How best to accurately measure /cut cable to length?

[sjb741]

We have some thick, twin-core coax to measure & cut as accurately as possible to 10m. It is very slow to get a good precision measurement.

Simply pulling it "straight" along the floor is unsatisfactory, because the cable has undulations due to the way it is sold as a coil.

I am thinking that if we close-wind a single layer onto a drum and empirically measure this accurately - and also calculate the expected length, then we could use this as a basis folr repaetable accuracy.

It is tempting perhaps to simply measure impedance, but this does change with cable coiling etc

 

[FvM]

Measuring mechanical and electrical length isn't the same, choice depends on your specification.

Industry standard method is mechanical cable length meter.

 

[KlausST]

How accurate?
What conditions?

cable datasheet (for diameter, specific weight, stiffness...)

Klaus

 

[D.A.(Tony)Stewart]

It depends if you want consistency, or accuracy or speed or all. A 1mm diameter error with ~ 6 turns results in a length error of ~ 2 cm. Then how will it be processed next? straight or coiled?

 

[dick_freebird]

Home Depot has measuring wheels w/ a classic
gear-driven counter. Accurate to the fractional
foot, seems like, good enough for them.

If you want electrical length I'd imagine a TDR
setup, cut it a little long and then figure out how
much to subtract in length, for how much flight
time excess to remove.

At 10m you might be able to use a pulse gen &
'scope if it has nice measurement (delay 1->2)
features. Figure about 60ns round trip, that's
easily handled with not-so-modern bench gear.