Q1. Discuss in detail isolation amplifier in detail with diagram?
Isolation amplifier as the name suggest is a form of differential amplifier that provides electrical isolation and an electrical safety barrier for measuring small signals in the presence of a high common mode voltage.
They “re essentially instrumental in practical shielding purposes as they protect data acquisition components from common mode voltages ,which are potential differences between the instrument and signal grounds.In case where common mode voltage interacts with instruments without isolation amplifier ,usually a noisy representation of the signal under investigation is the final product , this is because of no restrictions on the circulation of ground currents .in case of adequate level of mode voltage for the purpose ,instrument destruction is also a likely income.
Isolation amplifier also find implementation in medicine equipment (e.g life support) to ensure isolation of a patient from the leakage current via power supply.
These are also used in shielding the amplifier and instrument as a collective unit without salvaging accuracy of measurement as it allows the front end of the amplifier to float with respect to common mode voltage ,approaching the isolation barrier ‘s breakdown voltage lying in the excess of 1000 volts at times.
These amplifiers are also used for amplifying various low level signals in varied multiple channel applications .Measurement errors due to ground loops can also be evaded .Moreover ,amplifiers with internal transformers eliminate external isolated power supply, hence effectively changing the electric regularities to the user and instrument ‘s favour. They are usually used as analogue interface between
Systems with separate grounds.
Isolation amplifiers cam also include isolated power supplies for both input output stages ,or external power supplies on each isolated portions for the above usage.
Q2. Why do we need a saw tooth voltage to display a waveform on a CRO . Explain how Lissajous patterns are used in a CRO to measure an unknown frequency.
The time base generator which is responsible for producing the sweep and that will be amplified by the horizontal amplifier and then carried to the deflection plates of a CRO.
Sawtooth voltage play an important role to deflect the beam along X- axis and to refresh the CRO screen after every cycle giving stable image. Without sweep voltage the image displayed in screen will be a straight line.
CRO plays an important role in analysing the wave form of different signals. The main part of the CRO is CRT consist of
(vertical deflection plate, horizontal deflection plate ,electron beam).
When two different sine waves simultaneously applied to horizontal and vertical plates the pattern which is obtained in CRO screen is called Lissajous pattern. If the shape of Lissajous pattern has slight change then it also reflects into the phase difference and also in the ratio of frequencies of two sine waves .
Q.3 A DMM has 4 ½ digit display .What is the maximum number it can read ? What is the resolution ?
If the DMM has 4 ½ digit display then it means that there will be five segments , one half digit and 4 half digits. The maximum number it can read would be 19999.
If we want to display 10 KV on a 4 ½ digital display we will use the leading half digit and in this case we will have five digit of resolution.