一個簡單的電路監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議所用時間的計數值。當給交流負載供電時，光耦以交流線頻率，向單線計數器DS2423芯片的輸入端提供脈沖。從而，無論何時給負載供電，計數器都不斷遞增。在線循環的負半周期，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 簡單的電路監控連接交流負載供電所用的時間
舉個例子，電路監控240V交流井泵操作間隔的持續時間，從而間接實現對井泵注水總量和能量消耗數量的測量。單線主計數器，例如一個上位機Linux系統，每分鐘讀一次計數器值。任何從讀到下一個動作的計數改變表示泵供電和運行。既然這樣，通過簡單的微分，計數器值除以線頻率60Hz，變為以秒為單位計算時間長度。以秒計時間等于新計數減去舊計數值除以60Hz。
這個電路能夠監控水加熱器、爐子、空調或其他交流負載。需要調整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計數器B的輸出端，來監測兩個電阻負載。
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.