Module 2 - Industrial Instrumentation and Automation

H330 Automotive Engineering MODULE 2 MICRO ELECTROMECHANICAL SYSTEM (MEMS) : ADVANTAGES AND APPLICATIONS, MEMS MICRO SENSORS AND ACTUATORS, MANUFACTURING PROCESS: BULK MICRO MACHINING AND SURFACE MICROMACHINING, MEMS ACCELEROMETERS VIRTUAL INSTRUMENTATION SYSTEM: ARCHITECTURE OF VIRTUAL INSTRUMENTS, VIRTUAL INSTRUMENTS AND TRADITIONAL INSTRUMENTS, CONCEPTS OF GRAPHICAL PROGRAMMING MICRO ELECTROMECHANICAL SYSTEM (MEMS) - A MEMS (micro-electromechanical system) is a miniature machine that has both mechanical and electronic components. - The physical dimension of a MEMS can range from several millimeters to less than one micrometer, a dimension many times smaller than the width of a human hair. - The label MEMS is used to describe both a category of micro mechatronic devices and the processes used when manufacturing them. - Some MEMS do not even have mechanical parts, yet they are classified as MEMS because they miniaturize structures used in conventional machinery, such as springs, channels, cavities, holes and membranes. - Because some MEMS devices convert a measured mechanical signal into an electrical or optical signal, they may also be referred to as transducers. 2 - In Japan, MEMS are more commonly known as micromachines, and in European countries, MEMS are more commonly referred to as microsystems technology (MST). - MEMS is an umbrella term for a wide range of microfabrication designs, methods and mechanisms that involves realizing moving mechanical parts at microscopic scale. - In a nutshell, MEMS is concerned with transforming the traditional bulky mechanical systems into miniature, better performing and highly mass producible alternatives, analogous to what the integrated circuit and semiconductor technologies have done to the electrical and electronics systems. Construction of MEMS - MEMS are composed of parts such as microsensors, microprocessors, micro actuators, units for data processing and parts that can interact with exterior pieces. - Unlike conventional mechatronic devices, MEMS are often manufactured with the same batch fabrication techniques used to create integrated circuits (ICs) and many commercial MEMS products are integrated and packaged together with ICs. - MEMS fabrication allows micro-sensors, which gather data, and micro-actuators, which convert energy into motion, to integrate on the same substrate. 3 - Although MEMS have a low per-device production cost, packaging can be a challenge. - Each MEMS must be packaged so that electrical or optical circuitry and other device components remain free from air and water contamination, while still being able to interact with the surrounding environment and accommodate motion Schematic representation of MEMS - MEMS are microscopic integrated devices that are a combination of electronics, electrical and mechanical elements, all working together for a single functional requirement using a technology called Microsystems Technology (MST). - The schematic representation of MEMS is shown in figure 4 Application of MEMS - MEMS are used in a wide range of sensors, actuators, generators, energy sources, biochemical and biomedical systems and oscillators. - Some examples of MEMS applications include: Sensors such as MEMS accelerometers, MEMS gyroscopes, MEMS pressure sensors, MEMS tilt sensors and other types of MEMS resonant sensors Actuators such as MEMS switches, micro-pumps, micro-levers and micro-grippers Generators and energy sources such as MEMS vibration energy harvesters, MEMS fuel cells and MEMS radioisotope power generators Biochemical and biomedical systems such as MEMS biosensors, lab-on-chips, and MEMS air microfluidic and particulate sensors MEMS oscillators for accurate time keeping and frequency control applications 5 Advantages of MEMS Extremely scalable in manufacturing, resulting in very low unit costs when mass produced MEMS sensors possess extremely high sensitivity MEMS switches and actuators can attain very high frequencies MEMS devices require very low power consumption MEMS can be readily integrated with microelectronics to achieve embedded mechatronic systems Scaling effects at microscopic levels can be leveraged to achieve designs and dynamic mechanisms otherwise not possible at macro-scales Also, MEMS has many other advantages, such as lightweight, high resolution, stable performance and ease of integration with other devices and systems. Disadvantages of MEMS Very expensive during the research and development stage for any new MEMS design or devices Very expensive upfront setup cost for fabrication cleanrooms and foundry facilities Fabrication and assembly unit costs can be very high for low quantities. Therefore, MEMS are not suitable for niche applications, unless cost is not an issue 6 Testing equipment to characterize the quality and performance can also be expensive Classification of MEMS - According to the operation of the designed chip, MEMS can be divided into different categories as shown in figure 7 - It can be used to execute the sensing for measuring, monitoring and detecting hazardous gases. - Another classification is using MEMS as action type device which act upon the body or with the body materials, like fluids or acting outside the body, such as devices used in drug delivery systems. - MEMS devices have been incorporated into four distinct categories based on the core application