Choice of sensing cable for a water leak detector - Page 1
Forum section: electronics / beginners

author: sebdehne
author_rank: Contributor
timestamp: April 25, 2015, 06:39:47 pm
content: Hi,I would like to build a water leak detector simply by measuring the resistance between two exposed terminals. Does anyone know if there exists a type of cable (and where I can buy it cheaply) which is basically two exposed coper wires which run in parallel without touching (separated by some spacers or something); such that when the cable comes in contact with water, the water conducts electricity between the two coper wires and I can detect that.Thanks!

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 25, 2015, 06:55:49 pm
content: "Open ladder line" is a type of RF cable where there are just two uninsulated wires with insulator/spacers at intervals to hold them apart, rather like ties on a railroad track. You did not disclose the length or width of your proposed solution so we don't know whether it would be practical for your situation.Another possibility might be the old cloth-insulated wire. The fiber insulation keeps the wires from touching, but would be "permeable" to water. Of course, it has a very low "frequency response" because it would take a while to dry out after exposure. Again, since we know nothing of your project (or your location), we have no idea whether this might be practical.

author: sebdehne
author_rank: Contributor
timestamp: April 25, 2015, 07:07:05 pm
content: The project is about detecting leakage water in typical household places, like under dishwasher and fridge. So the cable should be between 50-100cm.I liked the idea of using cable sleeve. I have some of that. :-) Thanks!

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 25, 2015, 07:14:34 pm
content: But surely you don't need to sense moisture ALONG the whole length of the wire???You just need ordinary wire over to to the sensing device.Most people just use an ordinary PC board with a serpentine or interdigital trace to maximize sensitivity.

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 25, 2015, 07:19:02 pm
content: Try searching for:Fluid Sensing CableLeakage Sensing CableFluid Leakage DetectorBut they seam to be rather expensive.How about a etched and gold plated PCB wich a few meters of track running on them, twenty 10x10cm from Itead for considerably less.

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 25, 2015, 07:20:30 pm
content: Quote from: Richard Crowley on April 25, 2015, 07:14:34 pmExactly what i was thinking of

author: sebdehne
author_rank: Contributor
timestamp: April 25, 2015, 07:24:05 pm
content: PCB is of course simple, but I am a bit worried about when I place the PCB in the floor that the leakage water does reach above the PCB hight/thickness.I think using two bare copper wires and putting one of them into a cable sleeve (like you suggested) might do the trick. I can cover a larger area using a cable like this.I guess I will try both the PCB suggestion and the cable suggestion and see what works best.Thanks!

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 25, 2015, 07:27:27 pm
content: The sensing side of the PC board does not need to be on the top.You can place it with the sensing side DOWN.

author: sebdehne
author_rank: Contributor
timestamp: April 25, 2015, 07:32:26 pm
content: True. Then the capillary forces should ensure the water reach the traces in the PCB... I will try that.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 25, 2015, 07:36:38 pm
content: You can get generic "strip-board" prototyping PCB material for dirt-cheap.Then you can cut it to size/shape as desired. Even lay out a string of them connected in parallel.