单线计数器和光耦 实时测量 交流负载 。

　　一个简单的电路监控连接交流负载供电所用的时间（如图1）。可以存取标准单线协议所用时间的计数值。当给交流负载供电时，光耦以交流线频率，向单线计数器DS2423芯片的输入端提供脉冲。从而，无论何时给负载供电，计数器都不断递增。在线循环的负半周期，电阻R₁和R₂限流，二极管D₁保护光绝缘体远离负极性电压。

图1 简单的电路监控连接交流负载供电所用的时间

　　举个例子，电路监控240V交流井泵操作间隔的持续时间，从而间接实现对井泵注水总量和能量消耗数量的测量。单线主计数器，例如一个上位机Linux系统，每分钟读一次计数器值。任何从读到下一个动作的计数改变表示泵供电和运行。既然这样，通过简单的微分，计数器值除以线频率60Hz，变为以秒为单位计算时间长度。以秒计时间等于新计数减去旧计数值除以60Hz。

　　这个电路能够监控水加热器、炉子、空调或其他交流负载。需要调整R₁和R₂的值来满足线电压不等于交流240V或其光耦特性。也可以通过配另一个光绝缘体电路到单DS2423计数器B的输出端，来监测两个电阻负载。

　　英文原文：

　　Voltage timer monitors line-connected ac loads

　　A one-wire counter and an optoisolator keep track of the on-time of an ac load.

　　MIChael Petersen, Maxim Integrated Products, Sunnyvale, CA; Edited by Charles H Small and Fran Granville -- EDN, 8/16/2007

　　A simple circuit monitors the elapsed time over which a line-connected ac load energizes (Figure 1). You CAN then

aCCess the elapsed-time count over a standard one-wire protocol. When you energize the ac load, the optoisolator provides pulses at the ac-line Frequency to the input of the one-wire counter, a DS2423 IC. Thus, the counter continuously increments whenever you energize the load. Resistors R1 and R2 limit the current, and diode D1 protects the optoisolator from reverse-polarity voltages during the negative half of the line cycle.

　　As an example, the circuit can monitor the duration of operating intervals for a 240V-ac well pump, thereby giving an indirect measure of the amount of water the well pumps and the approximate amount of power it consumes. The one-wire master counter—a Linux-based PC, for example—reads the elapsed count once per minute. Any change in the count from one reading to the next inDICates that the pump is energized and running, and you calculate the length of time in seconds by simply taking the difference in counter values divided by the line frequency—60 Hz, in this case. The time in seconds equals the new count minus the old count divided by 60 Hz.

　　The circuit can monitor a water heater, a furnace, an air-conditioning unit, or any other ac-connected load. You may need to adjust the R1 and R2 values to accommodate line voltages other than 240V ac or the characteristics of other optoisolators. You can also monitor two independent loads by attaching a second optoisolator circuit to the Counter B input of a single DS2423.

　　英文原文地址： http://www.edn.com/article/CA6466210.html