areas which include: fluidic, Radio frequency (RF), optical, and bio MEMS MEMS sensors & Actuators - Sensors & actuators designed & manufactured using MEMS technology are known as MEMS sensors & actuators - MEMS sensors and MEMS actuators are widely used for different applications - A MEMS sensor converts a physical quantity (motion, sound, light etc.) into an electrical signal - A MEMS actuator converts electrical signal into a physical quantity 8 MEMS actuators - An actuator is a control device that makes something move. - Actuators use input energy and release output energy in a controlled manner. - Mechanical actuators act upon something and move it with force or torque. - The process of micro movement is called micro actuation - MICRO ACTUATORS are light in weight , conformable and precision devices - There are many types of actuators. 1. Based on the type of output energy released 2. 3. Based on the way output energy is released Based on the input energy used 9 1. Based on the type of output energy released - Based on the output energy released, actuators are classified as below a) Mechanical actuators - These convert input energy into controlled mechanical energy in the form of motion, force, torque, oscillations, deformations etc. - Eg. MEMS motors, engines, pumps etc. b) Acoustic actuators - These actuators produce sound c) Optical actuators - These actuators produce light - Eg. LEDs, solid state lasers d) Others - Other types include output in the form of radiation (antenna), field etc. 10 2. Based on the way output energy is released - Based on the way the output energy is released, it is classified into a) Electrostatic b) c) d) e) f) Electro-magnet based Thermal Chemical Piezo-electric Shape memory alloy (SMA) g) Smart material-based h) Light-induced i) Biological 11 Application of MEMS actuators • Actuation of micro mirrors to scan laser beams • Printing applications • Driving of cutting tools for microsurgical applications • Driving micro pumps and valves for fluid and gas transportation • Data reading and recording tool • RF signal tuning • Optical signal switching 12 MEMS Sensors - A sensor is a device that measures information from a surrounding environment and provides an electrical output signal in response to the parameter it measured - A Sensor which is designed and manufactured using the MEMS Technology is known as a micro sensor or MEMS sensor - A sensor also consists of a signal processing unit like an amplifier, filter or ADC or a combination of these elements. - The MEMS sensors are classified based on the measurand and also based on the way they measure physical quantities Classification of sensors based on the measurand - Based on the measurand, sensors are classified as follows 1. Accelerometer – measures acceleration 2. 3. 4. Gyroscope – measures angular rate Pressure sensor – measures pressure Viscosity meter – measures viscosity 13 5. Anemometer –measures wind speed 6. Bolometer –measures radiation 7. Blood analyzer – measures presence or quantity of chemicals in blood 8. Virus detector – detects virus - MEMS sensors are used to sense the following types of energy Mechanical - force, pressure, velocity, acceleration, position Thermal - temperature, entropy, heat, heat flow Chemical - concentration, composition, reaction rate Radiant - electromagnetic wave intensity, phase, wavelength, polarization, reflectance, refractive index, transmittance Magnetic - field intensity, flux density, magnetic moment, permeability Electrical - voltage, current, charge, resistance, capacitance, polarization 14 - The following is a list of MEMS Sensors that are used in a modern car. • Accelerometers – For Electronic Stability Control and Airbag deployment. • Inertial Measurement Units or IMU (they are combination of MEMS Accelerometer and MEMS Gyroscope) – For measuring yaw, pitch and roll for autonomous driving. • Magnetometer – For direction used in navigation. • Pressure and Inertial Sensor – For braking control. • Pressure Sensor – Tire Pressure Monitoring System. • • • • Airflow Sensor – Air intake monitoring. Fuel Sensor – Fuel Level Indicator. Impact and Crash Sensor – Impact detection and Airbag deployment. MEMS Microphone – For communication and Noise Cancellation. • Temperature Sensor – For Automatic Climate Control and Engine Temperature Monitoring. • There are many other MEMS based devices for various applications. 15 Application of MEMS sensors - MEMS Sensors are already being used in a variety of applications like controlling and handling equipment, managing robots, cars, grippers, etc. - Some of the sectors of applications of MEMS based Sensors are mentioned below: Automotive Chemical and Pharmaceutical Aircraft Industrial Automation and Manufacturing Defense, Space and Aeronautical Environmental and Health Sciences Computing and Communications Consumer Products 16 MEMS manufacturing process - MEMS are manufactured with the same process as semiconductor integrated circuits, meaning they are made by combining together extremely thin layers of engineering materials (metals and insulators in combination with silicon) and patterned with micron or sub-micron size features - Similar to semiconductor integrated circuit manufacturing, MEMS devices are manufactured on a silicon or glass “wafer” by using micromachining. - [The term ‘micro-machining’ refers to a machining process by which small (‘microscopic’) bits