Measurement and Instrumentation Unit 1-standards and Instruments Functions of Instruments and Measurement Systems Instruments or measurement system are classified based upon the function they performed. 1. Indicating Function:- Different kinds of methods for supplying information concerning the variable quantity under measurement 2. Recording Function:- Stores or write the value of quantity under measurement. 3. Controlling Function:- In this case the information is used by the instrument or the system to control the original measured History of Instruments The history of development of instrument encompasses three phases of instruments Mechanical Instruments Very reliable for static and stable condition Unable to respond rapidly to measurements of dynamic and transient condition Due to rigid, heavy and bulky parts have large mass hence cannot faithfully follow the rapid change are potential source of noise pollution Electrical Instruments Electrical instrument are more rapid than mechanical type An electrical system normally depends upon a mechanical meter movement as indicating device. Electronic Instruments Today’s requirement of measuring instrument is very fast response Electronic instrument uses semiconductor devices Since in electronic devices, the only movement involved is that of electrons the response time is very small Application of measurement Systems 1. Monitoring of process and operation- simply indicating the value or condition of parameter under study. For example- water and electricity meter 2. Control of process and operations- automatic control system a very strong association between measurement and control for example: refrigeration with thermostatic control 3. Experimental Engineering analysis: engineering problem, theoretical and experimental methods may be used depending upon the nature of the problem Units: A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same quantity.[1] Any other value of that quantity can be expressed as a simple multiple of the unit of measurement. INTERNATIONAL SYSTEM OF UNITS: The International System of Units (French: Système international d'unités pronounced abbreviated as SI) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units. The system was published in 1960 as the result of an initiative that began in 1948. It is based on the metre-kilogram-second system of units (MKS) rather than any variant of the centimetre- gram-second system (CGS). SI is intended to be an evolving system, so prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves. SI Units are category as follows: 1.Fundamental-6 2.Supplementry-2 3.Derived -27 FUNDAMENTAL UNITS: SI base units Unit Dimensio Unit Quantity symbo Definition (incomplete)[n 1] n name name l symbol Original (1793): 1/10000000 of the meridian through Paris between the North Pole and the Equator.FG Interim (1960): 1650763.73 wavelength s in a vacuum of the radiation corresponding to the L metre m length transition between the 2p10 and 5d5 quantum levels of the krypton- 86 atom. Current (1983): The distance travelled by light in vacuum in 1/299792458 second. Original (1793): The grave was defined kilogram[ as being the weight [mass] of one cubic n 2] kg mass decimetre of pure water at its freezing M point.FG Current (1889): The mass of the international prototype kilogram. Original (Medieval): 1/86400 of a day. Interim (1956): 1/31556925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time. second s time T Current (1967): The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. Original (1881): A tenth of the electromagnetic CGS unit of current. The [CGS] electromagnetic unit of current is that current, flowing in an arc 1 cm long of a circle 1 cm in radius, that creates a field of one oersted at the electric centre.[39] IEC ampere A I current Current (1946): The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2×10−7 newtons per metre of length. Original (1743): The centigrade scale is obtained by assigning 0 °C to the freezing point of water and 100 °C to the boiling point of water. thermodynam kelvin K Interim (1954): The triple point of Θ ic temperature water (0.01 °C) defined to be exactly 273.16 K.[n 3] Current (1967): 1/273.16 of the thermodynamic temperature of the triple point of water Original (1900): The molecular weight of a substance in mass grams.ICAW amount of mole mol Current (1967): The amount of N substance substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.[n 4] Original (1946): The value of the new candle is such that the brightness of the full radiator at the temperature of solidification of platinum is 60 new luminous candles per square centimetre. candela cd J intensity Current (1979): The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 5.4×1014 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. SUPPLEMENTARY UNITS Unit of plane angle : radian ( rad) Unit of solid angle : steradian (sr) DERIVED UNITS The derived units in the SI are formed by powers, products or quotients of the base units and are unlimited in number.[22]:103[33]:3 Derived units are associated with derived quantities, for example velocity is a quantity that is derived from the base quantities of time and length, so in SI the derived unit is metres per second (symbol m/s). The dimensions of derived units can be expressed in terms of the dimensions of the base units. Named units derived from SI base units[33]:3 Expressed in Expressed in Name Symbol Quantity terms of terms of other SI SI base units units −1 radian rad angle m·m 2 −2 steradian sr solid angle m ·m −1 hertz Hz frequency s −2 newton N force, weight kg·m·s 2 −1 −2 pascal Pa pressure, stress N/m kg·m ·s 2 −2 joule J energy, work, heat N·m kg·m ·s 2 −3 watt W power, radiant flux J/s kg·m ·s electric charge or quantity of coulomb C s·A electricity voltage (electrical potential 2 −3 −1 volt V W/A kg·m ·s ·A difference), electromotive force −1 −2 4 2 farad F electric capacitance C/V kg ·m ·s ·A electric 2 −3 −2 ohm Ω V/A kg·m ·s ·A resistance, impedance, reactance −1 −2 3 2 siemens S electrical conductance A/V kg ·m ·s ·A 2 −2 −1 weber Wb magnetic flux V·s kg·m ·s ·A 2 −2 −1 tesla T magnetic flux density Wb/m kg·s ·A 2 −2 −2 henry H inductance Wb/A kg·m ·s ·A degree °C temperature relative to 273.15 K K Celsius lumen lm luminous flux cd·sr cd 2 −2 lux lx illuminance lm/m m ·cd −1 becquerel Bq radioactivity (decays per unit time) s 2 −2 gray Gy absorbed dose (of ionizing radiation) J/kg m ·s 2 −2 sievert Sv equivalent dose (of ionizing radiation) J/kg m ·s −1 katal kat catalytic activity mol·s Standard In measurements • International standards • Primary • Secondary • Working Functional Elements of an Instrumentation system An Instrument may be defined as a device or a system which is designed to maintain a functional relationship between prescribed properties of physical variables and must include ways and means of communication to a human observer Most of the measurement system contains following main functional elements as shown in figure 1. Primary Sensing Element. 2. Variable Conversion Element 3. Variable Manipulation Element 4. Data Transmission Element 5. Data Presentation Element Primary Sensing Element: - The Measurand is first detected by primary sensing element. The primary sensing element transfers the measurand to variable conversion element for further processing. The output signal of a primary sensing element is a physical variable such as displacement or voltage. Variable Conversion Element: - The output signal of a primary sensing element may require to be converted to more suitable variables while preserving its information content. This function is performed by variable conversion element and it may be considered as an intermediate transducer Variable Manipulation Element: - This element is an intermediate stage of a measuring system. It modifies the direct signal by amplification, filtering, etc; so that a desired output is produced the physical nature of the variable remains unchanged during this stage. Data Transmission Element: - when the functional elements of the measuring system are spatially separated then it becomes necessary to transmit signals from one element to another. This function is performed by data transmission element. It is an essential functional element where remote control operation is desired. Data Presentation Element: - usually information about the quantity being measured is to be communicated to human observer for monitoring control and analysis purpose. This is therefore, to be presented in form of human sensory capability. This function is done by data presentation element. STATIC & DYNAMIC CHARACTERISTICS OF MEASUREMENT SYSTEM: The performance characteristics of an instrument are mainly divided into two categories: i) Static characteristics ii) Dynamic characteristics Static characteristics: The set of criteria defined for the instruments, which are used to measure the quantities which are slowly varying with time or mostly constant, i.e., do not vary with time, is called ‘static characteristics’.