Instrument connections

Information supplied by instruments is vital for column control and operation. False information prompts wrong operator (or control loop) action, erratic column operation, and incorrect diagnosis of problems. Numerous experiences (7, 71, 97, 203, 210, 232, 237, 239, 255, 268) have been reported where faulty instrument readings caused, or directly contributed to, column problems. 

The connection must be located where the desired measurement can be properly made. For instance, if liquid temperature is specifically desired, the measurement connection must be close to the tray or downcomer floor, and not in a vapor space. 

The instrument must be accessible for operation and maintenance. If an instrument reading is suspect, a check of the instrument is required, often in a hurry, and inaccessibility may impose a serious limitation. 

The instrument connection should not be too small so that it easily breaks or plugs V2-in connections are often considered too small 1 to 2 in is normally adequate. 

Instrument lines should be kept as short and as free of elbows and bends as possible. Internal instrument lines should be avoided. This is most important when there is a tendency to plug. One experience has been reported (237) where overlooking this rule caused plugging and loss of level indication. 

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FIG. 11-44 Typical construction of a tube bundle with plug headers (1) tube sheet (2) plug sheet (3) top and bottom plates (4) end plate (5) tube (6) pass partition (7) stiffener (8) plug (9) nozzle (10) side frame (11) tube spacer (12) tube-support cross member (13) tube keeper (14) vent (15) drain (16) instrument connection. (API Standard 661.)... 

This is the ratio of instrument limit primary current to the rated primary current. Consequently a high SF will mean a high transformation of the primary current and can damage instruments connected to its secondary. For measuring instruments therefore it is kept low, as it is required to measure only the normal current and not the fault current. 

VAi = VA of the load (instrument) connected on the secondary of the interposing CTs, including the connecting leads. 

The summated current is the sum of all the CT secondary currents of the different circuits. The rating of the instrument connected on the secondary of the summation CT should be commensurate with the summated current. The error of measurement is now high, as the errors of all individual CTs will also add up vectorially. 

Manifold/instrument Instrument connected to sampling manifold which draws ambient... 

All piping and instrument connections should be made on the lower half of the housing to aid in removal of the top half. Other connections, if they must be made in the top half, should have easily accessible joints. 

Sensitive differential pressure Instrument connected to Pitot tube... 

W. H. Doyle, Some Major Instrument Connected CPI Losses, Paper presented at Chemical Process Industry Symposium, Philadelphia, Pa., 1972. 

The two types of lines on a flowsheet are (1) those representing outlines and details of equipment, instruments, etc., and (2) those representing pipe carrying process or utility liquids, solids, or vapors and electrical or instrument connections. The latter must be distinguished among tliemselves as suggested by Figure 1-21. 

The sensor usually consists of a coil of wire made from the material that is wound on a former and the whole sealed to prevent oxidization, although a film of the metal deposited on a ceramic substrate can also be used. The resistor is connected in a Wheatstone bridge network (Figure 17.17), using fixed resistors in the other three arms. The instrument connected across the bridge is calibrated directly in terms of temperature. The range is limited by the linearity of the device and the upper temperature, which can be measured, must be well below the melting point of the material. 

Elbolef is used on 90° Long Radius Elbows (can be manufactured for Short Radius Elbows) for thermowell and instrumentation connections Available butt-weld to meet your specific reinforcement requirements, and 3000 and 6000 classes for socket weld and threaded applications. 

DU Q z, KE c Q and ITO Y (1998) Separation of epigaUocatechin gaUate and gallocatechin gallate using multiple instruments connected in series , JLiq Chromatog Related Technol, 21, 203-8. 

Breaking off of a small-bore pipe such as an instrument connection... 

The instrument connecting lines should be drawn in a manner to distinguish them from the main process lines. Dotted or cross-hatched lines are normally used. 

W. H. Doyle, Instrument-Connected Losses in the CPI, Instrument Technology (October 1972), pp. 38- 42. 

Definition of any initial preparation procedures involving instrument connections, HPTC plumbing requirements or sample/test mix preparation... 

Hewlett Packard gas chromatograph type 5890 with an FID plus injector (or similar instrument) connected to a PC with Chromeleon integration software. 

As a purge medium, to prevent pressure taps and other instrument connections and relief valves, from plugging... 

For process equipment controlled by computers, the events are recorded at the time of occurrence by the computer systems. Instrumentation connected to computer systems may measure process parameters or document actions such as addition of ingredients as a specific process event. The recording of processing events and operator actions must be audit trailed immediately, and should not wait for approval. 

Overall system requirements such as number of users, locations where the system will be used, and the instruments connected to the system will terminal emulation be used ... 

Count all valves in P ID s, including control valves. Allow one valve for every utility subheader. Do not count vents, drains, and instrument connections they are built into the pipe unit costs. 

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