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Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages-Instrumentation

In this article, we will tell you about Rectifier instruments and their types. Also, all the information on the Half or Full Wave rectifier is available here.

Rectifier Instruments

Rectifier instruments are no new type. Rather, they are permanent magnet moving coil instruments. The only difference between these instruments is that they have a rectifier unit attached to them. Which converts AC to DC. This way the instrument can also measure such value with DC.

Rectifier instruments are commonly used in communication circuits. They are especially suitable for measuring very low AC voltages and currents. With the help of shunts, multipliers, and instrument transformers it can increase the range of instruments.

Rectifier

A rectifier is a device or component that converts an AC supply into a pulsating DC. Rectifier allows current to flow in only one direction. So when AC passes through a rectifier, the current passes through one of its directions. While the rectifier in the opposite direction offers much higher resistance. And the flow of current from it stops.

Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages
Rectifier

Types of Rectifier

The following two types of rectifiers are commonly used in electrical instruments.

1. Metal Rectifiers

Types of Metal Rectifiers

1.1 Coper Oxide Rectifiers

These rectifiers consist of copper discs with copper oxide mounted on one side. In this way, current can pass from copper to copper oxide but not in the opposite direction i.e. from copper oxide to copper. The diameter of a disk is usually 1/2 inch. Multiple discs are joined together in series and joined together by insulated bolts to form a larger unit. Brass washers on both sides of the discs and metal fins for heat dissipation are also installed. Copper oxide can pass a maximum of 0.1 amperes to 0.15 ampere current at 8 volts per disc of a rectifier. The discs have to be enlarged for more current or the rectifier is connected in parallel.

Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages
Copper Rectifiers

1.2 Selenium Rectifiers

These rectifiers consist of iron discs. One side of them is covered with selenium. In this way, the current flow from the iron to the selenium but the current does not flow at all due to the high resistance of the current in the opposite direction. The current and voltage rating of a disc of the selenium rectifier is higher than that of the copper rectifier. One of its discs can carry 0.2 to 0.3-ampere current at 16 to 18 volts.

Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages
Selenium Rectifiers

2. Semiconductor Rectifiers

It is a circuit in which alternating current (AC) is converted to pulsating DC using one or more diodes. The diode is made by combining a P-type semiconductor and an N-type semiconductor. It is also called a PN junction.

Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages
Semiconductor Rectifiers

Compared to other rectifiers, they have the following features.

  1. They are small in size.
  2. The texture is simple, easy to prepare.
  3. Do not be disturbed by tremors and branches etc.
  4. Their current density is high.
  5. There is very little heat dissipation.
  6. Their age is double and their efficiency is high.

Types of Semiconductor Rectifiers

2.1 Half-Wave Rectifiers

This instrument consists of a moving coil (PMMC) and a diode. Diode converts AC supply to half-wave placing DC. When the measured voltages are given between X and Y. When the positive half cycle of these voltages reaches the diode, the resistance of the diode decreases to zero or very low due to the forward bias. Therefore the current passes through it easily and shows the PMMC instrument reading.

Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages
Half Wave Rectifiers


When the diode gets a negative half cycle, the resistance of the diode is very high due to the reverse bias. And no current passes through it so the meter does not get current Meanwhile the meter control tries to bring the spring pointer back to zero. But until the control torque returns to the pointer, before the next positive off-cycle, the diode conducts and the meter begins to receive current.

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In this way, the interval between the current received by the meter is so short that the moving system of the meter is not affected by it. Therefore this voltmeter deflates in terms of the average amount of supply voltage. To calibrate the instrument key scale with the supply RMS quantity, the average quantity displayed is multiplied by the form factor 1.11.

2.2 Full-Wave Rectifiers

The full-wave rectifier consists of a PMMC and four diodes. When the measured AC voltage is supplied to the X and Y terminals, the diodes D1 and D3 will be forward biased in case of a positive half cycle. And the current will pass through them and get to the meter. And will embrace to display meter readings. (Note that during this time diodes D2 and D4 become reverse bias. Therefore no current passes through them).

In the case of the negative half cycle, diodes D2 and D4 will be forward bisected and the current will pass through them to the meter and the meter will start showing readings. (Note that during this time diodes D1 and D3 are reverse biased. Therefore no current will pass between them).

Rectifier Instruments-Rectifier Types & Uses-Half/Full Wave Rectifiers-Rectifier Advantages
Full Wave Rectifiers


In this way, both the half-cycle (positive and negative) conducts from the bridge. Also, the direction of the current passing through the meter during both half cycles is the same. However, the quantity does not remain the same at different intervals. Therefore, its output is called Full-Wave Pulsating DC. The PMMC meter provides straight and uniform deflection even on this type of supply without swinging back and forth. This is because their moving system does not follow the rapid changes in placement DC. Therefore this voltmeter deflates in terms of the average amount of supply voltage. To calibrate the scale of the instrument by the RMS quantity of the supply, the average quantity shown is multiplied by the form factor 1.11.

Uses of Rectifiers

  1. Rectifier instruments can be used as ampere meters. But their current range is very small, from zero to 100 mille amperes. An instrument transformer is usually used to increase the range.
  2. These instruments can be used as voltmeters. It also has a low voltage range, from zero to 300 volts. But for low range, there is no scale linear so a step-up transformer is used.

Rectifier Advantages

  • Can be used on both A and DC supplies.
  • Used up to very low frequencies.
  • It consumes very little power.
  • Very suitable for measuring small amounts of current and voltage.
  • Are more sensitive than ordinary AC instruments.
  • Possess a high degree of accuracy.
  • The textures are simple and reliable.
  • They can also be used in high-power circuits.
  • The magnetic field of the atmosphere does not affect them.

Rectifiers Disadvantages

  • It can be used as an ampere meter directly in a very short range.
  • They are used to measure low voltage. Also, enough voltage drops parallel to the diode.
  • The scale of the rectifier is not linear for different values of resistance, voltage, and current. Therefore, their scale is narrower from the beginning.
  • Give accurate readings only on a pure sine wave of supply.
  • Temperature change has little effect on readings.


Disclaimer

All the information on the rectifier is given here exactly. Types of Rectifier and Half / Full Wave Rectifier, Uses and Benefits of Rectifier are explained.

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2 Comments

  1. Very NCY and Informative article about Rectifier.
    Full Explanation with Diagrams.
    Admin: Thank You.

    ReplyDelete