BioE 408 Biomeasurements PDF

(✿◡‿◡) BioE 408 Biomeasurements Assoc. Prof Angelica A. Macalalad | Tue, 7:00 - 10:00 / ICL; Thu 7:00 - 10:00 / HEB 302 (PB) | A.Y. 2024-2025 ✿ COLOR PALETTE ✿ BEFORE measurement...

(✿◡‿◡) BioE 408 Biomeasurements Assoc. Prof Angelica A. Macalalad | Tue, 7:00 - 10:00 / ICL; Thu 7:00 - 10:00 / HEB 302 (PB) | A.Y. 2024-2025 ✿ COLOR PALETTE ✿ BEFORE measurement ➔ Procedure of measurement: Identified the parameter or variable to be measured, how to ✿ Important Note ✿ record the result This file is intended for personal use only. ➔ Characteristics of parameter: Should know the Redistribution, resale, or unauthorized sharing is parameter that to be measured; ac, dc, frequency strictly prohibited. Thank you for understanding! or etc. ➔ Quality: Time and cost of equipment, the Concepts of Measurement instrument ability, the measurement knowledge and suitable result I. Measurements ➔ Instrument: Choose a suitable equipment; A. Basic reqs for meaningful measurements multimeter, voltmeter, oscilloscope or etc. B. BEFORE measurement C. DURING measurement DURING measurement D. AFTER measurement E. Measurement System Design ➔ Quality: Make sure the chosen instrument is the F. Basic Units and Derived Units best, the right position when taken, the G. Standards frequency of measurement. H. Two major functions of all branch of ➔ Safety first: Electric shock, overload effect, engineering limitation of instrument. II. Methods of Measurement ➔ Sampling: See the changing of parameter during A. Direct Methods measurement, which value should be taken B. Indirect Methods when the parameter keeps changing. Take C. Measurement Systems enough samples and it is accepted. III. Evolution of Instruments AFTER measurement A. Classification Of Instruments B. Types of measuring instruments ➔ Every data recorded must be analyzed, statically, C. Functions of instrument and measuring mathematically and the result must be system accurately and completed. D. Application of measurement systems Measurement System Design E. Types Of Instrumentation System F. Elements of Generalized Measurement ➔ A unit is a particular physical quantity, defined System and adopted by convention, with which other G. Functional Elements of an Instrumentation particular quantities of the same kind are System compared to express their value. H. Static Characteristics Of Instruments And ➔ The general unit of a physical quantity is defined Measurement Systems as its dimension I. Dynamic Characteristics of Measurement Basic Units and Derived Units System J. Errors in Measurement ➔ A unit system can be developed by choosing, for K. Arithmetic Mean each basic dimension of the system, a specific L. Deviation unit. Such a unit is called a basic unit. The M. Standard Deviation corresponding physical quantity is called a basic N. Variance quantity. O. Probable Error ➔ All units that are not basic are called derived P. Calibration units. Q. Standard Standards I Measurements ➔ The international system of units (SI) is the internationally agreed on system of units for ➔ Comparison between standard and what we expressing the values of physical quantities. want to measure (measurand) ➔ Two quantities are compared and the result is expressed in numerical values ➔ Quantity is a quantifiable or assignable property ascribed to phenomena, bodies, or substances Basic reqs for meaningful measurements ➔ The standard used for comparison purposes must be accurately defined and should be commonly accepted. ➔ The apparatus used and the method adopted must be provable (verifiable) Fenilla Kim R. Orense – BioE 3101 | 1 (✿◡‿◡) BioE 408 Biomeasurements (4 units) simple multiple measurements measurements Significant (formulas, Mathematical Little to none equations, involvement relationships) Measurement Systems ➔ Measurement involves the use of instruments as a physical means of determining quantities or variables. ➔ Because of modular nature of the elements within it, it is common to refer the measuring instrument as a MEASUREMENT SYSTEM 1. Measured Variable (Measurand): Physical quantity being measured (e.g.,temperature,pressure, force,...) 2. Sensor: Detects or senses the measurand and converts it into a corresponding signal, usually electrical 3. Variable Conversion Element: The signal generated by the sensor may need to be converted to a different form or modified (such as changing a mechanical signal into an electrical one). This block represents the element responsible for such conversions 4. Signal processing: After conversion, the signal Two major functions of all branch of engineering might need to be processed to improve accuracy or Design of equipment and processes make it easier to interpret, This could involve Proper Operation and maintenance of equipment and amplifying the signal, filtering out noise, or digitizing processes. an analog signal 5. Output Measurement: Once the signal has been processed, it becomes the output measurement II Methods of Measurement that can be used. Sometimes this measurement is transmitted to a remote location Direct Methods 6. Signal transmission: If the processed signal is ➔ the unknown quantity (called the measurand) is being sent to a remote point for further use or directly compared against a standard. display, this block handles the transmission. The transmission might involve sending the signal Indirect Methods through wired or wireless means. ➔ Measurements by direct methods are not always 7. Use of measurement at remote point: If the possible, feasible and practicable. In engineering measurement is transmitted, this is where it is used applications measurement systems are used at a remote point. This could be for controlling a which require the need of indirect methods for system, logging data, or further analysis measurement purposes. 