Mitsubishi VS-6043 Uživatelský manuál stáhnout pdf (Strana 4)

EXTRONEWS MAY/JUNE 1999

4

MANDI SPEER

Taking the Strain Out

by Mandi Speer,

National Sales Manager

A cable with strain relief is better

than a cable without strain relief,

right? Not quite. Understanding what

strain relief is, and what to look for,

will help you evaluate the effective-

ness of a cable’s strain relief. All strain

relief cables aren’t created equal.

Although two strain reliefs may look

the same, one may be effective while

the second may provide little or no

strain relief. Figures 1–3 each show a

cable that is being pulled at a 90

degree angle to the BNC connector.

The way the cable responds depends

on whether proper strain relief is

present, and on the quality of the strain

relief.

Figure 1 shows a cable without a

strain relief. Note how sharply the

cable is bent. This is referred to as a

small bend radius. The small radius is

displayed on the graph within figure 1.

The coaxial cable may be crushed, torn

or completely severed at the point of

the bend since it is being pressed

against the sharp edge of the BNC

connector. The dielectric will most

likely be crushed by the bend,

changing the distance between the

cable’s shield and the center conductor.

This will change the impedance,

resulting in signal reflection. The

result will be signal degradation or

signal loss. Considering the number of

cables in a typical AV system, the

potential for such a problem is consid-

erable. In a complex system locating a

damaged cable could take substantial

time.

Good strain relief increases the bend

radius, preventing the cable from

being damaged. Figure 2 shows

Extron’s new BNC cable which

features strain relief. Strain relief is

accomplished by means of a boot. The

boot is a semi-rigid protective

covering at the BNC-cable connection.

Note that the bend radius is now

increased, even with tension on the

cable. The cable no longer has the

sharp bend. Notice how the

sections/notches of the strain relief

boot compress evenly, so there is no

kink at any point. The result is a more

gradual and consistent bend, which

prevents damage to the cable. Good

strain relief results when the boot is

neither too rigid nor too flexible.

As was stated earlier, all strain reliefs

are not created equal. Consider Figure 3.

This cable appears to have a strain

relief. However, when actually tested,

the cable still bends too sharply. The

boot is too rigid and does not bend,

so the cable still kinks. All that has

changed is that the point of the kink

has been moved away from the

connector. Other cables may have

boots that are too flexible, allowing

sharp bends within the boot section.

Again, proper strain relief does not

occur. The best way to test the

quality of a cable’s strain relief is to

bend it at a 90 degree angle to the

connector. Watch for binding

between the sections and resulting

sharp kinks. Cable with proper

strain relief will always produce the

result seen in Figure 2.

Extron’s BNC-4 HR cable and

BNC-5 HR cable feature strain

relief. Feel free to test the quality

of our strain relief. We are sure you

will be pleased with the results.

Small bend radius

FIGURE 1.

A cable without a strain relief

Bend radius increased

through the use of

strain relief

FIGURE 2.

A cable with Extron's strain relief

Small bend radius

FIGURE 3.

A cable with an ineffective strain relief

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