Selecting the right cable - Page 1
Forum section: electronics / projects

author: Tectonic
author_rank: Contributor
timestamp: February 20, 2016, 10:40:54 pm
content: I'm designing a device to probe water temperature of a lake at different depths. The initial design will have two temperature sensors at the end of the wire as well as a bit of weight. The measurements will be done with a microcontroller displayed on a small LCD screen.I'm looking to select the right cable for my application. The criteria are:Low cost (trying to keep it under $1.5/ft)4 conductorsGood flexibility (I want the wire to be straight when unrolling it. I want minimal weight required to keep it straight and not coiling when it's lowered into the water.)Temperature range from 5C to 35CKeep the wire's diameter at a minimumI'm looking for recommendations on jacket material, insulation material (if needed), and stranding. I've done some research and it appears silicone-rubber would be ideal but the price for it is ~$6-8/ft. There's plenty of alternatives but mere descriptions aren't enough to go by. Once I get an idea of what is a good choice I'll go ahead and get some samples.

author: dwpatter53
author_rank: Contributor
timestamp: March 01, 2016, 11:12:32 pm
content: What type of sensor? and what will the voltage and current be?I would go as small a AWG as possible.24 or 28 AWG 4 cond stranded should work.CAT 5E 24/4PR RISER 100 Feet GRAY is cheap, $20. in Canada.

author: calexanian
author_rank: Super Contributor
timestamp: March 02, 2016, 03:18:37 am
content: I would think any four conductor would work. I would not go below 22 AWG as soldering becomes difficult. A fishing weight at the end sould keel it nice and straight. If you can get neoprene jacketing it will be more pliable and not hold kinks. PVC should be avoided because it holds kinks and gets stiff at low temperatures. bundling 4 silicone or Teflon conductors would be good as well. I would encapsulate the sensors in a sharpie cap filled with epoxy or something of the like at the end to keep the water out and fouling your measurement.

author: dom0
author_rank: Super Contributor
timestamp: March 02, 2016, 07:30:53 am
content: Soft PVC would work (for a few years. Microphone cable comes to mind. Soft PVC, light, thin conductors, many configurations available, cheap.), but you probably want cable with a rubber or silicone jacket, which tend not to lie flat.

author: made2hack
author_rank: Frequent Contributor
timestamp: March 02, 2016, 10:21:32 am
content: LAN / ethernet cable. It's AWG 24, usually solid copper conductor. If you want some extra shielding, buy FTP/s-FTP type that has some more shielding on it. Cheap as in the $1 - $2 / meter. Also, it's 4 Pairs, or 8 wires. So it gives you some redundancy.

author: dexters_lab
author_rank: Unknown
timestamp: March 02, 2016, 12:53:01 pm
content: CAT5 or other PVC cable would turn very rigid in cold wateri would head over to the Chinese sites like aliexpress or alibaba and look for silicone cable that would be used on headphones or in other audio applications where you have multicore cable.

author: ajb
author_rank: Super Contributor
timestamp: March 02, 2016, 02:04:00 pm
content: I can't think of many high-volume applications that require four conductor cabling. You might have more luck if you can find a way to get away with only three conductors (might need a small MCU at the sensor end to multiplex the data from the two sensors onto a UART stream or something?), as that could allow you to use much more widely available commodity 3-wire audio cable and similar.You'll need to pay special attention to sealing the sensor end, especially if you go with a silicone jacket, to which a lot of sealants won't stick very well. It may be best if you can somehow incorporate a gland at the sensor end.

author: dom0
author_rank: Super Contributor
timestamp: March 02, 2016, 02:48:58 pm
content: 2x2 / 4x (+ shield) microphone cables are pretty much standard. Telco cables with 2x2 are common, too, but normal PVC cable isn't a good match for this (see above).