shorts on the DC power lines to the stations, and excessive peak loads during power-on and sometimes
during use. The mission of an intercom power supply is torn between giving its all to provide power in
the face of these adverse conditions and protecting itself from them. This mission finds an intelligent
balance in the PS-232. The following features are incorporated into the PS-232 power supply to make it
quickly react to shorts and overloads yet provide a long, reliable product life:
AUTOMATIC SHORT CIRCUIT PROTECTION: The microprocessor in the PS-232 checks each
channel for a short or current overload 100 times per second. If a short lasting longer than 700 mS
is detected, the microprocessor will shut down that channel. An short lasting less than 700 mS will
not cause the PS-232 to interrupt power. However, during this 700 mS, the output current will be
limited to 2 amperes.
AUTOMATIC OVERLOAD PROTECTION: The PS-232 senses the difference between shorts and
overloads. If an overload lasting longer than 2.5 seconds is detected, the microprocessor will shut
down that channel. An overload lasting less than 2.5 seconds will not cause the PS-232 to interrupt
power. During this 2.5 seconds, the output voltage will be reduced to limit the current to 2 amperes.
AUTOMATIC POWER RESTORE: The PS-232 microprocessor senses the difference between
short-term and long-term shorts and overload conditions. After the first few times a short or overload
occurs the PS-232 will try to restore power after only 0.5 seconds. If the short or overload persists
or repeatedly happens, the microprocessor will take progressively longer (to a maximum of 20
seconds) to try to restore power. This protects the PS-232 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:
INDIVIDUAL CHANNEL SHORT CIRCUIT PROTECTION: Each individual channel is separately
overload and short circuit protected and may draw as much as 2 Amps, though the total to both
channels is limited to 2.25 Amps. A short on any one intercom line will not bring the whole system
down.
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FRONT PANEL INDICATIONS: There are two Overload indicators on the front panel (one for each
channel) and a Power indicator for the power supply. The Overload indicators light steady when an
overload or short condition is detected. They blink if power to a channel has been shut off as a
result of an overload or short. There is also an indicator to show when channels A and B are linked.
PARALLELING MULTIPLE POWER SUPPLIES: Multiple power supplies can be paralleled to
increase system capacity. The PS-232 microprocessor will automatically detect the actions of other
power supplies during overloads and shorts circuits to restore power as quickly as possible.
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Power supply lines connected together at remote stations will disable the individual channel s h o r t
circuit protection feature.
Number of Recent
Shorts or Overloads
Number of
Seconds to
Restore
5
10
15
2
4
6
8
10
12
14
16
18
20
20
0
1
3
5
7
9
11
13
15
17
19
0.5
2
4
7
14
20
0
Clear-Com PS-232 Power Supply
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