" CURRENT SENSOR:INRODUCTIONA current sensor is a device that detects electrical current (AC or DC) in a wire, and generates asignal proportional to it. The generated signal could be analog voltage or current or even digitaloutput. It can be then utilized to display the measured current in an ammeter or can be stored forfurther analysis in a data acquisition system or can be utilized for control purpose.The sensed current and the output signal can be:? AC current input.? Analog output, which duplicates the wave shape of the sensed current.? Bipolar output, which duplicates the wave shape of the sensed current.? Unipolar output, which is proportional to the average or RMS value of the sensed current.? DC current input.? Unipolar with a unipolar output, which duplicates the wave shape of the sensed current.Digital output, which switches when the sensed current exceeds a cer 1CONSTRUCTION & WORKING OF CURRENT SENSOR:High-wattage appliances like electric irons, ovens and heaters result in unnecessary power loss ifleft =on‘ for hours unnoticed. Here is a circuit that senses the flow of current through theappliances and gives audible beeps every fifteen minutes to remind you of power-‘on‘ status.This is a non-contact version of current monitor and can sense the flow of current in high-currentappliances from a distance of up to 30 cm. It uses a standard step-down transformer (0-9V,500mA) as the current sensor. Its secondary winding is left open, while the primary windingends are used to detect the current. The primary ends of the transformer are connected to a full- wave bridge rectifier comprising diodes D1 through D4. The rectified output is connected to thenon-inverting input of IC CA3140 (IC1).IC CA3140 is a 4.5MHz BIMOS operational amplifierwith MOSFET input and bipolar transistor output. It has gate-protected MOSFET (PMOS)transistors in the input to provide very high input impedance (1.5 T-ohms), very low inputcurrent (10 pa) and high-speed switching performance.2The inverting input of IC1 is preset with VR1. In the standby mode, the primary of thetransformer accepts e.m.f. from the instrument or surrounding atmosphere, which results in low- voltage input to IC1. This low voltage at the non-inverting input keeps the output of IC1 low.Thus transistor T1 doesn‘t conduct and pin 12 of IC2 goes high to disable IC2. As a result, theremaining part of the circuit gets inactivated. When a high-current appliance is switched on,there will be a current drain in the primary of the transformer to the negative rail due to anincrease in the e.m.f. caused by the flow of current through the appliance. This results in voltagerise at the non-inverting input and the output of IC1 becomes high. This high output drivestransistor T1 into conduction and the reset pin of IC2 becomes low, which enables IC2.IC CD4060 (IC2) is a 14-stage ripple counter. It is used as a 15-minutetimer by feeding Q9 output to the piezo buzzer for aural alarm through the intermediate circuitry.Resistors R5 and R6 along with capacitor C1 maintain the oscillations in IC2 as indicated byblinking LED1. The high output from IC2 is used to activate a simple oscillator comprisingtransistors T2 and T3, resistors R8 and R10, and capacitor C2. When the Q9 output of IC2 becomes high, zener diode ZD1 provides 3.1 volts to thebase of transistor T2. Since transistor T2 is biased by a high value resistor (R8), it will notconduct immediately. Capacitor C2 slowly charges and when the voltage at the base of T2increases above 0.6 volt, it conducts. When T2 conducts, the base of T3 turns low and it alsoconducts. The piezo buzzer connected to the collector of T3 gives a short beep as capacitor C2discharges. This sequence of IC2 output at Q9 becomes high and conduction of transistors T2and T3 resulting in beep sound repeats at short intervals.3 "