| 摘要 |
PURPOSE:To make a prediction alarm tone function inoperative during picture transmission, by restricting the transmission of prediction alarm tone during the picture transmission. CONSTITUTION:When the main trunk responds after a caller of the extension makes a dialing, since the loop of the main trunk is inverted, a main trunk response detection relay E is operative and its contact e<2> activates a timer circuit TM. After a prescribed time, a prediction alarm tone transmission relay ST is operative and restored its contact st<4>. During the operation of the relay ST, the prediction alarm tone is transmitted from a sound source TONE to the extension with st<1> and st<2> contacts and forms a DC loop with a st<3> contact so as not to be restored to the main trunk. After the response of the main trunk, if a control signal such as facsimile signal is incoming, the control signal is detected at a signal detector SD to a operate a control signal detection relay FA. The relay FA is self-held through a fa<1> contact until end of the call, and fa<2> contact stops the operation of the TM. |
