Oscillographs  The devices is used to measure very small quantities; i.e. microamperes. The deflection of moving coil is corded holding a small mirror.  A minor deflection of the mirror is routed through magnifying lens on photosensitive rolled paper for recording sensitive readings.

Oscilloscope

Cathode-ray-Tube 1. Three Electron guns (for red, green, and blue phosphor dots) 2. Electron beams 3. Focusing coils 4. Deflection coils 5. Anode connection 6. Mask for separating beams for red, green, and blue part of displayed image 7. Phosphor layer with red, green, and blue zones 8. Close-up of the phosphor- coated inner side of the screen

Electronic Gun

Cathode Ray Tube Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a tube. To release electrons into the tube, they first must be detached from the atoms of the cathode. In early vacuum tubes (Crookes tubes) this was done solely by the high electrical potential between the anode and the cathode. In modern tubes this is assisted by making the cathode a thin wire filament and passing an electric current through it. The current heats the filament red hot. The increased random heat motion of the filament atoms assists in knocking electrons out of the atoms at the surface of the filament, into the evacuated space of the tube. This process is called thermionic emission and can reduce the anode to cathode voltage needed to obtain effective currents.atoms vacuum tubesCrookes tubesfilament electric current thermionic emission

Working of CRT It works on the following principles : (i)thermionic emission (ii)deflection of the electron beam by the electric and magnetic field (iii)fluorescence produced by the electron beam on a fluorescent screen

CRT

Electrodynamics a y = eV d md y v vxvx vyvy L d EdEd VdVd ; v y = a y t = eV d L mv x d  ;  = tan -1 vyvy vxvx

Oscilloscopes The signal travels directly to the vertical deflection plates of the cathode ray tube (CRT). Voltage applied to these deflection plates causes a glowing dot to move. (An electron beam hitting phosphor inside the CRT creates the glowing dot.) A positive voltage causes the dot to move up while a negative voltage causes the dot to move down.

Oscilloscopes The signal also travels to the trigger system to start or trigger a "horizontal sweep." Horizontal sweep is a term referring to the action of the horizontal system causing the glowing dot to move across the screen. Triggering the horizontal system causes the horizontal time base to move the glowing dot across the screen from left to right within a specific time interval. Many sweeps in rapid sequence cause the movement of the glowing dot to blend into a solid line. At higher speeds, the dot may sweep across the screen up to 500,000 times each second.

Oscilloscopes Together, the horizontal sweeping action and the vertical deflection action traces a graph of the signal on the screen. The trigger is necessary to stabilize a repeating signal. It ensures that the sweep begins at the same point of a repeating signal, resulting in a clear picture as shown in following figure.

Oscilloscopes Block Diagram

Tutorial The force exerted on electrons beam by an electric field : F = q.E Where F is force in Newton. N q is charge on electron in Coulomb,C E is electric filed intensity in volt/meter When an anode voltage V a is applied to the accelerating anode, the potential energy associated with an electron having charge q is: PE = q.V a while K.E.=½mv 2 so the velocity of electron

Tutorial When such an electron enters a deflecting plate, the velocity of electron motion in x-direction remains the same through the deflecting plates, but in Y-direction: Therefore the force in y- direction is and other variables are:

Instrument Tape Recorder

Functional layout of tape recorder

Applications Tape speed BandwidthStudio recording 38 cm/s (15 ips)20 Hz–20 kHzHigh-quality home recording 19 cm/s (7½ ips) 30 Hz–15 kHz 40 Hz–13 kHz General domestic music and speech 9.5 cm/s (3¾ ips)30 Hz–15 kHzRecording speech (dictation)

Industrial Tape Recorder

Industrial Tape Recorder…. Tape recorders rely on magnetic tape to store data. Typically used for the recording and playback of voices or music, tape recorders have also been used for recording and storing computer information. Floppy and hard disks rely on the same principles of magnetic recording to store data as regular tape recorders use. Though this technology has been surpassed in recent years by laser- based recording processes, magnetic tape recording is still an affordable and widespread means of storing information.

How it works The recording process itself relies on the principles of magnetism. The tape recorder uses electromagnets (the heads) to apply a magnetic flux to the ferric oxide on the tape. Each electromagnet is made of an iron core wrapped with wire. There is a small gap in the electromagnet head which actually allows the recording to take place. When you press record on the machine, the audio data flows through the wire, creating a magnetic field around the iron core. Magnetic flux flows in to bridge the gap in the head of the electromagnet. The flux creates a particular pattern, and it magnetizes the ferric oxide in the tape as it rolls across the head. The ferric oxide instantly stores the sound by recording the pattern created by the flux.

How it works …… Stereo tape recorders have two heads that in combination span about half of the tape's width. Each records one channel, the end result being two channels recorded on half the tape. This enables you to turn the cassette over and to record another two separate channels on the other half of the tape's width. Due to this placement of the heads, most tape recorders enable you to record on side A and side B of a cassette without sound overlapping.

Hyperlink orials/java/taperecorder/index.html orials/java/taperecorder/index.html

Tape Recording Process

Erase Head Before passing over the record head, a tape in a recorder passes over the erase head which applies a high amplitude, high frequency AC magnetic field to the tape to erase any previously recorded signal and to thoroughly randomize the magnetization of the magnetic emulsion. Typically, the tape passes over the erase head immediately before passing over the record head.record headmagnetic emulsion The gap in the erase head is wider than those in the record head; the tape stays in the field of the head longer to thoroughly erase any previously recorded signal.

Tape Playback When a magnetized tape passes under the playback head of a tape recorder, the ferromagnetic material in the tape head, magnetic field penetrates a coil of wire which is wrapped around it. Any change in magnetic field induces a voltage in the coil according to Faraday's law. This induced voltage forms an electrical image of the signal which is recorded on the tape.ferromagneticFaraday's law

Problem The magnetization of the magnetic emulsion is proportional to the recorded signal while the induced voltage in the coil is proportional to the rate at which the magnetization in the coil changes. This means that for a signal with twice the frequency, the output signal is twice as great for the same degree of magnetization of the tape. It is therefore necessary to compensate for this increase in signal to keep high frequencies from being boosted by a factor of two for each octave increase in pitch. This compensation process is called equalization.magnetic emulsionequalization

Multi-channel Tape Head