of material are removed by using a micro tool in order to achieve a high geometrical accuracy that otherwise is unattainable. Because the amount of material removed locally in a micro-machining process is rather small and removal rates often are very low, micro-machining is particularly suited for manufacturing of micro-structures and micro-parts.] - Unlike other types of “micromachining”, the MEMS microfabrication process offers significant cost benefit, high reliability and performance. - This platform provides an economy of scale as hundreds or thousands of devices are manufactured at once in a batch process. - Further, many wafers can be processed simultaneously using automated or semi-automated 17 equipment. - MEMS fabrication has building block processes including successive iterations of material deposition, patterning using photolithography and both wet and dry etching to create the final three dimensional MEMS device structure. - As the purpose of MEMS fabrication is to make micro-machines, mechanical properties are crucial, especially for material forming the structures. - Properties such as yield strength, density, residual stress and long term stability require optimization. - Sophisticated measurement tools are used throughout the microfabrication manufacturing process as part of a quality system. - MEMS devices can be fabricated by two generic routes: bulk micromachining, and surface micromachining. - Bulk micromachining was the first of the fabrication methods to be investigated, material is removed from a substrate in order to create micro-features. - Surface micromachining is fundamentally different from bulk micromachining in that the process is additive - material is added to the base substrate to form 3-dimensional structures. 18 Bulk micromachining - Bulk micromachining is the oldest model of silicon-based MEMS. The whole thickness of a silicon wafer is used for building the micro-mechanical structures. - Silicon is machined using various etching processes. - Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that changed the sensor industry in the 1980s and 90’s. - Usually, silicon wafers are used as substrates for bulk micromachining, as they can be anisotropically wet etched, forming highly regular structures. - Wet etching typically uses alkaline liquid solvents, such as potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) to dissolve silicon which has been left exposed by the photolithography masking step. - These alkali solvents dissolve the silicon in a highly anisotropic way, with some crystallographic orientations dissolving up to 1000 times faster than others. - Such an approach is often used with very specific crystallographic orientations in the raw silicon to produce V-shaped grooves. - The surface of these grooves can be atomically smooth if the etch is carried out correctly, and the dimensions and angles can be precisely defined. - Pressure sensors are usually created by bulk micromachining technique. 19 - Bulk micromachining starts with a silicon wafer or other substrates which is selectively etched, using photolithography to transfer a pattern from a mask to the surface. - Like surface micromachining, bulk micromachining can be performed with wet or dry etches, although the most common etch in silicon is the anisotropic wet etch. - This etch takes advantage of the fact that silicon has a crystal structure, which means its atoms are all arranged periodically in lines and planes. - Certain planes have weaker bonds and are more susceptible to etching. - The etch results in pits that have angled walls, with the angle being a function of the crystal orientation of the substrate. - This type of etching is inexpensive and is generally used in early, low-budget research. 20 Surface micromachining - Surface micromachining builds microstructures by deposition and etching structural layers over a substrate. - This is different from Bulk micromachining, in which a silicon substrate wafer is selectively etched to produce structures. - Generally, polysilicon is used as one of the substrate layers while silicon dioxide is used as a sacrificial layer. - The sacrificial layer is removed or etched out to create any necessary void in the thickness direction. - Added layers tend to vary in size from 2-5 micrometers. - The main advantage of this machining process is the ability to build electronic and mechanical components (functions) on the same substrate. - Surface micro-machined components are smaller compared to their bulk micro-machined counterparts. - As the structures are built on top of the substrate and not inside it, the substrate's properties are not as important as in bulk micro-machining. 21 - Expensive silicon wafers can be replaced by cheaper substrates, such as glass or plastic. - The size of the substrates may be larger than a silicon wafer, and surface micro-machining is used to produce thin-film transistors on large area glass substrates for flat panel displays. - This technology can also be used for the manufacture of thin film solar cells, which can be deposited on glass, polyethylene terepthalate substrates or other non-rigid materials. Fabrication process - Micro-machining starts with a silicon wafer or other substrate upon which new layers are grown. - These layers are selectively etched by photo-lithography; either a wet etch involving an acid, or a dry etch involving an ionized gas (or plasma). - Dry etching can combine chemical etching with physical etching or ion bombardment. - Surface micro-machining involves as many layers as are needed with a different mask (producing a different pattern) on each layer. - Modern integrated circuit fabrication uses this technique and can use as many as 100 layers. - Micro-machining is a younger technology and usually uses no more than 5 or 6 layers. - Surface micro-machining uses developed technology (although sometimes not enough for demanding applications) which is easily repeatable for volume production. 