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120
5.
ELECTRICAL PARTS
2
3
Fig.
5.
3,4
Construction of selenium rectifier
(D
Coating which presents short circuits
®
Antielectrode
Selenium
©
Sheet
Positive direction
As shown in the figure to the left, the rectifier
wafers are either circular or square nickel plated
steel or aluminum sheet, vacuum coated with highly
purified selenium, combined with proper amount of
foreign element and heat treated under controlled
condition to produce a metallic selenium on which
cadmium, bismuth and tin ore appiied.
An electric
charge is passed in the opposite direction to the
arrow shown in figure 5. 34 to set up on electro-
chemical reaction.
This will allow the current to
readily flow in one direction while creating a large
resistance of several thousand tines in the opposite
direction, permitting only a negligible flow.
This
is the rectifying function of the selenium wafer.
It
is known as the recti+1cation function of selenium
and is due to the formation of
displayed
by the lamination effect created by the surface
between the semi-conductive metallic selenium wafer
and dielectric layer.
DIRECTION
Of
CURRENT
Fig.
5. 35
Selenium symbol
Humidity has a deteriorating effect on the selenium
wafer, therefore, waterproof coating is applied to
the rectifier, this will also prevent corrosion.
The symbol shown in Fig. 5. 35 is used to
note the rectifer.
This indicates that the rectifier
consists of one or more selenium wafers arranged
in either series or parallel, and the direction of the
arrow indicates the normal direction of current flow.
{Fig. 5.
35)
Selenium rectifier is durable and since it does not
deteriorate with age or usage, its life is practically
indeflnate.
It is relatively efficient for use with low voltage
load, therefore, it has found broad usage as a small
rectifier.
Further, it has a high overload capacity for a
short period of time as compared to the silicon
or geranium type rectifiers,
oriel
its long service life
is another advantage.
Note:
Rectifier is normally referred to an equipment
which performs the complete rectifying function
and including such accemssories such as the trans-
former, switches, filter, meter, and etc.
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