Electrical Heights

Basic Principles of Transducer Pressure Transducer The task of a process control system is to control the physical parameters like force, pressure, level etc and to maintain their value near the desired value.This is because the physical parameters may vary due to disturbances. To maintain these parameters at a required level certain corrective action requires to be taken. Fig. shows a process control loop. Process control loop The process control loop consists of four blocks process,parameter measurement, control element and controller. It is essential to measure the actual value of parameter P to achieve proper feedback. Nowadays most of the controllers are electronic and hence they require an electrical input. Thus,the feedback signal is required in electrical form. The measurement block includes two functions like to measure the parameter and to produce a suitable analog signal in electric form. Sometimes the parameter measurement...

Classification of Instrumentation System Instrumentation system Null and Deflection type Instruments: Deflection type instruments: The instruments in which deflection of the instrument forms the basis of measuremenl are called as deflection type instruments. The example of deflection type instruments is the permanent magnet moving coil (PMMC) ammeter. PMMC AMMETER The deflection of the coil is proportional to the current that is to be measured. Torque Td, that acts on the moving coil is proportional to current.The opposing effect is produced by a spring, having torque Tc which is proportional to the deflection. When the spring is balanced Tc=Td. The value of the current depends on the deflection.Thus,the value of the measured quantity depends upon the calibration of the instrument. Null type Instruments The instrument in which, a null or zero indication will lead to the determination of the magnitude of the measured quantity such instruments are c...

Active and Passive Instruments: Active and passive Instruments Passive Instruments: The instruments where the output is produced completely by the quantity that is measured are called passive instruments. The example of passive instrument is a pressure gauge.Fig  shows a pressure gauge. Passive  Instrument As the pressure in the liquid changes, the piston moves.The pointer is connected to the piston. No other source of energy is used. The liquid pressure is the only source. Thus,the piston and pointer movement while measurement is entirely dependent on the liquid pressure. Active Instruments: Active instruments are the instruments in which the quantity to be measured activates the magnitude of external power input source that produces the measurement. The liquid level indicator is an example of an active instrument.Fig.1.4.2 shows a liquid level indicator. Active Instruments The power source is required in or...

Functional elements of an Instrumentation System: Instrumentation system Any instrumentation system can be described with the help of a block diagram.The block diagram of an instrumentation system describes the essential elements and their functions in a measuring system. Fig. shows the block diagram showing the functional elements of an instrumentation system.                     Instrument system The elements can be grouped as: Primary sensing element. Data conditioning element. Data presentation element. Each element comprises of a number of distinct components that perform a particular function in the measurement procedure.The function of each element is important.  Primary Sensing Element: To the primary sensing element the quantity to be measured is applied.e.g.in an ammeter, coil carrying current to be measured is a primary sensing element. Generally a transducer follows a primary sensing e...

  Definition of Measurement and Calibration Measurement and Calibration Measurement: Measurement of a given quantity is the act or result of a quantitative comparison between an unknown quantity and a predefined standard quantity e.g.for measuring the weight of a quantity, the standard taken is 1 kg. Measurement  using an instrument as a physical means of determining a quantity or variable. Instrument: Define an instrument: Instrument can be defined as a device for measuring the value or magnitude of a quantity or variable. The electronic instrument is based on electrical or electronic principles for their measurement. Calibration: What do you mean by calibration?  Calibration is a process of estimating the value of a quantity by comparing that quantity with given standard quantity. The standard with which comparison is made is called as standard instrument. The unknown quantity is to be calibrated.This quantity is called as test qu...