Measuring system, requirements

To avoid the apparent complications with absolute rheologic measurement techniques, a number of investigators (4,5). have used relative measurement systems to make rheologic measurements. The major difference between the relative and absolute measurement techniques is that the fluid mechanics in the relative systems are complex. The constitutive equations needed to find the fundamental rheologic variables cannot be readily solved. Relative measurement systems require the use of Newtonian and non-Newtonian calibrations fluids with known properties to relate torque and rotational speed to the shear rate and shear stress (6). 

In order that the data acquisition system can obtain information about the spatial location and orientation of the probe, a four-channel incremental encoder interface board is installed. Three channels are used to define position in three-dimensional space, while the fourth monitors the skew of the probe (skew is defined as rotation about an axis normal to the probe face). Although six measurements are required to completely define the location and orientation, it is assumed that the probe remains in contact with the inspection surface. 

In order to be able to reduce prices, even more and more test- and measurement systems are integrated on PC-boards. The powerful and inexpensive PC eomponents can be directly u.sed for these (virtual) instruments. The limited dimensions of the PC boards require a reduction to the absolute necessity of the electronic components. Analogue signal proeessing must carried out by software as far as possible. 

Acts before the effect of a disturbance has been felt by the system Requires measurement of all possible disturbances and their direct measurement... 

Figure 20-9 shows the negative effect of uninsulated heating elements on corrosion protection. In a 250-liter tank, an electric tube heating element with a 0.05-m surface area was screwed into the upper third without electrical separation, and in the lower third a tinned copper tube heat exchanger with a 0.61 -m surface area was built in. The Cu heat exchanger was short-circuited for measurements, as required. For cathodic protection, a potential-controlled protection system with impressed current anodes was installed between the two heating elements. The measurements were carried out with two different samples of water with different conductivities. 

Failure modes analysis Statistical process control Measurement systems analysis Employee motivation On-the-job training Efficiency will increase through common application of requirements for Continuous improvement in cost Continuous improvement in productivity Employee motivation On-the-job training... 

Process instructions including set-up and set-up verification Handling requirements Operator competency requirements Measurement systems analysis plan... 

The standard refers you to ISO 10012 for guidance in meeting these requirements and indeed this standard should be consulted when setting up your measurement system. ISO 10012, however, does not cover all the aspects of element 4.11 of ISO 9001. 

Although the concept of a measurement system is not specifically addressed in ISO 9001, the requirements in element 4.11 serve to establish and maintain a measurement system, hence the reason for its inclusion in the model in Figure 11.1. 

In ISO 9001 the terms accuracy and precision are used and these were explained previously. ISO/TS 16949 takes the study of measurement further and divides variation into five classes. Although, ISO/TS 16949 has not deleted the requirement on measurement uncertainty, compliance with the measurement systems analysis requirement achieves the same purpose. 

Measurement systems must be in statistical control so that all variation is due to common cause and not special cause. ISO/TS 16949 therefore requires that you devise a measurement system for all measurements specified in the control plan in which all variation is in statistical control. 

All audits should be conducted against a standard for the performance being measured. Examinations without such a standard are surveys, not audits. Audits can also be conducted against contracts, project plans, specifications - in fact any document with which the organization has declared it will comply. The standard now requires system audits to be conducted to verify compliance with ISO/TS 16949 and any other system requirements. 

The ability of a measuring system (device, person, and environment) to measure true values to the accuracy and precision required. 

Some measures of PSM and ESH performance are easy to identify, establish and track. These include accident rates, effluent tonnages and composition and number of days lost to illness. Almost all of these traditional performance measures are end-of-pipe that is, they measure the output of the management system and allow corrective action only after a failure has occurred. The ideal measurement system identifies potential problems ahead of actual failure allowing corrective action to be taken. This requires using techniques such as audits and hazard assessments. 

As mentioned earlier some measures will be chosen because improvements in these areas were part of the project justification. It is most likely that these will be efficiency measures. Calculation of these measures generally requires analysis of data or specific data collection exercises. There is a relatively high cost associated with preparing these measures so they should be used prudently. In choosing efficiency measures, you should use only those where you have comparative data about the current management systems. For example, if there is no information on the number of hours dedicated to PSM and ESH, don t use this to try to demonstrate the improvement in efficiency. 

Although direct methods for small and medium size systems require more CPU time than disk based methods, this is in many cases irrelevant. For the user the determining factor is the time from submitting the calculation to the results being available. Over the years the speed of CPUs has increased much faster than the speed of data transfer to and from disk. Many modem machines have quite slow data transfer to disk compared to CPU speed. Measured by the elapsed wall clock time, disk based HF methods are often the slowest in delivering the results, despite the fact that they require the least CPU time. 

Assume that a plant air system requires 10,000 fti/min of dry air measured at 14.7 psia and 60°F. The air is required at 100 psia. Intake conditions are... 

This is especially true in applications that use microprocessor/computer-based systems. These systems require a database that specifies the monitoring parameters, measurement routes, analysis parameters, and a variety of other information. This input is needed to acquire, trend, store, and report what is referred to as conditioned vibration data. 

Most computer-based systems require data-acquisition routes to be established as part of the database setup. These routes specifically define the sequence of measurement points and, typically, a route is developed for each area or section of the plant. With the exception of limitations imposed by some of the vibration monitoring systems, these routes should define a logical walking route within a specific plant area. A typical measurement is shown in Figure 44.15. 

Computer simulations of these systems require that some measures be taken to prevent possible memory overflows, such as would happen in cases either of pure coupling, where links are continually added and none deleted, or in isolated regions of a graph where for a few sites more neighbors arc added than are allowed by memory. We thus introduce working link transition rules... 

The traditional arrangement of simple spherical glassware and Isomantles with full-power on-off controllers monitored by mercury thermometers, would still be widely recognised. So too would be the plug-shot piston pumps set up and monitored by use of measuring cylinders. Although tried and tested this hardware system requires constant attention by a skilled lab. technician to achieve control and reproducibility of even the first-order process parameters manual data collection is hardly feasible at better than 10-15 minute intervals. 

The other major source of noise is vibration from the environment. The entire measuring system is, of course, mounted on appropriate rubber isolation pads. However, these are not adequate for the level of accuracy required. The residual vibration is eliminated from the signal by mounting the lower part of the optical reflection system on a spring which is driven by servo electronics that detects its movement. An effective free period for the spring of up to 60 s can be achieved in this way, and virtually all environmental vibration is eliminated from the measured signal. 

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