This non contact inductive current sensor circuit is designed to detect an alternating current (AC) flow within any circuit and its cables, without undergoing any direct contact with the conductor, or breaking of the insulation.
In the Figure below, you can observe this circuit is able to sense almost anything that moves through a wire or via a component lead with a frequency of 60 Hz to more than 10 kHz. The versatile Inductive Current Sensor makes life a little easy by helping you to troubleshoot the washer, dryer or any other appliances at home.
This non contact current sensing circuit consists a IC 1458 dual op-amp (U1). The signal input is the circuit is inductively coupled to the circuit via L1; which is a 10 K to 2 K audio transformer where the 2 K winding isn’t utilised.
When L1 is held closely to a conductor transporting an alternating voltage AC, another voltage is induced in the coil. The voltage across L1 is supplied to the inputs of U1-a, where it is boosted to deliver a gain of roughly 100.
The output of U1-a is supplied via potentiometer R7 (the Gain Control) to the inverting input of U1-b.
This is also where the input delivers a gain of 100. The output of U1-b is supplied via a voltage-doubler/rectifier circuit comprising C3, C4, D1 and D2.
Then, the output of the doubler/rectifier is channeled to Q1’s base where it gets turn on. In return, a voltage gets applied to the anode of LED1 via R6. This resistor is chosen to limit the current that passes through the LED.
How to Make the Sensor Coil
The pickup coil, L1, was made from dismantling the clamping frame of a 10K-to-2K miniature audio transformer and then eliminating the “E” and “I” laminations from the transformer core.
The “I” parts were thrown away and the leads to the 2K winding clipped near the windings of the transformer. Then, every “E” piece was plugged back into the core opening (which forms and open-loop core) and joined with adhesives. This elevates the sensitivity of the pick-up element.
How to Assemble
The remaining circuit components were assembled on a perfboard or PCB and contained in a tiny plastic case. The GAIN control, R7, the power switch, and the LED were placed on end of the cabinet. You can mount inductor L1 either on the winding flush side and parallel with the cabinet’s end. Or you can place it on the outside end for highest sensitivity. The pickup’s maximum sensitivity to an external field is recognized when the conductor is parallel with L1.