A PRESENTATIONONEEM

BY:- RUMITA KUMARI 11101150717

CONTENTSFrequency measurement

Need for measurement

Digital frequency meter

Basic circuit & working

Grounding 1) theory & example

Shielding 1) purpose & practical guidelines.

FREQUENCY MEASUREMENTFrequency:- Frequency can be defined as the number of occurrences within a given period of time.

NEED FOR MEASUREMENT Following parameters can be found using this :-

Time period ( f = 1/T) Angular frequency ( ω = 2Лf) Wave number ( ϋ = 2Л/λ) wavelength velocity (f = v/λ)

MEASUREMENT OF FREQUENCY

Different devices which are used to measure frequency :- Revolution per minute(traditionally)

StorboscopeFrequency counterCathode ray oscilloscopeWien bridge oscillatorDigital frequency meter

A BOUNCING BALL IS CAPTURED WITH A STORBOSCOPIC FLASH AT 25 IMAGES PER SEC.

DIGITAL FREQUENCY METER

BASIC CIRCUITThe block diagram of the basic circuit of a digital frequency meter is shown below:-Unknown

frequency source

Amplifier Schmitt trigger

Start-stop gateCounters

COMPLETE CIRCUIT DIAGRAM FOR NORMAL DFM.

GROUNDING AND SHIELDING Good design of electronic circuits and

systems begins with grounding and shielding. Grounds and shields improve safety and reduce interface from noise. Properly grounded circuits and instruments reduce dangerous voltage differentials between them. Shields minimize interference from noise by reducing noise emission and noise susceptibility.

GROUNDING

GROUNDINGThe term ground in electrical circuits refers to a current return path through the earth. It is represented by the following symbol:-

THE CONCEPT OF EARTH GROUND Being electrically neutral, earth is

considered to be at zero potential and establishes a convenient reference frame for voltage measurements. Note that voltmeters read only the difference in potential between two points , absolute measurements can be made by using earth as a reference. A true earth ground, as defined by the National electrical code, physically consists of conductive pipe rod driven into the earth to a minimum depth of 08 feet.

EXAMPLE…The connection of a power

supply:-The supply is represented as a

variable voltage battery . The three terminals are shown as +ve, -ve , and a ground terminal. The ground terminal of the supply is tied to the case of the instrument , which in turn is wired to a true earth ground.

THE CONNECTION OF A POWER SUPPLY

earthload

SHIELDING

SHIELDING Shielding is a way of protecting

conductors from corrosion , rusting or depletion. Shielding can be anything from using a coaxial or shielding cable , to a sealed conductive chamber for circuit isolation.

Purpose :- 1) It protects the circuit from noise or unwanted signals.

2) It protects the outside world from interference of its own.

3) It is mostly used to block E-fields.

PURPOSE AND GUIDELINES It is especially useful where open frame

transformers or unshielded coils are used and would otherwise exchange signals by mutual inductance.

For a shield to be effective there must be no currents flowing through the shield itself.

Practical guidelines :- 1) Twisted pair cable is usually effective

up to 1MHz . It is cheaper and flexible.

PRACTICAL GUIDELINESCoaxial cables are expensive , less

flexible , low loss and less variance in characteristic impedance from dc to very high frequencies (>200MHz).

Ribbon cable is ubiquitous in instrumentation. These are much more expensive , useful and less flexible. It is good for low frequency operations.

THE END

Thanks…