In The Name of Allah The Most Beneficent The Most Merciful 1

Engr. Ijlal Haider 2 ECE 2161: Instrumentation & Measurements Lecture: Spatial Variables Measurements

Outline 3 Spatial Variables Position Measurement Acceleration Measurement Velocity Measurement Level Measurement

Introduction 4 Spatial Variables relating to the position, area and size of things (Cambridge Dictionary)

Level Measurements 5 Single point sensing actual level of the material is detected when it reaches a predetermined level, so that the appropriate action can be taken to prevent overflowing or to refill the container. Continuous level sensing level of the liquid is measured on an uninterrupted basis. In this case the level of the material will be constantly monitored and hence, the volume can be calculated if the cross-sectional area of the container is known.

6 Direct Measurement of Level Indirect Measurement of Level

Level Sensing 7 Sight Glass

8 Floats

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10 Probes Conductive Capacitive Ultrasonic

11 Conductive Probes for set level detection

12 Capacitive probes for continuous level

13 Ultrasonic Probes for set level and continuous level detection

14 Radiation Attenuation

15 Bubbler Device

16 Paddle Wheel

17 Load Cells

Important Relationships for Indirect Sensing of Level 18 Pressure increases as the depth increases in a fluid.

19 The weight of a container can be used to calculate the level of the material in the container. The volume V of the material in the container is given by where r is the radius of the container and d is the depth of the material.

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Position Measurement 21 Many Industrial process require linear and rotational position and distance measurements Common applications Robots Manufacturing Conveyer Belts location and position of objects on a conveyor system Rolling Mills orientation of steel plates in a rolling mill Location and position of work piece in automatic milling operations

22 Linear position is the distance measured with respect to a reference point. Angular position is a measurement of the change in position of a point about a fixed axis measured in degrees or radians, where one complete rotation is 360° or 2 pi radians.

23 Absolute position Incremental position

24 Potentiometers Linear Variable Differential Transformer Hall Effect Sensors Magneto resistive Sensors Magnetostrictive Sensors Laser Interference Sensor Ultrasonic, IR and Microwave Optical Encoders Resolvers Synchros

Resistive Displacement Senors 25 “Potentiometer” or “Pots” Convenient way to convert distance into electrical variable The wiper or slider arm of a linear potentiometer can be mechanically connected to the moving section of a sensor Suffer from mechanical wear and tear

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LVDT 28 Consists of a single primary winding positioned between two identical secondary windings The primary winding is energized by a high-frequency 50 Hz to 20 kHz ac voltage. The two secondary windings are made identical by having an equal number of turns and similar geometry. They are connected in series opposition so that the induced output voltages oppose each other

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Magnetostrictive 30

Velocity and Acceleration 31 Controlling the speed at which metal stock is fed into a machine tool. Measuring the approach speed of a robotic tool onto its target. Monitoring the speed of a generator in an electric power station. An airport radar system measuring the speed of an approaching aircraft using the Doppler effect. Measuring an automobile’s wheel speed in order to provide feedback to an antilock brake system.

Acceleration Measurements 32 Acceleration is measured by accelerometers as an important parameter for general-purpose absolute motion measurements, and vibration and shock sensing.

Piezoelectric 33 A voltage is generated across the crystal when stressed. A piezoelectric crystal is spring-loaded with a test mass in contact with the crystal. When exposed to an acceleration, the test mass stresses the crystal by a force (F = ma), resulting in a voltage generated across the crystal. A measure of this voltage is then a measure of the acceleration. Output levels are typically in the millivolt range.

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Differential Capacitance 35 Differential-capacitance accelerometers are based on the principle of change of capacitance in proportion to applied acceleration. They come in different shapes and sizes. In one type, the seismic mass of the accelerometer is made as the movable element of an electrical oscillator. The seismic mass is supported by a resilient parallel-motion beam arrangement from the base. The system is characterized to have a certain de fi ned nominal frequency when undisturbed. If the instrument is accelerated, the frequency varies above and below the nominal value, depending on the direction of acceleration.

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Seismic Accelerometer 37 Potentiometric

Seismic Accelerometers 38 Strain Gauge

Velocity Measurement 39 The linear velocity of an object, or more correctly a particle, is defined as the time rate of change of position of the object. Vector quantity, meaning it has a direction as well as a magnitude, and the direction is associated with the direction of the change in position. The magnitude of velocity is called the speed (or pace), and it quantifies how fast an object is moving. The rotational velocity (or angular velocity) of an object is defined as the time rate of change of angular position, and it is a measure of how fast an object is turning.

40 There are not many instruments available for velocity measurements. Velocity is often obtained by differentiation of displacement or integration of acceleration.

Linear Velocity Transducers 41 Commonly called LVT’s based on a linear generator. When a coil cuts the magnetic field lines around a magnet, a voltage is induced in the coil, and this voltage is dependent on the following relation: e BLV where e= induced voltage B= magnetic field strength L= length of wire in the coil V= speed of the coil relative to the magnet.

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Light Interference Method 43 A beam of monochromatic light is split into two beams. One beam is directed onto a stationary mirror. The other beam is directed onto a moving target. The observer sees the superposition of the two beams. As the mirror moves in one direction, summation of the waves of the two beams will alternately reinforce and cancel each other. The amount of motion for one cycle of light intensity variation is the wavelength of the light being used. The frequency of these light-to-dark transitions is proportional to the velocity of the moving target.

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45 “All the effects of Nature are only the mathematical consequences of a small number of immutable laws.” ― Pierre-Simon Laplace ( )

Thank You! 46