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[TCML] Concrete Form Secondary Resistance Measurements



I did some resistance measurements on a cardboard concrete form tube from Home Depot. Home Depot's brand is "Quick-Tube". I used a Megger MIT 430 for the measurements. It uses up to 1100 volts DC to measure the resistance. It was at that voltage for all these measurements.

To do the test I used a caliper set at 0.1 inches lightly scribed 3 pairs of lines on the inside the tube, 3 pairs on the outside where there was no black ink, and 2 pairs on the black ink. I made sure that the caliper did not scrape the ink or surface away as I wanted to be in contact with it.

I did the test twice. First test was done about an hour after the tube had been brought in from the garage where the temp was about 45 degrees F and 50% humidity. The second time I did the test the tube had been sitting in the lab for about 5 hours at 75 degrees F with much lower humidity. I am assuming that the tube dried some after sitting in the lab for 5 hours since most of the values went up. Here are the values. The letters indicate the test area.
1st test  after 1 hour inside.
Outside of tube, no ink Outside of tube on black ink Inside of tube

a) 4.5 gigohm d) 14.5 gigohm f) 7 gigohm b) 8.5 gigohm e) 25 gigohm g) 3.5 gigohm c) 11 gigohm h) 2 gigohm

2nd test  after 5 hours inside.
Outside of tube, no ink Outside of tube on black ink Inside of tube

a) 20 gigohm d) 27 gigohm f) 9.6 gigohm b) 60 gigohm e) 26 gigohm g) 16 gigohm c) 30 gigohm h) 30 gigohm It seems that the inside has quite low values as compared to the outside. The coating on the inside seems to be heavier. Humidity seems to have a pretty big part in the values, but there are a few that changed little where as others changed a lot. The ink vs no ink does not show up in this test. Maybe more data points are needed.
The same tests should be done with the "Sono-Tube" and the Menards tube.


Jeff
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