8. Signal presentation or recording: final processed signal is displayed or recorded for users. It can be Aspect Direct Method Indirect Method shown on a screen, shart, or other output devices Measures related 9. Output display/recording: The last stem is to actual Measures the process quantities and display or recording of the measured value, which quantity directly calculates the value allows the user to read, observed or store the data Ruler for length, Using trigonometry for examples thermometer for height, using Ohm’s law temperature for resistance III Evolution of Instruments Single-purpose Multiple instruments or 1. Mechanical: These are very reliable for static and instruments stable conditions. But their disadvantage is that instruments calculations needed they are unable to respond rapidly to measurements Generally more Accuracy depends on accuracy of dynamic and transient conditions. accurate for the precision of FKRO – BioE 3101 | 2 (✿◡‿◡) BioE 408 Biomeasurements (4 units) 2. Electrical: It is faster than mechanical, indicating Deflection Type Null Type the output is faster than mechanical methods. But it Feature Instruments Instruments depends on the mechanical movement of the Measures by meters. The response is 0.5 to 24 seconds. Measures the balancing the 3. Electronic: more reliable than other systems. It uses quantity based on Working unknown quantity semiconductor devices and weak signal can also be deflection or Principle with a known detected movement of a reference until null pointer. (zero) is achieved. Classification of Instruments Moderate accuracy, High accuracy ➔ Absolute: gives the magnitude of quantity under affected by because measurement terms of physical constants of the Accuracy mechanical factors measurement instrument like friction and depends on achieving ➔ Secondary: calibrated by comparison with temperature. a zero deflection. absolute instruments which have already been Quick and provides Slower, requires time calibrated. Response continuous, to achieve balance, Time real-time readings. but more precise. Types of measuring instruments More complex, may ➔ Deflection Type Instruments Simple to operate Complexity require skilled ○ The deflection method is one possible and read. operation mode of operation for a measuring Analog Ammeter, Wheatstone Bridge, instrument. Examples Pressure Gauge, Potentiometer, ○ A deflection instrument uses the deflection Spring Balance. Balance Scale. method for measurement. Used for precise and ○ The instrument is influenced by the Used for quick, sensitive measurand, causing a proportional Application continuous measurements, response within the instrument. measurements especially in ○ In typical operation, the measurand acts calibration. directly on a prime element or primary Requires adjustments circuit, converting its information into a Easy to use, read, Ease of Use and balancing, often detectable form. and understand. more technical. ○ The name comes from the physical Limited by deflection of a prime element linked to an High precision as no mechanical parts output scale (e.g., pointer or readout). Precision mechanical and external ○ The deflection of the prime element deflection is involved. factors. corresponds to the deflection of the output Generally less More expensive and scale. Cost expensive and specialized for ○ The magnitude of deflection is designed to widely available. precision work be proportional to the value of the measurand. Functions of instrument and measuring system ➔ Indicating Function ○ includes supplying information concerning the variable quantity under measurement. Several types of methods could be employed in the instruments and systems for this purpose. ○ Most of the time, this information is obtained as the deflection of a pointer of a measuring instrument. ○ A null instrument uses the null method for ➔ Recording Function measurement. ○ In many cases the instrument makes a ○ The instrument exerts an influence on the written record, usually on paper, of the value measured system to oppose the effect of of the quantity under measurement against the measurand. time or against some other variable. ○ The influence and the measurand are ○ This is a recording function performed by balanced until they are equal but opposite in the instrument. For example, a temperature value. indicator recorder in the HTST pasteurizer ○ The measurement is obtained when a gives the instantaneous temperatures on a balance or null state is achieved. strip chart recorder. ➔ Signal Processing: performed to process and modify the measured signal to facilitate recording / control. ➔ Controlling Function ○ one of the most important functions, especially in the food processing industries FKRO – BioE 3101 | 3 (✿◡‿◡) BioE 408 Biomeasurements (4 units) where the processing operations are Uses advanced required to be precisely controlled. technology like Simpler, typically ○ In this case, the information is used by the microprocessors or analog, without Technology instrument or the systems to control the embedded systems built-in processing original measured variable or quantity. for real-time capabilities. processing. Application of measurement systems Higher accuracy due Accuracy Potential for human ➔ Monitoring a Process/Operation to automatic and error in interpreting ○ simply indicate the value or condition of processing and Efficiency raw data. parameters under study and these readings reduced human error. do not provide any control operation. Generally more Less expensive, ○ For example, a speedometer in a car expensive due to Cost simpler to build and indicates