G UJARAT P OWER E NGINEERING A ND R ESEARCH I NSTITUTE, M EWAD PHILOSOPHY OF MEASUREMENT Created By: 1. Urvish Mehta ( ) 2. Viraj Shah ( ) 3. Anish Sumra ( ) 4. Narendra Rai ( ) Guided By: Manish Prajapati

D EFINITION OF MEASUREMENT Measurement is defined as the process of numerical evaluation of a dimension or the process of comparison with standard measuring instruments.

N EED OF M EASUREMENT Establish standard Interchange ability Customer Satisfaction Validate the design Physical parameter into meaningful number True dimension Evaluate the Performance

M ETHODS OF M EASUREMENT Direct method Indirect method Comparative method Coincidence method Contact method Deflection method Complementary method

D IRECT METHOD Measurements are directly obtained Ex: Vernier Caliper, Scales

I NDIRECT METHOD Obtained by measuring other quantities Ex : Weight = Length x Breadth x Height x Density

C OMPARATIVE M ETHOD It’s compared with other known value Ex: Comparators

C OINCIDENCE METHOD Measurements coincide with certain lines and signals Fundamental method Measuring a quantity directly in related with the definition of that quantity Contact method Sensor/Measuring tip touch the surface area

C OMPLEMENTARY METHOD The value of quantity to be measured is combined with known value of the same quantity Ex : Volume determination by liquid displacement

D EFLECTION METHOD The value to be measured is directly indicated by a deflection of pointer Ex: Pressure Measurement

M EASURING I NSTRUMENTS Deflection and null type instruments Analog and digital instruments Active and passive instruments Automatic and manually operated instruments Contacting and non contacting instruments Absolute and secondary instruments

DEFLECTION AND NULL TYPE Physical effect generated by the measuring quantity Equivalent opposing effect to nullify the physical effect caused by the quantity

ANALOG AND DIGITAL INSTRUMENTS Physical variables of interest in the form of continuous or stepless variations. Physical variables are represented by digital quantities.

ACTIVE AND PASSIVE INSTRUMENTS Instruments are those that require some source of auxiliary power The energy requirements of the instruments are met entirely from the input signal

A UTOMATIC AND MANUALLY OPERATED Manually operated – requires the service of human operator Automated – doesn't requires human operator

C ONTACTING A ND N ON C ONTACTING I NSTRUMENTS A contacting with measuring medium Measure the desired input even though they are not in close contact with the measuring medium

A BSOLUTE AND S ECONDARY I NSTRUMENTS These instruments give the value of the electrical quantity in terms of absolute quantities Deflection of the instruments can be read directly.

C HARACTERISTICS OF M EASURING I NSTRUMENT Sensitivity Readability Range of accuracy Precision

D EFINITION Sensitivity- Sensitivity is defined as the ratio of the magnitude of response (output signal) to the magnitude of the quantity being measured (input signal) Readability- Readability is defined as the closeness with which the scale of the analog instrument can be read

D EFINITION Range of accuracy- Accuracy of a measuring system is defined as the closeness of the instrument output to the true value of the measured quantity Precision- Precision is defined as the ability of the instrument to reproduce a certain set of readings within a given accuracy

S ENSITIVITY If the calibration curve is liner, as shown, the sensitivity of the instrument is the slope of the calibration curve. If the calibration curve is not linear as shown, then the sensitivity varies with the input. This is the relationship between a change in the output reading for a given change of the input. (This relationship may be linear or non-linear.) Sensitivity is often known as scale factor or instrument magnification and an instrument with a large sensitivity (scale factor) will indicate a large movement of the indicator for a small input change.

R EADABILITY Readability is defined as the ease with which readings may be taken with an instrument. Readability difficulties may often occur due to parallax errors when an observer is noting the position of a pointer on a calibrated scale

A CCURACY Accuracy = the extent to which a measured value agrees with a true value The difference between the measured value & the true value is known as ‘Error of measurement’ Accuracy is the quality of conformity

P RECISION The precision of a measurement depends on the instrument used to measure it. For example, how long is this block?

A CCURACY VS. P RECISION High Accuracy High Precision Low Accuracy

U NCERTAINTY The word uncertainty casts a doubt about the exactness of the measurement results True value = Estimated value + Uncertainty

C HARACTERISTICS OF I NSTRUMENTS All instrumentation systems are characterized by the system characteristics or system response There are two basic characteristics of Measuring instruments, they are Static characteristic Dynamic characteristic

S TATIC C HARACTERISTICS (1) ACCURACY: Accuracy is the ability of an instrument to show the exact reading. Always related to the extent of the wrong reading/non accuracy. Normally shown in percentage of error which of the full scale reading percentage.

