Key telephone system
Number of patents in Portfolio can not be more than 2000
United States of America Patent
Stats
-
Oct 18, 1983
Issued Date -
N/A
app pub date -
Aug 16, 1979
filing date -
May 17, 1976
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A key telephone system in which a key service unit is provided for selectively connecting a plurality of key telephone sets to at least a pair of CO lines through at least one control line provided in correspondence to the CO lines and a common line. The key service unit comprises a DC power source for producing two outputs respectively having certain positive and negative potential differences with respect to a reference potential, at least one first detector provided in correspondence to the CO lines and selectively connected to the control line for detecting the state in which one of the two output voltages is applied across the control line and the common line to flow a current of predetermined value, at least one second detector provided in correspondence to the CO lines and selectively connected to the control line for detecting the state in which the other of the two output voltages is applied across the control line and the common line to flow a current larger than a certain value, and at least one switching means provided in correspondence to the CO lines for disconnecting the first detector from the control line and for connecting the second detector to the control line when the first detector produces an output.
First Claim
Family
International Classification(s)
Cited Art Landscape
Patent Citation Ranking
Recipient Email Address
Recipient Email Address
Comment
Recipient Email Address
Add to Portfolio(s)
To add this patent to one, or more, of your portfolios, simply click the add button.
This Patent is in these Portfolios:
Add to additional portfolios:
Last Refreshed On:
Changes done successfully