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1、AS 1141.11.220081 AS 1141.11.22008Australian StandardMethods for sampling and testing aggregatesMethod 11.2: Particle size distribution for vision sizing systems1 SCOPEThis Standard sets out the method for the determination of particle size distribution in coarse and fine aggregates by vision system
2、s. The VSS is limited by the discrimination of the optical system and, at present, is suitable for materials coarser than 1.18 mm. A calibration procedure is required to relate results from this procedure to particle distribution by sieving (AS 1141.11).NOTE: A summary of VSS technology is given in
3、Appendix A.2 APPLICATIONAS 1141.11 measures particle size distribution of a sample on the basis of mass of sample passing or retained on the square or round hole sizes of the AS 1152 screens used. VSS measures the length dimensions of images of particles in two dimensions, and derives a third dimens
4、ion. VSS does not measure mass and, hence, variations in particle density in particles within a sample or between samples, will cause a difference in calculating the particle size distribution between the two methods. Some of this difference can be reduced by source calibration especially where the
5、VSS is used in an in-plant application on a consistent source. The VSS has application in the production of rapid, automated particle size distribution data in production plants.3 REFERENCED DOCUMENTSThe following documents are referred to in this Standard: AS1141Methods for sampling and testing agg
6、regates1141.1Method 1:Definitions1141.2Method 2:Basic testing equipment1141.3.1Method 3.1: SamplingAggregates1141.11Method 11: Particle size distribution by sieving1152Specification for test sieves4433Guide to the sampling of particulate materials4433.1Part 1:Sampling procedures Standards Australia7
7、AS 1141.11.220084 DEFINITIONSFor the purposes of this Standard the definitions in AS 1141.1 and those below apply.4.1 Arithmetic mean size (AMS)The AMS is defined by VSS as follows: Standards Australiawww.standards.org.auwhereAMS =pd100p = individual percentage retained on each screend = mean size o
8、n each screen (screen above + this screen)/24.2 CalibrationThe procedure that converts VSS measurements to equivalent AS 1152 sieve sizes.4.3 Graded aggregateAn aggregate of which more than 15% of the total material is retained on at least three consecutive equivalent sieves in the set 75.0 mm, 37.5
9、 mm, 26.5 mm, 19.0 mm, 13.2 mm,9.50 mm, 6.70 mm, 4.75 mm, and 2.36 mm. Crushed rock, which consists of a mixture offine and coarse aggregates, the coarse fraction being graded, is considered a graded aggregate for the purpose of this definition.4.4 Nominal sizeDesignation of an aggregate, which give
10、s an indication of the largest size particle present.NOTE: The concept of nominal size aggregate is for convenience of reference and ordering. The nominal size is expressed as a whole number above the equivalent sieve size through which nearly all of the aggregate passes.4.5 One-sized aggregateAn ag
11、gregate of which at least 60% of the total material passes an equivalent sieve, selected from the set 75.0 mm, 37.5 mm, 26.5 mm, 19.0 mm, 13.2 mm, 9.50 mm, 6.70 mm, 4.75 mm and 3.35 mm, which is immediately less than the nominal size of the aggregate and is retained on the equivalent sieve immediate
12、ly following the selected equivalent sieve in this series.4.6 Particle size distributionProportions by mass of the various particle size classes present.NOTE: VSS measures the size of particles as they are imaged in a measurement window. The measurements are corrected to equivalent AS 1141.11 sieve
13、sizes by a calibration routine using source reference samples.4.7 Primary reference sampleAn instrument integrity sample supplied by the manufacturer, which allows the instrument to be checked in the factory and at the users site. The primary reference sample is used to create a primary calibration.
