how to measure wire length at warehouse

The link did not seem to work, here is alternate (I think you had an HTTP and an HTTPS in there )

https://en.wikipedia.org/wiki/Time-domain_reflectometer

https://en.wikipedia.org/wiki/Time-domain_reflectometry

yeah  the stupid Link puts in HTTP:// and then you need to be careful you've deleted it when you are in a hurry pasting it into the text box.

Any way I'm sure they can cut and paste manually if they are interested.

I Just paste the link directly and be done with it most times, If you want, you can then go back and edit the display text

Peter

Edited although I've now come up against one of those weird errors the Editor has ..It was placing the Link at the top even though I put the cursor in the right place. Cut and pasted the test above it eventually !

With wire that long, you should be able to do resistance measurement on the cable if you can get to both ends.

DAB

The obvious answer is often the best, only problem is that you need a reference for that type of cable (not too difficult you assume) and of course most reels tend to trap the one end inside the drum or underneath the rest of the cable making measurement a pain.

If you could gain access to both ends you could use the reel as one side of say a wien bridge and have quite a sensitive measurement of cable length or at least if they are short changing you.

If you have access to both ends then you can easily use the pulse (TDR method, the time it takes the pulse to get to the end of the cable is directly proportional to the length and about 80% the speed of light

Knowing this, a jig could be made that will measure the length of the cable quite easily, sending a rapid rise time pulse down the cable and measuring the time it takes for that edge to get to the other end

At the speed of light 300,000KM/Sec = 3.3333nS / Meter a 100M reel of cable will take 3.333*100 = 333.333nS to propogate less the velocity factor of copper of about 0.93 (TBC) means the pulse leading edge will take 333.33/0.93 = 358nS

to measure this to better than 1% I think a clock of better than 300MHz will be needed as if it takes 358nS to travel 100M then it takes 3.58nS for 1M or 3.58pS per mm, so now it is easy math to determin what resolution you need to capture

Only really need one end  to inject then measure the time of the reflection returning off the unterminated end.

With both ends you could do a simple time of flight measurement.

does the inductance of the drum of wire change the propagation speed .....er can't remember

Probably measure the resistance if I had both ends like DAB suggested .. low cost easy to do etc.