單線計數(shù)器和光耦實時測量交流負載。

　　一個簡單的電路監(jiān)控連接交流負載供電所用的時間（如圖1）。可以存取標準單線協(xié)議所用時間的計數(shù)值。當給交流負載供電時，光耦以交流線頻率，向單線計數(shù)器DS2423芯片的輸入端提供脈沖。從而，無論何時給負載供電，計數(shù)器都不斷遞增。在線循環(huán)的負半周期，電阻R₁和R₂限流，二極管D₁保護光絕緣體遠離負極性電壓。

圖1 簡單的電路監(jiān)控連接交流負載供電所用的時間

　　舉個例子，電路監(jiān)控240V交流井泵操作間隔的持續(xù)時間，從而間接實現(xiàn)對井泵注水總量和能量消耗數(shù)量的測量。單線主計數(shù)器，例如一個上位機Linux系統(tǒng)，每分鐘讀一次計數(shù)器值。任何從讀到下一個動作的計數(shù)改變表示泵供電和運行。既然這樣，通過簡單的微分，計數(shù)器值除以線頻率60Hz，變?yōu)橐悦霝閱挝挥嬎銜r間長度。以秒計時間等于新計數(shù)減去舊計數(shù)值除以60Hz。

　　這個電路能夠監(jiān)控水加熱器、爐子、空調(diào)或其他交流負載。需要調(diào)整R₁和R₂的值來滿足線電壓不等于交流240V或其光耦特性。也可以通過配另一個光絕緣體電路到單DS2423計數(shù)器B的輸出端，來監(jiān)測兩個電阻負載。

　　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.