22 Sacrificial layers - A sacrificial layer is used to build complicated components, such as movable parts. - For example, a suspended cantilever can be built by depositing and structuring a sacrificial layer, which is then selectively removed at the locations where the future beams must be attached to the substrate (i.e. the anchor points). - A structural layer is then deposited on top of the polymer and structured to define the beams. - Finally, the sacrificial layer is removed to release the beams, using a selective etch process that does not damage the structural layer. - Many combinations of structural and sacrificial layers are possible. The combination chosen depends on the process. - For example, it is important for the structural layer not to be damaged by the process used to remove the sacrificial layer. 23 24 25 Comparison between bulk and surface micromachining Bulk micromachining Surface micromachining Here elements are fabricated by etching away the unwanted Here elements are fabricated by building layers on layers part in silicon wafer This creates structures inside a substrate This creates structures on top of a substrate Larger structures are made with bulk micromachining It is difficult to build larger structures Straight forward and well documented process Complex masking design and production Sacrificial layer is not required Etching of sacrificial layer is required The process is less expensive but material loss is more The process is expensive but less material loss Mechanical properties are superior Mechanical properties are good Dimensional control is good Dimensional control is better CMOS integration is fair CMOS integration is good Size is small Size is smaller Typically uses wet etching techniques It uses dry etching techniques It causes a well known phenomenon in the micro electronics It does not causes undercut problem industry called undercut Suitable for simple geometry such as thermal sensor, micro machined neuron wells Suitable for complex geometry such as micro valves and 26 actuators MEMS Accelerometers - An accelerometer is an electromechanical device that is used to measure acceleration and the force producing it. - Many types of accelerometers are available in the market today - One of the most commonly used MEMS accelerometer is the capacitive type. Working of Capacitive type accelerometer - The capacitive MEMS accelerometer is famous for its high sensitivity and its accuracy at high temperatures. - The device does not change values depending on the base materials used and depends only on the capacitive value that occurs due to the change in distance between the plates. - If two plates are kept parallel to each other and are separated by a distance ‘d’ and if ‘E’ is the permittivity of the separating material, then capacitance produced can be written as C = (εA)/d A = area of the electrodes - A change in the values of E, A or d will help in finding the change in capacitance and thus helps in the working of the MEMS transducer. - Accelerometer values mainly depend on the change of values of d or A. 27 - A typical MEMS accelerometer is shown in the figure - It can also be called a simple one-axis accelerometer. If more sets of capacitors are kept in 90 degrees to each other you can design 2 or 3-axis accelerometer. - A simple MEMS transducer mainly consists of a movable microstructure or a proof mass that is connected to a mechanical suspension system and thus on to a reference frame. - The movable plates and the fixed outer plates act as the capacitor plates. - When acceleration is applied, the proof mass moves accordingly. - This produces a capacitance between the movable and the fixed outer plates. 28 - When acceleration is applied, the distance between the two plates displace as X 1 and X2, and they turn out to be a function of the capacitance produced. - From the image above it is clear that all sensors have multiple capacitor sets. - All upper capacitors are wired parallel to produce an overall capacitance C 1 and the lower ones produce an overall capacitance of C2. - If Vx is the output voltage of the proof mass, and V0 is the output voltage produced between the plates, then (Vx + V0) C1 + (Vx - V0) C2 = 0 - We can also write Vx = V0 [(C2-C1)/(C2+C1)] = (x/d) V0 - The figure below shows the circuit that is used to calculate the acceleration, through change in distance between capacitor plates. - The output obtained for different values of acceleration is also shown graphically. - When acceleration is given, such as (a>0), the value of value of Vx changes in proportion to the value of V0. - When a deceleration is given, such as (a<0), the signals V x and Vy become negative. 29 - The demodulator produces an output equal to the sign of the acceleration, as it multiplies both the values of Vy and V0 to produce VOUT, which has the correct acceleration sign and correct amplitude. 