單線計(jì)數(shù)器和光耦實(shí)時測量交流負(fù)載。
一個簡單的電路監(jiān)控連接交流負(fù)載供電所用的時間（如圖1）。可以存取標(biāo)準(zhǔn)單線協(xié)議所用時間的計(jì)數(shù)值。當(dāng)給交流負(fù)載供電時，光耦以交流線頻率，向單線計(jì)數(shù)器DS2423芯片的輸入端提供脈沖。從而，無論何時給負(fù)載供電，計(jì)數(shù)器都不斷遞增。在線循環(huán)的負(fù)半周期，電阻R1和R2限流，二極管D1保護(hù)光絕緣體遠(yuǎn)離負(fù)極性電壓。
圖1 簡單的電路監(jiān)控連接交流負(fù)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(shí)現(xiàn)對井泵注水總量和能量消耗數(shù)量的測量。單線主計(jì)數(shù)器，例如一個上位機(jī)Linux系統(tǒng)，每分鐘讀一次計(jì)數(shù)器值。任何從讀到下一個動作的計(jì)數(shù)改變表示泵供電和運(yùn)行。既然這樣，通過簡單的微分，計(jì)數(shù)器值除以線頻率60Hz，變?yōu)橐悦霝閱挝挥?jì)算時間長度。以秒計(jì)時間等于新計(jì)數(shù)減去舊計(jì)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(fù)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(jì)數(shù)器B的輸出端，來監(jiān)測兩個電阻負(fù)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.