Moisture Meter Safety: Sharp Pins, Batteries and True Readings

The physical risks of a moisture meter are small and specific: sharp pins, a battery, and an electrical instrument used where it should not be. The practical risk is a wrong reading taken on trust. A meter that has been dropped, run on a weak battery or used straight out of a cold truck can read a few points off, and boards that are too wet get glued up and move later. How a meter reads explains the corrections. This page covers keeping the person and the meter safe.

• They are sharp. General's MMD4E manual warns users not to stab themselves with the extremely sharp test pins.
• Cap them. General says to replace the pin cap and rubber sleeves after measuring, for safety and to keep the pins from bending or dulling. Lignomat's mini-Ligno MD cap covers the pins for transport and doubles as a handle for pushing them in.
• Push, don't force. General warns never to force the pins into a hard surface. Delmhorst directs pins into the wood parallel to the grain, pushed to full depth. A bent pin reads at the wrong depth as well as being a hazard.
• Keep them tight and replace them when worn. Delmhorst says to keep contact pins hand-tightened and change them as needed; the MMD4E comes with spare pins.
• Hammer electrodes. For thick stock Delmhorst uses a separate hammer electrode with insulated pins. The J-2000 manual reviewed gives no handling instructions for it, so follow the electrode's own.

General also says not to immerse the MMD4E or take it apart. Wagner's pinless meters read through the wood into the space below it, so the manual asks for a 1 in air gap under the board and no hand beneath the meter. A hand there is not a hazard, but it gives a false reading.

• After a drop. Wagner recommends returning an Orion to the factory for a diagnostic check after a drop or damage. If a reading is suspect, recalibrate it on its own On-Demand Calibrator, and send it back if it will not calibrate. General says not to drop the MMD4E.
• The boot stays on. Wagner's rubber boot is meant to stay on the Orion 930 at all times, including on the calibrator. Fitted the wrong way round it causes inaccurate readings, and if it is taken off the meter must be recalibrated without it.
• Cleaning. Delmhorst says to clean the J-2000 and its pins with a biodegradable cleaner, sparingly and on external parts only, keeping it out of the electrode connector.
• Storage. Delmhorst says clean and dry, in the case.

• Temperature swings. General says to wait at least 30 minutes after a large change in ambient temperature before measuring with the MMD4E.
• Wood temperature. The J-2000 needs correcting outside 50–90 °F (10–32 °C), by Delmhorst's table. Wagner asks users to contact it about very hot or frozen wood.
• Treated or salt-wet lumber. Wagner's manual says further corrections may be needed for frozen wood, wood permeated with salt water, and lumber treated with CCA, ACQ or other treatments containing metals, because they can bias the reading.
• Very wet wood. Above about 30% MC the Handbook treats any meter reading as qualitative. A high number means wet, not a precise figure to decide on.

Before a reading decides whether a board gets cut, run the check your meter's maker provides. The J-2000's check key should show 12% ±0.2. The MMD4E's pins in the cap's resistor should show 18.3% ±1% in wood mode. The Orion meters are recalibrated on their calibrator. A check shows that the instrument is working; it does not show the board's moisture content, which only an oven-dry test measures. Then set the reading against the target for where the wood will live, using choosing lumber. The wood movement calculator shows what a gap between the two would mean in width.

Meters by their makers' specifications are set out in choosing a moisture meter.