MC PRO 2021: KilnScout-Wired

Batch Kiln Moisture Measurement Background

Drying lumber using a kiln has been traced back as far as the 1800s. Properly dried lumber has greater dimensional stability than ‘green’ lumber, thus making it more valuable for construction. From the beginning, the challenge has been to know when to stop drying. Without today’s technology, operators had to rely upon experience and/or trial-and-error. When lumber was plentiful and cheap, it was no problem to scrap bad pieces or lots. However, today, lumber is a scarce resource with significantly higher prices, therefore, mistakes are costly.

Early methods of moisture measurement were weight samples or handheld stack probes. Both of these options were unreliable and disruptive to the drying process as they required a person to enter the kiln to perform the tests. Later versions tried to wire metal probes into the pieces, but these probes only measured a small area – thus proving to be ineffective at estimating the entire kiln charge of lumber.

In the late 1990s, continuous, in-kiln moisture measurement using capacitance was pioneered by kiln operators as a way to measuring a greater sample size – typically an entire lumber pack – throughout the entire kiln charge. By adding multiple measurement points in the kiln, the sample size was statistically representative of the entire charge. The most important elements were to have a system that is both robust yet sensitive enough to identify small changes in moisture content. Given the extreme heat and humidity in the environment, these two competing items proved difficult to overcome. It wasn’t until Signature Control Systems, a predecessor company to Finna Sensors, developed its in-kiln system, “MMS”, that companies didn’t have to sacrifice robustness for accuracy. The unique architecture took advantage of software to simplify hardware to increase reliability and robustness.

Moisture matters in lumber drying because if it is done properly, the plant is rewarded with significantly higher prices. Kiln-dried, or “KD”, lumber is highly sought after by builders for framing throughout North America. A lumber supplier’s reputation is at stake with these builders as improper drying can lead to mold. Mold has been the scourge of the industry for years, leading to multiple lawsuits. The tendency is to over-dry lumber to avoid mold, yet this means longer drying times. As there are a fixed number of kilns, drying times are the driver of total production. The lower the cycles, the more lumber that can be produced. Therefore, mills are always seeking greater efficiencies.

Key Features, Advantages and Benefits

KilnScout-Wired™ is the newest model provided by Finna Sensors. It combines the ground-breaking architecture of the Signature system with the latest advancements in software and electronics. The focus remains on software so that features can be upgraded via simple Web-based upgrades to the HMI. Additionally, the company remains committed to keeping costs down by utilizing off-the-shelf hardware wherever possible. The modular design ensures sensitive electronics remain away from the harsh environments. Added reporting and diagnostic tools enhance Internet of Things (IOT) functions to prevent costly downtime and determine future maintenance needs.

The benefits of adding KilnScout-Wired™ to a dry kiln are both increased throughput and improved quality. From a throughput perspective, by optimizing kiln drying times, operators can run more charges through existing assets, thus improving productivity by an average of 10%. This has been proven with many species at hundreds of installs. The improved quality results from a lower standard deviation of moisture content because mills are able to more consistently shut down at a target point. Over the course of many kiln charges, more consistent shut downs means a tighter standard deviation at the planer. By increasing throughput and improving the standard deviation, a typical plant will realize a 6-month payback on investment in normal economic times. If the price of lumber is higher than normal, this will rapidly reduce the payback time frame.