1 laxmanarao

Slide 1

BASIC INSTRUMENTATION SYSTEMWhat are basic instrumentsThe instruments which are used for the purpose to measure basic quantities (like voltage , current) are called basic instruments.Electrical measurements and electronic measurements(instrumentation)

Main Basic characteristics or properties of an instrument AccuracyPrecisionLinearitySensitivityDead time Dead zoneResolution

Accuracy4Accuracy of a measurement describes how close the measurement approaches the true value of the process variable.

% error over a range x% over% of full scale% of spanAbsolute over a range x units overfull scalespan

Precision5Precision is the reproducibility with which repeated measurements can be made under identical conditions.This may be referred to as drift.Resolution6Resolution is the smallest amount of input signal change that the instrument can detect reliably.Resolution is really a function of the instrument span and the controllers input capability.The resolution of a 16 bit conversion is:

The resolution of a 12 bit conversion is: The bit error.

Why is precision preferred over accuracy? Temperature measurement7

Instrumentation Dynamic properties: Gain and Dead Time8The gain of an instrument is often called sensitivity. The sensitivity of a sensor is the ratio of the output signal to the change in process variable.The dead time of an instrument is the time it takes for an instrument to start reacting to process change. ERRORSTrue value(At)Measured value(Am)

What is an errorERRORDeviation of measured quantities from the true values is called as the errorLIMITING ERRORlimiting error will specify the range of errorit is always W.R.T true valueRelative static errorError taken over the true value is called relative static error.% RSE=(Am-At)/At%RSE indicate the quality of the instrument.Guarantied accuracy errorsIt is the constant errors in the instrument.

Different types of errorsGross erros: Error because of human negligenceSystematic erros : (a)instrumental error: error in instrument (b)observational error: like parallax error (c)environmental error: error due to environmentRandom error

WHAT ARE TRASDUCERS?

INTRODUCTION OF TRANSDUCERSA transducer is a device that convert one form of energy to other form. It converts the measurand to a usable electrical signal.In other word it is a device that is capable of converting the physical quantity into a proportional electrical quantity such as voltage or current.PressureVoltageA transducer is a device that converts one form of energy into another

Mechanical Transducers

The mechanical transducers are the mechanical elements that are used for converting one form of energy into other form that can be measured easily. There are number of mechanical transducers, some of the commonly used ones are described below:1) Bellows: These are the elastic elements that convert the air pressure into displacement, and it is commonly used for the measurement of pressure.

bellow

2) Bourdon tube: This elastic tube converts air pressure to the rotary motion of the pointer used to indicate the pressure.

3) Spring: The spring tend to expand when force is applied to them, thus they are used for the measurement of force.4) Proving rings: Like the springs the proving rings also convert applied force to the displacement.5) Diaphragm: It converts applied pressure to the displacement.6) Manometer: The manometer converts the applied pressure into variable displacement of the liquid within it enabling to measure the pressure.

7) Thermocouple: Thermocouple is the devise that produces electric current when one of its end is heated. The current produce by the devise can be measured, which can be calibrated against the temperature enabling us to measure the temperature of the body.8) Bimetals: These are the bimetallic strips comprising of two different metals having different coefficient of thermal expansion, joint together. When the strip is heated one metal expands lesser while the other metal expands more leading to the deflection of the bimetallic strip, which is converted into the rotary motion of the pointer that indicates the temperature.9) Hydropneumatic transducers: These include devices like orifice, venturi, pitot tube, vanes and turbines that are used for measurement of pressure, velocity, flow rate and force of water.

THANKYOU