Free electrical instrumentation training - Learn about the errors in measurement

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In this article (and the next few) I will be talking about electrical instrumentation and give you a free training on the various aspects of the same. We will take up the matter of of measurement using instruments and the various errors that could arise due to several factors.

To take a good measurement only the use of proper instrument is not necessary enough, but also proper reading of instrument and recording the data is required. Our little carelessness during a reading could make a huge error in measurements.

Error in measurement are classified into following three categories

  1. Gross error
  2. Systematic errors
  3. Random/Accidental error

Gross error

Such type of error appears in measurement due to user mistake in using the instrument, recording data or calculating data. A person may read a watt meter indication of 211W as 112W.Similarly using a watt meter to measure low power factor load, may leads to error. Some people memorize string of data and then write down it collectively, which may induce error in data.

Systematic error

Non calibrated measuring equipment induces such type of error. They are also called inherent errors, as they part of equipment. They are further divided as:

Constructional error: It is impossible to manufacture equipment that fulfills all requirements for measurement. A designer always reveals all potential errors in design.

Error in reading or observation :There are many factors that lead to such type of error in reading.They include:

Construction of scale :Error is induced in measurement if scale is not uniform or it is blurred.

Straightness and fairness of indicator :Error is induced in reading if indicator is not fine and straight.

Parallax :if mirror under indicator/pointer is missing then it could induce error in reading.

Efficiency of viewer: Working efficiency of observer could also affect the error in measurement. Observer may become tired physically or mentally, if continuous readings are being recorded for long time. This mental tiredness could possibly create error in reading.

Error associated with methods :There are different ways to take measurement or taking reading. Every approach has possible drawback, and induces error in measurements.

Some other factors that also contribute for error in measurement mainly are;

Temperature variation Temperature variation changes the parameter of components installed in measuring equipment. The small effect of each component leads to a noticeable error in measurement.

Aging effect :Due to wear and tear in measuring equipment, errors are induced in reading. Un-calibrated equipment also creates such errors.

Electrostatic and electromagnetic induction: Weak shielding could allow electrostatic and electromagnetic waves, there by inducing voltage or could change binary from value from"0” to “1” and vice versa. This result in errors in measurements.

Mechanical error :Due to friction, wear and tear errors are induced in measuring equipments.

Random or Accidental Errors: After tuning all the parameters to get a precise result, there is possibility that some level of tolerance might be left. The origin of these errors is not clear. There may be several factors that contribute for such errors like; noise, incapability of a person to take proper reading. Corrective actions to avoid these random errors are to take several readings.