The document discusses secondary instruments used for measurement. It defines secondary instruments as those that must be calibrated by comparison with an absolute instrument or another calibrated secondary instrument. Secondary instruments are further classified as indicating, integrating, and recording instruments. Indicating instruments show the magnitude of a quantity, integrating instruments measure total quantity or energy over time, and recording instruments provide a continuous record of a quantity's variation over a period of time through pen tracings. The document also discusses concepts such as precision, accuracy, resolution uncertainty, types of errors including gross, systematic, and random, and the loading effect.

1. Concept of Measurement
System (Part B)
EE-401 Instrumentation and Measurement

3. Secondary Instruments
• These instruments are required to be calibrated by comparison with
either an absolute instrument or with another secondary instrument,
which has already been calibrated before the use.
• Secondary instruments are further classified as:
Indicating instruments
Integrating instruments
Recording instruments

4. Secondary Instruments

5. Indicating Instrument
• Indicating instruments are those which indicate the magnitude of an
electrical quantity at the time when it is being measured.
• The indications are given by a pointer moving over a calibrated (pre-
graduated) scale.
• Ordinary ammeters, voltmeters, watt-meters, frequency meters,
power factor meters, etc., fall into this category.

6. Integrating
• Integrating instruments are those which measure the total amount of
either quantity of electricity (ampere-hours) or electrical energy
supplied over a period of time. (sometime called as total measuring
instrument)
Sound Level Meter Watt Meter

7. Recording
• Recording instruments are those which
keep a continuous record of the variation
of the magnitude of an electrical quantity
to be observed over a definite period of
time.
• In such instruments, the moving system
carries an inked pen which touches lightly
a sheet of paper wrapped over a drum
moving with uniform slow motion in a
direction perpendicular to that of the
direction of the pointer.

8. Recording
Examples
ECG(Electrocardiographs)
Video Cameras.
Weather Monitoring Device.
Pedometer.
Fitness Tracker.
People Counter.
Thermoscope.
Graphical Temperature Meter.

9. Recording
.

11. Definitions of Some Static Characteristics

12. Definitions of Some Static Characteristics

13. Definitions of Some Static Characteristics

14. Definitions of Some Static Characteristics
Precision is the closeness of the various measured values
to each other. Accuracy, on the other hand, is the
closeness of the measured values with the true value of
the quantity.

15. Definitions of Some Static Characteristics
Ures = Resolution Uncertainty
Ri = Resolution of instrument scale
fi = fineness that scale divisions can be sub-divided

16. Definitions of Some Static Characteristics
Resolution uncertainty is important because it considers the limitations of measurement
equipment. The accuracy, precision, and capability of your measurements are limited by
the resolution of the measurement standard and unit under test.
No matter how careful or scientific measurements are…………….your measurement results
are limited by the resolution of your measurement standards and the unit under test.

17. Definitions of Some Static Characteristics

18. Definitions of Some Static Characteristics

19. Definitions of Some Static Characteristics

20. Example on Resolution
I

21. Types of Error
• Gross Error
• Systematic Error
• Random Error

22. Gross Error
• Gross Errors – gross errors occur when a mistake is made while recording data results,
using a measurement instrument, or calculating measurement.
• Can’t be subjected to mathematical treatment or rectification
• Occurs when the same instrument is used for a relatively different condition.
Examples
1. Low voltage calculating voltmeter when used for high voltage
2. Resistance when used for longer time that heats up the circuit
3. Two or more reading should be taken to avoid such situation
4. The most common human error in measurement falls under this category of
measurement errors. For example, the person taking the reading from the meter of
the instrument may read 23 as 28.

23. Systematic Error
• These are the errors that remain constant or change according to a definite
law on repeated measurement of the given quantity.
• Can be Instrumental error or Environmental error
The two primary causes of systematic error are faulty instruments or
equipment and improper use of instruments.

24. Systematic Error
Avoiding Instrument Error (mechanical structure and calibration or operation)
1. Selecting a proper measuring device for the particular application
2. Calibrating the measuring device or instrument against a standard
3. Applying correction factors after determining the magnitude of
instrumental errors.

