Clear-Com MS-222 User Manual

INSTALLATION / Clear-Com MS-222 2-Channel Main Station
SECTION
2
INSTALLATION OF THE MS-222 2-CHANNEL MAIN STATION
2.1 INSTALLATION OVERVIEW
The MS-222 is a combination of a very versatile intercom station and a system power
supply. Installations can vary
depending on what features are used.
The fundamental concept of Clear-Com Party-Line intercom is that all stations
provide high impedance current sourced signals into a single common system
termination. The line
drivers in a station have a
source impedance greater
than 10
KOhms.
The termination of an intercom line (or channel) is a 220 Ohm resistor in series with a
4.7 KOhm that is paralleled with a 10 uF capacitor. The impedance of the network at
audio frequencies is 220 Ohms. The DC resistance of the network is 5 KOhms. The
high DC resistance allows a CALL voltage to be placed on the line without drawing
too
much current. A CALL signal is a
DC voltage greater than 10 volts on
the line.
The DC source for this CALL signal is also a current source there by providing a high
impedance and not affecting the audio signal.
The receive or "listen" section of stations contain a 'hybrid null' circuit that attempts to
reject (null) any "talk" signal being sent by that station on that channel. The 'hybrid
null' circuit depends on a known impedance on the intercom line to accomplish this.
Variations
in impedance on the
line upset the 'null'.
Clear-Com main
and some remote stations
provide switch selectable
termination
networks on all intercom output lines. It is up to the user to determine where the
termination will be provided. An unterminated line will cause excessive levels,
possible oscillation of line drivers, and sever unbalance of hybrid null networks. A
double or
multiple terminated line will
cause low levels and sever
unbalance of hybrid
null circuits.
CAUTION: All Clear-Com
Intercom lines must be terminated.
Care must be taken
not to fail to terminate
or to 'double' terminate a line. All unused intercom inputs
must be terminated
to keep the line drive
circuits stable.
CLEAR-COM STATION TYPES:
Clear-Com party-line intercom stations all fall into one of four distinct catagories that
relate to system powering and termination. The four types are as follows:
A. MAIN STATION:------ Supplies system power for external stations.
Provides switch selectable terminations.
B. MASTER STATION: - Contains a power supply just for itself.
- Provides switch selectable line terminations.
C. REMOTE STATION: - No power supply. Derives power from the intercom line.
- May or may not have terminations.
D. POWER SUPPLY: --- Supplies system fower for external stations.
--- Provides switch selectable terminations.
11/90 Rev. 1.0 Page 9

Clear-Com MS-222 Specifications

General

Brand	Clear-Com
Model	MS-222
Category	Intercom System
Language	English