Basic concepts about Signal Generator, Electronic Multimeter and Digital Multimeter

● Signal Generator

Oscillator is the basic element of all signal generators. Depending upon the oscillator design or application, terms such as sine-wave generator, test oscillator, signal generator, audio signal generator, function generator etc. are used. In all these types of generators, the frequency and amplitude of the signal are accurately known and controlled over a wide range. The simple sine-wave generator consists of an oscillator and an attenu- ator. A function generator is an instrument which is capable of delivering different types of nonsinusoidal signals (pulse, square wave, triangular wave, sawtooth wave) in addition to sine wave signals. The most commoh general- purpose audio signal generator consists of a Wien-bridge oscillator. The oscillator is tuned with a variable capacitor while it is band switched by using different resistors. The output level can be changed by using an attenuator.

● Electronic  Multimeter 

Electronic meters use are most suitable for measuring low voltages and currents. In electronic ac voltmeters the ac input voltage is rectified and amplified and then applied ordinary dc meters. In some cases ac signal is rectified after amplification. The solid-state electronic multimeter is one of the most versatile instruments capable of measuring dc and ac voltages as well as currents and resistances. It generally contains the following basic elements:
(i) amplifier and indicating meter (may be a de microammeter),

(ii) a rectifier section to convert ac into dc 
(iii) input attenuator or range switch, 

 (iv) function switch to select various  measurement functions, 

(v) internal battery or built-in power supply for ac line operation. 

● While using an electronic multimeter the following precautions are to be taken

(i) The meter should be properly adjusted for zero setting.

(ii) After switching on one must wait for a few minutes for steady state measurement, particularly for vacuum-tube-made meters.

 (iii) instead of open test leads which may pick up stray signals, shielded coaxial cable should be used for measurements. 

● Electronic measuring devices have a number of advantages over the instru- ments based on the d' Arsonval meter or permanent magnet moving coil instruments: 

 (i) Electronic measuring instruments have very high input impedance and therefore draw extremely low current from the test circuit and do not load the instruments: test circuit,

 (ii) Conventional meters are not suitable for very low voltages and currents. Electronic meters are very sensitive and can measure extremely low voltages with sufficient accuracy. 
(iii) The most important feature of electronic meters is their good frequency response.

●Digital Multimeter 

A digital multimeter displays the measured values of different quantities directly as discrete numerals instead of a pointer deflec- tion on a continuous scale as in analog devices. Numerical readout is advan- tageous because it reduces humam reading and interpolation errors, eliminates parallax error and increases the speed of reading. A digital meter is a versatile and accurate instrument that can be used in many laboratory measurements. Smaller size, lower power requirement, lower cost and better performance of digital making them more and more meters than its analog counterpart are popular in the laboratory Now-a-days some digital meters are being available at reasonably low cost, which can be used to measure capacitance, inductance, frequency, transistor current gain and temperature in addition to voltage, current and resistance. Also they can be used to test semiconductor diodes and also to check the continuity of electrical circuits. Some modern digital meters give sound signals to indicate the continuity of a circuit.

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