S TATIC C HARACTERISTICS (2) PRECISION : An equipment which is precise is not necessarily accurate. Defined as the capability of an instrument to show the same reading when used each time (reproducibility of the instrument).

S TATIC C HARACTERISTICS (3) SENSIVITY : Defined as the ratio of change in output towards the change in input at a steady state condition. Sensitivity (K) = Δθο, Δθi Δθο : change in output; Δθi : change in input

S TATIC C HARACTERISTICS (4) RESOLUTION : This is defined as the smallest input increment change that gives some small but definite numerical change in the output. (5) THRESHOLD : This minimum value of input below which no output can be appeared is known as threshold of the instrument.

S TATIC C HARACTERISTICS (6) DRIFT : Drift or Zero drift is variation in the output of an instrument which is not caused by any change in the input; it is commonly caused by internal temperature changes and component instability. Sensitivity drift defines the amount by which instrument’s sensitivity varies as ambient conditions change.

S TATIC C HARACTERISTICS (7) ERROR – The deviation of the true value from the desired value is called Error. (8) REPEATABILITY – It is the closeness value of same output for same input under same operating condition. (9) REPRODUCIBILITY - It is the closeness value of same output for same input under same operating condition over a period of time.

S TATIC C HARACTERISTICS (10) RANGE : The ‘Range’ is the total range of values which an instrument is capable of measuring. (11) HYSTERESIS : This is the algebraic difference between the average errors at corresponding points of measurement when approached from opposite directions, i.e. increasing as opposed to decreasing values of the input.

S TATIC C HARACTERISTICS (12) ZERO STABILITY : The ability of the instrument to return to zero reading after the measured has returned to zero (13) DEAD BAND : This is the range of different input values over which there is no change in output value.

S TATIC C HARACTERISTICS (14) LINEARITY- The ability to reproduce the input characteristics symmetrically and linearly

S TATIC C HARACTERISTICS (15) BACKLASH – Lost motion or free play of mechanical elements are known as backlash (16) TRUE VALUE – The errorless value of measured variable is known as true value (17) BIAS – The Constant Error (18) TOLERANCE- Maximum Allowable error in Measurement

D YNAMIC C HARACTERISTICS The set of criteria defined for the instruments, which are changes rapidly with time, is called ‘dynamic characteristics’.

D YNAMIC C HARACTERISTICS Steady state periodic Transient Speed of response Measuring lag Fidelity Dynamic error

D YNAMIC C HARACTERISTICS (1) STEADY STATE RESPONSE – Magnitude has a definite repeating time cycle (2) TRANSIENT – Magnitude whose output does not have definite repeating time cycle (3) SPEED OF RESPONSE- System responds to changes in the measured quantity

D YNAMIC C HARACTERISTICS (4) MEASURING LAG- Retardation type :Begins immediately after the change in measured quantity Time delay lag : Begins after a dead time after the application of the input (5) FIDELITY- The degree to which a measurement system indicates changes in the measured quantity without error (6) DYNAMIC ERROR- Difference between the true value of the quantity changing with time & the value indicated by the measurement system

E RRORS IN I NSTRUMENTS Error = True value – Measured value or Error = Measured value - True value

T YPES OF E RRORS Error of Measurement Instrumental error Error of observation Based on nature of errors Based on control

E RROR OF M EASUREMENT SYSTEMATIC ERROR -Predictable way in accordance due to conditions change RANDOM ERROR - Unpredictable manner PARASITIC ERROR - Incorrect execution of measurement

I NSTRUMENTAL ERROR Error of a physical measure Error of a measuring mechanism Error of indication of a measuring instrument Error due to temperature Error due to friction Error due to inertia

E RROR OF OBSERVATION Reading error Parallax error Interpolation error

N ATURE OF E RRORS SYSTEMATIC ERROR : It is defined as the constant uniform deviation of the operation of an instrument. RANDOM ERROR : It is defined as errors due to unknown causes and occur invariably.

B ASED ON CONTROL Controllable errors Calibration errors Environmental (Ambient /Atmospheric Condition) Errors Stylus pressure errors Avoidable errors Non - Controllable errors