Measures in-process

It is important to emphasize that, especially in process measurements, radiation can have an essential influence on the wet bulb temperature, and therefore generally the wet bulb temperature is dependent on the mea,surement device and the method of measurement. If the airflow is very low, the radiation can have a remarkable contribution in addition to the convective heat transfer. Basically, an equation analogous to Eq. (4.138) can be empirically determined for each wet bulb temperature and method of measurement. 

Better measurement of performance. A common frustration in PSM and ESH is that end-of-pipe measurement is all that is available and it is too late to correct a problem once the incident has occurred. Quality Management requires that we seek out in-process measures and leading indicators of performance that will warn of potential problems before they exhibit themselves as incidents. 

Measurement of performance. Quality Management requires that measures of performance be established for every activity. These measures include end-of-pipe measurement, such as amounts of material released into the environment or injury rates, and in-process measures of how efficiently you are managing, such as time to review safety improvement proposals or total resources expended on PSM. Each team should be required to identify potential performance measures for the processes they are developing and the activities these processes manage. Many of the end-of-pipe measures will already exist these should be critically examined to ensure that they truly measure performance and are not unduly influenced by other factors. For example, the number of accidents in a fleet of road vehicles is almost directly dependent on the number of miles driven with no improvement in performance, a reduction in miles driven would reduce the number of accidents. 

The team should be realistic about the time required to see improvements in end-of-pipe measures in most cases the pilot project success will be measured on efficiency improvements and other in-process measures alone. In this case it is important to demonstrate that all PSM and ESH issues are being managed. You should consider having a management systems audit (validation) conducted by a group independent of the integration project team. This may be done in conjunction with the next scheduled audit. This may be a corporate or divisional audit function or a consultant engaged specifically for this task. 

In-process measures that provide early indication of potential breakdowns which could lead to accidents or other unwanted events. 

When selecting in-process measures, try to use measures for which data are already available. For example, avoid using in-service failure data unless the maintenance systems can make this information readily available. These measures will be used to identify potential problems and correct them as early as possible. During the development of the integrated systems, data that will be available for in-process measurement should be identified and measures developed. These measures are most likely to be calculated annually as the volume of data required to provide useful data will be collected only over relatively long periods of time. 

Several significant challenges exist in applying data analysis and interpretation techniques to industrial situations. These challenges include (1) the scale (amount of input data) and scope (number of interpretations) of the problem, (2) the scarcity of abnormal situation exemplars, (3) uncertainty in process measurements, (4) uncertainty in process discriminants, and (5) the dynamic nature of process conditions. 

Uncertainty in Process Measurements. Sensor measurements are always subject to noise, calibration error, and temporary signal loss, as well as various faults that may not be immediately detected. Therefore, data preprocessing will often be required to overcome the inherent limitations of... 

Rollins, D., and Davis, J. (1992). Unbiased estimation of gross errors in process measurements. AlChE J. 38,563-572. 

Due to the complexity of bioprocesses, and the lack of direct in-process measurements of critical process variables, much work is being done on development of soft sensors and model predictive control of such systems. Soft sensors have long been used to estimate biomass concentration in fed-batch cultivations. The soft sensors can be integrated into automated control structures to control the biomass growth in the fermentation. 

Other types of transducers used in process measurements include mechanical drivers such as gear trains and electrical drivers such as a differential transformer or a Hall effect (semiconductor-based) sensor. 

Evaluating the results from development and/or scale-up batches of compressed tablets employs the use of control charting techniques, process capability analysis, and prediction intervals as described earlier. The techniques apply equally well to in-process measurements of hardness, thickness, and tablet weight, and compendial requirements such as assay, dose uniformity by content uniformity, and dissolution. 

The only way to obtain all necessary parameters is to apply model-based measurement techniques and electrical stimulation during wafer-level tests for each single device or by using test structures designed especially to obtain in-process measurement data (see [28, 29] and Section 5.10). This requires that the sensor s behavior is well understood and the dependencies of the various parameters can be expressed analytically according to Eq. 4.3. 