30 MEMS Accelerometers – Applications - MEMS sensors are being used in latest mobile phones and gaming joysticks as step counters, user interface control, and also for switching between different modes. - Used in mobile cameras as a tilt sensor so as to tag the orientation of photos taken. - To provide stability of images in camcorders and also to rotate the image to and fro when you turn the mobile. - A 3D accelerometer is used in Nokia 5500 so as to provide easier tap and change feature by which you can change mp3’s by tapping on the phone when it is lying inside the pocket. - Used to protect hard disk drives in laptops from getting damaged when the PC falls to the ground. The device senses the free fall and automatically switches off the hard disk. - Used in car crash airbag sensors, where it senses the sudden negative acceleration and determines the correct time to open the airbag. - Used in real-time applications like military monitoring, missile launching, projectiles, and so on. 31 Virtual Instrumentation - Virtual instrumentation in an inter disciplinary field that merges sensing, hardware and software technologies in order to create flexible and sophisticated instruments for control and monitoring applications - Virtual Instrumentation is the use of customizable software and modular measurement hardware to create user defined measurement systems called virtual instruments. - Virtual instrument provides all the software and hardware needed to accomplish the measurement or control task - Traditional hardware instrumentation systems are made up of pre-defined hardware components, such as digital multimeters and oscilloscopes that are completely specific to their stimulus, analysis, or measurement function. - Because of their hard-coded function, these systems are more limited in their versatility than virtual instrumentation systems. - The primary difference between hardware instrumentation and virtual instrumentation is that software is used to replace a large amount of hardware. - The software enables complex and expensive hardware to be replaced by already purchased computer hardware; e. g. analog-to-digital converter can act as a hardware complement of a virtual oscilloscope 32 History of virtual instrumentation - A history of virtual instrumentation is characterized by continuous increase of flexibility and scalability of measurement equipment. - Starting from first manual-controlled vendor-defined electrical instruments, the instrumentation field has made a great progress toward contemporary computer-controlled, user-defined, sophisticated measuring equipment First phase - The first phase is represented by early "pure" analog measurement devices, such as oscilloscopes or EEG recording systems. - They were completely closed dedicated systems, which included power suppliers, sensors, translators and displays - Use of data was not part of the instrument package and an operator had to physically copy data to a paper notebook or a data sheet. - Performing complex or automated test procedures was rather complicated or impossible, as everything had to be set manually. 33 Second phase - Second phase started in 1950s, as a result of demands from the industrial control field. - Instruments incorporated rudiment control systems, with relays, rate detectors, and integrators. - Instruments started to digitalize measured signals, allowing digital processing of data, and introducing more complex control or analytical decisions Third phase - In the third phase, measuring instruments became computer based and begun to include interfaces that enabled communication between the instrument and the computer. - Initially, computers were primarily used as off-line instruments. They were further processing the data after first recording the measurements on disk or type. - As the speed and capabilities of general-purpose computers advanced exponentially general-purpose computers became fast enough for complex real-time measurements. - Although computers’ performance soon became high enough, computers were still not easy to use for experimentalists. - An important milestone in the history of virtual instrumentation happened in 1986, when National Instruments introduced LabVIEW 1.0 on a PC platform - LabVIEW introduced graphical user interfaces and visual programming into computerized instrumentation, joining simplicity of a user interface operation with increased capabilities of computers. - Today, the PC is the platform on which most measurements are made and the graphical user interface has made measurements user-friendlier. - As a result, virtual instrumentation made possible decrease in price of an instrument. - As the virtual instrument depends very little on dedicated hardware, a customer could now use his own computer, while an instrument manufactures could supply only what the user could not get in the general market Fourth phase - The fourth phase became feasible with the development of local and global networks of general purpose computers. - Since most instruments were already computerized, advances in telecommunications and network technologies made possible physical distribution of virtual instrument components into telemedical systems to provide medical information and services at a distance. 