Apparatus and method for detecting telephone line status
CA 2118731 C · Owner: Keen, Donald Marion · Inventors: Means, Donald Richard; Karpicke, John Arthur; Burger, Theodore Othmar
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
Telephone line status indication is improved by making measurements of the differential voltage across the Tip-Ring terminals of a telephone set (100). The telephone set is connected to a telephone line which is shared with other parallel-connected telephone sets. The measurement of differential line voltage is made each time the set changes state (i.e. between on-hook and off-hook). The maximum magnitude of one of the last three measurements is stored to represent the on-hook state and, is arithmetically averaged with the maximum magnitude of one of the last three stored for the off-hook state to create a reference voltage. The reference voltage is updated each time the telephone set …
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Listed from its CIPO record in Patent Yard's archive of Canadian patents past their term. Its claims, description and drawings are in the CIPO record and on Google Patents, and the Claude kit works from them.
Why it's free to use
- Filed March 10, 1994 and granted November 18, 1997. A Canadian patent filed from October 1, 1989 lasts 20 years from filing, so its term ended March 10, 2014.
- A certificate of supplementary protection adds at most two years for a drug, so even that would have ended by March 10, 2016.
- We check Canadian rights only. A patent in its family in another country could still be in force: check its family on Google Patents.
Timeline
Timeline From CIPO dates
Sources & verification
Official CIPO records
Everything on this page comes from the CIPO record linked above. Contains information licensed under the Open Government Licence – Canada.