Instrumentation & Process. Control. Tom Koporetz. City of Kalamazoo. Page 2. Five Processes to Control. T__________. P__________. F____. L_____. 1ª letter: measured variable. 2ª letter: may qualify the first one. D differential. F proportion. S safety. Q integration. 3ª y sig: Function of the Instrument. I indicator. R. applied technology and instrumentation for process control douglas wm-greece.infoá taylor & francis n Process Control Instrumentation Technology 8th wm-greece.info
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Fundamentals of. Industrial Instrumentation and Process Control. William C. Dunn. McGraw-Hill. New York Chicago San Francisco Lisbon London Madrid. Station. ®. Innovative Solutions from the Process Control Professionals. Practical Process Control. ©. “Fundamentals of Instrumentation and Process Control”. Instrumentation & Control · Process Control Fundamentals The Importance of Process Control. . Process Control Terms.
The term indicate applies only to the readout of an actual measurement. A pilot light that is part of an instrument loop is designated by a first letter followed by succeeding letter L. A pilot light that indicates an expired time period may be tagged KL. However, if it is desired to tag a pilot light that is not part of a formal instrument loop, the pilot light may be designated by a single letter L. A running light for an electric motor may be tagged either EL, assuming that voltage is the appropriate measured variable, or XL.
The action of a pilot light may be accompanied by an audible signal.
Use of succeeding letter U for multifunction instead of a combination of other functional letters is optional. A device that connects, disconnects, or transfers one or more circuits may be either a switch, a relay, an on-off controller, or a control valve, depending on the application.
The functions associated with the use of succeeding letter Y will be defined outside a balloon on a flow diagram when it is convenient to do so. This need not be done when the function is self-evident, as for a solenoid valve in a fluid signal line. Use of modifying terms high, low, and middle or intermediate, correspond to values of the measured variable, not of the signal, unless otherwise noted.
A high level alarm derived from a reverse-acting level transmitter signal is an LAH, even though the alarm is actuated when the signal falls to a low value. The terms high and low, when applied to positions of valves and other open-close devices, are defined as follows; high denotes that the valve is in or approaching the fully open The functional identification is made according to the function and not according to the construction.
Each instrument loop shall have a unique identification number. This number in general common to all instruments of a loop.
Because each instrument should have unique identification, suffix letters A, B, C, etc. However, multipoint recorders may more conveniently use suffix numbers, e. An instrument that performs two or more functions may be designated by all its functions.
Instrument relays may perform various functions such as computing, logic, and signal conversion. The function of a relay represented on a diagram is usually clarified by placing on of the symbol designations of Table 5. The miscellaneous symbols used in flow sheets are listed in Table 5. The miscellaneous symbols include the instrument line symbols, such as, mechanical, pneumatic or electrical etc. The heating fluid is modulated by some type of control valve. The type of control signal is not specified.
Records of gas, flow, pressure, and outlet temperature, and a low temperature alarm are required on the instrument board. The flow record FR is obtained by use of an orifice plate, flow transmitter FT , square-root extractor FY mounted behind the board, and two-pen recorder on the board.
The input to the pressure recorder PR is provided by a pressure transmitter PT that measures on the downstream side of the orifice plate. The signals are pneumatic. The gas outlet temperature is measured by a resistance type element, mounted in a thermowell, connected to a board-mounted temperature recording controller TRC , with an electric output that modulates a ball-type control valve having a cylinder-type actuator and, by implication, with internal conversion from the electric signal to a fluid signal.
The temperature recording controller has an integral low temperature switch that actuates an alarm on the board. Logic symbol diagramming is applicable to any process control system that uses switching devices to initiate normal or emergency operations. The method is primarily process-based rather than hardware-based. It describes operations in terms of the essential process functions that can be carried out by any class of hardware, whether electric, pneumatic, hydraulic, or other.
The method is directed to the needs of an engineer who may have only a rudimentary knowledge of hardware circuit design but who knows what the process-sensing instruments are and how the process is supposed to operate.
