TERMS IN MEASUREMENT

MEASUREMENTS:

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.

Indirect Method:

Obtained by measuring other quantities.

Ex:Diameter measurement by using three wires.

Comparative Method:

It’s compared with other known value.

Ex:Comparators.

Coincidence 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.

Ex:Vernier Caliper.

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.

Complementary Method:

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.

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.

Error:

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

Error = V_t – V_m

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.

TERMS IN MEASUREMENT

MEASUREMENTS:

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.

Indirect Method:

Obtained by measuring other quantities.

Ex:Diameter measurement by using three wires.

Comparative Method:

It’s compared with other known value.

Ex:Comparators.

Coincidence 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.

Ex:Vernier Caliper.

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.

Complementary Method:

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.

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.

Error:

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

Error = V_t – V_m

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.

MEASUREMENT

Calibration:

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:

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.

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.

Range:

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

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.

Backlash:

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

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.

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.

Parallax:

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

 

 

MEASUREMENT

Calibration:

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:

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.

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.

Range:

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

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.

Backlash:

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

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.

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.

Parallax:

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