Ex:- fore casting weather it predicting in the earth case. Methods of measurement:1. Direct and indirect measurement. 2. Primary and secondary & tertiary measurement. 3. Contact and non-contact type of measurement. 1. Direct and indirect measurement: Measurement is a process of comparison of the physical quantity with a standard depending upon requirement and based upon the standard employed, these are the two basic methods of measurement. Direct measurement: The value of the physical parameter is determined by comparing it directly with different standards. The physical standards like mass, length and time are measured by direct measurement. Indirect measurement: The value of the physical parameter is more generally determined by indirect comparison with the secondary standards through calibration. The measurement is convert into an analogous signal which subsequently process and fed to the end device at present the result of measurement. 2. Primary and secondary & tertiary measurement: The complexity of an instrument system depending upon measurement being made and upon the accuracy level to which the measurement is needed. Based upon the complexity of the measurement systems, the measurement are generally grouped into three categories. i. Primary ii. Secondary iii. Tertiary. In the primary mode, the sought value of physical parameter is determined by comparing it directly with reference standards the required information is obtained to sense of side and touch. Examples are: a) Matching of two lengths is determining the length of a object with ruler. b) Estimation the temperature difference between the components of the container by inserting fingers. c) Use of bean balance measure masses. d) Measurement of time by counting a number of strokes of a block. Secondary and tertiary measurement are the indirect measurements involving one transmission are called secondary measurements and those involving two convergent are called tertiary measurements. Ex: The convergent of pressure into displacement by means of be allows and the convergent of force into displacement. Pressure measurement by manometer and the temperature measurement by mercury in glass tube thermometer.
The measurement of static pressure by boundary tube pressure gauge is a typical example of tertiary measurement. 3. Contact and non-contact type of measurements: Contact type: Where the sensing element of measuring device as a contact with medium whose characteristics are being measured. Non-contact type: Where the sense doesn't communicate physically with the medium. Ex: The optical, radioactive and some of the electrical/electronic measurement belong to this category. Objectives of instrumentation:1. The major objective of instrumentation is to measure and control the field parameters to increase safety and efficiency of the process. 2. To achieve good quality. 3. To achieve auto machine and automatic control of process there by reducing human. 4. To maintain the operation of the plan within the design exportations and to achieve good quantity product. Generalised measurement system and its functional elements:- 1) Primary sensing element. 2) Variable conversion (or) Transducer element. 3) Manipulation of element. 4) Data transmission element. 5) Data processing element.
6) Data presentation element. The principal functions of an instrument is the acquisition of information by Sensing and perception, the process of that information and its final presentation to a Human observer. For the purpose of analysis and synthesis, the instrument s are considered as systems (or) assembly of inter connected components organised to perform a specified function. The different components are called elements. 1) PIMARY SENSING ELEMENT: An element that is sensitive to the measured variable .The sensing element sense the condition , state (or) value of the process variable by extracting a small part of energy from the measurement and produces an output which is proportional to the input. Because of the energy expansion, the measured quantity is always disturb. Good instruments are designed to minimise this loading effect. 2) Variable conversion (or) transducer element: An element that converts the signal from one physical for to Another without changing the information content of the signal. Example: Bourdon tube and bellows which transfer pressure into displacement. Proving ring and other elastic members which converts force into displacement. Rack and Pinion: It converts rotary to linear and vice versa. Thermo couple which converts information about temperature difference to information in the form of E.M.F. 3) MANIPULATION ELEMENT: It modifies the direct signal by amplification, filtering etc., so that a desired output is produced. [input]× constant = Output 4) DATA TRANSMISSION ELEMENT: An element that transmits the signal from one location to another without changing the information content. Data may by transmitted over long distances (from one location to another) or short distances (from a test centre to a nearby computer). 5) DATA PROCESSING ELEMENT: An element that modifies data before it is displayed or finally recorded. Data processing may be used for such purposes as: Corrections to the measured physical variables to compensate for scaling, non-linearity, zero offset, temperature error etc.
Covert the data into useful form, e.g., calculation of engine efficiency from speed, power input and torque developed. Collect information regarding average, statistical and logarithmic values. 6) DATA PRESANTION ELEMENT: An element that provides record or indication of the output from the data processing element. Ina measuring system using electrical instrumentation, an exciter and an amplifier are also incorporated into the circuit. The display unit may be required to serve the following functions. transmitting Signalling Registering Indicating recording The generalised measurement system is classified into 3 stages: a) Input Stage b) Intermediate Stage i. Signal Amplifications ii. Signal Filtration iii. Signal Modification iv. Data Transmission c) Output Stage