When working with hard, “flat” surfaces (e.g. common rolled steel), thickness measurements taken with contact and non-contact methods are generally correlated. However, the situation changes once the tested material is both compressible and uneven- pasted lead plates being a prime example of this. While we try to keep measurement and processing as simple as possible, in the context of different applications, the definition of “thickness” may need to be clarified.
Some applications may benefit from alternative control parameters than just the average thickness of the plate. For example, AGM battery plates may be deemed as scrap if “high” peaks are present on the material surface. Unlike traditional contact measurement tools, laser gauges provide accurate readings for both soft and hard materials.
Co-efficient’s laser thickness gauges scan material surfaces at a rate of 3000Hz to 5000Hz. This data rich signal allows our software to create a detailed surface thickness profile that can be further examined:
Engineers can then choose between two main thickness measurement methods: center line average and peak-weighted average. Each method provides a different approach towards interpreting the material profile.
Please note: peak-weighted average and center line average can be applied to all scan modes: single scan, dual scan, and 3x3 scans. Read more about the different scanning modes here.
Center line average
The center line average method considers all the data points from a given scan, providing the best correlation with volume and weight. The thickness displayed on the operator screen represents an average of all possible data points, including all peaks and valleys in the material surface.
This measurement method more accurately represents the nominal thickness of the sample, and accounts for any outliers in the material surface.
Traditional contact measurement tools (e.g. micrometer), are heavily biased by peaks in the material surface. The center line average method accounts for areas in the material surface not previously accessible by legacy tools.
The peak-weighted average is a processing method that discards the thinnest points, and only includes a percentage (adjustable) of the thickest points.
Upper and lower bounds can be manually set, using the Co-efficient software, to reflect your application and/or quality assurance methodology of choice:
Some products may be severely impacted by outliers in the material profile. For example, AGM battery plates must fit tightly into their housing- moderate peaks in the plate surface may deem the sample unusable, even if the center line average is on spec.
Correlation with historic measurements- contact measurement tools are typically biased by peaks in the material surface. Therefore, enabling peak-weighted averaging will be more closely related to past measurements, while still improving accuracy and reliability.
When measuring compressible uneven surfaces with laser thickness gauges, it is best to evaluate how thickness is reported. We aim to make this decision to be as simple as possible by pre-screening the materials- our customers can provide us with samples of their materials before the systems are shipped. We provide our customers with scanning reports and study the impacts of using center line averaging vs. peak-weighted averaging methods.
Want to start taking better thickness measurements? Send us your samples and we will generate a free MSA report for you. Our team of engineers will help customize one of our inline or offline gauges to meet your quality control requirements.