Patent GB-396626-A (GB)
Title: Improvements in or relating to dial switches for use in telephone systems
IPC: H04M17/02
Filed: 1933-01-17
Abstract: 396,626. Impulse transmitters. TELEPHON-APPARATFABRIK E. ZWIETUSCH & CO., GES., 6, Salzufer, Charlottenburg, Berlin. Jan. 17, 1933, No. 1557. Convention date, March 4, 1932. [Class 40 (iv).] A dial transmitter which prevents certain calls from being set up comprises a device operated by certain digit sequences to prevent further impulsing and a device operated in accordance with the number of impulse trains to render the first device ineffective after the initial digits have been dialled, so that impulsing is prevented only if the sequences occur as initial digits. Impulse transmission may be prevented mechanically or electrically. In the arrangement shown in Fig. 1 for barring calls commencing with digits 00 and 09, the ratchet wheels 4, 5 loosely mounted on a shaft 6 and operable by spring mounted pawls 2, 3 on the dial shaft 1, are normally held by springs in the position shown with projection 12 of wheel 4 abutting against a fixed pin 7 and wheel 5 abutting against a fixed pin 8. On dialling 0, wheel 5 is first moved a step by pawl 3, and towards the end of the dialling movement pawl 2 moves wheel 4 through two steps, the wheels being held by pawls 9, 10. At the commencement of the next digit (9 or 0) the wheel is moved another step and towards the end of the dialling movement, wheel 4 moves one or two steps so that contacts 14 are closed by 12 to operate a relay (not shown) whose circuit includes closed contacts 15 which are not opened until the commencement of dialling the third digit when projection 13 on wheel 5 abuts against them. The relay locks up to the line and shunts the impulse springs. If the initial digits are those of an allowable call, contacts 15 open at the commencement of the third digit to prevent operation of the. relay in case the sequences 00, 09 occur later and close contacts 14. Digits 1 to 8 do not operate wheel 4 since the angular rotation of th'e dial shaft is insufficient. In the modification shown in Fig. 3, the contacts 15 are dispensed with and wheel 5 at the commencement of the third digit moves arm 13 against a catch 18 on the lower spring 14 so that catch 18 engages over the upper spring 14 if the contacts have been closed or under the spring if the contacts have not been closed. The contacts are therefore held closed or open according as to whether the initial digits are barred or not. Contacts 14 are connected across the impulse springs. In another , modification, Fig. 4, the springs 14 are closed by a member 19 pivoted on wheel 4, but if the initial digits signify an allowable call, arm 13 on wheel 5 moves member 19 to an ineffective position. In the mechanical locking arrangement shown in Fig. 6, arm 33 on wheel 4 operated by barred digits moves a member 29 against the lower end of a lever 30 the upper end of which locks a disc 32 fixed to the dial shaft.. The member 29 is pivoted to a spring arm 40 and if the initial digits are allowable, arm 34 on wheel 5 moves member 29 to an ineffective position on commencement of the third digit. Wheel 5 may control an additional contact for differentiating between free and changeable calls. The parts are restored to normal by a lever 11, Fig. 1, operated the by switch hook.