Multimeter

Multimeter  is a multi-purpose electronic measuring instruments, mainly used to measure the field of physical, electrical, electronic, etc., generally contain ammeter (ammeter), a voltage meter (voltmeter), resistance meter (ohmmeter) and other functions , also known as universal design, multi-meter, multimeters, multimeter or multimeter.

Pointer multimeter known as VOM (Volt-Ohm meter, volt - ohm meter) in English, but this name is not usually used for digital multimeter.

Multimeter with a portable device used for basic troubleshooting, but also a desktop device is placed in a factory or laboratory workbench.

Some meter resolution can reach seven or eight digits; such a device, it often occurs in the laboratory is used as a reference voltage or resistance, or to adjust the standard multi-function performance.

Basic measurement functions:
Current, voltage and resistance measurements, generally regarded as the universal plan of basic functions. Early multimeter manufacturers AVO brand name of these three is the unit of measurement device capable of measuring the abbreviation: Ampere (Ampere), V (Volt), ohms (Ohm)

Generally we have a basic multimeter measurement functions:

DC voltage (DCV)

DC current (DCmA, DCA)

AC voltage (ACV)

Resistance (Ω, KΩ, MΩ)

AC current (ACmA, ACA) not all multimeters have, especially low-level multimeter.
Pointers and digital multimeter:

Pointer multimeter, using a magnetic field deflecting pointer dial, this watch head and the same classic galvanometer; digital multimeter is used to display LCD, vacuum fluorescent display (VFD), LED, OLED, etc. In addition, it also uses digital tube early.

Pointer multimeter on the new and second-hand market are hard to find. But because zero and accurate readings from the instrument panel are prone to error, and difficult to scale subdivision restrictions in accuracy and resolution are not as digital meters. And the digital meter voltage profile with a high input impedance, and can immediately read the number, the pointer meter unless there are marked directly refers to the value of large-scale , It shall be observed and counted within the meaning of the small-scale relations with neighboring large measure, it read really value. However, in some cases, such as speed of response header, easy to quickly outline that value, or the value of the response in terms of jitter, etc., remain some of the advantages, and the internal circuit is simple, easy to learn measuring circuit theory, therefore, part of the some situations or circumstances are still in use. In addition, some digital meters have reacted faster than the number of changes strip show, emulate pointer effects to quickly grasp the changes in the value of the benefit.

In order to improve pointer multimeter input impedance voltage profile and reduce the impact of treatment of the circuit under test, and some high-end pointer multimeter uses vacuum tubes to amplify the input signal, this design is also known as vacuum multimeter voltmeter (VTVM, Vacuum Tube Volt Meters) or vacuum multimeter (VTMM, Vacuum Tube Multimeters). Such as the use FET to amplify the input signal, it is FETVM.

Digital multimeter with digital meter based and is specifically called a digital multimeter (DMM, Digital MultiMeter). In this device, the measured signal is converted into a digital voltage and digital pre-amplifier, and then by the digital display directly display the value; thus avoiding parallax when reading the error caused.

Similarly, better systems and electronic circuit technology, but also to improve the measurement accuracy. General basic accuracy pointer instrument (DC voltage range) between 2% to 5%, the common basic accuracy of 3 to 4%. Digital portable digital multimeter common portable type basic accuracy of 0.5% to 1%, advanced models, it can reach ± 0.025%, and the table device as much as one millionth of accuracy.

Resistor or Resistance

In electromagnetism, the resistance is the ability of an object to hinder current through to the equation is defined as

R= v/r

Wherein, R is the resistance, V is the voltage across the object, I is the current through the object.
Assuming that the object has a uniform cross-sectional area, the resistance and resistivity, proportional to the length, and inversely proportional to the cross-sectional area.

SI units, the resistance in ohms (Ω, Ohm). Resistance reciprocal conductance in siemens (S).
The temperature is assumed constant, many substances will abide by Ohm's law, objects consisting of these substances, the resistance is constant, not with the current or voltage. These substances referred to as "ohm substance"; failure to comply with Ohm's law matter is "non-ohmic material." R circuit symbol often used to represent, for example: R1, R02, R100 and so on.

