Q: We have recently purchased an in-line moisture meter and some people are not convinced that it is giving accurate readings. We do follow the manufacturer's instructions, but there is still doubt. Can you help us determine the overall reliability of this equipment?
A: To begin, I think that the key is for you to conduct four tests to prove to everyone whether the in-line meter is working well or not.
The first test is to measure the MC of at least 20 pieces of lumber with a standard pin meter - use a good meter with insulated pins. Drive the pins 1/5 of the thickness. Measure the lumber at three spots: 2 feet from each end and in the center. Take the readings approximately mid-width. Discard any pieces that are under 6.5 percent MC, as the pin meter doesn't work well at these low MCs. Then run the pieces through the in-line. Compare the average pin meter reading with the in-line. (Correct both sets of readings for species. Do this test with lumber at room temperature.) Also, drive the pins in another 1/4 inch and see if the reading changes - a large change in readings means a steep gradient and will explain why the meters do not agree well.
Next, run some pieces through the in-line. Then turn them over and run again. The readings should not change much if the in-line is working well.
Next, run 10 pieces through the in-line when the lumber is cold. Immediately wrap each piece separately in plastic wrap. Then warm up the lumber for a few hours, remove the plastic and run them again. The plastic prevents any moisture loss during the warming. The readings should not change appreciably.
Finally, I would get some pieces of lumber that are quite dry, run them through the in-line and then expose them to humid conditions, perhaps outside on a foggy day for a few hours. Then run them again. The short humid exposure will only result in moisture gain on the surface, but the entire piece would be at the same MC. We hope that the meter readings do not change appreciably
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