How can inline moisture measurement data be used to characterize "cold spots" in a kiln?
I would appreciate any feedback.
"Cold spots" in a kiln are characterized by a larger than "typical" or "normal" standard deviation. If one's standard deviation of moisture content determined at the planer for a particular charge of lumber from a kiln has increased significantly, then one possibility is that the kiln may have developed a "cold spot", especially if the incoming lumber diet has not changed.
In order to detect this occurrence, one must be tracking the moisture content at the planer inline moisture measurement system on a "charge by charge" basis. This is easily done with one of our systems; even if the packages coming in are not sequential from the same kiln or kiln charge, our tracking software can manage and segregate the data appropriately. Comparing previous charge standard deviations from a baseline to current standard deviations will help easily identify when something is amiss.
Taking this one step further to aid in fault identification, one can track the location of each package in the kiln charge for multiple charges (3-5) and average the average MC of those 3-5 packages for each location, then compare these averages for all 3-5 charges to determine where inside the kiln the "cold spot" actually is located. This will greatly help in taking steps to either "fix" a critical system within the kiln, or modifying operational steps to further improve overall kiln charge variability.
Since running 3-5 charges through an under-performing kiln resuts in loss of opportunity cost, we recommend a regimented program where this type of analyses are performed on a continual basis; doing so creates a program that identifies drying issues in as fast a manner as possible and allows for a minimal of delay in fault identification and resolution.