How to make sure your moisture meter is working correctly.
Every floor installer and inspector should have a meter to check the moisture in wood floors. Having a moisture meter and knowing how to use it is not all there is to know. It is also important to know how to check calibration and function of the meter to avoid false measurements.
Floor installers should measure the moisture content upon delivery, before and after acclimation and when the floor has been installed.
Recently I had a phone call from a customer asking me, why two meters he is using on the same floor read differently. He said one meter consistently reads around 6%, whereas the other meter from a different manufacturer read consistently no values lower than 8%. We finally figured out the reason for the discrepancy by checking the default readings for both meters. (Default reading is the value a meter indicates, when the read button is depressed with nothing connected and pins pointing into the air.)
The default reading for one meter was 6% the other meter read 8% even though the pins were not touching any wood. A moisture meter will never read any lower than the default reading, which means the meter with the 8% default reading will never be able to indicate any moisture content below 8%, even when measuring drier wood.
Since the moisture meter user may not be aware of any malfunctioning of the meter, it is advisable to check the basic functions of a pin and pinless meter before and after each test series. In addition, the calibration of moisture meters can be checked with calibration test blocks available from the moisture meter manufacturers. These external check blocks are essential for a valid check procedure. Moisture meters often have internal calibration checks, but those checks do usually not include the connection to the measuring plates for pinless meters or the connection to the pins, cables or hand probes for pin meters.
Basic function check for pin meters:
When the on-off switch or read button is depressed by hand without touching the pins, the lowest moisture value for the chosen wood species setting should be displayed (default reading). This test indicates there is no short within the circuitry. Meters may also show higher values if the area between the 2 pins is contaminated or has condensation.
This meter from Lignomat shows the lowest value (default reading for wood group setting #3) with the decimal point blinking. On-off switch between the pins is depressed, but fingers are not touching the pins.
When the on-off switch or read button is depressed and both pins (integral pins on the meter or pins of the external probe) are touched at the same time with two fingers, at least 12% should be indicated. Continuity test indicates that the connection from pins to circuit board to display is working.
Calibration check:
Last, the calibration can be checked with the pin test block. The pin check block consists of one or two resistors which produce a certain moisture value when pins are touching the contact points of the calibration check block.
Only an external check block can confirm, that probe, cable and meter are functioning properly. Measurements are supposed to be within +/-1% of 12% for this calibration check block.
Basic function check for pinless meters.
When the on-off switch or read button is depressed and nothing is touching the measuring plates on the back of the meter, the lowest moisture value for the chosen wood group is displayed (default reading).
Hold meter in the air to make sure no material is touching the measuring plates and the lowest possible value appears on the screen with “Min”.
For the continuity test, place the pinless meter on your forearm and depress the read key, a high moisture value should be indicated. An additional meter check can be performed by measuring a realm of paper. If the paper test is done repeatedly with the same setting, the indicated value should not vary significantly over the course of a year. This can be used to check consistency and accuracy of the calibration over time.
Last, the calibration can be confirmed with the calibration check block. The check block for pinless meter is usually a material plate which produces a defined reading when the meter is lightly pressed against the surface.
Always press down slightly on the meter when taking measurements and when checking the calibration with a calibration test block.
After checking the meter with the above described methods, you think you are ready to take measurements. Stop. A very important next step is to set the meter for the correct wood species. Find out about the wood species. Find out if it is an engineered floor and what the hardwood species of the top layer is, set the dual-depth meter for that species and the ¼” measuring depth. Now you are ready to start a test series.
Last, your moisture measuring report should include place, date, moisture meter brand and instrument name, pin or pinless, wood species setting and measuring depth, location where the reading was taken and indicated moisture value in percent. A photo of the meter while taking readings is always helpful.
What if all of the above has been followed, but accidently the wrong species setting has been used for the measurements. If you cannot go back to take the readings again, ask the meter manufacturer, if they can tell you what the readings would have been with the correct setting.
www.lignomat.com — Email: sales@lignomat.com – 800-227-2105 — Grete Heimerdinger
Product Manager at Lignomat.
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