Discrete Control
Discrete control functions can be represented by discrete levels of current sent over a loop. This would allow multiple control functions to be operated over a single pair of wires. Currents required for a specific function vary from one application or manufacturer to another. There is no specific current that is tied to a single meaning. It is almost universal that 0 mA indicates the circuit has failed. In the case of a fire alarm, 6 mA could be normal, 15 mA could mean a fire has been detected, and 0 mA would produce a trouble indication, telling the monitoring site the alarm circuit had failed. Some devices, such as two-way radio remote control consoles, can reverse the polarity of currents and can multiplex audio onto a DC current.
These devices can be employed for any remote control need a designer might imagine. For example, a current loop could actuate an evacuation siren or command synchronized traffic signals.
Read more about this topic: Current Loop
Famous quotes containing the words discrete and/or control:
“One can describe a landscape in many different words and sentences, but one would not normally cut up a picture of a landscape and rearrange it in different patterns in order to describe it in different ways. Because a photograph is not composed of discrete units strung out in a linear row of meaningful pieces, we do not understand it by looking at one element after another in a set sequence. The photograph is understood in one act of seeing; it is perceived in a gestalt.”
—Joshua Meyrowitz, U.S. educator, media critic. “The Blurring of Public and Private Behaviors,” No Sense of Place: The Impact of Electronic Media on Social Behavior, Oxford University Press (1985)
“Grown-up people do very little and say a great deal.... Toddlers say very little and do a great deal.... With a toddler you cannot explain, you have to show. You cannot send, you have to take. You cannot control with words, you have to use your body.”
—Penelope Leach (20th century)