Broadcast Tools DSC-20 Installationshandbuch PDF herunterladen (Seite 8)

Preliminary 8-2002 RSHD Smartcaster Installation Manual

Far greater protection is available with an Uninterruptible Power Supply (UPS). A UPS

starts off by having a very good quality surge protection circuit, and in addition contains

one or more large rechargeable batteries. If the electric power goes off, or drops below a

safe voltage, a high speed sensing circuit boosts or replaces it with battery power in a tiny

fraction of a second preventing damage to the connected equipment or data loss, and

gives

you time to save your data, and shut down.

The amount of time that a UPS can keep a system running depends on the capacity of the

UPS and the current drawn by the connected equipment. In other words, the bigger your

monitor and more powerful your computer, the bigger the UPS you will need to have a

reasonable run time when the power fails. A UPS is rated in watts or VA (Volts X

Amperes) or both. The best way to determine how big a UPS you need is to go to the

UPS manufacturer's website. You will find a calculator to fill in listing what components

you own, and the calculator will determine what size UPS will provide a specific number

of minutes of battery protection. Decide the length of backup time you wish and buy that

size UPS.

A simple rule of thumb is to buy a UPS that has VA rating at least twice the computers

power supply rating in watts. For example, a computer with a 300-watt supply would

need at least a 600VA UPS.

http://www.apc.com

Electrical Safety

In electronics we must be concerned with the protection of out equipment from damage

and ourselves from electrical shock or worse. Let's discuss protecting ourselves first,

since if we get killed we won't be able to finish whatever project we are working on.

All of the circuits you can come into contact with inside a computer are harmless to

human beings because they operate at 12 volts or less. The sole exception to this is inside

the power supply where the connections to house current are made, and before it is

reduced to the low voltage DC supplied to the computer circuits. Anyone foolish enough

to take apart the power supply without disconnecting it from the power cord may as well

go for the Darwin Award for eliminating stupidity from the gene pool.

Human skin has a surface resistance to electricity of about 22,000 ohms. Because of this

you would need to contact about 25 volts before you would even start to feel anything.

The component of electricity that can hurt you is the current. Interestingly, small currents,

well under an ampere are the most dangerous. A shock of an ampere or more will cause

the heart to clamp (stop) and often it will start beating again on its own as soon as the

current is eliminated. A shock in the 20 to several hundred milliamp range can cause the

heart to fibrillate (quiver) and in that condition it is much more difficult to restart.

Many of you have been told that charged capacitors are dangerous. Only large capacity

ones at fairly high voltages, as stated above, can overcome skin resistance. No such

http://www.pcnineoneone.com/howto/electricity3.html?

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Broadcast Tools DSC-20 Installationshandbuch Seite 8