the speed of the car at a given built-in processing maintain. moment, an ammeter or a voltmeter and display systems. indicates the value of current or voltage being monitored at a particular instant. Elements of Generalized Measurement System ○ Similarly, water and electric energy meters ➔ Primary sensing element: The quantity under installed in homes and industries provide measurement makes its first contact with the the information on the commodity used so primary sensing element of a measurement that its cost could be computed and system realized from the user. ➔ Variable conversion element: It converts the ➔ Control a Process/Operation output of the primary sensing element into ○ Measurement of a variable and its control suitable form to preserve the 35 information are closely associated. content of the original signal. ○ To control a process variable, e.g., ➔ Data presentation element: The information temperature, pressure or humidity etc., the about the quantity under measurement has to be prerequisite is that it is accurately conveyed to the personnel handling the measured at any given instant and at the instrument or the system for monitoring, control desired location. Same is true for all other or analysis purposes. process parameters such as position, level, velocity and flow, etc. and the Functional Elements of an Instrumentation System servo-systems for these parameters. ➔ Experimental Engineering Analysis ○ Carried out to find out solutions to engineering problems. These problems may be theoretical designs or practical analysis. The exact experimental method for engineering analysis will depend upon the nature of the problem. Types of Instrumentation System Static Characteristics of Instruments and ➔ Intelligent Instrumentation: data has been Measurement Systems refined for the purpose of presentation ➔ Application involving measurement of quantity ➔ Dumb Instrumentation: data must be processed that is either constant or varies slowly with time by the observer is known as static. Intelligent Dumb ➔ Accuracy: the closeness of a measured value to Feature Instrumentation Instrumentation the true or accepted value. It indicates how Data is presented correctly an instrument measures the actual Data is processed, raw, requiring quantity. Data refined, and manual processing ○ Example: If a thermometer reads 100°C Processing presented in a clear or interpretation by when the actual temperature is 100°C, it is format. the observer accurate. Minimal effort ○ Importance: High accuracy ensures reliable required from the Requires the user to and trustworthy results in measurements. User Effort user; the instrument manually interpret ➔ Drift: gradual change in a measuring does most of the or process the data. instrument's output over time when the input is work held constant. Drift can occur due to changes in Analog meters, environmental conditions, wear and tear, or Digital multimeters, mercury aging of the instrument components. Examples smart thermostats, thermometers, ○ Example: A scale that shows a slight weather stations. spring balances. increase in weight reading over time even if More effort is no object is placed on it. Easy to use with ○ Types: Zero drift, span drift, and zonal drift required, as the user Ease of Use direct, ready-to-use are common forms of drift. must calculate or outputs. interpret the results. FKRO – BioE 3101 | 4 (✿◡‿◡) BioE 408 Biomeasurements (4 units) ○ Importance: Drift affects the stability and Time delay: The response of the long-term reliability of an instrument, measurement system begins after a requiring recalibration to maintain accuracy. dead zone after the application of the ➔ Dead Zone: range of input in which a change in input. input does not result in any change in the output. ➔ Fidelity: the degree to which a measurement It represents the insensitivity of an instrument to system indicates changes in the measured small changes in the measured quantity. quantity without any dynamic error ○ Example: A pressure gauge that does not ➔ Dynamic error: It is the difference between the show any reading change until the pressure true value of the quantity changing with time and exceeds 5 psi, even though small pressure the value indicated measurement system if by variations exist. no the static error is assumed. It is also called ○ Importance: Instruments with a large dead measurement error. It is one of the dynamic zone may not detect small changes in the characteristics. measured quantity, leading to loss of precision in certain applications. Errors in Measurement ➔ Static Error: difference between the true value of ➔ Limiting Errors (Guarantee Errors) the measured quantity and the value indicated ➔ Known Error by the instrument under static (steady) conditions. It is essentially the inaccuracy of the instrument when the quantity being measured does not change over time. ○ Example: If the actual voltage is 50V and the voltmeter shows 48V, the static error is 2V. ○ Importance: Static errors give insight into the baseline inaccuracies present in an instrument's measurement. They can be corrected through calibration. ➔ Sensitivity: ability of an instrument to detect ➔ Gross Error small changes or differences in the measured ○ Human Mistakes in reading , recording and quantity. It is the ratio of the change in output to calculating measurement results. the change in input. ○ The experimenter may grossly misread the ○ Example: A high-sensitivity thermometer scale. detects even minute changes in ○ E.g.: Due to oversight instead of 21.5°C, temperature, while a low-sensitivity one they may read as 31.5°C might not show small temperature ○ They may transpose the reading while fluctuations. recording (like reading 25.8°C and record as ○ Importance: Instruments with high 28.5°C) sensitivity are preferred in applications ➔ Systematic Errors where precision is critical, such as in ○ INSTRUMENTAL ERROR: These errors arise laboratory measurements or control due to 3 reasons: systems. Due to inherent shortcomings in the ➔ Reproducibility: ability of an instrument to give instrument consistent results when the same measurement Due to misuse of the instrument is repeated under identical conditions over time. Due to loading effects of the instrument It reflects how well an instrument maintains its ○ ENVIRONMENTAL ERROR: These errors are performance. due to conditions external to the measuring ○ Example: If a balance scale gives the same device. These may be effects of reading every time a 10-gram weight is temperature, pressure, humidity, dust or of measured, it is highly reproducible. external electrostatic or magnetic field. ○ Importance: Reproducibility ensures ○ OBSERVATIONAL ERROR: The error on reliability in measurements, which is crucial account of parallax is the observational in research, manufacturing, and quality error. control processes. ➔ Residual error: also known as residual error. These errors are due to a multitude of small Dynamic Characteristics of Measurement System factors which change or fluctuate from one ➔ Speed of response: rapidity with which a measurement to another. The happenings or measurement system responds to changes in disturbances about which we are unaware are measured quantity. It is one of the dynamic lumped together and called “Random” or characteristics of a measurement system. “Residual”. Hence the errors caused by these are ➔ Measuring lag: retardation delay in the response called random or residual errors. of a measurement system to changes in the Arithmetic Mean measured quantity. ➔ often referred to simply as the mean or average ○ 2 types: ➔ a measure of central tendency that represents Retardation type: The response begins the sum of all the values in a data set, divided by immediately after a change in measured the total number of values. quantity has occurred. FKRO – BioE 3101 | 5 (✿◡‿◡) BioE 408 Biomeasurements (4 units) ➔ gives a single value that summarizes the overall 4. Sum the squared deviations. level of the data. 5. Divide the sum by N (for population) or n − 1 Arithmetic Mean (for sample) to obtain the variance. 𝑛 ∑ 𝑥𝑖 𝑥̄ = 𝑥1+𝑥2+𝑥3+... +𝑥𝑛 or 𝑥̄ = 𝑖=1 Probable Error 𝑛 𝑛 Where: ➔ statistical measure used to express the reliability - 𝑥1 + 𝑥2 + 𝑥3 +... + 𝑥𝑛 = individual values in or precision of a set of measurements. ➔ indicates the range within which half of the the data set observed errors are expected to lie. - n = total number of values ➔ gives an estimate of how much a particular 𝑛 - ∑ = sum of all values measurement might deviate from the true or 𝑖=1 expected value, with a 50% probability. Deviation ➔ departure of the observed reading from the arithmetic mean of the group of readings. ➔ how far a data point is from a central value, typically the mean (arithmetic mean) of the data set. Deviation 𝐷 = 𝑥𝑖 − 𝑥̄ Where: - 𝑥𝑖 = individual data point - 𝑥̄ = arithmetic mean of the data set Standard Deviation ➔ The SD of an infinite number of data is defined as the square root of the sum of the individual deviations squared / the number of readings. Calibration ➔ Calibration of all instruments is important since it affords the opportunity to check the instruments against a known standard and subsequently to find errors and accuracy. Variance ➔ Calibration Procedure involve a comparison of the particular instrument with either ➔ measure of how much the values in a data set ○ Primary standard differ from the mean (or average) of the data set. ○ secondary standard with a higher accuracy ➔ quantifies the spread or dispersion of the data than the instrument to be calibrated points. ○ an instrument of known accuracy. ➔ A higher variance indicates that the data points are more spread out from the mean, while a Standards lower variance indicates they are closer to the mean. ➔ physical representation of a unit of Variance measurement. The term ‘standard’ is applied to a 𝑛 piece of equipment having a known measure of 2 𝑖=1 ( ∑ 𝑥𝑖−𝑥̄ )2 physical quantity 𝑠 = 𝑛−1 Where: Types of Standards 2 - 𝑠 = sample variance International - 𝑥𝑖 = individual data points defined based on international agreement Standards - x̄ = sample mean Primary maintained by national standards - 𝑛 = number of data points in the sample Standards laboratories - 𝑛 − 1 = degrees of freedom, used to correct Secondary used by industrial measurement for bias in estimating population variance Standards laboratories from a sample ➔ Steps to calculate variance 1. Calculate mean (μ for population or x̄ for sample). 2. Find the deviation of each data point from the mean (𝑥𝑖 – μ). 3. Square the deviations 𝑥𝑖 − 𝑥̄. ( )2 FKRO – BioE 3101 | 6 (✿◡‿◡) BioE 408 Biomeasurements (4 units) TRANSDUCERS visual, auditory, or other sensory feedback, providing the user with the needed information, I. Basic Sensors and Principles such as a heart rate readout or an alarm A. How It Works Together indicating an abnormal condition. II. Transducer ➔ Control and Feedback: This block represents A. Overall System Flow feedback mechanisms that help the system B. Introduction of Transducers self-regulate. For example, if the signal exceeds C. Block Diagram of Transducers a certain threshold, the system may provide D. Advantage of Electrical Transducers feedback to adjust settings, apply calibration, or E. Characteristics of Transducers trigger an alarm. F. Transducers Selection Factors ➔ Calibration Signal: Calibration ensures that the G. Classification of