Sonic Lumber Grader


Metriguard’s newest machine grading system, the Model 2350 Sonic Lumber Grader (SLG), is a transverse flow grader that combines key components designed for installation in either a sawmill to measure weight or in a planermill to determine modulus of elasticity (E) to produce machine stress rated lumber (MSR).

The scale system can be used to weigh lumber in the sawmill for resource allocation before drying. Each Model 2350 scale assembly has multiple rollers on the skids to reduce friction and improve accuracy. A proprietary flexure spring in each scale unit compensates for off-axis loading improving accuracy and repeatability in the weight measurement.

Each scale unit has an auto-zero feature which provides a stable calibration by continuously adjusting for drift caused by environmental changes. In addition, each scale has an actuator to put a known weight on the load cell for frequent calibration checks. Monitoring the auto-calibration helps the operator decide when a complete calibration is needed.

With the addition of additional components, the planer mill system evaluates lumber for MSR potential. A rugged electro-mechanical hammer strikes the end of each piece of lumber to initiate an acoustic signal. Design of the hammer is simple, rugged and low maintenance – it has only one moving part and requires no air supply.

Coupled with the hammer assembly is the acoustic signal receiver. Sophisticated, proprietary signal processing, developed and maintained in-house by Metriguard engineers, analyzes the sound from each board even in a noisy mill environment.

Piece density and acoustic signal are used to determine the modulus of elasticity (E) at speeds up to 250 lugs/minute. If needed, data can be handed off to an optical scanner for final MSR grade determination. Remote access capability allows for trouble-shooting issues as they arise.

The American Lumber Standards Committee (ALSC) and Canadian Lumber Standards Accreditation Board (CLSAB) have approved the Model 2350 SLG for machine grading.

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