Three-way two-block data can be encountered, e.g., in modeling and multivariate statistical process control of batch processes. The first block contains the measured process variables at certain points in time of different batch runs. The second block might contain the quality measurements of the end products of the batches. Creating a relationship between these blocks through regression analysis or similar, can shed light on the connection of the variation in quality and the variation in process measurements. This can be used to build control charts [Boque Smilde 1999, Kourti et al. 1995], Another application is in multivariate calibration where, for example, fluorescence emission/excitation data of samples are used to predict a property of those samples [Bro 1999],... 

The first of the separation techniques to be used in process measurement was gas chromatography (GC) in 1954. The GC has always been a robust instrument and this aided its transfer to the process environment. The differences between laboratory GC and process GC instruments are important. With process GC, the sample is transferred directly from the process stream to the instrument. Instead of an inlet septum, process GC has a valve, which is critical for repetitively and reproducibly transferring a precise volume of sample into the volatiliser and thence into the carrier gas. This valve is also used to intermittently introduce a reference sample for calibration purposes. Instead of one column and a temperature ramp, the set up involves many columns under isothermal conditions. The more usual column types are open tubular, as these are efficient and analysis is more rapid than with packed columns. A pre-column is often used to trap unwanted contaminants, e.g. water, and it is backflushed while the rest of the sample is sent on to the analysis column. The universal detector - thermal conductivity detector (TCD)-is most often used in process GC but also popular are the FID, PID, ECD, FPD and of course MS. Process GC is used extensively in the petroleum industry, in environmental analysis of air and water samples" and in the chemical industry with the incorporation of sample extraction or preparation on-line. It is also applied for on-line monitoring of volatile products during fermentation processes" ... 

The first analytical instruments adapted for use in in-process measurements were electrochemical pH meters used as immersion probes. On-line potentiometric analysers can give continuous, real-time results for various analytes in a process. They are rugged ISEs that are not affected by the colour or turbidity of the process stream. Arrays of potentiometric sensors can even be used in fermentation broths. The sample can be taken into a loop, passed through a filter to protect the ISE surface and measnred. A feedback mechanism allows control of other parameters in order to keep the process in check. Applications... 

F. Flehmig, R. Vonwalzdorf and W. Marquardt, Identification of Trends in Process Measurements using the Wavelet Transform, Computer Chemical Engineering. 22 (1998), S491-S496. 

To improve the competitive position of all sectors of European industry (including SMEs) by promoting better measurements at the research and development levels, better definition and control of the quality of products, more efficient in-process measurements and technical assistance to the mutual recognition of certificates in accordance with the Global Approach to Conformity Assessment... 

The final chapter deals with the increasingly important area of process analytical science. There is increasing interest in in-process measurements from the FDA and other regulatory bodies, and this seems certain to be a rapidly expanding area of the analytical sciences in the pharmaceutical industry. 

In-process measurements of dioxins in a hot blast cupola with dry dedusting have shown that high PCDD/F-levels (5 ngTEQ/Nm ) occur in the heat-exchanger. Other parts of the flue-gas system show much lower values. Reduction measures should therefore aim at minimising the... 

Metal melting and molten metal treatment For each furnace type, different techniques may be considered for optimisation of the furnace efficiency and minimisation of any residue production. These mainly involve in-process measures. Environmental considerations can also be taken into account in the selection of the furnace t3 e. Special attention is paid to cleaning of the aluminium melt and the melting of magnesiiun, due to the high pollution potential of the products used until recently (HCE and SFg). 

Waste water prevention and treatment In many cases, waste water can be prevented or minimised by taking in-process measures. Waste water that cannot be prevented, will contain mineral or metal dust, amines, suphates, oil or lubricants, depending on its source within the process. The applicable treatment techniques differ for each of these compounds. 

In adaptive bending the predicted bend angle as a function of the punch displacement is compared to the instantaneous bend angle obtained during the bend stroke. Based on the observed deviation an updated target punch displacement can thus be determined. Several in-process measurement systems have been developed for this purpose. An overview of different measurement principles can be found in (Duflou et al. 2005) see Fig. 8. 

With a sufficiently high sampling rate for the in-process measurement system, adaptive bending can be performed without significant productivity loss. Adaptive control allows to control bend angles with a precision of 20 (Semiys 2011). 

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