14、4.8 Source Reference SampleA stable representative aggregate sample that has been accurately hand-sized for a defined size range using AS 1141.11, and used to create a source calibration, which is established on-site.4.9 Vision sizing system (VSS)A non-contact instrument that determines particle siz
15、e in aggregates using an imaging process.5 APPARATUSThe following shall be required:(a) Sampling devicecomplying with AS 4433.1.NOTE: For a laboratory VSS, a sampling device is not required.(b)Hopperof sufficient volume to store the sample increment.(c) Vibrating-feederwhich operates at aconstant (p
16、re-set)amplitude,andis independent of the load on the tray. The tray shall have minimum dimensions defined by the nominal size of the material being measured.(d)Environmental enclosurefitted with a suitable camera and light source, and constructed such that ingress of external light and dust are min
17、imized.(e) Collection bin or reclaim conveyorto retain/reclaim the measured sample increment.(f) Imaging stationconsisting of sampling devices, a hopper, vibrating feeder, environmental enclosure, and a collection bin or reclaim conveyor.(g)Central processing unit (CPU)connected to the imaging stati
18、on by suitable means.The CPU shall have proprietary and application software to determine the required particle parameters and compute the required data.(h)Operators control panel (OCP)which includes human machine interface (HMI) type software, which allows users to manipulate VSS to review data and
19、 images collected by the system.(i) Output and data storage devicesto view, store and distribute the data and results.(j) Other apparatusas specified in AS 1141.2, AS 1141.3.1, and AS 1141.11, in order to complete necessary calibration procedures.6 SOURCE REFERENCE SAMPLE6.1 Initial preparation of s
20、ource reference sampleThe initial selection and preparation of a source reference sample shall be as follows: (a)Recover the sample from the quarry stock piles in accordance with AS 1141.3.1.NOTE: A sample should be taken for each product that will be analysed by the VSS.(b)Wash the sample to remove
21、 dust and all particles finer than 1.18 mm diameter. (c)Oven dry the sample in accordance with AS 4133.1.(d)Reduce the sample to the mass given in Table 1, using a sample splitter or other suitable device, taking care to maintain the representative nature of the sample.6.2 Calibration of source refe
22、rence samplesCalibration of source reference samples shall be undertaken following any maintenance procedure that requires replacement or realignment of any component of the optical system, or any change or upgrade to the system software package or every six months, whichever occurs first.A record o
23、f the calibration factors and the reported sizing analyses for each source reference sample shall be maintained as evidence of system stability. The system software shall maintain a record of times and authorization of changes to the VSS calibration factors.NOTE: The calibration factors are stored i
24、n the system software. Secure systems should be established to ensure that the calibration factors can only be accessed and changed by authorized personnel.The calibration of a source reference sample shall be as follows:(a) Sieve the reference sample in accordance with AS 1141.11.(b)Measure the ref
25、erence sample using the VSS in accordance with the manufacturers instructions, using at least five runs.NOTE: Additional runs may be required until the software develops calibration factors that return a calculated particle size distribution comparable to the AS 1141.11 analysis.(c) Collect and stor
26、e the reference sample, avoiding loss of sample, or sample contamination.7 TEST PORTION7.1 GeneralThe minimum mass of the test portion taken shall be related to the nominal size of the aggregate in accordance with Table 1. For an in-plant VSS, the sampling device shall deliver a test portion mass to
27、 the hopper, which equals or exceeds the applicable mass as defined within Table 1. The test portion should be of such a mass as to provide a similar number of particles to those contained in the source reference sample.TABLE 1MINIMUM MASS OF TEST PORTION FOR VSS OR SIEVINGNominal size (mm)754028201
28、41075Graded aggregate (kg)301553g1.50.80.50.3One-sized aggregate (kg)251041.50.70.50.30.27.2 Mixtures of coarse and fine aggregatesMixtures of coarse and fine aggregates shall be measured without separation, with the percentage passing each calculated sieve.7.3 Preparation of test portionFor in-plan
29、t systems, test portions may be analysed without further preparation.NOTES:1Test portions of aggregates with a free moisture content of 3% may be measured in-line. For higher moisture values, in-line drying by infra-red or the like may be necessary.2The VSS method may be limited if moisture in the t
30、est portion causes agglomeration of particles passing through the imaging station. If this occurs, action should be taken to reduce the agglomeration of the sample.7.4 WashingTest portions are not required to be washed.8 PROCEDUREThe test procedure shall be as follows:(a) Insert a representative inc
