mecn 4600 inter - bayamon lecture 11111111 mechanical measurement and instrumentation mecn 4600...

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LectureLecture

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Mechanical Measurement and Mechanical Measurement and InstrumentationInstrumentation

MECN 4600 MECN 4600

Professor: Dr. Omar E. Meza CastilloProfessor: Dr. Omar E. Meza [email protected]

http://www.bc.inter.edu/facultad/omeza

Department of Mechanical EngineeringDepartment of Mechanical Engineering

Inter American University of Puerto RicoInter American University of Puerto Rico

Bayamon CampusBayamon Campus

Lecture 11Lecture 11MEC

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Tentative Lecture ScheduleTentative Lecture Schedule

TopicTopic LectureLecture

Basic Principles of MeasurementsBasic Principles of MeasurementsResponse of Measuring Systems, System DynamicsResponse of Measuring Systems, System DynamicsError & Uncertainty AnalysisError & Uncertainty Analysis

1, 2 and 31, 2 and 3

Sensor & TransducersSensor & TransducersBasic Electronics, Signal ProcessingBasic Electronics, Signal Processing

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Measurement of PressureMeasurement of Pressure 55

Measurement of TemperatureMeasurement of Temperature 6, 7, 86, 7, 8

Measurement of Stress-StrainMeasurement of Stress-Strain 99

Measurement of Time ConstantMeasurement of Time Constant 1010

Measurement of LevelMeasurement of Level 1111


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Differential Pressure CellDifferential Pressure Cell(DP Cell) (DP Cell)

Topic 11: Level MeasurementTopic 11: Level Measurement

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To measure the level of a tank using a To measure the level of a tank using a differential pressure cell (DP Cell).differential pressure cell (DP Cell).

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Course ObjectivesCourse Objectives


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Introduction:Introduction:

The sensing and control of product levels The sensing and control of product levels in containers involves a wide range of in containers involves a wide range of materials-liquids, powders, slurries, and materials-liquids, powders, slurries, and granular bulk. granular bulk. All level measurement All level measurement involves the interaction of a sensing involves the interaction of a sensing device, element, or system with material device, element, or system with material inside a containerinside a container. You can use a wide . You can use a wide variety of physical principles to measure variety of physical principles to measure level-sight, pressure, radiation, and level-sight, pressure, radiation, and electric and sonic principles.electric and sonic principles.

Three sight-type level sensors are Three sight-type level sensors are glass glass gauges, displacers, and tape floatsgauges, displacers, and tape floats..

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Glass gauges: Glass gauges: are the most widely used are the most widely used instruments for measuring process tank instruments for measuring process tank level. Two types of level glass gauges level. Two types of level glass gauges measure liquid level in process tanks: measure liquid level in process tanks: tubular and flat gauges. The tubular type tubular and flat gauges. The tubular type works on the same principle as a works on the same principle as a manometer. As the liquid level in an open manometer. As the liquid level in an open tank rises or falls, the liquid in the glass tank rises or falls, the liquid in the glass tube will rise or fall. The gauges consist of tube will rise or fall. The gauges consist of glass, plastic, or a combination of the two glass, plastic, or a combination of the two materials.materials.

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Tape float: Tape float: One of the most simple, direct One of the most simple, direct methods of float level measurement is the methods of float level measurement is the tape float gauge. A tape connects to a float tape float gauge. A tape connects to a float on one end and to a counterweight on the on one end and to a counterweight on the other to keep the tape under constant other to keep the tape under constant tension. The float motion results in the tension. The float motion results in the counterweight riding up and down a direct-counterweight riding up and down a direct-reading gauge board, thereby indicating reading gauge board, thereby indicating the level in the tank.the level in the tank.

Standard floats are normally cylindrical for Standard floats are normally cylindrical for top-mounted designs and spherical or top-mounted designs and spherical or oblong for side-mounted designs. Small-oblong for side-mounted designs. Small-diameter floats see use in higher density diameter floats see use in higher density materials. materials.

