Mudcat said:
Subsequent to my recent post on the measured LCR parameters of Carol 12 gauge 4 conductor cable, I measured a 6 foot section of Alpha Wire 85104CY. This is a 10awg 4 conductor shielded cable. Each conductor is 658 strands of 38 awg wire. And it is really expensive at $15/foot wholesale (I found what I was told was about 100 foot, but when measured turned out to be closer to 48 feet - no one to complain to because it was a garage sale and they moved, but still I only paid $25) .
I tested this cable three ways, and always the same two conductors. The first number will be the two conductors with the other two conductors open, the second number will be with the other two conductors shorted, and the third number - if any, will be with the outer jacket and shield removed and only the inner jacket covering the conductors.
Anyway the data you are all looking for. All results are per foot.
DCR = 0.0033 - 0.0033 (ohms)
RAC@100Hz = 0.0025 - 0.0022 (ohms)
RAC@120Hz = 0.0025 - 0.0022 (ohms)
RAC@1000Hz = 0.0022 - 0.0028 (ohms)
RAC@10000Hz = 0.0141 - 0.0146 (ohms)
Cp@100Hz = 45.65 - 45.4 - 31.3 (picofarads)
Cp@120Hz = 45.2 - 45.13 - 31 (picofarads)
Cp@1000Hz = 41.95 - 41.79 - 28.2 (picofarads)
Cp@10000Hz = 38.1 - 37.95 - 26.4 (picofarads)
Ls@100Hz = 0.24 - 0.259 (uH)
Ls@120Hz = 0.21 - 0.257 (uH)
Ls@1000Hz = 0.21 - 0.21 (uH)
Ls@10000Hz = 0.215 - 0.218 (uH)
Notice that I only measure the capacitance after I removed the shield. Also notice that the capacitance went way down after the shield was removed. So, is there an electrophysicist out there who can anlyze this data and explain why the capacitance droped after removing the shield when all else remained the same, and explain the minor differenced when the unused conductors were shorted oppposed to open?
The shield is acting as a capacitor to each wire, so the wire to wire capacitance is paralleled by the wire to shield contribution.
My guess on the small diff in capacitance with others shorted, is it's so small, that test lead errors and meter capability are coming into play..the inductance, I'd guess the cable probably has geometric imbalance, just from the spiralling machine and insulation tolerances..Ideally, there'd be no inductive coupling, but wire forming ain't exactly ideal, and a 4 wire twist is not a stable geometry..3 is, as well as 3,4,5 and (marginally)6 around 1, depending on twist of the exterior wires.
In the user manual for the 885, they show 4 wire inductance setups, and how the shield currents are supposed to cancel..You're setup will typically have .1 to .2 uH errors just from that connection set..If you want to really be "a stickler" about resolution, that'd be the first place I'd look.
As for the small diff?? Geeze, you mechanical engineers....always gotta be nine digit accurate..Reminds me of a two headed puppeteer..(bet ya don't know where that comes from...)
Cheers, John
