3D-camcorder from Panasonic

After the overwhelming success of "Avatar" and a string of films released in theaters in 3D, many wanted to shoot in volume family gatherings, weddings and parties. Just for them, the company "Panasonic" released a special attachment to their stereoscopic camera series HDC-SDT750K, allowing to implement a residential filming in 3D-format Full-HD. For the line of photographic LUMIX G Micro System «Panasonic" also offers a removable lens that allows you to create 3D-images. So, every now for reasonable money ($ 1,300 for video attachment and $ 250 for the camera lens) can enter the era 3D-shooting. The camera shoots in the side-by-side 3D format, much like Sky 3D, so it's not Full HD. But images are sharp enough, and the 3D effect itself can be really spectacular. Careful composition is the key to creating engaging 3D footage -- flowers positioned a metre or less from the lens, for example, provide an effective forward-facing focal plane, with the background stretching into the distance. Without the subject really close to the glass, the dimensional effect is diminished. For everyday family shooting, this works really well. Shoot someone in close-up and they'll pop out of the frame.

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part 3 chapter 1

3.3  Induced Voltage on a Conductor Moving in a Magnetic Field

1.       If a conductor moves or ‘cuts’ through a magnetic field, voltage will be induced between the terminals of the conductor at which the magnitude of the induced voltage is dependent upon the velocity of the wire assuming that the magnetic field is constant. This can be summarised in terms of formulation as shown:

e_ind = (v x B) l

         where:

        v – velocity of the wire

        B – magnetic field density

        l– length of the wire in the magnetic field

2.       Note: The value of l (length) is dependent upon the angle at which the wire cuts through the magnetic field. Hence a more complete formula will be as follows:

e_ind= (v x B)l cosθ

where:

q - angle between the conductor and the direction of (v x B)

3.       The induction of voltages in a wire moving in a magnetic field is fundamental to the operation of all types of generators.

 

4.  The Linear DC Machine

Linear DC machine is the simplest form of DC machine which is easy to understand and it operates according to the same principles and exhibits the same behaviour as motors and generators. Consider the following:

Equations needed to understand linear DC machines are as follows:

Production of Force on a current carrying conductor

Voltage induced on a current carrying conductor moving in a magnetic field

e_ind = (v x B) l

Kirchoff’svoltage law

                                            

Newton’s Law for motion

F_net = ma

Starting the Linear DC Machine

1.     To start the machine, the switch is closed.

2.     Current will flow in the circuit and the equation can be derived from Kirchoff’s law:

                               

At this moment, the induced voltage is 0 due to no movement of the wire (the bar is at rest).

3.     As the current flows down through the bar, a force will be induced on the bar. (Section 1.6 a current flowing through a wire in the presence of a magnetic field induces a force in the wire).

                                 

                Direction of movement: Right

                                               

4.     When the bar starts to move, its velocity will increase, and a voltage appears across the bar. 

Direction of induced potential: positive upwards

5.     Due to the presence of motion and induced potential (e_ind), the current flowing in the bar will reduce (according to Kirchhoff’s voltage law). The result of this action is that eventually the bar will reach a constant steady-state speed where the net force on the bar is zero. This occurs when e_indhas risen all the way up to equal V_B. This is given by:

6.     The above equation is true assuming that R is very small.  The bar will continue to move along at this no-load speed forever unless some external force disturbs it.   Summarization of the starting of linear DC machine is sketched in the figure below:

 

The Linear DC Machine as a Motor

1.         Assume the linear machine is initially running at the no-load steady state condition (as before).

2.         What happen when an external load is applied? See figure below:

3.         A force F_load is applied to the bar opposing the direction of motion. Since the bar was initially at steady state, application of the force F_loadwill result in a net force on the bar in the direction opposite the direction of motion.

4.         Thus, the bar will slow down (the resulting acceleration a = F_net/mis negative).  As soon as that happen, the induced voltage on the bar drops (e_ind  = v↓ Bl).

5.         When the induced voltage drops, the current flow in the bar will rise:

6.         Thus, the induced force will rise too. (F_ind   ↑  = i↑ lB)

7.         Final result à the induced force will riseuntil it is equal and opposite to the load force, and the bar again travels in steady state condition, but at a lower speed. See graphs below:

8.         Now, there is an induced force in the direction of motion and power is being converted from electrical to mechanical form to keep the bar moving.

9.         The power converted is P_conv = e_indI = F_ind  v  à An amount of electric power equal to  e_ind i is consumed and is replaced by the mechanical power F_ind v  à MOTOR

10.   The power converted in a real rotating motor is: P_conv =  τ_ind ω

The Linear DC Machine as a Generator

1.         Assume the linear machine is operating under no-load steady-state condition. A force in the direction of motion is applied.

2.         The applied force will cause the bar to accelerate in the direction of motion, and the velocity vwill increase.

