Length & Dimension Standards Group has developed a new methodology using image processing and wavelet transform is developed to measure the size of the wire sieves and their spacing. Wire sieves are used in pharmaceuticals/chemical industries for filtering the grains of chemical powder.

Experimental results show that the diameter and spacing of the wire in the sieves can be measured with the accuracy of 1μm and uncertainty of measurement of ± 1 μm at 95% confidence level. The method is also found suitable for detecting any missing wire or any other defect like bending or kink in the wire. In this techniques wavelet transform (Symlet wavelet) analyses the image of sieve in such a way that the discontinuity (cracks, defects, nonuniformity) can be detected more precisely and the spacing/ wire diameter can be measured accurately. Once the image has been acquired and stored in the computer it is available for off line analysis of the sieve sample. Discrete wavelet transform is used to analyze the acquired image as shown in Fig. 1.1. The two-dimensional wavelet transform decomposes the image in horizontal, vertical and diagonal components at different levels of intensities containing mesh information content as shown below.

The Indian patent (Indian Patent 197541) titled “An apparatus for measuring sieve dimensions and a method thereof” has been granted and the copy right (SW-2353) of the software entitled “Gauge Block Interferometry” has also been obtained through CSIR, New Delhi. Technology transfer process is in progress.

The Group also participated in the following intercomparisons:

APMP LK 5: Step Gauge Measurement: 620 mm: APMP comparison for the 3 step gauge of length 620 mm has been completed. In this nine NMIs have participated and KRISS Korea was the Pilot lab. Results of the measurements have been submitted to the Pilot lab. The final report is awaited.

APMP LK 3: Angle Gauge Blocks and Polygon measurement: 4 Angle Gauge Blocks of size 5², 5¢, 30¢ & 5° and one polygon. Thirteen laboratories are participating.

APMP DEC INTERCOMPARISON: Calibration of Gauge Blocks: (5 steel & 5 tungsten carbide Gauge blocks) completed. Final report is awaited.

SAARC PTB: Calibration of 10 steel gauge blocks: Measurement completed and dispatched to next country in progress. NPL India is the Pilot Lab.

APMP LK 6: Calibration of CMM Ball Plate & Hole Plate (Two D artifact): Measurements completed and the artifacts have been dispatched to NMI Japan that is the pilot laboratory. Final report is awaited.