Technical description 7000 series TouchLine station

The 7000 series of TouchLine master stations are loudspeaking intercom stations, with or without handset, and with or without display. In this document, the full-featured stations with handset and display are describes. These are the 70013 desk station and the 70343 eall/desk stations, wich functionally are the same.

Functional Description

For the description of the station, refer to circut diagrams and block diagrams.

The station is connected to the exchange by 4 wires; a-, b-, c-, and d-wires. The a/b-wires are the loudspeaker wires, and the c/d-wires are the microphone and digit selection wires. The currents in the a/b-wires when display module is installed is shown in parantheses.

Functions of the a- and b-wires:

Loudspeaker

The loudspeaker is connected in series with a volume control and a reed contact, witch disconnects the loudspeaker when the handset is lifted. A capacitor prevents DC currents from flowing through the loudspeaker. A high-value resistor keeps the capaciror charged to avoid clicks when the handset is replaced.

Handset operation:

This is a DC current control circuit consisting of a 6K8 resistor in series with a reed contact. Both reed contacts are situated in the base part of the station and are kept close by the built-in magnet in the handset. When handset is in place, the current in the a/b-loop is approximately 3 mA (13 mA). When handset is lifted, the current is reduced to zero (10 mA). This is a signal for the exchange to:

• Reduce the central amplifier gain by 10 dB to compensate for higher michrophone level.
• Accept an incoming call when station is in private.
• Prepare for automatic disconnection when handset is replaced.
• Prepare for open duplex function when handset is lifted at both sides.
• Mark the station busy while the handset is lifted.

Handset loudspeaker circuit:

This consists of a small loudspeaker witch is connected in series with a DC-blocking capacitor and a series resistor to reduce power to the loudspeaker.