Emergency telephone with pushbutton switch=over - changes from high-ohmic quiescent state to low-ohmic speak state

摘要

The emergency telephone uses a code to change its mode from quiescent to voice. A sprung pushbutton changes the telephone (NRT) from high ohmic to low ohmic in order to establish a voice connection. The line is briefly interrupted to mark the change in mode. The interruption is accomplished by interrupting the hold-current circuit of a switch (A) using a contact (T1) belonging to the pushbutton. The resistance of the switch and its parallel capacitor (C) determine the duration of the interruption. Once the switch has returned to normal, the mode changeover switch (B) is operated by another contact (T2) belonging to the pushbutton and the low-ohmic state produced.