Instrumentation pneumatic

A pnenmatic tubing schedule is a list of all field instrument pneumatic tubing (single and multi tube) in identification number order and is used for allocating tubing numbers and providing installation information. Each schedule should contain the following for each tube/multitube ... 

The manual proof test is assumed to be 100% effective and to occur annually (ca. 8000 hrs). One maintenance crew is assumed to be available for each of the three equipment types (PES, Instrumentation, Pneumatics). 

Hot water layer system instrumentation Reactor water treatment system instrumentation Demineralized water system instrumentation Active effluents system instrumentation Supervised area ventilation system instrumentation Reactor hall ventilation system instrumentation Non restricted area ventilation system instrumentation Ventilation system water supply instrumentation Pneumatic transport system instrumentation... 

Instrument Society of America 400 Stanwix Street Pittsburgh, Pa. 15222 Standards l ibrary for Measurement and Control, 12th ed., 1994. Instmmentation standards and recommended practices abstracted from those of 19 societies, the U.S. Government, the Canadian Standards Association, and the British Standards Institute. Covers control instmments, including rotameters, aimunciators, transducers, thermocouples, flow meters, and pneumatic systems (see... 

The flow capacity of the transducer can be increased bv adding a booster relav like the one shown in Fig, 8-7.3/ , The flow capacity of the booster relav is nominally fiftv to one hundred times that of the nozzle amplifier shown in Fig, 8-7.3 3 and makes the combined trans-diicer/booster suitably responsive to operate pneumatic actuators. This type of transducer is stable into all sizes of load volumes and produces measured accuracy (see Instrument Society of America [ISA]-S5l, 1-1979, Process Instrumentation Terminology for the definition of measured accuracy) of 0,5 percent to 1,0 percent of span. 

From a dynamic-response standpoint, the adjustable speed pump has a dynamic characteristic that is more suitable in process-control apphcations than those characteristics of control valves. The small amphtude response of an adjustable speed pump does not contain the dead baud or the dead time commonly found in the small amphtude response of the control valve. Nonhnearities associated with frictions in the valve and discontinuities in the pneumatic portion of the control-valve instrumentation are not present with electronic... 

In many designs, a combination of the choice items are used such as air- and water-cooling, steam and electric driven pumps and electronic and pneumatic instrumentation. As much as possible, these type decisions should be made by results of side studies rather than simple edict. 

Instrumentation is rapidly becoming more electronic. However, many users prefer pneumatic, and computer compatibility is available with either although electronic interface with computers is generally preferred. One coal gasification company prefers pneumatic because they feel the inherent corrosive atmosphere around such plants is not kind to electronic equipment. 

The following handy tabulation from the GPSA Data Book compares pneumatic and electronic instrumentation. 

Fail Closed (usually normally closed)-An instrument that will go to the closed position on loss of power (pneumatic, electric, etc.). 

The case study described here concerns a human factors audit of a computer controlled process system which was being introduced in a distillation imit of a chemical plant. The unit was in transition from replacing its pneumatic panel instrumentation with the new system. However, control had not yet been transferred and the staff were still using the panel instrumentation. The role of the project was to evaluate a preliminary design of the computer-based display system and provide recommendations for future development. 

Compressed air is needed for general use and for the pneumatic controllers that usually seiA e for chemical process plant control. Air is often distributed at a pressure of 100 psig. Rotary and reciprocating single-stage or two-stage compressors are used. Instrument air must be dry and clean (free from oil). 

Pressure recording controller (differential), pneumatic transmission with pressure recorder, combined instrument board mounted... 

The basic purpose of an oil separator is to clean the pressurized air of any oil contamination, which is highly detrimental to pneumatically controlled instrumentation. A separator consists of an inlet, a series of internal baffle plates, a wire mesh screen, a sump, and an outlet. The pressurized air enters the separator and immediately passes through the baffle plates. As the air impinges on the baffle plates it is forced into making sharp directional changes as it passes through each baffle section. As a result, the oil droplets separate from the air and collect on the baffles before dropping into the separator s sump. 

The degree of drying desired will vary with the pneumatic equipment and application involved. The aim is to eliminate further condensation in the airlines and pneumatic tools or devices. Prevailing atmospheric conditions also have an influence on the approach that is most effective. In many 100-psig installations, a dew point at line pressure of from 500°F to 350°F is adequate. Other applications, such as instrument air systems, will require dew points of minus 500°F. 

Another value sometimes involved when the gas pressure is reduced before it is used is the dew point at that lower pressure condition. A major example is the use of lOOpsig (or higher) gas reduced to 15psig for use in pneumatic instruments and controls. This dew point will be lower because the volume involved increases as the pressure is decreased. The dew point at atmospheric pressure... 

Some proportional detectors are combined in the same instrument with a suitable transducer which can perform some of the functions of a controller. For example, for pneumatic systems the primary sensing element actuates a variable air jet, thus modulating an air pressure which is transmitted to a further controller or direct to the controlled device. Electric and electronic detectors such as the infrared detector include the sensing and amplifying circuits of the instrument. 

Pneumatic controllers, which may include part of the sensing instrument, are supplied with compressed air at 1 bar gauge which is allowed to escape from an orifice controlled by a detector. The resulting pressure modulates about 0.4 bar and is used in a servo... 

A central component of the LC instrument is the pump, for its characteristics can strongly influence an analysis (e.g., flow reproducibility). The three principal types of systems— pneumatic, syringe type and reciprocating piston—have been reviewed in the literature (18-20). 

In the pneumatic pumping system, the pressure (and not the flow rate) is maintained constant as variations in chromatographic conditions occur. Thus, a change in mobile phase viscosity (e.g. gradient elution) or column back pressure will result in a change in flow rate for these types of pumps. The gas displacement pump in which a solvent is delivered to the column by gas pressure is an example of such a pneumatic pump. The gas displacement system is among the least expensive pumps available and is found in several low cost instruments. While the pump is nonpulsating and hence, produces low noise levels with the detectors in current use, its flow stability and reproducibility are only adequate. In addition, its upper pressure limit is only 2000 psi which may be too low in certain applications. 

In Figure 8.12, the basic set-up of an ICP-MS instrument is presented as a block diagram, consisting of a sample introduction system, the inductively coupled argon plasma (ICP) and the mass-specific detector. By far the most commonly applied sample introduction technique is a pneumatic nebuliser, in which a stream of argon (typically 1 I.min ), expanding with high... 

Indirectly actuated valves pneumatically or electrically operated valves, which are activated by pressure-sensing instruments. 

---