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Bubblers: Bubblers: The air bubbler is another The air bubbler is another pressure-type level sensor where you pressure-type level sensor where you install a dip tube in a tank with its open install a dip tube in a tank with its open end a few inches from the bottom. A fluid end a few inches from the bottom. A fluid forces itself through the tube; when the forces itself through the tube; when the fluid bubbles escape from the open end, fluid bubbles escape from the open end, the pressure in the tube equals the the pressure in the tube equals the hydrostatic head of the liquid. As liquid hydrostatic head of the liquid. As liquid level (head) varies, the pressure in the level (head) varies, the pressure in the dip tube changes correspondingly.. dip tube changes correspondingly..

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Ultrasonic Level MeasurementUltrasonic Level Measurement

Ultrasonic level sensors measure the time Ultrasonic level sensors measure the time required for sound waves to travel required for sound waves to travel through material. Ultrasonic sound waves through material. Ultrasonic sound waves generally have frequencies above 20 generally have frequencies above 20 kiloHertz. Ultrasonic instruments operate kiloHertz. Ultrasonic instruments operate at frequencies inaudible to the human ear at frequencies inaudible to the human ear and at extremely low power levels, and at extremely low power levels, normally a few thousandths of a watt. The normally a few thousandths of a watt. The velocity of a sound wave is a function of velocity of a sound wave is a function of the type of wave transmitted and the the type of wave transmitted and the density of the medium in which it travels.density of the medium in which it travels.

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Ultrasonic Level MeasurementUltrasonic Level Measurement

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Pressure-typePressure-type instruments: DP CELLinstruments: DP CELL

Another common example is closed-tank Another common example is closed-tank level measurement. If the pressure in the level measurement. If the pressure in the closed tank changes, an equal force closed tank changes, an equal force applies to both sides of the differential applies to both sides of the differential pressure (dP) transmitter. Because the dP pressure (dP) transmitter. Because the dP cell responds only to changes in cell responds only to changes in differential pressure, a change in static differential pressure, a change in static pressure on the liquid surface will not pressure on the liquid surface will not change the output of the transmitter. change the output of the transmitter. Thus, the dP cell responds only to Thus, the dP cell responds only to changes in liquid level when the specific changes in liquid level when the specific gravity of the liquid is constant.gravity of the liquid is constant.

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The Principle of the Differential PressureThe Principle of the Differential Pressure

Small and moderate pressure differences Small and moderate pressure differences are often measured by using a device are often measured by using a device know as a know as a MANOMETERMANOMETER, which mainly , which mainly consists of a glass or plastic U-tube consists of a glass or plastic U-tube containing a fluid such as mercury, water, containing a fluid such as mercury, water, alcohol, or oil.alcohol, or oil.

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The Principle of the Differential PressureThe Principle of the Differential Pressure

AnalysisAnalysis PP22 = P = P11

APAP1 1 = AP= APatmatm + W + W W = mg = ρVg = ρAghW = mg = ρVg = ρAgh PP11 = P = Patmatm + ρgh (kPa) + ρgh (kPa)

La pressure difference can be expressed as:La pressure difference can be expressed as: ΔΔP = PP = P11 – P – Patmatm = ρgh (kPa) = ρgh (kPa) h = h = ΔΔP/(ρg) = P/(ρg) =

[(kgm/s[(kgm/s22)/m)/m22]/[(kg/m]/[(kg/m33)(m/s)(m/s22)]= m)]= m

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DP Cell SystemDP Cell System

In the DP Cell System, the pressure is In the DP Cell System, the pressure is transformed by a system of data transformed by a system of data acquisition (LABVIEW) and converted in acquisition (LABVIEW) and converted in VoltsVolts

The expression for this is a lineal The expression for this is a lineal expression:expression:

Where Where aa and and bb are calculated by the are calculated by the Least Least Squared MethodSquared Method

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ba(V) h ba(V) h


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ka(V) h ka(V) h

Laboratory: Measurement of Level in a tankLaboratory: Measurement of Level in a tank

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Table of DataTable of Data

Setup the systemSetup the system Take the data discharging the tankTake the data discharging the tank

bmxy

## Height Height (m)(m)

Voltage (V) Voltage (V) Group 1Group 1

Voltage (V) Voltage (V) Group NGroup N

AverageAverageVoltage (V)Voltage (V)

1 30

2 28

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mecn 4600 inter - bayamon lecture 11111111 mechanical measurement and instrumentation mecn 4600...

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