moving cable reliability

[zappedagain]

I have a sensor cable that was designed for stationary applications where the sensor is not moving. We now have a potential application to mount the sensor on a stage so it will be moving about 12 feet (single axis) over a stationary part. Are there any guidelines out there for cables in motion? I know there are specific high flex cables available, so I'm attempting to ballpark what the lifetime of my existing cable will be so we can determine if it is worth the expected cost increase of high flex cables.

A few details:

- My smallest conductor is #30 (7/38), with polypropelene (PP) insulation (is stress on the foil shield an area of concern?)

- I expect I'll be able to run a cable guide, so I can keep the bending radius fairly large (6-12").

- My highest potential between wires in the cable is 30V (+/-15V).

- I expect that I will be able to strain relief the cable, so connector stress is not an issue, only cable stress.

- My existing cable is made somewhere in China, so I don't expect I can ask these questions to the manufacturer.

- Initial plans are for the sensor to move about once per minute, so that means about 262000 cycles per year running 24/7. Ideally I'd like 10 years out of it, so that puts me at 2.6 million cycles. Is that reasonable?

Or are there any good tests to run, (i.e. bend it to N-radius M-times and if the O-degradation is less than T then your cable will survive for X)?


While it looks like I have some research to do, any quick leads or comments are welcome!

Thanks,

Z

 

[MacGyverS2000]

not sure about guidelines, but it sounds like a good application for flex cables...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

No specific information...

> Be wary of how the insulation might rub against stationary objects, or even against insulation of other wires; we've had, in the past, wearout of the insulation causing shorts.

> You might just go directly to high-flex cable and conductors; copper does work harden, and standard copper cables can work harden in less than 100,000 cycles if the bend radius is small, ~1 in. I vague recall some mention of needing to use oxygen free copper for the wiring.

> You should definitely start doing life testing. You might be able to push the rep rate up to 6-10 times per minute, so you could start seeing some interesting effects after about a month, with your current cable. Look for both intra-wire shorts and increased cable resistance.

TTFN

FAQ731-376

 

[CharlieGill]

Your requirements are reasonable, ratings of 10 million flex cycles are common for cables rated for that application.

No you cannot extrapolate n,m,o,x, or rather I should say that you should not. There are various formulas in use by "quality" types that look good on paper but just do not hold up in the real world. Testing electronic components at high temperature to extrapolate long term failure and drift rates is an example. The theory is sound and it is good within its limitations but there is far more considerations that come into play.

Having said that, there are plenty of cable manufacturers that have flex cycle specifications based on theory AND long term experience.

If you will fully specify your requirements, number of conductors, awg, current, I'll be happy to help look around. It's best if you can settle on a common wire size for all conductors, but there are companies that specialize in hybrid assemblies. These are typically for OEM's that purchase in quanity. If you just need a few cables, it would be best to pick an off-the-shelf cable.
Charlie

 

[zappedagain]

Thanks all. I'm presently using HDMI cable because it has multiple shielded conductors and is light weight and has a small outer diameter. As it is designed to lay behind a TV, I have concerns about the lifetime in motion.

Presently I am purchasing it from a reseller who has it in 500' rolls. One roll is about a years supply for me so I'm just at the lower limit for getting a custom cable made; unfortunately a custom cable will be about 4x in cost/ft. There are always tradeoffs!

Z

 

[IRstuff]

IF you're limited in that regard, you can only make the service loop as large and loose as practically possible.





and cross your fingers ;-)

and, you should start on doing some testing as soon as possible to collect enough life data to make some decisions.


Make sure you can get decent measurements of the cable resistance and potential shorts

TTFN

FAQ731-376