35 Architecture of virtual instruments - Figure shows the general architecture of a virtual instrument 36 - A virtual instrument is composed of the following blocks: 1. Sensor Module 2. Sensor Interface 3. Processing Module 4. Database Interface 5. Medical Information Systems Interface and 6. User Interface - The sensor module detects physical signal and transforms it into electrical form, conditions the signal, and transforms it into a digital form for further manipulation. - Through a sensor interface, the sensor module communicates with a computer. - Once the data are in a digital form on a computer, they can be processed, mixed, compared, and otherwise manipulated, or stored in a database. - Then, the data may be displayed, or converted back to analog form for further process control. 37 1. Sensor module - The sensor module performs signal conditioning and transforms it into a digital form for further manipulation. - Once the data are in a digital form on a computer, they can be displayed, processed, mixed, compared, stored in a database, or converted back to analog form for further process control. - The database can also store configuration settings and signal records. - The sensor module interfaces a virtual instrument to the external, mostly analog world transforming measured signals into computer readable form. - A sensor module principally consists of three main parts: 1. the sensor 2. the signal conditioning part and 3. the A/D converter. - The sensor detects physical signals from the environment. - If the parameter being measured is not electrical, the sensor must include a transducer to convert the information to an electrical signal, for example, when measuring blood pressure 38 - The signal-conditioning module performs (usually analog) signal conditioning prior to A/D conversion. - This module usually does the amplification, transducer excitation, linearization, isolation, or filtering of detected signals. - The A/D converter changes the detected and conditioned voltage into a digital value. The converter is defined by its resolution and sampling frequency. 2. Sensor interface - There are many interfaces used for communication between sensors modules and the computer - According to the type of connection, sensor interfaces can be classified as wired and wireless. - Wired Interfaces are usually standard parallel interfaces, such as General Purpose Interface Bus (GPIB), Small Computer Systems Interface (SCSI), system buses [PCI extension for Instrumentation (PXI) or VME Extensions for Instrumentation (VXI), or serial buses (RS232 or USB interfaces)] - Wireless Interfaces are increasingly used because of convenience. - Typical interfaces include 802.11 family of standards, Bluetooth, or GPRS/GSM interface - Wireless communication is especially important for implanted sensors where cable connection is impractical or not possible 39 3. Processing Module - Integration of the general purpose microprocessors/microcontrollers allowed flexible implementation of sophisticated processing functions. - As the functionality of a virtual instrument depends very little on dedicated hardware, which principally does not perform any complex processing, functionality and appearance of the virtual instrument may be completely changed utilizing different processing functions. - Broadly speaking, processing function used in virtual instrumentation may be classified as analytic processing and artificial intelligence techniques. Analytic processing - Analytic functions define clear functional relations among input parameters. Some of the common analyses used in virtual instrumentation include spectral analysis, filtering, windowing, transforms, peak detection, or curve fitting. Artificial intelligence techniques - Artificial intelligence technologies could be used to enhance and improve the efficiency, the capability and the features of instrumentation in application areas related to measurement, system identification and control - These techniques exploit the advanced computational capabilities of modern computing systems to manipulate the sampled input signals and extract the desired measurements 40 4. Database interface - Computerized instrumentation allows measured data to be stored for off-line processing or to keep records as a part of the patient record. - There are several currently available database technologies that can be used for this purpose. - Many virtual instruments use Database Management Systems (DBMSs) - They provide efficient management of data and standardized insertion, update, deletion and selection 5. Medical information system interface - Virtual instruments are increasingly integrated with other medical information systems, such as hospital information systems. - They can be used to create executive dashboards, supporting decision support, Realtime alerts and predictive warnings 6. Presentation and control - An effective user interface for presentation and control of a virtual instrument affects efficiency and precision of an operator do the measurements and facilitates result interpretation. - Since computer’s user interfaces are much easier shaped and changed than conventional instrument’s user interfaces. - According to presentation and interaction capabilities, we can classify interfaces used in virtual instrumentation in four groups: a) terminal user interfaces, b) graphical user interfaces, c) multimodal user interfaces, and d) virtual and augmented reality interfaces. Biomedical Applications of Virtual Instrumentation - Virtual instrumentation is being increasingly accepted in biomedical field. - In relation to the role of a virtual instrument, we may broadly classify biomedical applications of virtual instrumentation in four categories Examination, where a physician does online or off-line examination of patient measurements Monitoring, which can be used as a basis for real-time alerts and interactive alarms Biofeedback, where measured signals are presented back to a patient in real-time, and Training and education, where a virtual instrument may simulate or playback earlier measured signals. 