An Excluding Device for Automatic Telephone Equipment

1,196,132. Automatic exchange systems. G. PUGLIESE. 19 June, 1967. No. 28136/67. Heading H4K. A device for preventing the establishment of a connection for a trunk or toll call from a particular line (from a subscriber or PBX) counts the dialling pulses of the first digit and if a predetermined number of pulses is detected inserts a resistor or capacitor in the line to damp the subsequent dial pulses to a level at which they will not operate the selector equipment. As shown when the handset is lifted a first relay R1 is enabled and maintained until the first inter-digit pause is detected. While enabled it holds a non-return pawl n in engagement with a ratchet wheel rd secured to a shaft W. A relay I responds to each dialling pulse of the first digit to increment the ratchet wheel by one tooth. During the inter-digit pause relay R1 is released causing the relay I to be permanently enabled over its hold winding, thus preventing that relay from responding to further pulses. If the number of pulses detected was between 1 and 9 the shaft W is set so that a cam s 2 holds a contact set i 2 closed disabling the relay R1 and thus preventing any response to subsequent digits until after the handset has been replaced on its rest. The remaining dialling pulses are thus allowed to pass unattenuated. If however the first digit is a zero; ten pulses are detected by the relay I and the shaft is rotated into a position in which a cam S 3 closes a contact set i 3 simultaneously with the closing of the contact set i 2 . The closing of the contact set i 3 connects a resistor in the telephone line to suppress the level of subsequent pulses. Several alternative wiring arrangements are described including provisions to prevent false operation immediately following the lifting of the receiver or due to short breaks in line current.