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  • Understanding HVI and how to make it serve a global market

    Chapter 2 - Cotton value addition - Harmonization of rapid machine testing of fibre qu 


    HVI was made possible by applying computerization to the control and delivery of instrument measurements. Before computerization, high-volume measurements were fundamentally impossible. The addition of facilitating robotics made sample delivery, preparation and handling of samples go even faster and resulted in fewer errors.

    The central question to be considered in this section is: How can HVI technology be applied over a large geographic area as the basis for buying and selling cotton? The answer, in summary, is that it requires the imposition of an adequate system of process and quality controls. This system encompasses more than the HVI machines and related protocols. It must extend back toward the cotton production and ginning sectors, through the classification system, and forward toward the cotton fibre market (see figure 2.29). Therefore, the system that is developed for different countries or regions of the world must be appropriate for the realities in the production and marketing sectors. It may be possible in some cases to alter these controlling realities at the margins, in order to accommodate the system of process and quality controls, but the feasibility of this would have to be evaluated case-by-case.

    Figure 2.29: Sectors encompassed in a harmonized HVI system



    The major components of this system of process and quality controls include:

    • Well engineered and constructed HVIs
    • Representative sampling
    • Laboratory conditioning
    • Sample conditioning
    • Calibration
    • Check-tests
    • Standards cottons
    • Transportation
    • Certification and communication

    Discussion of these components is aided by reference to the only large-scale HVI classing system currently in existence, in the United States. It bears re-emphasizing that the particular approaches used in different parts of the world can, indeed must, be altered to accommodate structural limitations and differences. However, while the specific approaches to the necessary components may vary, these components cannot be ignored.

    Of course, well engineered and constructed HVIs are a ‘cornerstone’ of a reliable system. The HVI technology is well known, but the quality of the materials and components, along with exacting tolerances in machining and construction, are critically important. The key point is that machine error must be minimized, in order that other sources of errors in data generated may be adequately managed.

    The sampling procedures are fundamentally important, for at least two reasons: sample variations are the single largest source of errors in HVI data; and the sample must be representative of the larger package of cotton that it is drawn from. Procedures to ensure this would have to be very different for large-scale, mechanized farms than for small-scale, subsistence farms. The key point is that the sample must be ‘representative’ or the HVI data will be useless.

    Laboratory and sample conditioning procedures deserve special emphasis for two reasons. First, these are required to achieve either accuracy or precision in HVI testing. And second, around the world there is a remarkable tendency to fail in meeting this requirement. Apparent causes for this failure are an inability to bear the necessary expense and a lack of appreciation of the sensitivity of test results to conditioning. The key point is that ambient conditions in diverse laboratories must be kept stable at targeted levels in order to achieve agreement between measurements produced from those laboratories.

    Since cotton fibres will reach equilibrium moisture content under any given ambient conditions, it is necessary for this equilibrium to occur before testing the fibres. In the United States, it has been determined that conditioned samples will have a moisture content between 6.75% and 8.25% (dry weight basis). As a matter of standard operating procedure, samples moving toward the HVI lines for testing are checked to verify that the moisture content falls within this interval.

    The time required to achieve equilibrium depends, among other things, on the moisture content of the fibres going into conditioning and the extent of exposure of individual fibres to the ambient conditions. There have been attempts to achieve equilibrium conditioning within air conditioning units incorporated with an HVI, but without success. It has been shown that forcing ambient air from a conditioned room through cotton fibre samples that are already in a near-equilibrium condition can achieve adequately conditioned samples in as little as 10 minutes. However, if the samples are simply exposed to the ambient air within a conditioned room, proper conditioning may take as long as 48 hours. Regardless of the technologies and procedures used, the key point is that equilibrium moisture content must be achieved if consistent measurements are to be obtained across space and time.

    The calibration and check-test procedures require a designated, centralized quality control facility, where top-down guidance about calibration procedures is given to other cotton classing facilities throughout the country. In the United States, 1% of cotton samples tested at USDA satellite HVI facilities are randomly selected each day and air-shipped overnight to Memphis, in order to be tested on the quality control HVI machines there. Daily check-testing has been found necessary to identify calibration problems and correct them before they become untenable. The key points are that calibration procedures must be adequate and consistent among the satellite HVI facilities, and that frequent verification of satellite HVI machines is necessary for adequate quality control.

    Standards cottons are absolutely necessary for meaningful calibration procedures. A designated authority should be the official source of standards cottons. Furthermore, this is one function for which there should be only one authority for the entire world; otherwise, cooperation and collaboration among the different HVI classification systems around the world would be greatly impeded. In the United States and in most other HVI testing facilities around the world, the standards cottons are provided by the USDA/AMS facility in Memphis, Tennessee.

    The standards cottons must exhibit very low sample variations; i.e. the fundamental, real-world problem of large natural variations in cotton samples must be systematically alleviated. Lack of homogeneity must be alleviated by careful blending and mixing of the fibres. The more homogeneous the fibres, the less painstaking the blending and mixing will have to be. The key point is that the end result must be standards cottons that are exceptionally homogenous.

    Transportation procedures must be reliable and fast enough for moving the samples of the ginned fibres from the gins or other departure point to the classing facilities, and from the classing facilities to the calibration/check-test centre. In the United States, where producers maintain ownership of the cotton after it is ginned, the samples are collected at the gin points. The cotton samples are packaged and labelled as the cotton bales come out of the gin bale press. Trucks under contract to AMS systematically run designated routes to gins and deliver the collected samples to the classing facilities.

    The transportation process for producers’ samples is a primary determinant of the locations of classing facilities throughout the United States. The locations must allow for both the production densities and the driving distances in the production regions across the country.

    As previously mentioned, randomly selected samples are shipped by air to the centralized check-test centre. Time is of the essence for maintaining adequate quality control, so air shipment is a necessary expense.

    For movement from gins to classing facilities, the key point is that the bale record represented by samples must be accurate and delivered in a timeframe that does not interfere with the orderly marketing of the cotton. For movement to a calibration/check-test centre, the key point is that samples must be delivered and tested rapidly, in order to maintain the integrity of quality control.

    Certification and communication procedures are indispensable supports for acceptable verification, identity preservation and efficiency of market transactions. Computerization and telecommunication technologies have revolutionized these components of the system in the United States. At the classing facilities, a barcoded tag sent with each sample is scanned into the computer database and the data collected on the sample is automatically accumulated in the electronic files, without manual entry of information. (Exceptions are human classers’ determination of leaf grade and extraneous matter, which are entered once by hand.) The result is a combination of high speed, low error rates and excellent identity preservation that could only be wished for a decade ago. The system is highly reliable, yet does not produce a traditional ‘paper trail’; a paper copy of the information generally occurs only when the owner of the cotton prints it out at his or her own computer terminal. All these developments have removed substantial costs from the marketing system.

    Of course such record keeping and communication of data can be done in a multitude of ways. The key point is that certification of bale identities and accompanying fibre property data must be reliable and must be communicated in a timely manner.