Intrinsically safe telephone systems
US4064366A · kind A · utility
10Cited by
1References
14Claims
0Family size
Assignee
Inventors
Key dates
| Filing date | Jan 15, 1976 |
| Grant date | Dec 20, 1977 |
| Priority date | — |
| Expiry date | Jan 15, 1996 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/18
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
An intrinsically safe telephone system for use in mines or similar hazardous areas including a battery charging circuit arranged to supply charging current of a predetermined low value to the battery of an operational unit located in the hazardous area during on-hook periods. A circuit is provided for modulating the charging current below the predetermined value to generate both the incoming and outgoing call signals during signaling periods.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.