CLB 21121Introduction of

Process Instrumentation

OBJECTIVES

After this lesson, you will able to:

Explain the basic concept of process control. Relate the process instrumentation with process control. Define the meaning of process instrumentation

terminologies. Apply the concept of instrumentation symbols. Describe the important of process instrumentation in

industry.

DEFINITIONControl Instrument / apparatus to regulate mechanism

Instrument Devices for indicating / measuring condition,

performance, position, direction or sometimes controlling operation

Measurement Extent, quantity, size which determined by measuring

BASIC CONCEPT OF PROCESS CONTROL

Process control: automatic control of an output variables by sensing the amplitude of the output parameter from the process and comparing it to the desired or set level and feeding an error signal back to control an input variable.

A temperature sensor attached to the outlet pipe senses the temperature of the water flowing.

As the demand for hot water increases or decreases, a change in the water temperature is sensed and converted to an electrical signal, amplified, and sent to a controller that evaluates the signal and sends a correction signal to an actuator.

The actuator adjusts the flow of steam to the heat exchanger to keep the temperature of the water at its predetermined value.

PRINCIPAL OF PROCESS INSTRUMENTATION

Part of process control

4 basic component for measuring process variables:

sensor: devices to measure the elementcontroller: intelligent unit to control the processcontrol element: control valve, pump speed, heating element

controlled variables: element to control

2 important component to measure value:

Sensor: conduct the process variable measurementTransmitter: convert measurement by sensor to signal (4-20 ma)

Relation between sensor and transmitter:- Linear- Non- linear

TERMINOLOGIESAccuracy

The amount of error that may occur when measurements are taken. It determines how precise or correct the measurements are to the actual value and is used to determine the suitability of the measuring equipment.

Accuracy can be expressed as any of the following:

error in units of the measured value

percent of span percent of upper range value percent of scale length percent of actual output

value

Range of operation/instrument The high and low operating limits between

which the device will operate correctly, and at which the other specifications are guaranteed.

Span of instrument The difference between the low and the high

value of process variables measured by the instrument

Zero of instrument The lowest value measured by the instrument

Hysteresis This is where the

accuracy of the device is dependent on the previous value and the direction of variation.

Linearity Linearity is how close a

curve is to a straight line. The response of an instrument to changes in the measured medium can be graphed to give a response curve.

Repeatability Repeatability defines how close a second

measurement is to the first under the same operating conditions, and for the same input.

Response When the output of a device is expressed as a

function of time (due to an applied input) the time taken to respond can provide critical information about the suitability of the device.

Calibrate To configure a device so that the required output

represents (to a defined degree of accuracy) the respective input

Controller A device which operates automatically to regulate the

control of a process with a control variable.

Ramp Defines the delayed and accumulated response of the

output for a sudden change in the input.

Sensitivity This defines how much the output changes, for a

specified change in the input to the device.

Set Point Used in closed loop control, the set point is the ideal

process variable. It is represented in the units of the process variable and is used by the controller to determine the output to the process.

Steady state Used in closed loop control where the process no

longer oscillates or changes and settles at some defined value.

Transducer A device that converts information from

physical, (temperature or pressure) and converts it to electrical, (volts or millivolts or resistance change).

Transmitter A device that converts from one form of

energy to another. Usually from electrical to electrical for the purpose of signal integrity for transmission over longer distances and for suitability with control equipment.

Variable The quantity of the system or process.

Instrumentation Symbols and Identification

ISA 5.1 (1984) Suitable for use in the chemical, petroleum, power

generation, air conditioning, metal refining, and numerous other, process industries.

Certain fields, such as astronomy, navigation, and medicine, use very specialized instruments that are different from the conventional industrial process instruments.

Each instrument or function to be identified is designated by an alphanumeric code or tag number as shown

The loop identification part of the tag number generally is common to all instruments or functions of the loop. A suffix or prefix may be added to complete the identification.

Typical letters

Line Symbols

Function Symbol

Control Valve Body Symbol

Actuator Symbol

Self-actuated Regulators, Valves and other Devices

Symbols for Actuator Power Failure

Primary Element Symbols

SELECTION DEVICES CRITERIA Wide operating range Fast response Good sensitivity High accuracy High over range protection Simple design and maintenance Cost Repeatability Size Stable Resolution Robust Self generated signal Simple to adjust Suitable for various material Reliable performance Unaffected by density, moisture content an dconductvity

APPLICATIONSHVAC (Heating, ventilation and air conditioning) Applications Heat transfer Billing Axial fans Climate control Hot and chilled water flows Forced air Fumehoods System balancing Pump operation and efficiency

Petrochemical Applications Co-generation Light oils Petroleum products Steam Hydrocarbon vapours Flare lines, stacks

Natural Gas Gas leak detection Compressor efficiency Fuel gas systems Bi-directional flows Mainline measurement Distribution lines measurement Jacket water systems

Power Industry Feed water Circulating water High pressure heaters Fuel oil Stacks Auxiliary steam lines Cooling tower measurement Low pressure heaters Reheat lines Combustion air

Emissions Monitoring Chemical incinerators Trash incinerators Refineries Stacks and rectangular

IMPORTANT

Safety concern within allowable limit Production specification optimum

variables maximize production Environmental regulation within specified

limits Operational constrains - equipment Economics min operating cost, max profit

Slide 1OBJECTIVESDEFINITIONBASIC CONCEPT OF PROCESS CONTROLSlide 5PRINCIPAL OF PROCESS INSTRUMENTATIONSlide 7Slide 8TERMINOLOGIESSlide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Instrumentation Symbols and IdentificationSlide 20Typical lettersLine SymbolsFunction SymbolSlide 24Control Valve Body SymbolActuator SymbolSlide 27Self-actuated Regulators, Valves and other DevicesSlide 29Slide 30Symbols for Actuator Power FailurePrimary Element SymbolsSlide 33Slide 34Slide 35Slide 36Slide 37SELECTION DEVICES CRITERIAAPPLICATIONSSlide 40Slide 41IMPORTANT