General Guidelines

Some guidelines and recommendations are discussed below, together with a few examples of their application. The books by Buckley (Techniques of Process Control, Wiley, 1964) and Shinskey (Process-Control Systems, McGraw-Hill, 1967) arc highly recommended for additional coverage of this important topic. 

Keep the control system as simple as possible. Everyone involved in the process, from the operators up to the plant manager, should be able to understand the system. Use as few pieces of control hardware as possible. Every additional gadget that is included in the system is one more item that can fail or drift. The instrument salesperson will never tell you this, of course. 1 Use feedforward control to compensate for large, frequent, and measurable disturbances. 

Avoid lags and deadtimes in feedback loops. Control is improved by keeping the lags and deadtimes inside the loop as small as possible. This means that sensors should be located close to where the manipulated variable enters the 

Example g.l. Consider the two blending systems shown in Fig. 8.8. The flow rate or composition of stream 1 is the disturbance. The flow rate of stream 2 is the manipulated variable. In scheme A the sensor is located after the tank and therefore the 

Blending systems, (n) With tank inside loop (A) with tank outside loop. 

The following general guidelines are used to design pressure protection from fire  

Hepatitis B Vaccination and Post-Exposure Evaeuation and Follow-up General Guidelines 

The employer should make available Hepatitis B vaccine and vaccination series to all employees who have occupational exposure, and post-exposure evaluation and follow-up to all employees who have had an exposure incident. 

Made available to the employee at a reasonable time and place. 

Performed by or under the supervision of a licensed physician or under the supervision of another licensed healthcare professional. 

If the measured a-activity is less than 0.1 Bq/1 or less than 3 pCi/1, no additional analysis is required. 

If the a-activity is considerably higher, radon 222 is to be determined and subtracted if it was included in the total a-activity. 

If the a-activity is then still clearly in excess of 3 pCi/1, radium 226 is to be determined. If a-activity due to radium 226 is substantiated, the water is not to be used as drinking water for permanent consumption. If, on the other hand, it is demonstrated that the increased a-radioactivity does not stem from radium 226, the water can be used even in the event of an increased a-radioactivity level. 

however, the measured a-radioactivity is in excess of 0.5 Bq/1 (in excess of roughly 15 pCi/1), a nuclide analysis is required in order to 

If the B -activity of water is less than 1 Bq/1 than 27 pCi/1 no further analyses are required. 

Typically, two species are required for a test (e.g., mouse and rat). Both sexes must be tested in equal numbers. Three dose levels are required, plus control animals (i.e., those not given the chemical). Fifty to one hundred animals are required per group, per dose, and per sex. For each species tested, this would include a minimum of four hundred animals, broken down as follows  

For the second species, the same calculations apply. This means that a chronic test conducted under the guidelines presented above (and which are used for cancer studies) would require a minimum of 928 animals. 

The scientific approach to a chronic study is to eliminate all variables among the animals except one, which should be exposure to the chemical under study. Typically, all test animcds of a given species are of one specific strciin, which reduces genetic variability among the animals. All of the animals are about the same age and are maintained identiccdly in the laboratory. They cu e fed the same diet and the same water, and breathe the same air. For some studies, the chemical will be administered through a tube directly into the stomach of each cmimcd (i.e., gavage). This is done to ensure that the total measured amount of the chemiccd reaches the stomach of the cmimals. 

While these environmental controls are necessary to identify minuscule subcellu-lar differences between cmimals, they limit the value of the test when applied to the real world where young, old, sick, and pregnant receptors will also be exposed. This is an inherent limitation of laboratory studies, even those cis extensive as discussed here. Extrapolating laboratory results to the environment, whether on whole animals or tissues, involves uncertainty. Uncertainty should be lower using tests from whole animals than tissues because the differences between the laboratory and the environment are smaller for tests on whole animcds. 

Although chronic tests can be conducted to evaluate only target-organ specific effects (e.g., kidney damage), they are generally conducted to evaluate either cancer, reproductive, or developmental effects. The testing methods and features specific to these are discussed in the following sections. 

First of all analyse your needs. Which types of compounds you want to work on, which properties you are mostly interested in, how accurate results you require, the intended amount of work if you dare predict it. 

Secondly examine your possiblities. Computer and consultant availability, your own or your associates programming skills, your budget. 

When pondering the above, be aware that you may easily get ideas on new types of substances which have not been parametrized, and you may want to calculate properties which are not available in any or most programs. As to accuracy, remember that high accuracy on conformations does not necessarily cost many parameters but that good vibrational spectra certainly do. 

Good ideas are sometimes gotten in awkward places. You may be working at an institution with few or no computer facilities.. Then you must drop the idea or go elsewhere. Or you might have all the facilities you can wish for, but lack the skill to use them. Then you are at the mercy of your splendid graduate student. 

