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Samphng

Figure 8-5 illustrates the concept of samphng a continuous function. At integer values of the saiTmling rate. At, the value of the variable to be sampled is measured and held until the next sampling instant. To deal with sampled data systems, the z transform has been developed. The z transform of the function given in Fig. 8-5 is defined as... [Pg.721]

A dynamic model of the process is used to predict the future outputs over a prediction horizon consisting of the next p samphng periods. [Pg.739]

In principle, the step-response coefficients can be determined from the output response to a step change in the input. A typical response to a unit step change in input u is shown in Fig. 8-43. The step response coefficients are simply the values of the output variable at the samphng instants, after the initial value y(0) has been subtracted. Theoretically, they can be determined from a single-step response, but, in practice, a number of bump tests are required to compensate for unanticipated disturbances, process nonhnearities, and noisy measurements. [Pg.740]

The historical data is sampled at user-specified intervals. A typical process plant contains a large number of data points, but it is not feasible to store data for all points at all times. The user determines if a data point should be included in the list of archive points. Most systems provide archive-point menu displays. The operators are able to add or delete data points to the archive point hsts. The samphng periods are normally some multiples of their base scan frequencies. However, some systems allow historical data samphng of arbitraiy intei vals. This is necessaiy when intermediate virtual data points that do not have the scan frequency attribute are involved. The archive point lists are continuously scanned bv the historical database software. On-line databases are polled for data. The times of data retrieval are recorded with the data ootained. To consei ve storage space, different data compression techniques are employed by various manufacturers. [Pg.773]

Process-Gas Sampling In samphng process gases either to... [Pg.1581]

Detention Test This test utihzes a 1- to 4-L beaker or similar vessel. The sample is placed in the container, flocculated by suitable means if required, and allowed to settle. Smah samples for suspended-sohds analysis are withdrawn from a point approximately midway between liquid surface and settled solids interface, taken with sufficient care that settled solids are not resuspended. Samphng times may be at consecutively longer intei vals, such as 5, 10, 20, 40, and 80 min. [Pg.1679]

The control of processes involving the treatment of solids generally requires means for careful samphng and analysis of solids and slurries at various points in an operation. Unlike liquids, particulate solids are not homogeneous. The composition of individual particles will vaiy with particle size and particle density. It follows that care must be... [Pg.1755]

Estimations based on statistics can be made for total accuracy, precision, and reproducibility of results related to the sampling procedure being applied. Statistical error is expressed in terms of variance. Total samphng error is the sum of error variance from each step of the process. However, discussions herein will take into consideration only step (I)—mechanical extraction of samples. Mechanical-extracdion accuracy is dependent on design reflecding mechanical and statistical factors in carrying out efficient and practical collection of representative samples S from a bulk quantity B,... [Pg.1756]

Variations in measurable properties existing in the bulk material being sampled are the underlying basis for samphng theory. For samples that correctly lead to valid analysis results (of chemical composition, ash, or moisture as examples), a fundamental theoiy of sampling is applied. The fundamental theoiy as developed by Gy (see references) employs descriptive terms reflecting material properties to calculate a minimum quantity to achieve specified sampling error. Estimates of minimum quantity assumes completely mixed material. Each quantity of equal mass withdrawn provides equivalent representation of the bulk. [Pg.1757]

The alternative method of sample extrac tion is termed the ctoss-sti eam samphng method, or ci o.s.s-belt when used in conjunc tiou with a belt conveyor. Sample extraction typically take place with a belt conveyor in motion. However, with a rotary table-feeder conveyor, extractions are made with the table stopped. A cutter can perform extractions by this means from a machined flat surface with neghgible... [Pg.1758]

Criteria for mechanical delimitations in samphng by the alternative cross-stream method to fulfih through-stream extraction requirements are revised from gravity-sampling criteria in the following respec ts ... [Pg.1758]

When samphng from moving belt conveyors, the cutter operates in a radial mode with the belt surrace contoured at the point of samphng by idlers, fixing radial curvature to the outer radius of the cutter. Clearance is minimized between outer edges of cutter blades and belt surface by cutter-shaft adjustment in the drive-clamping bracket. [Pg.1759]

