ECE-govt exam and ese preparation : Measurements &Instruments

SYLLABUS

To brush up your basics you can try A. K. Sawhney -A course in Electrical and Electronic Measurements and Instrumentation.

I. Electrical Measurements

S No.	Topics to be covered
01	Error Analysis, Units & Standards
02	Basics of Electrical Instruments
03	Electromechanical Indicating Instruments
04	Measurement of Power &Energy
05	Bridge Measurement of R, L & C
06	Measurement of frequency and PF
07	Potentiometers & Instrument

II.Electronic Measurements

01	Basics of Transducers
02	Resistive, Inductive & Capacitive Transducers
03	Piezo Electric Transducers
04	Measurement of Temperature
05	Measurement of Flow, Viscosity & Humidity

III.Instrumentation

01	Cathode Ray Oscilloscope
02	Digital Voltmeter
03	Analog Electronic Voltmeters
04	Q-Meter

Let's go through each and every topic and its related important terms day by day.

Specifications of Instruments:

• Accuracy - Error between the measurement and the true value i.e. conformance between the measurement and the standard.

When accuracy is measured in terms of error and guaranteed accuracy error (GAE) is measured with respect to full scale deflection. Limiting error (in terms of measured value) is defined as

$LE=\frac{GAE*(Full scale deflection)}{Measured Value}$

• Precision: Consistency of the measurement. It is associated to the capacity of the sensor to give the same output (measurement) under same input (Stimulus).

• Precision: Quality of the system to give always the same output under the same stimulus (input).

•Sensitivity Change the output quantity per unit change in input quantity.

$S=\frac{\Delta q_{o}}{\Delta q}$

.• Resolution: The smallest increment of the input that can be sensed.

Errors in Measurements

TYPES OF ERROR

a) Gross Error : Error due to human negligency,i.e. due to loose connection, reading the value etc.

b) Systematic error : Errors are common for all observers like instrumental errors environmental errors and observational errors.

c) Random errors : Error due to unidentified causes & may be positive or negative.

Absolute Errors :

   $\delta _{A}=A{_{m}}-A{_{r}}$

   $A{_{m}}=$ Measured Value

$A{_{r}}=$ True Value

Relative Errors :

$\epsilon _{r}=\frac{Absolute Errors}{True Value}=\frac{\delta _{A}}{A_{T}}$

Composite Error :

(i) Sum of Quantities

$X=X_{1}+X_{2}$

$\delta _{x}=\pm(\delta _{x1}+\delta _{x2})$

(ii) Difference of Quantities

      $X=X_{1}-X_{2}$

$\delta _{x}=\pm(\delta _{x1}+\delta _{x2})$

So for sum & difference absolute errors are added.

(iii) Multiplication of Quantities

   $X=X_{1}*X_{2}*X_{3}$

$\frac{\partial X}{X}=\pm \left ( \frac{\partial X_{1}}{X_{1}}+\frac{\partial X_{2}}{X_{2}}+\frac{\partial X_{3}}{X_{3}} \right )$

(iv) Division of Quantities

   $X=\frac{X_{1}}{X_{2}}$

   $\frac{\partial X}{X}=\pm \left ( \frac{\partial X_{1}}{X_{1}}+\frac{\partial X_{2}}{X_{2}} \right )$

So, for multiplication & division, fractional or relative errors are added and if

$X=\frac{X_{1}^{m}X_{2}^{n}}{X_{3}^{p}}$

$\frac{\partial X}{X}=\pm \left ( m\frac{\partial X_{1}}{X_{1}}+n\frac{\partial X_{2}}{X_{2}}+p\frac{\partial X_{3}}{X_{3}} \right )$

Standard deviation of combination of quantities

$\sigma _{x}=\sqrt{\left ( \frac{\partial X}{\partial X_{1}} \right )^{2}\sigma _{x_{1}}^{2}+\left ( \frac{\partial X}{\partial X_{2}} \right )^{2}\sigma _{x_{2}}^{2}+..................+\left ( \frac{\partial X}{\partial X_{n}} \right )^{2}\sigma _{x_{n}}^{2}}$

ECE-govt exam and ese preparation

Pages

Monday, March 23, 2020

Measurements &Instruments