Measurement and Instrumentation
The thermocouple instruments do not have

Absence of frequency error
High sensitivity
High degree of measuring accuracy
Independence of ambient temperature

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Measurement and Instrumentation
In DC potentiometer measurments, a second reading is often taken after reversing the polarities of the DC supply and the unknown voltage and the average of the two reading is taken. This is with a view of eliminate the effects of

 Ripples of the DC supply.
  Stray thermal emfs.
 Errorneous standardisation.
 Stray magnetic fields.

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