Archive for the ‘MMM’ category

TERMS IN MEASUREMENT

August 23, 2011

MEASUREMENTS:

01-Imperial-Measurements-CONCEPTS OF MEASUREMENT-BASICS-OUTCOME OF A RESULT-EXAMPLES-MEASURING TAPES-LENGTH-HEIGHT

A Measurement is the outcome of an opinion formed by observers about some physical quantity.

CLASSIFICATION OF MEASUREMENTS:

  • Standards –  ( Reproduce the value of given quantity )
  • Fixed Gauges – (Check Dimensions)
  • Measuring Instruments – (Determine the measured value)

NEEDS FOR MEASUREMENT:

1. To Determine the true dimensions of a part.

2. To increase our knowledge and understanding of the world.

3. Needed for ensuring public health and human safety.

4. To convert physical parameters into meaningful numbers.

5. To test if the elements that constitute the system function as per the design.

6. For evaluating the performance of a system.

7. For studying some basic laws of nature.

8. To ensure interchangeability with a view to promoting mass production.

9. To evaluate the response of the system to particular point.

10. To check the limitations of theory in actual situations.

11. To establish the validity of design and for finding new data and new designs.

METHODS OF MEASUREMENT:

1. Direct Comparison

2. Indirect Comparison

3. Comparative Method

4. Coincidence Method

5. Fundamental Method

6. Contact Method

7. Transposition Method

8. Complementary Method

9. Deflection Method

Direct Method:

Measurements are directly obtained.

Ex:Vernier Caliper,Scales.

01-electroniccaliper-VERNIER CALIPER-DIGITAL VERNIER CALIPER-DIRECT MEASUREMENTS-ACCURATE-PRECISION MEASUREMENTS-CALIBRATED INSTRUMENTS

Indirect Method:

Obtained by measuring other quantities.

Ex:Diameter measurement by using three wires.

01-DIAMETER MEASUREMENTS-INDIRECT MEASUREMENTS-CAPACITIVE TRANSDUCER BY WHEATSTONE BRIDGE CIRCUITS

Comparative Method:

It’s compared with other known value.

Ex:Comparators.

01-comparator_stand_dial_gauge-precisional measurements-surface finish-height measurements-tolerance measurements

Coincidence Method:

Measurements coincide with certain lines and signals.

01-coincident methods-coincidence line-simplify lines-measurements 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.

Ex:Vernier Caliper.

01-proximity_sensor-distance measurements-long distance-measuring probe-sensing device

Transposition Method:


Quantity to be measured is first balanced by a known value and then balanced by an other new known value.

Ex:Determination of mass by balancing methods.

01-tool-balancing-balance methods-determination of mass-scale

Complementary Method:

01-volume-measurement-lighter-solids-volume displacement-liquid measure level-liquid displacement

The value of quantity to be measured is combined with known value of the same quantity.

Ex:Volume determination by liquid displacement.

Deflection Method:

The value to be measured is directly indicated by a deflection of pointer.

Ex:Pressure Measurement.

01-pressure measurement-pressure gauges-measurement of pressure-deflection of pointer

TERMS OF MEASUREMENT:

Precision:

The ability of the instrument to reproduce it’s readings or observation again and again for constant input signal.

Accuracy:

Closeness/conformity to the true value of the quantity under measurement.

01-Accuracy-Precision-uncertainity analysis-systematic errors-reproducibility errors

Error:

The difference between true value and measured value is known as measurement error.

Error = Vt – Vm

Reliability:

It is defined as the probability that a given system will perform it’s function adequately for it’s specified period of lifetime under specified operating conditions.

01-reliability-analysis-life time analysis-life time warranty

ERRORS

August 23, 2011

Errors in Measurement :

Error = Measured Value – True Value

E= V– Vt

1. Absolute Error :

01-errors in measurement-absolute error-greater accuracy and precision


            True absolute error :

= Result of measurement – True Value

            Apparent Absolute error :

= Result of measurement – Arithmetic Value

2. Relative error :


It is defined as the results of the absolute error and the value of comparison used for 450

calculation of that absolute error.

01-relative error-percentage relative error-absolute error

Causes of Errors :

1. Calibration Error:

These are caused due to the variation in the calibrated scale from it’s normal value.

01-error-calibration test-calibration of gauges-calibrate a instrument by a standard gauge-Panametrics-NDT_Calibration_Test_Blocks

2. Environmental Error :

These are caused due to humidity condition,Temperature and altitude.

3. Assembly Error:

i. Displaced Scale (incorrect Fitting)

ii. Non –uniform division of the scale.

iii. Due to bent /distorted pointer.

01-parallex error-eye fault defect by human-bias error

4. Random Error:

Naturally Occurred

No specific reasons

5. Systematic errors (or) Bias errors:

These are caused due to repeated readings.

01-errors-types of error-systematic error-random error-bias error

6. Chaotic errors :

These are caused due to vibrations,noises and shocks.

MEASUREMENT

August 23, 2011

Calibration:

01-the weighing scale-weighing machines-balance-calibration example

If a known input is given to the measurement system the output deviates from the given input, the corrections are made in the instrument and then the output is measured. This process is called “Calibration”.

Sensitivity:

Sensitivity is the ratio of change in the output signal to the change in the input signal.

