ringing current การใช้

• Fixed phones of the late 20th century and later detect this ringing current voltage and trigger a warbling tone electronically.
• To alert the operator, or another subscriber on the same line, the subscriber turned the crank to generate ringing current.
• The Trimphone was the first in the GPO range to use a tone caller which warbled at around 2000 Hz modulated by ringing current.
• The various levels provided various tones, and ringing current of various durations and cadences ( especially valuable for tip side or ring side.
• LED indicator lights on the front typically show signal strength and voicemail ringing current for more than one phone and one externally powered device, such as a telephone answering device or the base station for a cordless phone.
• Ringing current magnetos were used in the public switched telephone network ( PSTN ) as late as the 1980s, when they were still used with private manual branch exchanges ( PMBX ), small business switchboards worked by operators.