CALIBRATION

1. Lecture-7
Calibration

2. CALIBRATION
• Calibration is the process of making an adjustment or marking a scale so that the
readings of an instrument agree with the accepted and the certified standard.
• In other words, it is the procedure for determining the correct values of measurand
by comparison with the measured or standard ones.
• The calibration offers a guarantee to the device or instrument that it is operating
with required accuracy, under stipulated environmental conditions.
• The calibration procedure involves the steps like visual inspection for various
defects, installation according to the specifications, zero adjustment etc.,

3. Contd.,
• Thus calibration is the procedure for determining the correct values of
measurand by comparison with standard ones.
• The standard of device with which comparison is made is called a standard
instrument.
• The instrument which is unknown & is to be calibrated is called test
instrument.

4. Types of calibration methodologies:
There are two methodologies for obtaining the comparison between test
instrument and the standard instrument. These methodologies are
• Direct comparisons
• Indirect comparisons

5. Direct comparisons:
• In a direct comparison, a source or generator applies a known input to the
meter under test.
• The ratio of what the meter is indicating and the known generator values
gives the meter’s error. In such case the meter is the test instrument while the
generator is the standard instrument.
• The deviation of the meter from the standard value is compared with the
allowable performance limit.
• With the help of direct comparison a generator or source also can be
calibrated.

6. Indirect comparisons:
• In the indirect comparison, the test instrument is compared with the
response standard instrument of same type i .e., if test instrument is a
meter, the standard instrument is also a meter, if the test instrument is a
generator; then the standard instrument is also a generator & so on.
• If the test instrument is a meter then the same input is applied to the test
meter as well a standard meter.
• In case of generator calibration, the output of the test generator as well as
the standard, are set to same nominal levels.
• Then the transfer meter is used which measures the outputs of both
standard and test generator

7. Calibration of an ammeter

8. Calibration of voltmeter

9. Calibration of wattmeter

10. Thank you