RECTIFICATION

RECTIFIER

An electrical device that allows current to flow easily in only one direction

DIODE

An electronic device that contains two electrodes

Full wave Rectification

Changing the negative half to a positive -converts opposing half of AC cycle so current (electrons) is always moving in the same direction.

X-ray tubes operate best when recieving?

Direct current from the cathode to the anode.

This has 120 pulses per 60Hz current

Full wave rectification

This has 60 pulses per 60Hz current

Half wave rectification

What happens when a single rectifier fails in a full wave circuit?

It will act as a half wave unit going from 120 pulses to 60 pulses per second.

Disadvantage of self-rectification:

Low heat loading capacity of an x-ray tube -danger of overheating the anode, causing thermionic emission. -can destroy filament

Half wave rectification is also called what?

One-Pulse Rectification -it has one voltage peak per cycle -accomplished in self rectification -can use one or two diodes to work -60 pulses per 60 Hz

Advantages of full rectification:

Permits a large (significant) increase in the tube rating or heat loading capacity (output capacity) -results in larger exposures that can be used w/out damaging the tube -higher mA and kVp settings

Rectifier function-

Permits electrons to flow easily in one direction while offering high resistance to movement in the other direction.

What is the advantage of full rectification in relation to a radiograph machine:?

Rectification permits a large increase in the tube rating or heat-loading capacity.

HALF WAVE RECTIFICATION

Suppresses the opposing half of the incoming AC cycle. (Represented by the half of the curve that lies below the line.)

Negative Half cycle

The opposing half of the flow is ignored and not utilized

What is the principle disadvantage of self-rectification in relation to a radiograph machine?

The principle disadvantage of self-rectification is the low heat loading capacity of an xray tube in a circuit and exposure factors are limited to lower values.

What is the definition for rectification?

The process of changing alternate current to direct current

RECTIFICATION

The process of changing alternating current to direct current.

Full wave rectification is also called what?

Two pulse recitfication since there are two voltage peaks per cycle. -four rectifier diodes are connected -120 pulses per 60HZ

Disagvantages of full rectification:

Using the entire AC wave results in the production of a high percentage of low energy x-rays, or low kV range

What determines rectifier failure in a single phase system?

When one rectifier fails in a single phase full wave (four rectifier) it operates as a two diode half wave rectifier which produces a drop in reading to half one half the normal value.

Diode rectification

When the n-type material are combined to form p-n junction, electrons are allowed to flow only in one direction.

Diode rectification: (during forward bias):

When the negative terminal of the AC source is connected to the N-end and the positive terminal to the P-end, electrons flow toward each other reducing the barrier voltage allowing current to flow across junction and external circuit.

Diode rectification(during reverse bias):

When the positive terminal of the AC source is connected to the N-end and the negative terminal to the P-end, electrons and holes move away from each other increasing the barrier voltage and preventing current across the junction.

Half wave Rectifier Circuit

X-ray tube connected to secondary of high voltage transformer through diode rectifiers. Has alternating voltage applied to secondary of high voltage transformer.

Full wave rectifiers consist of:

four diode "bridge" configuration with single phase.

P type semiconductors

have electorns traps, spaces where electrons can be found.

N type semiconductors

have loosely bound electrons that are relatively free to move about inside the material.

Semiconductors are classed in two types:

n type and p type

The x-ray tube serves as a Diode.

the xray tube allows passage of electrons only from the cathode to the anode during the positive half-cycle of the AC curve.

Diode rectification

uses solid-state diode rectifiers -made of semiconductors of which silicon is the most commonly used.

determing rectifier failure

when one rectifier fails in a single phase full wave (four) rectifiers, it operates as a two diode (half wave) rectifier. -produces a drop in the millimeter reading to about one half the normal value -this causes radiographic underexposure.

self tube rectified circuit

xray tube acts as a rectifier current only flows from cathode to anode. -cathode is source of free electrons