So if my meter reads 1 volt, I know that the resistance is 80 megohms. I should see an 8 volt drop across the wood and a 1 volt drop across the meter. My meter has a 10 megohms resistance, and my battery is 9 volts, Knowing that current is equal to voltage divided by resistance, and that the current throughĮach element is the same, we can express this as:įor example, if the wood between the probes has an 80 megohm resistance, And the voltage drops across the meter and the probes willīe in the same proportion as their resistances. With each other, the voltage drop across my meter and the wood will be equal to theĩ volts from the battery.
#Wood moisture meeter series
So now if I use a 9-volt battery, and hook the volt meter and my wood probes in series Using another multimeter, that this meter was one of those with the 10 megohm Resistor that just happens to display the voltage across it. That is to say, the meter itself is like a 10 megohm Most of these multimeters, when in voltage measurement mode, have an internal So the multimeter wouldn't be able to measure it.īut there is a trick to measuring much higher resistance with a cheap multimeter. Moisture content is often in the hundreds of megohms. Resistance mode, and the resistance between the two probes for any "normal" The catch with this is that a typical multimeter will read up to about 20 megohms in So I figured, why not just use a multimeter to measure the resistanceĪnd calculate the moisture content myself? I found thatĪll they do is measure DC electrical resistance of the wood, and use that to calculate Next I researched how moisture meters actually work on the web. Using a multimeter to measure wood moisture Off a log, so it's still saturated with moisture. The piece of wood I'm checking here is still relatively fresh from having been sliced The probe unit can be driven into the wood with a mallet to ensure that it penetrates Soldered some wires to where the probes used to be. I took the original probes out of the meter and just I also attached a wooden knob as a handle. Over the points to serve as a limit for how far the tips could be pushed I put a nut over the points of my probes, then added three more layers of plastic If I mounted the probes in wood, that would completely mess up my readings. Normally, I would have been tempted to just use a block of wood to mount the probes in,īut moisture meters work by measuring conductivity of the wood. I mounted the probes in some layers of white plastic that I had cut from a bucket.Ī block of UHMW plastic would have been better, but I didn't have any of that stuff handy. Would make it easier to pull them back out of the wood. I figured getting the sides of the probes smooth I smoothed them to a shine with a buffing wheel. I started with some long narrow screws and ground them to a point. These would be probes that I could drive in with a hammer. So I set out to make a new set of external probes for the meter.
It would just break again next time I'd use it. With such flimsy construction, there wasn't much sense trying to repair One of the pads hadĬome off the circuit boards and the trace to the next circuit component (right where The probe points were soldered directly into the circuit boards. Very firm taps to get even minimal penetration into the hardwood, butĪfter just a few readings, it stopped working. Make contact, I kept tapping the meter in with my wrist.
Penetration into the wood makes a big difference in terms of how well they Unfortunately, the moisture meter didn't last very long. I never actually tried it out until IĬut up some fresh lumber on my bandsaw and wanted to get I bought one of those cheap wood moisture meters on sale for $25 at Princess Auto