42 43 Advantages of Virtual Instrumentation - Lower cost of instrumentation - Easy to use graphical user interface - Portability between various computer platforms - Increases the utility of computer - Flexibility Disadvantages of Virtual Instrumentation - Sensitive information may be accessible to public users - Since many devices need to run simultaneously, it consume a large power 44 Traditional Vs Virtual instruments Traditional instrument Vendor defined Function specific – standalone with minimum connectivity Hardware is the key Expensive Closed, fixed functionality Slow turn on technology High development and maintenance cost Recalibration required It has lower computational power It uses IC for data processing Virtual instrument User defined Application oriented system with connectivity to networks, peripherals and applications Software is the key Low cost, reusable Open, flexible functionality Fast turn on technology Software minimizes development and maintenance cost Recalibration required It has higher computational power It uses software for data processing 45 46 Graphical programming - The graphical approach to programming allows a computer to process spatial representations in 2 or more dimensions - In contrast to text based programming, which uses lines of code, graphical programming replaces text with pictures or symbols of physical things - Graphical programming is often called visual programming or visual programming language (VPL) - Its different from Microsoft’s Visual Basic, which defines picture by using text based language Use of graphical programming - Graphical programming is most frequently used in the stages of engineering systems design engineers and programmers might use graphical programs to translate information about physical events, such as vibrations that occur during the testing of automotive engines into visual readouts - Graphical programming tools also might be used to employ block diagrams, connectors and virtual instruments such as temperature gauges - The result is a user interface that can be used to control and monitor an automated process 47 - There are several graphical programming languages Graphical programming in LabVIEW - LabVIEW, short for Laboratory Virtual Instrument Engineering Workbench, is a programming environment in which you create programs using a graphical notation (connecting functional nodes via wires through which data flows) - However, LabVIEW is much more than a programming language. It is an interactive program development and execution system designed for people, like scientists and engineers, who need to program as part of their jobs. - The LabVIEW program development environment is different from standard C or Java development system in one important respect: while other programming systems use text based languages to create lines of code, LabVIEW uses a graphical programming language, often called “G” to create programs in a pictorial form called a block diagram - Graphical programming eliminates a lot of the syntactical details associated with text based languages, such as where to put semicolons and curly braces 48 - The block diagram is the VI’s source code, constructed in LabVIEW's graphical programming language, G - The block diagram is the actual executable program - The components of a block diagram are lower level vis, built in functions, constants and program execution control structures - You draw wires to connect the appropriate objects together to define the flow of data between them - Front panel objects have corresponding terminals on the block diagram so data can pass from the user to the program and back to the user - In order to use a VI as a subroutine in the block diagram of another VI, it must have an icon with a connecter - A VI that is used within another VI is called a sub VI and is analogous to a subroutine - The icon in a VI’s pictorial representation and is used as an object in the block diagram of another VI 49 - A VI’s connecter is the mechanism used to wire data into the VI from other block diagrams when the VI is used as a sub VI - Much like parameters of a subroutine, the connector defines the inputs and outputs of the VI LabVIEW terms and their conventional equivalents LabVIEW Conventional language VI Program Function Function or method subVI Subroutine, subprogram, object Front panel User interface Block diagram Program code G C, C++, Java, Pascal, Basic etc. 50 Previous University Questions 1. What are the advantages and disadvantages of MEMS? 2. 3. 4. 5. With the help of a diagram explain the principle of MEMS accelerometer? Differentiate between bulk and surface micromachining. Explain the concept of graphical programming in virtual instruments With the help of a block diagram explain the architecture of virtual instruments 51