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Timber Drying

Timber Drying

Timber Drying in General

Wood is probably one of the oldest building materials on the planet. But before wood can be used as a construction material, whether it be a structural support in a building or to manufacture furniture, it has to undergo treatment to gain the required properties defined by the application where the wood is used.

The first and most important treatment is the drying process. The fastest and most effective way to drying timber is in Kilns. Kilns drying is done in a closed chamber in which air temperature, relative humidity and airflow can be controlled to dry timber to a specified moisture content. The temperature for the drying is usually between 40-90°C depending on type, size and the later use of the timber.

There are many different types of kilns such as vacuum systems, traditional heat and vent type kilns and radio frequency dryers. The cost of installing and maintaining kilns may often be prohibitive unless a large amount of timber can be processed. However, if the value of specific species is high enough, it becomes more feasible to kiln dry green timber.

Some other options to try timber are: Solar drying where the green timber gets put into a glass house. This option is rather used for drying small amounts of timber. For bigger amounts the Air drying option is used more often. Both drying options are only controllable to a very limited extent since they strongly depend on weather conditions.

Why the Need to Measure Humidity?

Controlling humidity during the timber drying process is essential for many factors. An incorrect level of %ERH in wood will have the following effects on product and process:

Dimensional Changes

A controlled drying process prevents the timber from unacceptable shrinkage after the installation.

But since wood is a natural hygroscopic product it will always change its size to a minor extend.


Drying the timber below a water content of 25 % to 30 % will maximize the mechanical strength. It is nearly twice as strong and twice as stiff as green wood.


To reduce susceptibility to fungal decay: Timber maintaining less than 20 % moisture content is unlikely to be attacked by wood decaying fungus.


To increase the effectiveness of preservative treatments: Many preservatives should only be applied when the humidity of the timber has been reduced.


Dry timber prevents the corrosion of metal fixings such as metallic foundation, holders, nails and screws.


Dry wood is much lighter in weight than wet wood. For many species, dry wood is nearly half the weight of wet wood

What Solution can Rotronic Offer?

The heart of the latest humidity measurement equipment comes with the Rotronic capacitive foil sensor: HygroMer IN-1. This thick film sensor, with the best long term stability on the market is ideal for the tough application of timber drying, where high temperatures and humidity levels are pre-sent.

AirChip3000 Advantages:

  • Relative humidity, temperature and dew point outputs
  • Can store 2’000 points
  • Sensor self test function

And much, much more….

Rotronic Products:

Humidity and temperature probes: 

  • HC2-IM402 -100…200°C, 0…100%rh, Ø15mm, ±0.8%rh and ±0.1K…
  • HC2-IC402 -100…200°C, 0…100%rh, Ø15mm ±0.8%rh and ±0.1K…
  • HC2-IC402-A -100…200°C, 0…100%rh, Ø15/25mm, ±0.8%rh and ±0.1K…


  • HF5 series For interchangeable probes, Various analogue and digital outputs, Display, All psychrometic calculations available…
  • HF7 series Stainless steel probe, -100…200°C, 3/4 wire configuration, Various analogue outputs, Display…
  • HF8 series For 2 interchangeable probes, Various analogue and digital outputs, Display, Relais outputs All psychrometic calculations available…

Dataloggers: (e.g. for solar drier)

  • HL-NT range For interchangeable probes (up to 7 probes with docking station) 32MB flash card, Display, Conform to FDA21 CFR Part 11 and GAMP4…
  • LOG-HC2-RS Wireless logger for one inter-changeable probes. Stores up to 500000 data points 6 Year battery lifetime Range 100m free field -40 to 85°C Conform to FDA21 CFR Part 11 and GAMP4…


Customer Benefits:


Choosing Rotronic gives you the best accuracy on the market.

Precise humidity measurements enables the dryers to work at their maximum performance to try the timber as fast as possible but not too fast so structural damage in the wood can occur.


Networking with Rotronic is an easy affair! With all of the different communication methods, from conventional analog output signals to RS-485, Wireless or Ethernet RJ45, Rotronic can provide the needed interface to your drying control unit or any third party monitoring sys-tem.

Long term stability:

With a long term stability of under 1%rh per year (depending on the environment), Rotronic offers the possibility to “plug & play”: install the device and leave it. We would recommend frequent spot checks in-between calibrations.


In order to calibrate humidity measurement devices, we can offer a factory calibration certificate or even an SCS certificate if this is required. We can also supply a humidity and temperature generator, the HG2-S as well as unsaturated salts for on-site calibration.

Source: Rotronic

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