Readability:

01-electroniccaliper-VERNIER CALIPER-DIGITAL VERNIER CALIPER-DIRECT MEASUREMENTS-ACCURATE-PRECISION MEASUREMENTS-CALIBRATED INSTRUMENTS-readability

Refers to the ease with which the readings of a measuring instrument can be read.

True size:

Theoretical size of a dimension which is free from errors.

Actual size:

Size obtained through measurement with permissible error.


01-true size-actual size-feet size-example-shoe-footwear

Hysteresis:

All the energy put into the stressed component when loaded is not recovered upon unloading. so the output of measurement partially depends on input called Hysteresis.

01-tachometer-digital tachometer-hysteresis due to pressure of force

Range:

The physical variables that are measured between two values. One is the higher calibration value Hc and the other is Lower value Lc.

01-range - read values from 0 to 11000 rpm - bezel meter - tachometer

Span:

The algebraic difference between higher calibration values to lower calibration values.

Resolution:

The minimum value of the input signal is required to cause an appreciable change in the output known as resolution.

Dead Zone:

It is the largest change in the physical variable to which the measuring instrument does not respond.

Threshold:

The minimum value of input signal that is required to make a change or start from zero.

01-threshold-minimum input given to start the engine-bike kick start action

Backlash:

The maximum distance through which one part of the instrument is moved without disturbing the other part.

01-backlash - continuous rotation possible without applying brake-SINGLE 3-PHASE AC ASYNCHRONOUS ELECTRIC MOTOR

Response Time:

The time at which the instrument begins its response for a change in the measured quantity.

Repeatability:

The ability of the measuring instrument to repeat the same results during the act measurements for the same quantity is known as repeatability.

Bias:

It is a characteristic of a measure or measuring instruments to give indications of the value of a measured quantity for which the average value differs from true value.

Magnification:

It means the magnitude of output signal of measuring instrument many times increases to make it more readable.

01-magnification-objective lens-magnify-loupe-ring

Drift:

If an instrument does not reproduce the same reading at different times of measurement for the same input signal, it is said to be measurement drift.

Reproducibility:

It is the consistency of pattern of variation in measurement. When individual measurements are carried out the closeness of the agreement between the results of measurements of the same quantity.

Uncertainty:

The range about the measured value within the true value of the measured quantity is likely to lie at the stated level of confidence.

Traceability:

It is nothing establishing a calibration by step by step comparison with better standards.

01-traceability-calibration step by step-vacuum calibration

Parallax:

An apparent change in the position of the index relative is to the scale marks.

 

 

01-parallax-error-measurement of length-eye view

MEASUREMENT

August 23, 2011

Calibration:

01-the weighing scale-weighing machines-balance-calibration example

If a known input is given to the measurement system the output deviates from the given input, the corrections are made in the instrument and then the output is measured. This process is called “Calibration”.

Sensitivity:

Sensitivity is the ratio of change in the output signal to the change in the input signal.

Readability:

01-electroniccaliper-VERNIER CALIPER-DIGITAL VERNIER CALIPER-DIRECT MEASUREMENTS-ACCURATE-PRECISION MEASUREMENTS-CALIBRATED INSTRUMENTS-readability

Refers to the ease with which the readings of a measuring instrument can be read.

True size:

Theoretical size of a dimension which is free from errors.

Actual size:

Size obtained through measurement with permissible error.


01-true size-actual size-feet size-example-shoe-footwear

Hysteresis:

All the energy put into the stressed component when loaded is not recovered upon unloading. so the output of measurement partially depends on input called Hysteresis.

01-tachometer-digital tachometer-hysteresis due to pressure of force

Range:

The physical variables that are measured between two values. One is the higher calibration value Hc and the other is Lower value Lc.

01-range - read values from 0 to 11000 rpm - bezel meter - tachometer

Span:

The algebraic difference between higher calibration values to lower calibration values.

Resolution:

The minimum value of the input signal is required to cause an appreciable change in the output known as resolution.

Dead Zone:

It is the largest change in the physical variable to which the measuring instrument does not respond.

Threshold:

The minimum value of input signal that is required to make a change or start from zero.

01-threshold-minimum input given to start the engine-bike kick start action

Backlash:

The maximum distance through which one part of the instrument is moved without disturbing the other part.

01-backlash - continuous rotation possible without applying brake-SINGLE 3-PHASE AC ASYNCHRONOUS ELECTRIC MOTOR

Response Time:

The time at which the instrument begins its response for a change in the measured quantity.

Repeatability:

The ability of the measuring instrument to repeat the same results during the act measurements for the same quantity is known as repeatability.

Bias:

It is a characteristic of a measure or measuring instruments to give indications of the value of a measured quantity for which the average value differs from true value.

Magnification:

It means the magnitude of output signal of measuring instrument many times increases to make it more readable.

01-magnification-objective lens-magnify-loupe-ring

Drift:

If an instrument does not reproduce the same reading at different times of measurement for the same input signal, it is said to be measurement drift.

Reproducibility:

It is the consistency of pattern of variation in measurement. When individual measurements are carried out the closeness of the agreement between the results of measurements of the same quantity.

Uncertainty:

The range about the measured value within the true value of the measured quantity is likely to lie at the stated level of confidence.

Traceability:

It is nothing establishing a calibration by step by step comparison with better standards.

01-traceability-calibration step by step-vacuum calibration

Parallax:

An apparent change in the position of the index relative is to the scale marks.

 

 

01-parallax-error-measurement of length-eye view