Quality loop

Data should be available at every phase of the service quality loop from soliciting business through client reaction and feedback. The collection and analysis of data is a means of improving the service or conversely can detect the onset of an insidious degradation of the service before it becomes a major issue. 

Devices that you use for product verification at all stages in the quality loop need to be controlled and this includes devices used for inspection and test on receipt of product, in-process, and final acceptance before release to the customer. It also includes devices used during design and development for determining product characteristics and for design verification. Some characteristics cannot be determined by calculation and need to be derived by experiment. In such cases the accuracy of devices you use must be con-... 

Some clauses of ISO/TS 16949 address particular phases in the quality loop and others are independent of any phase. It should not be assumed that, for example, all the requirements that apply to purchasing are in clause 4.6. This matrix should help identify which requirements apply to any given phase. 

Then design the composition control loops for each unit operation. Buckley called these the product-quality loops. Determine the closedloop time constants of these product-quality loops. 

Size the holdup volumes so that the closedloop time constants of the material-balance loops are a factor of ten bigger than the closedloop time constants of the product-quality loops. This breaks the interaction between the two types of loops. 

He then proposed establishing the product-quality control loops by choosing appropriate manipulated variables. The time constants of the closed-loop product-quality loops are estimated. We try to make these as small as possible so that good, tight control is achieved, but stability constraints impose limitations on the achieveable performance. 

It should be noted that establishing the product-quality loops first, before the material balance control structure, is a fundamental difference between our plantwide control design procedure and Buckley s procedure. Since product quality considerations have become more important in recent years, this shift in emphasis follows naturally. 

We briefly discussed in Chap. 2 (Sec. 2.5) one important aspect of distillation column control when one of the products leaving the column is a recycle stream. Should the composition of this recycle stream be controlled Probably not from the perspective of the isolated column because the control loop holding the composition of the other stream leaving the column, which is a product from the plant, could then be more tightly tuned. However, the plantwide control perspective may show that the performance of the reactor can be improved by holding the purity of the recycle stream more constant, and this could result in smaller disturbances to the column. The overall effect may be better product quality control even though the product-quality loop is less tightly tuned. 

Then produet quality loops are closed on eaeh of the individual units. These loops typically use fast proportional-integral eontrollers to hold product streams as close to speciheation values as possible. Sinee these loops are typically quite a bit faster than the slow inventory loops, interaction between the two is often not a problem. Also, sinee the manipulated variables used to hold produet qualities are quite often streams internal to each individual unit, changes in these manipulated... 

LIMS are a key enabler in pharmaceutical operations for two main reasons (1) They enable paperless operation in the laboratory environment, thus handling procedures and specifications for laboratory analysis as well as laboratory analysis records. (2) They provide results and status information for materials, which enables systems in other environments such as production to close the quality loop by providing aitical feedback on the results from suppliers and the pharmaceutical company s own production processes. 

Problem Reporting and Corrective Action. A familiar problem with management systems is that although problems and issues might be effectively and accurately identified and recorded, their resolution can sometimes escape proper control. Procedures need to be in place to ensure that the quality loop is complete so that defect reports are properly tracked to their final resolution. 

Establish product-quality loops and tune for as tight control as possible. Decide what temperatures, pressures and compositions should be controlled and what manipulated variables should be used in each loop to achieve the smallest closedloop time constants as limited by closedloop robustness (reasonable closedloop damping coefficients). 

Although none of the sources presented here is guaranteed, and inclusion on this list does not imply an endorsement, at the time of this writing, the sites mentioned here were well maintained and appeared to offer high-quality loops. This is not a comprehensive list of loop sources but only a handful of places to get you started. Like any favorites list on the Internet, it is of only limited temporary value and you should try typing something like loop sample audio library into your favorite search engine to find more. 

In Chapter 1 we suggested a control system structure in which most control loops are vided into three classes (1) material balance, (2) product quality, and (3) constraints. If we look at these loops from the standpoint of classic single-loop theory, we see that the material-balance loops function as low-pass filters (slow dynamics) while the product-quality loops function as bandpass or high-pass filters (faster dynamics). 

To eliminate interaction between the two, we design the product-quality loops to have high, closed-loop natural frequencies compared with those of the material-balance loops. This design has two advantages. First, it eliminates interactions between the two classes of loops second, it provides great attenuation for disturbances that might otherwise upset product quality. The material-balance loops not only filter out flow disturbances, but also filter out composition disturbances if the holdups are well agitated. 

Figure 5. Quality loop with quality elements.

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