Logic symbol diagrams are appropriate whenever the operating requirements of the process have to be described to operating personnel, maintenance workers, designers, or others, and it is particularly useful for group discussions. It does not require knowledge of how to read relatively complex and specialized circuit diagrams. However, where it is necessary to trace the actions of a circuit in detail, there is usually no substitute for a complete circuit diagram.
The amount of detail in a logic diagram depends on the degree of refinement of the logic and on whether auxiliary, essentially non-logic, information is included. A logic system may have two opposing inputs; a command to open and a command to close, which do not normally exist simultaneously.
In addition, explanatory notes may be added to the diagram to record the logic rationale, Non-logic information reference document identification, tag numbers, terminal markings, etc. The existence of a logic signal may correspond physically to either the existence or the non-existence of an instrument signal, depending on the particular type of hardware system and the circuit design philosophy that are selected. A designer may choose a high flow alarm actuated by an electric switch whose contacts open on high flow; on the other hand, the high-flow alarm may be designed to be actuated by an electric switch whose contacts close on high flow.
The flow of information is represented by lines that interconnect logic statements.
The normal direction of flow is from left to right, or top to bottom. Arrowheads may be added to the flow lines wherever needed for clarity, and must be added to lines whose flow is not in a normal direction.
A summary of the status of an operating system may be put in the diagram wherever it is deemed useful, because a specified binary condition is sometimes unclear when it involves a device that does not have only two specific alternative states. For example, if it is stated that a valve is not closed, this could mean either a that the valve is open fully, or b that the valve is simply not closed: To aid accurate communication between writer and reader of the logic diagram, the diagram should be interpreted literally.
Therefore, possibility b is the correct one. If a valve is an open-close valve, it is necessary to do one of the following to avoid misunderstanding; 1. Develop the logic diagram in such a way that it says exactly what is intended. If the valve is intended to be open, then it should be so stated and not be stated as being not closed. Have a separate note specifying that the valve always assumes either the fully closed or fully open position Definitions Table 5.
The symbols shown with three inputs, A, B, and C, are typical for logic functions having any number of two or more inputs. In the several truth tables, 0 denotes the non-existence of the logic input or output signal or state given at the head of the column.
D denotes the existence of logic output signal or state as a result of appropriate logic inputs. The same can be represented by logic diagram as shown in Fig. The process must have high vacuum to proceed properly. Vacuum is normally maintained by an air ejector, but in case of failure or overload of the air ejector the system pressure rises. This switch also can be used to start and stop the pump manually.
However, the pump is not permitted to start or run if the discharge temperature, as sensed by a temperature switch TSH , is high or if the motor is overloaded and its circuit breaker is not manually reset. If high pressure is maintained for ten minutes, a high-pressure alarm PAH is actuated. High temperature is signalled by another alarm TAH. Pump motor overload is signalled by the alarm IAH.
If the pump control logic circuit loses power, the pump shall stop automatically but shall not be able to be restarted until the system is reset manually. Whenever the pump is required to operate, cooling water is automatically turned on. The water flow is controlled by an air-actuated control valve UV , which is operated by a solenoid valve UY that, in turn, is operated by auxiliary contacts of the pump motor circuit breaker. The water is automatically turned off when the pump is stopped.
The following instruments are on the instrument board: HS Manual control switch for pump operation. Instrumentation and Process Control. Outlines of Dairy: Module 1: Instruments and measurement system Lesson 1. Functions of instruments and measurement system Lesson 2. Elements of generalized measurement system. Module 2: Classification and selection of instruments Lesson 3. Classification of instruments Lesson 4.
Analog and digital modes of operation Lesson 5. Instrument selection criteria and installation procedures. Module 3: Characteristics of instruments and measurement systems Lesson 6.
Static characteristics of measuring instruments — I Lesson 7. Static characteristics of measuring instruments — II Lesson 8. Static characteristics of measuring instruments — III Lesson 9. Dynamic characteristics of measuring instruments. Module 4: Induction type indicating instruments Lesson Induction type wattmeter, watt-hour meter, dynamometer type power factor meter.