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The properties that are achieved in commercial stmctural foams (density >0.3 g/cm ) are shown in Table 3. Because these values depend on several stmctural and process variables, they can be used only as general guidelines of mechanical properties from these products. Specific properties must be deterrnined on the particular part to be produced. A good engineering guide has been pubHshed (103). 

Because of the diversity of cooling water systems, only general guidelines for altering system operation can be given. 

Due to the complexity of the SCC phenomenon, preventive techniques have been expressed in general rather than specific terms. It should be recognized that exceptions to these general guidelines may exist and that cracking could result in some specific circumstance even if the guidelines are followed. 

Rolaling electrical machines. Functional evaluation of insulation systems. General guidelines 7816/1991 BS EN 600.34-18-1/1994 -... 

General guidelines during installation and maintenance of a switchgear or a controlgear assembly 13/384... 

Correct oil level is critical. Consult the owner s manual. As a general guideline, the oil level should be half way up the lowest ball or roller in the bearing assembly. Too much, or too little oil will lead to premature... 

Pinch Point—This is defined as the differenee between the exhaust gas temperature leaving the evaporator seetion and the saturation temperature of the steam. Ideally, the lower the pineh point, the more heat reeovered, but this ealls for more surfaee area and, eonsequently, inereases the baek-pressure and eost. Also, exeessively low pineh points ean mean inadequate steam produetion if the exhaust gas is low in energy (low mass flow or low exhaust gas temperature). General guidelines eall for a pineh point of 15-40°F (8-22 °C). The final ehoiee is obviously based on eeonomie eonsiderations. 

In specifying settling chamber dimensions, gas flow velocities must be maintained below the reentrainment velocity (pick-up velocity) of deposited particulate. As a general guideline, linear gas velocities are kept below 10 ft/sec (600 ft/min = 304.8 cm/sec). This is satisfactory for most materials however, some low-density particulates are reentrained at lower velocities. 

The chemical propjerties of the contaminants have to be considered when selecting separation techniques. Some of the liquids are absolutely immiscible in water, and if the process stream involves water and the contamination is liquid/liquid, then the separation technique can greatly reduce the volume of contaminated water. For example, if acetone is the contaminant of concern, a simple vap>or stripping technique can be effective in making a separation. In the case of refined oil, which has a solubility limit of approximately 50 ppm, one of the oil/water separation techniques could be effective. Some general guidelines to consider are ... 

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate and it is necessary to account for the method of application and characteristics of filter aids. 

Immersion into the corrosive medium is important. Corrosion can proceed at different rates, depending on whether the metal is completely immersed in the corrosive medium, partially immersed or alternately immersed and withdrawn. Immersion should be reproduced as closely as possible since there are no general guidelines on how this affects corrosion rates. 

Because of the multitude of engineering materials and the profusion of material-oriented literature it is not possible to describe specific engineering practices in detail in a single chapter. However, we can outline general criteria for parallel evaluation of various materials that can assist in proper selection. The following is a list of general guidelines that can assist in material selection ... 

Rase [5] has presented several ease studies of different seale-up methods involving industrially important reaetions. Murthy [11] has provided a general guideline for the seale-up of slurry hydrogenation reaetors, and other seale-up proeesses are illustrated elsewhere [12]. 

A properly written HASP should contain worker health and safety program information, guidance, and alternatives. The HASP should quickly answer the following questions What hazards are present and How can we make sure that the tasks will be performed safely The following general guidelines will help to answer these questions ... 

Appendix B of the standard outlines a nonmandatory compliance section regarding hazard assessment and PPE selection. This Appendix outlines general guidelines for identifying, organizing, and analyzing sources of hazards and selection criteria for the appropriate PPE. 

Styragel columns can be used with a broad range of solvents and at elevated temperature. They can be converted to different solvents and temperatures following the general guidelines given in this section. Detailed conversion protocols are available in the care and use manual. 

Number of casing stages is determined by critical speed margins. These numbers are a general guideline only. 

Oil-base mud maintenance involves close monitoring of the mud properties along with the mud temperature, as well as the chemical treatment (in which the order of additions must be strictly followed). The following general guidelines should be considered ... 

Microbiocides. For a general guideline about 100 mg/L of the microbiocide with at least 50 wt% active ingredient should be added to the drilling fluid. Exact dosage and treatment frequency has to be estimated based on the severity of the problem. 

Insulation thickness While the actual thickness of insulation needed to comply with the Building Regulations will vary depending on insulation type, thermal conductivity and the structure into which it is fitted, some general guidelines can be given ... 

Materials used for gas pipework will depend on application, location, environment and operating pressure. General guidelines are as below. 

The method of jointing will depend on the material, the pipe size, the operating pressure and the location. General guidelines are given below. 

Table 44.6 is a vibration troubleshooting chart that identifies some of the common failure modes. This table provides general guidelines for interpreting the most common abnormal vibration profiles. These guidelines, however, do not provide positive verification or identification of machine-train problems. Verification requires an understanding of the failure mode and how it appears in the vibration signature. 

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