Wire like a class of objects, having a low resistance, can be very efficient current transfer, such objects called "conductor." Usually by conductor such as copper, gold and silver-metal manufacturing has excellent conductive properties, or inferior conductive properties of aluminum.

The resistor is a circuit element having a specific resistance. Raw materials used in the preparation of the resistor there are many; what materials should be used, depending on the specified resistance, energy dissipation, and so accurate, and cost factors.

Suppose wire conducting a high frequency alternating current, since the skin effect, the effective cross-sectional area of the wire decreases. Assume several parallel wires together, due to the proximity effect, the effective resistance of each wire will be greater than the resistance of a single wire. For ordinary household AC power, since the frequency is low, the effect is very small, you can ignore these effects.

Direct current

Direct Current, DC is the unidirectional flow of electric charge. DC current, by batteries, thermocouples, solar cells or commutator motor generator. Direct current can flow through the conductor such as wire, but may flow through the semiconductor, insulator, or even capable of electron or ion beam shape by vacuum. DC current is constant direction, and thus distinguished from alternating current (AC).

DC current can be called from by using rectifiers, which includes electronic components (usually) or electromechanical components  a current is supplied only on alternating current electric current switching apparatus of the flow in one direction. DC current can be made into an alternating current of the inverter or the motor generator.

The first commercial power transmission (by Thomas Edison in the late nineteenth century, the development of) the use of direct current. Since the DC current significant advantages over alternate transformation and transmission, and today almost all of the AC power distribution. In the mid-1950s, HVDC transmission, is now an option, rather than the long-distance high-voltage AC power system. For applications such as DC third rail power system, AC was assigned to a substation, which uses a rectifier power is converted to direct current.

DC current to charge the battery, and in almost all electronic systems as a power source. A very large number of DC power for the production of aluminum and other electrochemical processes. DC Some railway propulsion, especially in urban areas, is used to transmit large amounts of electricity HVDC on the remote site or an AC power grid interconnection.

Alternating Current

 Alternating Current, abbreviations: AC refers to the size and direction of the current varies cyclically, running average over a cycle is zero. Unlike direct current does not change direction over time.

Generally sinusoidal waveform. AC can effectively transmit electricity. But in fact there are other applications of waveform, such as triangular wave, square wave. Mains life is having to use the AC sinusoidal waveform.

Once discovered electromagnetic induction, the method generates an alternating current was known. Early finished by the British Michael Faraday (Michael Faraday) developed with the French Hippolyte Pike Xi (Hippolyte Pixii) at all.
In 1882, the British electrician James Gordon built a large two-phase alternators. Lord Kelvin and Sebastian Fei Landi (Sebastian Ziani de Ferranti) developed early alternators, frequency between 100 Hz to 300 Hz.

In 1891, Nikola Tesla made "high frequency" (15,000 Hz) of the alternator patents.
In 1891, the multi-phase AC generator is used to supply current, alternating current frequency thereafter alternator usually designed Hz to 100 Hz in 16 rooms, with an arc lamp, incandescent lamp or electric motor use.

According to the law of electromagnetic induction, when the magnetic field around the conductor changes, the induced current in the conductor. Normally, rotating magnet called the rotor conductor wound on the core of the coil fixed group, called the stator, a magnetic field when it is over, they generate electricity. It called basic machine to generate AC alternator.

Power Capacitors

Power capacitors for power systems and electric equipment capacitors. Any two metallic conductors separated by a dielectric medium, constitute a capacitor. The size of the capacitance of a capacitor, its dielectric properties and geometry between the two plates to decide. When the capacitor is used in the AC voltage.

Power capacitors use can be divided into eight kinds:

 01- shunt capacitor. Formerly known as phase shifting capacitors. Reactive power is mainly used to compensate the inductive load power system to improve power factor, improve voltage quality and reduce line losses.

02- series capacitor. Connected in series with the power frequency high voltage transmission and distribution lines to the distribution of the compensation circuit inductance, improving the system of static and dynamic stability, improve the quality of the line voltage, longer transmission distance and increasing transmission capacity.

