Classification of errors

1. Gross error 
2. Systematic error 

• Instrumental error
• Environmental error
• Observational error  

     3. Random error

Gross errors:

• These errors occurs due to human mistakes in reading instruments and recording and calculating results of measurements
• Impossible to eliminate gross error completely
• Mathematical analysis of gross error is impossible.
  These errors can be avoided by 2 means

1. Immense care should be taken while taking the reading and recording the data
2. Two THREE OR EVEN MORE READING should be taken for the quantity being measured

Systematic error:
 These are mainly due to the short comings of the instruments and the characteristics  of the material used in instruments such as defective or worn parts environmental effects etc.
    A constant uniform deviation of the operation of an instrument is known as systematic error
There are 3 types of systematic error

1. Instrumental error
2. environmental error
3. Observation error

1. Instrumental errors:
   These errors arise due to
   Inherent short coming in the instruments,misuse of the instruments,loading effects of the instruments
   
   Misuse of instruments : A good instrument used in an unintelligent way may give erroneous result
   
    
2. Environmental error:
   These errors are due to condition external to the measuring device
   ex: Effects of pressure, temperature dust,humidity
   
   These errors can be eliminated by the following  measure

• using instruments in controlled condition
• apply suitable correction to instruments reading 
• apply combated correction
• using sophisticated devices

     3.  Observational errors: These errors occurs due to carelessness of operators
Reasons:

• Working scale reading and working reading of data
• Inaccurate estimations of average reading
• In correct conversion of units 
• Tendency to read high or low.
   

    4.Random errors:
            Some errors still result though the systematic and instrumental errors are reduced or atleast accounted for.
The cause of such errors are unknown and hence the errors are called random error

These errors are generally due to the accumulation of large number of small effects.These errors are generally small,Hence these errors are of real concern only when the high degree of accuracy is required.

Modes of measurements

1. Primary measurement 
2. Secondary measurement
3. Tertiary measurement 

1. Primary measurement: 

•  In this case sought value of parameter is determined by comparing it directly withing reference standard 
• There is no conversation of measurand in terms of length
  1. measurement of time by counting the number of stroke of the clock.
  2. Matching of 2 length when determining the lenght of an object with a ruler
  3.   Matching of 2 colors when judging the temperature of a red hot steel.
     

2.Secondary measurement:

The indirect measurement ,these involving 1 translation. 

•  temperature measurement by  mercury in glass(Thermometers)
• pressure measurement by manometer.
  
  

3.Tertiary measurement:

The indirect measurement ,these are involving 2 translations

• The measurement of temperature of an object by thermocouple.

Standards of measurement

1. Primary standard
2. Secondary standard
3. Working standard 

1. Primary standard: The highest standard of either a base unit or a derived unit is called as primary standard.These standard are copies of international prototypes and are kept by national standard laboratory. These standardized units are quite stable independent invariant.The primary standards constitute the ultimate bases of the references and are used for the reference verification and calibration of secondary standards.The primary standard are not available for the use outside the national laboratories
   
   
2. Secondary standard: These are the reference calibrated standard designed and calibrated from the primary standards.These are sent periodically to the national standard laboratory for their calibration.These standard are kept by the measurement laboratories and the industrial organization
   
   
3. Working standard: These standard have an accuracy one order lower than that of the secondary standard.These are normal standard used by the workers and technician who actually carry out measurement.

Fundamental measuring process, Significance of measurements

The basic requirement for getting meaning full result or measurement are:

1. The standard employed for comparison purpose must be accurately defined and should be commonly acceptable
2. The standard must be of the same character as the measurand 
3. Standard is prescribed and defined by a legal or recognized agency  or organization example: INDIAN bureau of standards, ISO
4. The apparatus used and method adopted for the comparison purpose must be prove able

Significance of measurements:

1. Measurement plays a very significant role in every branch of scientific research and engineering processes which includes the following 

• Control system
• process instrumentation
• data reduction
• automation 

   2.  Through measurement a product can be designed or a process be operated with maximum efficiency minimum cost and with desired degree or reliability and maintainability

Measurement system

Measurement: it is the act or the result of a quantitative comparison between a pre-determined   standard and an unknown magnitude.
    The procedure and apparatus employed for obtaining the comparison must be prove-able the procedure  for this is called calibration.

         Measurand: The physical quantity or the characteristic condition which is the object of measurement in an instrument in an instrumentation system and it is variously termed as measurand or measurement  variable or instrumentation variable or process variable. The measurand may be fundamental or derived quantity. 


Fundamental quantity: It is the physical quantity which independent of any other quantities 

Derived quantity: It is the physical quantity which is derived from the fundamental quantity.
Eg. speed velocity acceleration. 

Instrumentation: The technology of using instruments to measure and control the physical and chemical properties of material is called instrumentation. 



Basic representation of measurement system 

Input signal===>measurement system===>output signal

Input to the measuring system is known as measurand ,output is called measurement 

Microsensors in Machatronics

The facilities which exist for the fabrication of miniature semiconductor components are adapted for  micro sensor design and development. The technology of sensor development is also known by the names micro mechanics and micro machining . 


     Micro sensor technology is an outgrowth of mechatronics industry because it uses the same materials and fabrication processes as integrated circuits. Fabricating a semi conductor device such as a transistor involves several processes

• Growing pure crystals of silicon
• growing layers of silicon dioxide
• Doping the silicon with impurities to change its semiconducting properties
• photo lithography
• etching.

Semiconductors are basically two-dimensional in nature and the devices are etched onto the top surface of silicon wafers. This technology has been extended to three dimensions in the case of micro sensors.


Sensing principle of micro sensors : 
     The primary characteristics of the micro sensors is that  it responds to a physical stimulus and transmits an impulse.
A signal is fed to the sensors that changes the form of energy, usually into electrical energy.The variable manipulation elements can convert the signal from analog to digital and can amplify or modulate the signal
Also contained in the sensing mechanism is a power supply for sensing and modulating purposes.

Manufacturing Management level and control level

Supervisory manufacturing is responsible for linking and co-ordinating the quality of production with the material , manufacturing process, energy and cost . These requirements are handled by sensors integrated with adaptive process control capability at plant level, manufacturing process and control level. 


      SENSOR LEVEL: 
At the sensory level, frequently required tasks in production processes are distance measurement, contour tracking, pattern recognition , identification of process parameters and machine diagnostics.