset.

Charlie

Doesn't Joe remove all of the copper except under the rail?

I seem to remember that Joe removes all of the copper cladding on his pc ties except for a bit about twice as wide as the rail flange where he actually solders.  If you did that, you would be creating such a large gap except right at the frog that you should not get any shorts.  Since the frog is then gapped from the rest of the turnout and either left dead or powered remotely to match the direction the switch is thrown, any potential short should be eliminated.

PC ties

Russ is correct, Joe does do this in his CVT turnout instructions.  I believe that was all about creating a suggestion of tie plates so the PC ties would blend in with the rest of the detailed CV plastic ties.

I run each PC tie over my 10" mill file to clean up the edges.  Another way of gaping copper cladding is to score the thin copper with a blade in two places and lift the cutout in between away from the substrate.

I remember seeing a homemade jig for filing/sanding PC ties on another forum.  As I recall it was a block of wood with notches to hold a few ties so they could be easily cleaned up.

PC Ties filing/sanding jig

Kevin,

I built a jig and detailed it on page 102 of Issue #5 Jan/Feb 2010 of my Roundhouse & Turntable article (Part 2).

 I do this for all my pcboard ties either track or turnout.

I also mention sanding ties in the next issue # 7 May/Juner 2010 on page 99 May/June issue.

The pcboard ties are glass polyester based and after having had some glass shards under my skin once, I sand each one to get rid of them.

This way as you mentioned there is no way you can have a short from those pesky whiskers.

look ma, no shorts