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Comparison of various camera tubes:

08

Parameter Photo electric Conversion Sensitivity Illumination (lumen) S/N Ratio Speed Resolution at 400 lines (5MHz) Special response Gamma

09 10

Operation Sizes

11 12

Cost Life (hours)

01 02 03 04 05 06 07

Image Orthicon Photo emission

Vidicon Photo conduction

Plumbicon Photo conduction

High 750 - 1000

Good 1500 - 2000

Better 750 - 1000

30 dB No lag 30 – 50 %

50 dB Severe lag 55 %

50 dB Reduced lag 40 – 50 %

Close to eye

Good

Poor in Red

1.0 near black.0.5 near high lights Elaborate Length- 15 to 20 inches. Diameter 3 to 4 inches Costliest 1500 – 6000 hours

0.4 to 0.9

0.9 to 1.0

Simple and Quick Length- 5 to 8 inches. Diameter 0.6 to 1.6 inches Cheapest 5000 – 20000 hours

Simple and Quick Length- 8 inches. Diameter 1.2 inches Costlier 2000 – 20000 hours

PROPERTIES

FERROMAGNETIC MATERIALS

PARAMAGNETIC MATERIALS

DIAMAGNETIC

State

They are solid.

They can be solid, liquid or gas.

They can be solid, liquid or gas.

Effect of Magnet

Strongly attracted by a magnet.

Weakly attracted by a magnet.

Weakly repelled by a magnet.

Behavior under non-uniform field

tend to move from low to high field region.

tend to move from low to high field region.

tend to move from high to low region.

Behavior under external field

They preserve the magnetic properties after the external field is removed.

They do not preserve the magnetic properties once the external field is removed.

They do not preserve the magnetic properties once the external field is removed.

Effect of Temperature

Above curie point, it becomes a paramagnetic.

With the rise of temperature, it becomes a diamagnetic.

No effect.

Permeability

Very high

Little greater than unity

Little less than unity

Susceptibility

Very high and positive

Little greater than unity and positive

Little less than unity and negative

Examples

Iron, Nickel, Cobalt

Lithium, Tantalum, Magnesium

Copper, Silver, Gold

Difference between Electric and Magnetic Circuit CHARACTERISTICS

ELECTROMOTIVE FORCE ( EMF) IN VOLTS

MAGNETOMOTIVE FORCE (MMF) IN AMPERE TURN

Current / Flux

Current= EMF/Resistance

Flux= MMF/Reluctance

Resistance / Reluctance

R=ρLA Where L is the length, ρ is resistivity, and A is the area.

ℜ=lμA Where l is the length, μ is the permeability, and A is the area.

Current / Flux Density

Current Density (amp/area) δ=IA

Flux Density ( Wb/area) B=φA

Series Circuit

Current in all elements is same, but voltage or emf is different across each element.

Same flux passes through all elements in series and sum of MMF’s across the elements equal to applied MMF.

Lines of Force

Electric lines of flux are not closed in an electric circuit.

Magnetic lines of flux are closed in a magnetic circuit.

Parallel Circuit

Voltage across all branches is same and equal to applied voltage whereas current in the branches is different.

MMF of each branch is same and equal to the applied MMF. Flux in each branch is different and their sum equals the resultant flux.

Insulation

Insulation confines the current to a definite path.

There is no perfect insulation for flux lines. It is impossible to confine all lines to the core path.

Temperature

Resistance of an electric circuit changes with change in temperature.

The permeability and therefore reluctance of a magnetic materials vary over a wide range if temperature changes.

Energy

Flow of an electric current in an electric circuit involves continuous dissipation of energy.

Energy is only needed for creating the flux initially and no energy is needed to maintain it.

Insulating Materials

There are certain materials which act as an insulator and current cannot flow through them

Since there are no magnetic insulators so flux can pass through any material.

Current / Flux Unit

Current is measured in Ampere (A).

Flux is measured in Weber (Wb).

Conductance / Permeance

Conductance=1/Resistance

Permeance=1/Reluctance

Electrons / Flux

In electric circuits, current flows (which is in fact the flow of electrons)

In magnetic circuits, flux sets up inside the magnetic circuit.

Electric / Magnetic Lines of force

Electric lines start from a positive charge and terminate to a negative charge

Magnetic lines start from a North pole and terminate to a South pole.

CHARACTERISTICS Representation

ELECTROMOTIVE FORCE ( EMF) IN VOLTS

MAGNETOMOTIVE FORCE (MMF) IN AMPERE TURN

We can summarise this in the following table: Type

Potentiometer

Rheostat

Number of Connections

Three Terminals

Two Terminals

Number of Turns

Single and Multi-turn

Single-turn Only

Connection Type

Connected Parallel with a Voltage Source

Connected in Series with the Load

Quantity Controlled

Controls Voltage

Controls Current

Type of Taper Law

Linear and Logarithmic

Linear Only