31、rement into the hopper, either manually (laboratory unit) or automatically (in-plant installation).(b)Following the procedures detailed in the operational manual supplied by the manufacturer, set up the VSS from the operators control panel (OCP). Attention shall be paid to pre-set alarms and alerts,
32、 such as increment size and desired specification limits provided in the OCP screen, based upon the product characteristics and predetermined criteria. The system shall provide error messages, such as insufficient volume of material measured (sample too small) to alert the user to situations that wo
33、uld compromise the VSS calculations and subsequent results.(c) When the test portion has been measured, make the data (raw and processed) available on the OCP screen and transfer to a data storage device, if required, where it can be subsequently distributed, reviewed and/or analysed.9 CALCULATIONST
34、he percentage of material passing (or retained on) each equivalent screen shall be calculated by summing all screens to 100%. AMS shall be determined (as defined in Clause 4.6).10 REPORTINGThe following shall be reported:(a) The percentage of equivalent screen size material passing each screen, to t
35、he nearest whole number.(b)The percentage of equivalent screen size material passing each screen, to the nearest whole number.(c) The cumulative percentage of material on each screen, to the nearest whole number. (d)The average mean size of the test portion.(e) The date of the last source calibratio
36、n (see Appendix A).(f) The number of this Australian Standard, i.e. AS 1141.11.2.APPENDIX ASUMMARY OF VSS TECHNOLOGY(Informative)1VSS technology currently requires four steps to produce a quantitative determination of AS 1141.11 equivalent sieve size measurements, as follows:(a) Sampling of a proces
37、s material to produce a manageable quantity of the bulk material, which is representative (within a defined precision) of that process stream. Refer to AS 4433.1 regarding sampling standards.(b)Calibration using hand-sized material.(c) Image acquisition of the sampled volume (increment) as it falls
38、through theimaging station.(d)Analysis and AS 1141.11 equivalent results of the images.2Existing VSS installations indicate an average standard deviation per screen size between 0.2% and 2%within errors established for mechanically developed sieve analysis. Depending on the specific requirements of
39、users, including laboratories and/or in-plant installations, different product streams may be transferred to a central imaging station, or individual imaging stations may be installed at various locations in the quarry to sample individual material streams.3In order to obtain site-specific reliable
40、results, a sufficient number of particles of accurately measured sieve-sized sample(s) from that site have to be measured by VSS. (Source calibrationThe larger the number of particles in the reference sample the better the repeatability. The Calibration requires that the same sample be used for a VS
41、S measurement and for the AS 1141.11 comparison test.)4The VSS Measurement requires that a test portion of material, in accordance with Table 1, is loaded into a hopper, which discharges on to a vibrating feeder, so that the material is separated as it falls under the influence of gravity through an
42、 imaging station, where the particles are analysed. Control signals and data are sent and received between the measurement station and a central processing unit (CPU). Proprietary software performs area and particle evaluations that are then converted to AS 1152 equivalent sieve sizes.5VSS software
43、has to include algorithms and proprietary software to calculate equivalent screen size measurements and mean size within the nominated size range(s) and reporting periods, either for each individual increment or a number of increments to form a composite.6The following items may affect the accuracy
44、and repeatability of the VSS method:(a) Increment size and particle stream variations to those used in the source calibration.(b)Equipment maintenance, such as sampler and vibratory feeder adjustments.(c) Changes to focus, alignment, or aperture settings of the camera established in both the primary
45、 and source calibrations.(d)Variation in light intensity (dust, extraneous lighting, degradation of image lighting).(e) Cleanliness of glass surfaces separating the camera and lighting from the falling particle stream.(f) Signal degradation over fibre optics caused by faulty fibre or video transmitt
46、ers and/or receivers.(g)CPU failure to acquire images and perform algorithm calculations due to mechanical failures or software corruption and/or interruption.If any of the above items change, or following maintenance to correct any of the identified issues, a new source calibration should be conducted.AS 1
