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SPI SuperGrid™ Index Grid (200 mesh) - Vials of 100 Grids
77% open area
20 µm bar width
105 µm grid square
5:1 aspect ratio
125 µm mesh pitch
Originally conceived by our own analysts doing TEM asbestos work, we realized the importance of not only having a good and easy-to-use "finder" or "index" grid, but it was also important that each grid square have the same, precisely controlled, open area. Other index grids did not have this feature. And we also knew that for verification counting (one person checking someone else's measurements), it was also important to be able to put the grid back into the TEM at precisely the same orientation as it was inserted the first time by the first analyst.
Hence the now well known SPI Index Grids for Quantitative TEM studies was developed and brought to market. In later years, others may have copied our concept and our design, but no one makes a better quality or more highly controlled index grid for quantitative TEM work than SPI.
Check out these features that have made these 200 mesh grids by far the favorite of high volume TEM asbestos laboratories:
Alpha-Numeric Indexing on Grid Perimeter: makes it easy to identify and relocate specific grid squares for verification counting.
Grid Squares are Indeed Square: consistent area (almost imperceptible standard deviation) from square-to-square on all grids within a given batch. SPI uses its own in-house SPI-Quant™ image analysis system to confirm that batch to batch, even grid to grid, variation is within our specifications. Also available are these same grids "pre-calibrated" according to US EPA (Environmental Protection Agency) and NVLAP (National Voluntary Laboratory Accreditation Program) requirements; such shipments are accompanied by the quantitative report on the square to square standard deviation.
Asymmetric Center Mark: yet another convenience for locating the same grid square again and again. This also means that the analyst always knows which quadrant of the grid they are in and such knowledge in a high through-put laboratory increases productivity and efficiency as well as accuracy.
SPI Logo on the Rim: helps ensure you always insert the grid into the microscope right side up and at the same orientation (if a second insertion). If your grid says "SPI" then you know you have the real thing and not a copy.
SPI Selection: choose your preference in grid style from SPI Regular, SPI SuperGrid™ or SPI Slim Bar®! And also select from copper, nickel or gold depending on the specific nature of your work (Note: for TEM asbestos work, NLVAP specifies the use of 200 mesh copper). We would also point out that the smaller the perimeter to area ratio, and the less important will be edge effects (e.g. fibers straddling a grid square). Therefore the SPI Slim Bar® style, for a given mesh size, would have an advantage and be preferred. However, carbon films tend to be slightly less stable because of the larger grid square opening (95 µm "regular" vs. 115 µm for the Slim Bar style). So like other things in life, grids and mesh sizes also represent a range of trade-offs. There has been some variation in the average grid opening area as measured in our grid calibration program, but typically the open area per grid square, irrespective of metal, is about 9,000 square micrometers (0.009 square millimeters) for 2270C-XA, 11,000 square micrometers (0.011 square millimeters) for 2280C-XA and 12,500 square micrometers (0.0125 square millimeters) for 2290C-XA.
Standard Deviation of the area, square to square: We are often asked this question and ordinarily such information for a grid manufacturer would not be available. However, a very large percentage of the index grids sold by SPI are precalibrated and therefore we have been able to build up quite a bit of knowledge about just what kind of standard deviations can be expected. We are happy to report that the standard deviation of all grids produced of these patterns is about 4%. For a particular batch, the variation has been as good as 2%. Occasionally, it is as bad as 4.5%. But we believe that the controls that are employed to keep the standard deviation to a minimum of the SPI Index Grids are superior to any other grid on the market.