Clear-Com MS-704 - Manual (Page 18)

M S - 7 0 4 / R M - 7 0 4 F O U R - C H A N N E L M A I N / R E M O T E S T A T I O N S 2 - 2
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 MS-704’s power supply:
• AUTOMATIC SHORT CIRCUIT PROTECTION: The MS-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 MS-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 MS-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 2-4: Automatic Power Restore Times
• INDIVIDUAL CHANNEL SHORT CIRCUIT PROTECTION: Each
individual channel is separately overload and short circuit protected and may
draw as much as 1.2 amperes, though the total to both channels is limited to
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
5
10
15
20
0
0
0.5
2
4
7
14
20
Number of
seconds to
restore
Number of recent shorts or overloads