Making a Hammer Electrode

[kelLOGg]

I have a Protimeter Timberlogger moisture meter with hammer electrodes. The electrodes are usually in lumber in the kiln and their wires are fed thru the wall to the meter. If I need the meter to measure MC in my air drying rack I have to open the kiln to get the electrodes, make the measurement and put them back in the kiln. (and repeat more often than desired.) A second pair of hammer electrodes would be nice to have so I googled them and they are expensive ~ $250. Even the needles are steep because I have to buy 10. I may get the needles and make my own slide hammer assembly. Has any of you done that? It seems doable; there are no electronics in the hammer - just a direct electrical connection from the hammer to the meter. Even simpler, it seems to me that I could get 2 insulated needles, drive them in independently the correct depth and distance apart, connect the electrodes to the meter and make a reading. It would be easy to compare results to my existing hammer electrode to check the agreement of the 2 measurements. Ideas?

[Larry]

One of my experiences on ways to screw up.  Years ago I got some pins and drove them into a board in the kiln.  I attached electric lamp zip cord to the probes and ran it outside the kiln so I could easily check MC.  It didn't take long to figure out my meter reading was not accurate.  What I found was the zip cord insulation was absorbing enough moisture that the cord itself was giving me a reading....in fact I could get a reading without the cord even attached to the probes.

I later found some single strand cord that didn't absorb moisture and ran two separate leads to the probes and that worked ok. 

I later found that wood around my probes was drying faster than the rest of the wood.  Probably because this was in a slow drying solar kiln.  In a faster drying kiln it might not be a problem.

[LeeB]

I don't see why you couldn't use some painted finish nails. leave a little bit of both ends unpainted the same as the needles are for measuring moisture at a certain depth or uncoated for average.

[K-Guy]

Part of the reason those pins are expensive is that they have to be made to very strict specifications to read correctly. Also they are specific to the brand or model of meter they are made for. Homemade ones will give readings you can never trust.

[LeeB]

So much for nails then.  :D :D :D

[kelLOGg]

I guess I'll get 10 needles. The pair in the hammer now are still good after 20 years. With 5 more pairs I'm set for another 100 years. 

[Nebraska]

I guess  my stainless steel finish nails aren't right then. I got similar readings on my  Mini Lignomat on fresh sawn wood  outside surface and at depth when I tested them.   It was repeatable
so that was good enough for me, but I don't sell any lumber either and you're  talking a bigger nicer tester as well.

[LeeB]

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr06.pdf


Substitute Electrodes 

When the pins of the available electrode are too short to measure either the average or the core moisture content of a specimen with large cross section, two nails may be substituted for electrode pins. The nails should be driven to the proper depth and about the same distance apart as the pins on the standard electrode. The reading then can be obtained by touching the standard electrode pins to the nailheads. It should be emphasized, however, that the reading is not influenced by the distance between the nails. When using two nails, as when using any two-pin electrode, a correction of 1 percent should be added when the indicated moisture content is over 15 percent

[kelLOGg]

That's a comprehensive article. I will print a copy for reference purposes. Thanks.