25. Systematic Error
Avoiding Environmental Error (temperature, light, pressure, humidity,
gravity, dust, etc. )
1. Use the measuring instrument in the same atmospheric conditions in
which it was assembled and calibrated.
2. If the above precaution is not possible then deviation in local
conditions must be determined and suitable compensations are
applied in the instrumental reading.
3. Automatic compensation, employing sophisticated devices for such
deviations, is also possible.

26. Systematic Error
• Systematic errors can be identified and eliminated after careful inspection of the
experimental methods, cross-calibration of instruments, and examination of
techniques.
• Gross errors are caused by experimenter carelessness or equipment failure.

27. Systematic Error Examples
• Forgetting to tare or zero a balance produces mass measurements that are always
"off" by the same amount. An error caused by not setting an instrument to zero prior
to its use is called an offset error.
• Not reading the meniscus at eye level for a volume measurement will always result in
an inaccurate reading. The value will be consistently low or high, depending on
whether the reading is taken from above or below the mark.
• Measuring length with a metal ruler will give a different result at a cold temperature
than at a hot temperature, due to thermal expansion of the material.

28. Systematic Error Examples
• An improperly calibrated thermometer may give accurate readings within a certain
temperature range, but become inaccurate at higher or lower temperatures.
• Measured distance is different using a new cloth measuring tape versus an older,
stretched one. Proportional errors of this type are called scale factor errors.
• Drift occurs when successive readings become consistently lower or higher over
time. Electronic equipment tends to be susceptible to drift. Many other instruments
are affected by (usually positive) drift, as the device warms up.

29. Systematic Error

30. Random Error
• These errors are of variable magnitude and sign and do not maintain any
known law. The presence of random errors become evident when different
results are obtained on repeated measurements of one and the same quantity.
• The effect of random errors is minimized by measuring the given quantity
many times under the same conditions and calculating the arithmetical mean of
the results obtained.
• The mean value can rightly be considered as the most probable value of the
measured quantity since random errors of equal magnitude but opposite sign
are of approximately equal occurrence when making a great number of
measurements.

31. Random Error Examples
• When weighing yourself on a scale, you position yourself slightly differently each time.
• Measuring the mass of a sample on an analytical balance may produce different values as
air currents affect the balance or as water enters and leaves the specimen.
• Measuring your height is affected by minor posture changes.
• Measuring wind velocity depends on the height and time at which a measurement is taken.
Multiple readings must be taken and averaged because draughts and changes in direction
affect the value.
• Readings must be estimated when they fall between marks on a scale or when the
thickness of a measurement marking is taken into account.

32. Loading Effect
• The incapability of the system to faithfully
measure the input signal in undistorted form is
called loading effect.
• This results in loading error as well.
• Sometimes loading effect occurs due to the
connection of measuring instruments in an
improper way. Suppose a voltmeter is connected
with parallel of a very high resistance. Due to the
high resistance of the voltmeter itself, the circuit
current changes.

33. Loading Effect
• Similarly, an ammeter has
a very low resistance. So
if an ammeter is
connected in series with a
very low resistance, the
total resistance of the
circuit changes, and in
succession, the circuit
current also changes.

34. Measurement of Error
• It is impossible to measure the exact value of the measurand. There is always
some difference between the measured value and the absolute or true value of
the unknown quantity (measurand), which may be very small or may be large.
• Let Am and A be the measured and absolute value
• Absolute Error
• Relative Error
• Percentage Error

35. The limiting error and area of reading
• Sometimes instruments and even measured quantities are given with a positive as well as
negative limits for error. Such error may an addition of percentage or absolute error to
the measured quantities.
• Thus the absolute value lies inside these limits and is often written in the form of limiting
error limits.
• Limiting error always gives least(small) error at full scale deflection. At lower values,
when calculated, the limit error is a larger addition to the measured value
• For example, a resistance band is drawn for 5% tolerance etc.

42. Thanks