Transducers system is providing accurate measurements. H. Active Transducers This signal might come from an internal or I. Piezoelectric Transducer external source to periodically adjust and correct J. Classification of Active Transducers for sensor drift or other inaccuracies. K. Passive Transducers ➔ Power Source: The system needs a source of L. Classification of Passive Transducers power to operate, whether it’s a battery, external M. Primary and Secondary Transducers electrical supply, or any other form of energy that III. Classification of Transducers powers the sensing and processing elements. A. According to Transduction Principle ➔ Data Storage: This component allows the B. Transducer and Inverse Transducer system to store the processed data for later C. Passive Transducers retrieval and analysis. This is particularly D. Thermocouples important in long-term monitoring systems, like E. Variable-Inductance Transducers wearable health monitors, where trends need to F. Variable-Reluctance Inductive Transducers be analyzed over time. G. Linear Variable Differential Trans. (LVDT) ➔ Data Transmission: The system may transmit data wirelessly or through wired connections to a central monitoring station, computer, or I Basic Sensors and Principles smartphone for real-time analysis or remote monitoring. ➔ Radiation, Electric Current, or Other Applied Energy: Some sensors require an external stimulus or applied energy to function, such as light (in pulse oximeters), electric current (in impedance measurements), or even radiation (in imaging techniques). How It Works Together ➔ Measurand: physical quantity or parameter ➔ The measurand (e.g., body temperature or heart being measured, such as heart rate, temperature, rate) is detected by the primary sensing element, blood pressure, or any other physiological signal. which converts it into an electrical signal. ➔ Primary Sensing Element: responsible for ➔ The variable conversion element processes the detecting the measurand and converting it into a signal, which is then refined through signal signal that can be interpreted. It is often a processing. transducer, such as a thermocouple for ➔ The final data is displayed for the user and may temperature or an electrode for electrical signals also be transmitted or stored for further like ECG. analysis. ➔ Variable Conversion Element: The output from ➔ The feedback system may adjust parameters to the primary sensing element often needs to be ensure accuracy or safety, and calibration converted into a more usable form. This element ensures long-term reliability. may amplify, filter, or condition the signal in some way. For example, it may convert a raw analog signal to a digital one. II Transducer ➔ Signal Processing: At this stage, the processed signal undergoes further refinement, such as noise reduction, scaling, or more complex transformations. It could also involve algorithms that interpret the raw data for easier understanding. ➔ Output Display:where the processed signal is visualized or presented in a way that is useful to the user. It could be a graphical display, ➔ This diagram outlines the fundamental building numerical readout, or some other form of blocks of a control or embedded system, where perceptible output (e.g., a sound or alarm). sensor data is processed, decisions are made by ➔ Perceptible Output: The final output, which the control logic, and actuators are triggered to user perceives. This could be in the form of perform specific tasks. The system also has FKRO – BioE 3101 | 7 (✿◡‿◡) BioE 408 Biomeasurements (4 units) user interaction and requires a power source to ➔ The user can interact with the system through operate efficiently. the I/O channel, providing input or receiving ➔ Sensors/Actuators feedback (output). ○ Sensors: measure physical quantities (e.g., ➔ Power supply provides the necessary energy for temperature, pressure, or motion) and all the components to operate continuously or at convert them into signals, usually electrical, required intervals. that can be processed by the system. ○ Actuators: take signals from the system Introduction of Transducers and convert them into physical actions (e.g., ➔ A transducer is a device that convert one form of motors, relays, or valves). energy to other form. It converts the measurand ○ In the diagram, sensor & actuator are in the to a usable electrical signal. same block, meaning the system can both ➔ a device that is capable of converting the sense & act based on the data it collects. physical quantity into a proportional electrical ➔ Interface Circuits quantity such as voltage or current. ○ The signals from sensors/actuators are typically in a form that is not directly usable by the control circuits. Therefore, interface circuits are needed to convert, amplify, or condition these signals. BLock Diagram of Transducers ○ For instance, if the sensor output is analog, ➔ Transducers contain two parts that are closely it might need to be converted into a digital related to each other i.e. the sensing element signal through an Analog-to-Digital and transduction element. Converter (ADC), or an actuator may need ➔ The sensing element is called the sensor. It is a signal amplification. device producing measurable response to ➔ Control and Processing Circuits change in physical conditions. ○ performs the computational tasks and logic ➔ The transduction element converts the sensor control. It can include a microcontroller, output to suitable electrical form. microprocessor, or any digital logic circuitry. ○ These circuits process the incoming sensor data, execute the control algorithms, and determine what actions need to be taken by the actuators. ○ The system also may store or analyze