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This straight forward circuit will protect electrical appliances from over voltage as well as under voltage. The circuit also produces an alarm when the power supply comes back. An ideal circuit for home to protect your valuable equipments from voltage fluctuations. The same circuit with some modifications can be used  to make a automatic voltage stabilizer. High and Low Voltage Cut-Off with Delay and Alarm Circuit Diagram : When the mains voltage is in the normal level, the voltage at the negative terminal of zener diode D4 will be less than 5.6 Volts. At this condition transistor T1 will not conduct. The same time voltage at the negative terminal of zener diode D5 will be greater than 5.6 and so the transistor T2 will be conducting. The relay will be activated and the green LED will be glowing. When the mains voltage is higher than the set limit the transistor T1 becomes conducting since the voltage at the negative terminal of  D4 is greater than 5.6 V. At the same time transist...

Some relays are constructed with a kind of “shock absorber” mechanism attached to the armature which prevents immediate, full motion when the coil is either energized or de-energized. This addition gives the relay the property of time-delay actuation. Time-delay relays can be constructed to delay armature motion on coil energization, de-energization, or both. Time-delay relay contacts must be specified not only as either normally-open or normally-closed, but whether the delay operates in the direction of closing or in the direction of opening. The following is a description of the four basic types of time-delay relay contacts. First we have the normally-open, timed-closed (NOTC) contact. This type of contact is normally open when the coil is unpowered (de-energized). The contact is closed by the application of power to the relay coil, but only after the coil has been continuously powered for the specified amount of time. In other words, the direction of the contact’s motion (eithe...

Types of Timers in PLC | OFF Delay Timer (TOF)   PLC Timers are generally used for delaying an event from taking place, or to delay a device from shutting off either on an on transition or an off transition.   There are three types of PLC timers:   The Timer ON delay (TON), Timer Off delay (TOF), and the Retentative Timer On delay (RTO). By default, timers are stored in the T4 Data file, however other time files can be created. A timer consists of the following components:   Preset word (PRE), Accumulate word (ACC), Done bit (DN), Timer Timing bit (TT), and Enable bit (EN).   For Timers, the Enable bit follows the rung condition. The entire timer is addressed by it's element (example: T4:0) Pieces of the timer can be used in logic however such as the DN bit on an XIC (T4:0/DN), or the Accumulated value in a MOV statement (T4:0.ACC) PLC Timer Off Delay (TOF)   The Off Delay Timer is generally used to delay an event from shutting off.   Image a lube sy...