Clear-com SB-704 User Manual download pdf (Page 20)

SB-704 MAIN STATION

2-2

link is activated. If there is more than one SB-704 or MS-704 in a system, the

link function can only be used at the station where the terminations are set on.

FAIL-SAFE POWER

An intercom power supply has special needs that are not met by traditionally

designed power supplies. An intercom power supply must work in adverse

conditions such as low AC line voltage, momentary shorts on the DC power

lines to the stations, and excessive peak loads during “power-on”conditions.

The following features are incorporated into the SB-704’s power supply:

• AUTOMATIC SHORT CIRCUIT PROTECTION: The SB-704’s

internal power supply checks each channel for a short or current overload.

If it detects a short the power supply will shut down that channel. A short

duration short circuit will not cause the power supply to interrupt power.

• AUTOMATIC OVERLOAD PROTECTION: The SB-704’s internal

power supply senses the difference between shorts and overloads. If an

overload is detected the power supply will shut down that channel. An

overload lasting a short period will not cause the power supply to

interrupt power.

• AUTOMATIC POWER RESTORE: The SB-704’s internal power

supply senses the difference between short-term and long-term shorts and

overload conditions. After the first few times a short or overload occurs,

the power supply will try to restore power after only 0.5 seconds. If the

short or overload persists or occurs repeatedly, the power supply will take

progressively longer (to a maximum of 20 seconds) to try to restore

power. This protects the power supply from damage due to overheating.

Once the short is removed, the channel will recover, even under a full load

condition. The automatic power restore times are shown in the following

chart:

Figure 2-2: Automatic Power Restore Times

14 15

0.5

Number of

seconds to

restore

Number of recent shorts or overloads

1 2 ... 15 16 17 18 19 20 21 22 23 24 25 ... 41 42

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Clear-com SB-704 User Manual Page 20