the Advantage of Electrical Transducers sensor data before making a decision. ➔ I/O Channel/User ➔ Power requirement is very low for controlling the ○ represents interaction with the external electrical or electronic systems environment/user. The user may provide ➔ Amplifier may be used to amplify the electrical input (buttons, dials, or a user interface), or signal according to requirement the system may output results or feedback ➔ Friction effect is minimized (display, alarms, or notifications). ➔ Mass-inertia effect s also minimized, because in ○ important for receiving external commands case of electrical or electronics signal the inertia /information & for providing the processed effect is due to the mass of electrons, which can information to a user for monitoring or be negligible control. ➔ Output can be indicated and recorded remotely ➔ Power Supply from the sensing element ○ The system needs a power source to operate, which can be a battery, external Characteristics of Transducers power source, or other forms of energy ➔ Ruggedness (e.g., solar power in remote applications). ➔ Linearity ○ supplies power to all other components, ➔ Repeatability including the sensors, actuators, and ➔ Accuracy control circuits. ➔ High stability and reliability ○ The power supply is also directly linked to ➔ Speed of response the sensors/actuators block, meaning these ➔ Sensitivity components need their own power to ➔ Small size function. Transducers Selection Factors Overall System Flow ➔ Operating Principle: The transducers are many ➔ The sensors collect data from the environment times selected on the basis of the operating and send it to the interface circuits. principle used by them. The operating principle ➔ The interface circuits process the raw sensor used may be resistive, inductive, capacitive , data and pass it to the control and processing optoelectronic, piezo electric etc. circuits. ➔ Sensitivity: The transducer must be sensitive ➔ Based on the processed data, the control system enough to produce detectable output. can make decisions and send commands to the actuators to take some action or perform a task. FKRO – BioE 3101 | 8 (✿◡‿◡) BioE 408 Biomeasurements (4 units) ➔ Operating Range: The transducer should stress. Similarly, if an electrical field is applied to maintain the range requirement and have a good these materials, they can physically deform, resolution over the entire range. generating mechanical movement. ➔ Accuracy: High accuracy is assured. ➔ Key Principles ➔ Cross sensitivity: It has to be taken into account ○ Direct Piezoelectric Effect: When when measuring mechanical quantities. There mechanical stress or pressure is applied to are situations where the actual quantity is being a piezoelectric material, it produces a measured in one plane and the transducer is proportional electrical charge. subjected to variation in another plane. ○ Inverse Piezoelectric Effect: When an ➔ Errors: The transducer should maintain the electric field is applied to the piezoelectric expected input- output relationship as described material, it causes a mechanical by the transfer function so as to avoid errors. deformation, producing physical movement ➔ Transient and frequency response: The or vibration. transducer should meet the desired time domain ➔ Structure: typically consists of a piezoelectric specification like peak overshoot, rise time, material (like quartz, lead zirconate titanate, or setting time and small dynamic error. barium titanate) sandwiched between two metal ➔ Loading Effects: The transducer should have a electrodes. high input impedance and low output impedance ○ When pressure or mechanical force is to avoid loading effects. applied, the material deforms, and an ➔ Environmental Compatibility: It should be electrical signal is generated. When an assured that the transducer selected to work electrical signal is applied, the material under specified environmental conditions deforms mechanically. maintains its input- output relationship and does ➔ Applications: used in various fields because they not break down. can detect & generate vibrations, pressure ➔ Insensitivity to unwanted signals: The changes, or electric fields. Some common uses: transducer should be minimally sensitive to ○ Ultrasound Devices: Piezoelectric unwanted signals and highly sensitive to desired transducers are used in medical ultrasound signals. equipment to generate high-frequency sound waves. These sound waves penetrate Classification of Transducers the body and reflect off tissues, allowing the creation of images of internal organs or detecting blood flow. ○ Microphones: converts sound pressure (mechanical vibration) into an electrical signal, which can be amplified and recorded. ○ Vibration Sensors: used in devices to measure vibrations or forces in industrial equipment for condition monitoring and ➔ Transducers may be classified according to their predictive maintenance. application, method of energy conversion, nature ○ Accelerometers: used to measure changes of the output signal, and so on. in acceleration, often found in applications like automotive airbag systems, consumer Active Transducers electronics (smartphones, gaming ➔ These transducers do not need any external controllers), and industrial equipment. source of power for their operation. Therefore ○ Piezoelectric Igniters: In devices like gas they are also called as self generating type stoves or BBQ lighters, the mechanical transducers. force applied to the piezoelectric material ○ The active transducers are self generating generates a high voltage that creates a devices which operate under the energy spark to ignite the gas. conversion principle. ○ Sonar and Hydrophones: In