1. UNIT – I (B)
Characteristics of Instruments

2. Characteristics of Instruments
Shows the performance of instruments to be used.
Divided into two categories
A)Static characteristics: Involves measurement of constant or slowly varying quantities.
B)Dynamic characteristics: Involves measurement of quantities that varies with time.

3. Accuracy
It is the degree of closeness with which an instrument reading approaches the true value of the quantity being measured.
Accuracy is the ability of an instrument to show the exact reading.
Normally shown in percentage of error which of the full scale reading percentage.

4. Precise = Clearly defined
Precision
Precise = Clearly defined
Defined as the capability of an instrument to show the same reading when used each time (reproducibility of the instrument).
Measure of consistency in measurement.

5. Accuracy & Precision

6. Sensitivity
Sensitivity is the ratio of change in output of an instrument to the change in input.
Sensitivity= 𝜟 𝒒 𝒐 𝜟 𝒒 𝒊

7. Dead Zone
It represents the largest changes of input quantity for which there is no output.
For e.g. the input that is applied to an instrument may not be sufficient to overcome friction. It will only respond when it overcomes the friction forces.

8. Dead Zone
Dead Space
Output
Reading
Measured
Variables - +

9. Range
The region between the limits within which an instrument is designed to operate for measuring, indicating or recording a physical quantity is called the range of the instrument.
The range is expressed by stating the lower and upper values.
Range -100°C to 100°C

10. Span
Span represents the algebraic differences between the upper and lower range values of the instrument.
An instrument which has a reading range of – 100°C to 100 °C span is 200 °C.

11. Linearity
The linearity is defined as the maximum deviation from the linear characteristics as a percentage of the full scale output.

12. Reproducibility
Reproducibility is defined as the degree of closeness by which a given value can be repeatedly measured.
Perfect reproducibility signifies that the given readings that are taken for an input, do not vary with time.
Means no drift
Also named as Repeatability.

13. Resolution
If the i/p is slowly increased from some arbitrary value (non zero), it is found that o/p does not change at all until there is certain increment.
This increment is
called Resolution
Resolution indicates the
minimum change in input
variable that is detectable.

14. Drift
The drift is defined as the gradual shift in the indication over a period of time where in the input variable does not change.
Because of environment factors like stray electric fields, stray magnetic fields, thermal e.m.fs, changes in temperature, mechanical vibrations etc.

15. Thank you