3.         When the velocity increase, e_ind= V ↑ Bl will increase and will be larger than V_B. 

4.         When e_ind > V_B the current reverses direction.

5.         Since the current now flows up through the bar, it induces a force in the bar (F_ind= ilB to the left).  This induced force opposes the applied force on the bar.

6.         End result à the induced force will be equal and opposite to the applied force, and the bar will move at a higher speed than before. The linear machine no is converting mechanical power F_ind  v to electrical power e_ind i à GENERATOR

7.         The amount of power converted : P_conv=  τ_indω

NOTE:

·            The same machine acts as both motor and generator.  The only difference is whether the externally applied force is in the direction of motion (generator) or opposite to the direction of motion (motor).

·            Electrically, e_ind> V_B à generator

·            e_ind < V_B à motor

·            whether the machine is a motor or a generator, both induced force (motor action) or induced voltage (generator action) is present at all times.

·            Both actions are present, and it is only the relative directions of the external forces with respect to the direction of motion that determine whether the overall machine behaves as a motor or as a generator.

·            The machine was a generator when it moved rapidly and a motor when it moved more slowly. But, whether it was a motor or a generator, it always moved in the same direction.

·            There is a merely a small change in operating speed and a reversal of current flow.

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chapter 1 part 2

II.   Eddy Current Loss

1.         A time-changing flux induces voltage within a ferromagnetic core.

2.         These voltages cause swirls of current to flow within the core – eddy currents.

3.         Energy is dissipated (in the form of heat) because these eddy currents are flowing in a resistive material (iron)

4.         The amount of energy lost to eddy currents is proportional to the size of the pathsthey follow within the core.

5.         To reduce energy loss, ferromagnetic core should be broken up into small strips, or laminations, and build the core up out of these strips. An insulating oxide or resin is used between the strips, so that the current paths for eddy currents are limited to small areas.

Conclusion:

Core loss is extremely important in practice, since it greatly affects operating temperatures, efficiencies, and ratings of magnetic devices.

3.   How Magnetic Field can affect its surroundings

3.1  FARADAY’SLAW – Induced Voltage from a Time-Changing Magnetic Field

Before, we looked at the production of a magnetic field and on its properties. Now, we will look at the various ways in which an existing magnetic field can affect its surroundings.

1.         Faraday’s Law:

‘If a flux passes through a turn of a coil of wire, voltage will be induced in the turn of the wire that is directly proportional to the rate of change in the flux with respect of time’

                                                          

If there is N number of turns in the coil with the same amount of flux flowing through it, hence:

where:     N – number of turns of wire in coil.

 Note the negative sign at the equation above which is in accordance to Lenz’ Law which states:

‘The direction of the build-up voltage in the coil is as such that if the coils were short circuited, it would produce current that would cause a flux opposing the original flux change.’

Examine the figure below:

§ If the flux shown is increasing in strength, then the voltage built up in the coil will tend to establish a flux that will oppose the increase.

§ A current flowing as shown in the figure would produce a flux opposing the increase.

§ So, the voltage on the coil must be built up with the polarity required to drive the current through the external circuit. So, -e_ind

§ NOTE: In Chapman, the minus sign is often left out because the polarity of the resulting voltage can be determined from physical considerations.

2.         Equation  e_ind = -d/dt assumes that exactly the same flux is present in each turn of the

coil. This is not true, since there is leakage flux. This equation will give valid answer if the windings are tightly coupled, so that the vast majority of the flux passing thru one turn of the coil does indeed pass through all of them.

3.         Now consider the induced voltage in the ith turn of the coil,

Since there is N number of turns,

            The equation above may be rewritten into,

where l (flux linkage) is defined as:

  (weber-turns)

4.         Faraday’s law is the fundamental property of magnetic fields involved in transformer operation. 

5.         Lenz’s Law in transformers is used to predict the polarity of the voltages induced in transformer windings.

3.2  Production of Induced Force on a Wire.

1.        A current carrying conductor present in a uniform magnetic field of flux density B, would produce a force to the conductor/wire. Dependent upon the direction of the surrounding magnetic field, the force induced is given by:

where:

        i – represents the current flow in the conductor

        l – length of wire, with direction of l defined to be in the direction of current flow

        B – magnetic field density

2.        The direction of the force is given by the right-hand rule. Direction of the force depends on the direction of current flow and the direction of the surrounding magnetic field. A rule of thumb to determine the direction can be found using the right-hand rule as shown below:

      Right Hand rule

3.        The induced force formula shown earlier is true if the current carrying conductor is perpendicular to the direction of the magnetic field. If the current carrying conductor is position at an angle to the magnetic field, the formula is modified to be as follows:

 Where:   q - angle between the conductor and the direction of the magnetic field.

4.        In summary, this phenomenon is the basis of an electric motor where torque or rotational force of the motor is the effect of the stator field current and the magnetic field of the rotor.

see part 3

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