sonar systems, ○ As the output of active transducers we get piezoelectric transducers generate sound an equivalent electrical output signal e.g. waves underwater and detect the reflected temperature or strain to electric potential, waves to measure distances or detect without any external source of energy being objects. Hydrophones are underwater used. microphones that detect sound waves using piezoelectric elements. Piezoelectric Transducer ○ Actuators: The inverse piezoelectric effect is used in actuators to generate precise ➔ device that converts mechanical energy (such as mechanical motion in response to electrical pressure, force, or vibration) into electrical signals. These actuators are used in energy or vice versa using the piezoelectric high-precision positioning systems, such as effect. The piezoelectric effect is a property of in microscopy and medical devices. certain materials, such as quartz, ceramics, and specific crystals, where they generate an electrical charge when subjected to mechanical FKRO – BioE 3101 | 9 (✿◡‿◡) BioE 408 Biomeasurements (4 units) Advantages Disadvantages ➔ The electrical device then converts this mechanical signal into a corresponding High Sensitivity: They can electrical signal. Such electrical devices are detect very small changes in Temperature known as secondary transducers. mechanical stress or vibrations. Sensitivity: Their ➔ Ref fig in which the diaphragm acts as primary Wide Frequency Range: performance can transducer. It converts pressure (the quantity to Piezoelectric transducers can degrade at extreme be measured) into displacement(the mechanical operate over a wide range of temperatures. signal). frequencies, making them Fragility: Piezoelectric ➔ The displacement is then converted into change suitable for high-frequency materials can be in resistance using strain gauge. Hence strain applications like ultrasound. brittle and break under gauge acts as the secondary transducer. Compact and Lightweight: excessive mechanical Piezoelectric transducers are stress. often small and can be III CLASSIFICATION OF TRANSDUCERS integrated into compact devices. According to Transduction Principle Classification of Active Transducers ➔ CAPACITIVE TRANSDUCER Passive Transducers ○ In capacitive transduction transducers the measurand is converted to a change in the ➔ These transducers need an external source of capacitance power for their operation. So they are not self ○ A typical capacitor consists of two parallel generating type transducers. plates of conducting material separated by ➔ A DC power supply or an audio frequency an electrical insulating material called a generator is used as an external power source. dielectric. The plates and the dielectric may ➔ These transducers produce the output signal in be either flattened or rolled. the form of variation in resistance, capacitance, ○ The purpose of the dielectric is to help the inductance or some other electrical parameter in two parallel plates maintain their stored response to the quantity to be measured. electrical charges. ○ The relationship between the capacitance Classification of Passive Transducers and the size of capacitor plate, amount of plate separation, and the dielectric is given by 𝐶 = ε0 ε𝑟 𝐴/𝑑 Where: - d = separation distance of plates (m) - C = capacitance (F, Farad) - ε0 = absolute permittivity of vacuum - εr = relative permittivity - A = effective (overlapping) area of capacitor plates (m2) ➔ ELECTROMAGNETIC TRANSDUCTION ○ In electromagnetic transduction, the measurand is converted Primary and Secondary Transducers to voltage induced in the ➔ Some transducers contain mechanical as well as conductor by change in electrical devices. The mechanical device the magnetic flux, in converts the physical quantity to be measured absence of excitation. into a mechanical signal. Such mechanical ○ The electromagnetic transducer are self devices are called generating active transducers the primary ○ The motion between a piece of magnet and transducers, an electromagnet is responsible for the because they deal change in flux with the physical quantity to be measured. FKRO – BioE 3101 | 10 (✿◡‿◡) BioE 408 Biomeasurements (4 units) 𝑅 = ρ𝐿/𝐴 Where: - R = resistance of conductor in Ω - L = length of conductor in m - A = cross sectional area of conductor in m2 - ρ = resistivity of conductor material in Ω-m. ➔ 4 type of resistive transducers ○ Potentiometers (POT) ○ Strain gauge ○ Thermistors ○ Resistance thermometer ➔ Potentiometers (POT) ○ used for voltage division. They consist of a resistive element provided with a sliding contact. The sliding contact - wiper. ○ The contact motion may be linear or ➔ INDUCTIVE TRANSDUCER: the rotational or combination of the two. The measurand is converted into a combinational potentiometers have their change in the self inductance of a resistive element in helix form and are single coil. It is achieved by called heliports. displacing the core of the coil ➔ Strain gauge that is attached to a mechanical ○ a passive, resistive transducer which sensing element. converts the mechanical elongation and ➔ PIEZO ELECTRIC INDUCTION: the measurand is compression into a resistance change. converted into a change in electrostatic ○ This change in resistance takes place due charge(q) or voltage(V) generated by crystals to variation in length and cross sectional when mechanically it is stressed as shown in fig. area of the gauge wire, when an external ➔ PHOTOVOLTAIC TRANSDUCTION: the force acts on it. measurand is converted to voltage generated TYPES OF STRAIN GAUGE when the junction between dissimilar material is Wire gauge illuminated as shown in fig. Unbonded ➔ use a wire stretched between two points in an insulating