| Number | Date | Country | Kind |
|---|---|---|---|
| 42 17 681.6 | May 1992 | DEX |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3183349 | Barnes et al. | May 1965 | |
| 3545005 | Gallagher | Dec 1970 | |
| 4323211 | Bambara et al. | Apr 1982 | |
| 5149025 | Utterback et al. | Sep 1992 |
| Number | Date | Country |
|---|---|---|
| 397759 | Feb 1966 | CHX |
| Entry |
|---|
| Advertisement in Railway Signaling and Communications, (Sep. 1961) p. 31. |