Cross-stream samphng from flat surfaces with material handled on a hnear conveyor or rotary table is best carried out with the conveyor stopped. Sample extraction is then performed by linear traverse. [Pg.1759]

Selection of hnear or radial (rotary cutter) samphng is made according to mechanical instahation factors often on a basis of flow quantity. Smaher flows can be sampled in a cost-effeciive manner by rotary cutter samplers (frequently termed vezin design samplers, see Fig. 19-4). [Pg.1759]

Method or samphng, location, size and number of samples, method of sample analysis, and fraction of the batch removed for samphng all contribute to how well the samphng study reflects the actual conditions. [Pg.1763]

Sometimes a system of mixing and dispersing is composed of one or more batch units providing a feed to a continuous intensive dispersion unit. Another possibihty would be a batch mixer and surge bin which provide a continuous feed to a final dispersion unit. Various combinations of this type with adequate samphng at the proper points may be used when continuous flow would be beneficial provided that certain features could be overcome. [Pg.1769]

The selection of a sampling site and the number of sampling points required are based on attempts to get representative samples. To accomplish this, the samphng site should be at least eight stack or duel diameters downstream and two diameters upstream from any flow disturbance, such as a bend, expansion, contraction, valve, fitting, or visible flame. [Pg.2197]

Once the samphng location has been decided on, the flue cross section is laid out in a number of equal areas, the center of each being the point where the measurement is to be taken. For rectangular stacks, the cross section is divided into equal areas of the same shape, and the traverse points are located at the center of each equal area, as shown... [Pg.2197]

Once a flow profile has been established, samphng strategy can be considered. Since samphng collection can be simphfied and greatly reduced depending on flow characteristics, it is best to complete the flow-profile measurement before sampling or measuring pollutant concentrations. [Pg.2197]

Each samphng method requires the use of complex samphng equipment that must be calibrated and operated in accordance with specified reference methods. AdditionaUy, the process or source that is being tested must be operated in a specific manner, usually at rated capacity, under normal procedures. [Pg.2197]

With the grab sampling technique, a samphng probe is placed at the center of the stack, and a sample is drawn direcfly into an Orsat analyzer or a Fyrite-type combustion-gas analyzer. The sample is then analyzed for carbon dioxide and oxygen content. With these data, the diy molecular weight of the gas stream can then be calculated. [Pg.2198]

A sample is taken at several designated points in the stack, which represent equal areas. The sampling probe is placed at each samphng... [Pg.2199]

Particulates Procedures for testing a particulate source are more detailed than those used for sampling gases. Because particulates exhibit inertial effects and are not uniformly distributed within a stack, sampling to obtain a representative sample is more complex than for gaseous pollutants. EPA Method 5 (as shown in Fig. 25-32) is the most widely used procedure for determination of particulate emissions from a stationary source. In-stack samphng guidehnes are presented in EPA Method 17. [Pg.2199]

As the gas stream proceeds through the sampling apparatus, the particulate matter is trapped on a filter, the moisture is removed, and the volume of the sample is measured. Upon completion of samphng, the collec ted material is recovered and sent to a laboratory for a gravimetric determination or analysis. [Pg.2200]


See other pages where Samphng is mentioned: [Pg.721]    [Pg.721]    [Pg.727]    [Pg.728]    [Pg.740]    [Pg.766]    [Pg.767]    [Pg.1427]    [Pg.1427]    [Pg.1582]    [Pg.1755]    [Pg.1758]    [Pg.1758]    [Pg.1758]    [Pg.1759]    [Pg.1759]    [Pg.1759]    [Pg.1759]    [Pg.1759]    [Pg.1760]    [Pg.1760]    [Pg.1761]    [Pg.2019]    [Pg.2161]    [Pg.2197]    [Pg.2200]    [Pg.2200]   
See also in sourсe #XX -- [ Pg.16 , Pg.281 ]




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