Here is a simple non-contact AC power screen for house appliances and laboratory equipment that should stay constantly switched-on. A fuse failure or power breakdown within the tools going overlooked may just result in irreparable loss. The monitor sounds an alarm on detecting energy failure to the equipment. The circuit is built round CMOS IC CD4011 utilising just a few components. NAND gates N1 and N2 of the IC are wired as an oscillator that drives a piezobuzzer instantly. Resistors R2 and R3 and capacitor C2 are the oscillator elements. The amplifier comprising transistors T1 and T2 disables the oscillator when primarys power is available. In the standby mode, the base of T1 picks up 50Hz primarys hum all the manner through the positive half cycles of AC and T1 conducts.
Circuit diagram:
Non-Contact Power Monitor circuit diagram
This offers base current to T2 and it additionally habitss, pulling the collector to ground potential. As the collectors of T1 and T2 are connected to pin 2 of NAND gate N1 of the oscillator, the oscillator will get disabled when the transistors behavior. Capacitor C1 forestalls upward throughst of the collector voltage of T2 once more right through the terrible half cycles. When the facility fails, the electrical field across the equipment’s wiring ceases and T1 and T2 turn off. Capacitor C1 begins charging via R1 and preset VR and when it will get sufficiently charged, the oscillator is enabled and the piezobuzzer produces a shrill tone. Resistor R1 give safety tos T2 from short circuit if VR is altered to zero resistance.
The circuit can be easily assembled on a perforated/breadboard. Use a small plastic case to enclose the circuit and a telescopic antenna as aerial. A 9V battery can be used to power the circuit. Since the circuit attracts only some microamperes current within the standby mode, the battery will closing a couple of months. After assembling the circuit, take the aerial close to the primarys cable and modify VR except the alarm stops to indicate the standby mode. The circuit will additionally be placed on the gear to be displayed as regards to the principles cable.
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