03-coupling capacitor. HF communications are mainly used high-voltage power lines, measurement, control, protection, and as a member of extracting electrical energy use.

 04- Breaker capacitors. Formerly known as the equalizing capacitors. Parallel play equalizing effect on fracture in EHV breakers, the voltage between each fracture in the breaking process and even when disconnected, and to improve the extinguishing characteristics of the circuit breaker breaking capacity increase.

05- Electric capacitors. For the frequency range of 40 to 24,000 Hz electric equipment system to improve power factor, improve voltage or frequency circuit characteristics.

06- Pulse capacitors. Mainly from the energy storage effect, it is used as impulse voltage generator, the impact of current generators, test tank circuit breakers and other basic energy storage element.

 07- DC and filter capacitor. For HVDC devices and high-voltage rectifier filter device.

08- Standard capacitor. For high voltage measuring dielectric loss frequency circuit, a capacitor or used as a standard measurement of high voltage capacitor voltage dividing means.

Carved in the power system HV power capacitors (6KV above) and low-voltage power capacitors (400V)

Low Voltage Power Capacitor oil paper divided by nature self-healing power capacitors and power capacitors, power capacitors by function common and intelligent power capacitors do not repeat the general formula, focusing on intelligent power capacitor.

Microphone

Microphone, also known as An electro-acoustic equipment, is a microphone, a sound transducer converts electrical voltage is generated by sound waves to the electro-acoustic components, and then converted to electricity. For a variety of public address equipment. Microphone wide range of simple circuit.

Analysis of the microphone circuit is mainly controlled by two things: (1) signal transmission loop analysis, relatively simple analysis of various microphone input jack circuits. (2) Analysis of the microphone amplifier, microphone amplifier is a low noise audio amplifier small-signal analysis mic level control circuit is not difficult

The microphone generates an electrical signal by the motion of the magnetic field conductor. Vibrating diaphragm driven by a coil so that the coil in a magnetic field generates an induced current. Features: Firm structure, stable performance, durability, low price; the frequency characteristics of a good, in the frequency range 50-15000Hz flat amplitude-frequency characteristic curve; good point; no DC voltage, easy to use, low noise.

Characteristics, amplitude-frequency characteristic curve flat in the audio frequency range, which is better than the dynamic microphones; non-directional; high sensitivity, low noise, sound soft; the output signal level is relatively large, low distortion, good transient response, this is less than the advantage of dynamic microphones; unstable operating characteristics, low frequency sensitivity with the increase in the use of time and decline, life is short, we need to create a DC power supply is inconvenient to use at work.

There condenser microphone preamplifier, of course you have to have a power supply, due to the volume relationship, the power supply is usually placed outside the microphone.
In addition to supplying the polarization voltage of the capacitor of the diaphragm, but also for the tube or transistor preamplifier supply voltage necessary. We call it the phantom power.

Integrated circuits

An integrated circuit (IC), also known as chip or microchip, is a structure of small dimensions of semiconductor material, a few square millimeters of area on which electronic circuits are generally manufactured by photolithography and which is secured in an encapsulated plastic or ceramic. The encapsulation has appropriate metallic conductors for connection between the IC and a printed circuit.

Integrated circuit is a pill or solid chip found in all or most of the necessary electronics embedded in a resin, to perform some function. These components are mostly transistors, although they also contain resistors, diodes, capacitors, etc.
Considering the level of integration (number of components) integrated circuits are classified as:

SSI (Small Scale Integration) small level: less than 12

MSI (Medium Scale Integration) means: 12-99

LSI (Large Scale Integration) Large: 100-9999

VLSI (Very Large Scale Integration) large: from 10 000 to 99 999

ULSI (Ultra Large Scale Integration) ultra large: not less than 100 000

As for the integrated functions, the circuits are classified into two groups:
Analog integrated circuits.
They can consist from simple encapsulated together without bonding between them until complete devices such as amplifiers, oscillators or even complete Radio receivers’ transistors.
Digital integrated circuits.

They can range from simple logic gates (AND, OR, NOT) to the most complicated as microprocessors.