Wood and Timber Drying

Relative humidity along with time and temperature affect wood drying. Normally these parameters are based on previous drying experience, with the goal being to optimize drying time while minimizing wood cracking. The process parameters are unique to the system used, with different woods and seasonal variations affecting the result. This makes wood drying a demanding process. To achieve the best results, relative humidity needs to be continuously monitored.

Wood is a porous material, i.e. it is hygroscopic, absorbing moisture to reach an equilibrium with the ambient environment. The mechanical properties of wood vary with the temperature, pressure and moisture content. In most applications the moisture in the wood cells must be removed to allow further processing and to protect wood from blue stain, fungi and mold, as well as from cracks and checks. The initial moisture content of green wood, i.e. freshly sawn timber, varies from 50 to 100%, depending on the species. When used as a construction material in, for instance, a normal temperate zone climate, the timber is dried to a moisture content of 18%, while for joinery and carpentry a moisture content of 10% to 15% is ideal.

Read how a sawmill minimized the drying time for timber goods

The accuracy of relative humidity measurements really matters. It directly affects the quality of the drying process and indirectly affects facility capacity. Inaccurate measurements can cause the following problems:

If relative humidity is inaccurately shown as too moist, wood may crack due to the overly dry conditions. Over-drying wastes energy and ties up expensive facility capacity unnecessarily.
If relative humidity is inaccurately shown as too dry, the overly moist conditions will slow the drying process, leading to longer drying times and reduced capacity.

Three main factors help to keep measurements accurate: use of the appropriate sensor, ensuring that the measurement device is installed correctly and regular calibration of the measurement device.

Watch webinar: Measuring humidity in condensing environments

Wood and timber drying related products

Relative Humidity and Temperature Probe HMP7

Vaisala HUMICAP® Humidity and Temperature Probe HMP7 is designed for applications which involve constant high humidity or rapid changes in humidity

Indigo200 Series Transmitters for Vaisala smart probes

Vaisala Indigo200 series transmitters are host devices for displaying measurement values from Vaisala's Smart Humidity, Temperature, Dew Point, Moisture in Oil, CO 2 and H 2 O 2 Probes.

Indigo500 Series Transmitters

The Vaisala Indigo500 series transmitters are host devices for Vaisala Indigo-compatible, stand-alone smart probes. The Indigo500 series include multi-functional Indigo520 transmitter and Indigo510 transmitter with basic features.

Indigo80 Handheld Indicator for portable measurements with Indigo-compatible probes

Indigo80 handheld measurement device

The latest addition to the Indigo family of transmitters and probes, the Indigo80 is a compact, handheld indicator and data logger.

Bringing out the beauty of wood: Veneer drying with humidity control

During manufacturing, veneer is dried in a drier circulating hot and humid air. This is a demanding processing step, and accurate dewpoint control is essential in obtaining the best quality veneer for demanding wood products and long-lasting finishes.

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Do I need an Indigo transmitter or just an Indigo probe?

There are many probe options to choose from measuring several parameters: humidity, temperature, dew point, CO2, moisture in oil, and vaporized hydrogen peroxide. The probes can be attached to Indigo500 or Indigo200 series transmitter. When is a probe sufficient on its own – and when do you need both a probe and a transmitter?