medium like air. The wires, typically made from copper, nickel, or alloys, are connected in a Wheatstone bridge for transducer applications. ➔ When preloaded, the strain and resistance of the four arms are equal, resulting in zero output voltage. ➔ Pressure causes a displacement that increases tension in two wires, raising their resistance, while reducing it in the other two, creating an imbalance in the bridge. This produces an output voltage proportional to the applied pressure. Bonded ➔ used for stress analysis & transducer ➔ PHOTO CONDUCTIVE TRANSDUCTION: the construction. measurand is converted to change in resistance ➔ Consists of a grid of fine resistance wire, of semiconductor material by the change in light cemented to a carrier (paper, bakelite, or teflon) incident on the material. for support. ➔ The grid is protected by a thin sheet to prevent Transducer and Inverse Transducer mechanical damage. ➔ TRANSDUCER: convert non electrical quantity to ➔ The carrier is bonded to the specimen with electrical quantity. adhesive for effective strain transfer. Parts: ➔ INVERSE TRANSDUCER: convert electrical ○ Base (carrier) materials: Various types, such quantity to a non electrical quantity as impregnated paper, used for room temperature applications. Passive Transducers ○ Adhesive: Ensures proper bonding between ➔ Resistive transducers the specimen and gauge, important for ○ resistance changes due to the change in accurate strain transfer. Should be some physical phenomenon. quick-drying and moisture-resistant. ○ The resistance of a metal conductor is expressed by a simple equation. FKRO – BioE 3101 | 11 (✿◡‿◡) BioE 408 Biomeasurements (4 units) Leads: Made from materials with low, Thermocouples stable resistivity and a low temperature ➔ See beck Effect coefficient of resistance. ○ When a pair of dissimilar metals are joined ○ Metal wire strain gauges have been at one end, and there is a temperature replaced by bonded metal foil strain difference between the joined ends and the gauges. open ends, thermal emf is generated, which ○ Metal foil strain gauges, made from the can be measured in the open ends. This same material as wire gauges, are used for forms the basis of thermocouples. general stress analysis and transducer applications. Foil type Semiconductor gauge ➔ Used in applications where a high gauge factor is desired. A high gauge factor means relatively higher change in resistance that can be measured with good accuracy. Variable-Inductance Transducers ➔ The resistance of the semiconductor gauge changes as strain is applied to it. The ➔ An inductive electromechanical transducer is a semiconductor gauge depends on their action transducer which converts the physical motion upon the piezo-resistive effect i.e. change in into the change in inductance. value of resistance due to change in resistivity. ➔ mainly used for displacement measurement & ➔ Silicon and germanium are used as resistive are of the self generating or the passive type. material for semiconductor gauges. The self generating inductive transducers use ➔ Resistance thermometer the basic generator principle i.e. the motion ○ Resistance of metal increases with between a conductor and magnetic field induces increases in temperature. Therefore metals a voltage in the conductor. are said to have a positive temperature ➔ The variable inductance transducers work on the coefficient of resistivity following principles. ○ This assembly is then placed at the tip of ○ Variation in self inductance probe ○ Variation in mutual inductance ○ This wire is in direct contact with the gas or liquid whose temperature is to be Variable Reluctance Inductive Transducers measured. ➔ Fig shows a variable ○ The resistance of the platinum wire reluctance inductive changes with the change in temperature of transducer. the gas or liquid ➔ As shown in fig the ○ This type of sensor have a positive coil is wound on the temperature coefficient of resistivity as they ferromagnetic iron. are made from metals they are also known The target and core as resistance temperature detector are not in direct ○ generally of probe type for immersion in a contact with each other. They are separated by medium whose temperature is to be an air gap. measured or controlled. ➔ The displacement has to be measured is applied ➔ Thermistors to the ferromagnetic core ○ contraction of the term “thermal resistor”. ➔ reluctance of the magnetic path is found by the ○ temperature dependent resistors. size of the air gap & self inductance of coil is: ○ made of semiconductor material which 2 2 have negative temperature coefficient of 𝐿 = 𝑁 / 𝑅 = 𝑁 / 𝑅𝑖 + 𝑅𝑎 resistivity i.e. their resistance decreases Where: with increase of temperature. - N = number of turns ○ widely used in application which involve - R = reluctance of coil measurement in the range of 0-60º - Ri = reluctance of iron path ○ composed of sintered mixture of metallic - Ra = reluctance of air gap oxides such as manganese, nickel, cobalt, copper, iron and uranium Linear Variable Differential Transformer (LVDT) ○ may be in the form of beads, rods & discs. ○ provides a large change in resistance for a ➔ An LVDT transducer comprises a coil for which small change in temperature. In some three coils are wound. cases the resistance of the thermistor at ➔ The primary coil is excited with an AC current, room temperature may decrease as much the secondary coils are wound such that when a as 6% for each 1ºC rise in temperature. ferrite core is in the central linear position, an equal voltage is induced into each coil. ➔ The secondary are connected in opposite directions so that in the central position the outputs of the secondary cancel each other out. FKRO – BioE 3101 | 12