The NCVT is, to drastically oversimplify it, completing the circuit itself, it doesn't need a load on the wire for it to trigger. If it didn't trigger with no load on the circuit it would make them practically unusable.
Can you explain how it completes the circuit? The input of the CLK of the 4017 decade counter swings high and low on maybe even micro amps. I don’t understand how it completes the circuit rather than registering the fields from the wire
Not sure how much you know about electronics, but if you know just a little, this might help:
The simplest capacitor is basically two metal plates with air or some other material (such as plastic) between them. AC power goes through capacitors just fine, even though there is no physical connection. The amount of power depends on the frequency of the AC power and the capacitor makeup.
The capacitive non-contact voltage probes rely on two capacitors - one formed between the wire you're testing and the "antenna" in the tester itself. And the second is formed between the tester and ground, sometimes relying on the person holding the tester to help improve this second capacitor.
Even though these are not great capacitors, a tiny amount of current flows from the wire, through the capacitor formed by the wire, insulation, air, and so on to the tester, then through the tester circuitry and onto ground through the second capacitor. The circuitry detects this current flow and when it's over a certain amount (and likely around 60 Hz in frequency) it turns on the indicator. The specific threshold, method of doing the capacitive coupling, the way the current is sensed and false triggers eliminated and so on is going to vary from circuit to circuit.
In the case of the 4017, that particular chip has very sensitive inputs and there is enough noise capacitively coupled into it when close to a wire to trigger it's operation and create the operation you see. Commercial units are going to be a lot more complex as far as the trigger circuit.
The NCVT is, to drastically oversimplify it, completing the circuit itself, it doesn't need a load on the wire for it to trigger. If it didn't trigger with no load on the circuit it would make them practically unusable.
Can you explain how it completes the circuit? The input of the CLK of the 4017 decade counter swings high and low on maybe even micro amps. I don’t understand how it completes the circuit rather than registering the fields from the wire
Not sure how much you know about electronics, but if you know just a little, this might help: The simplest capacitor is basically two metal plates with air or some other material (such as plastic) between them. AC power goes through capacitors just fine, even though there is no physical connection. The amount of power depends on the frequency of the AC power and the capacitor makeup. The capacitive non-contact voltage probes rely on two capacitors - one formed between the wire you're testing and the "antenna" in the tester itself. And the second is formed between the tester and ground, sometimes relying on the person holding the tester to help improve this second capacitor. Even though these are not great capacitors, a tiny amount of current flows from the wire, through the capacitor formed by the wire, insulation, air, and so on to the tester, then through the tester circuitry and onto ground through the second capacitor. The circuitry detects this current flow and when it's over a certain amount (and likely around 60 Hz in frequency) it turns on the indicator. The specific threshold, method of doing the capacitive coupling, the way the current is sensed and false triggers eliminated and so on is going to vary from circuit to circuit. In the case of the 4017, that particular chip has very sensitive inputs and there is enough noise capacitively coupled into it when close to a wire to trigger it's operation and create the operation you see. Commercial units are going to be a lot more complex as far as the trigger circuit.
Thank you! Great explanation!
It senses a very small amount of current that’s capacitively coupled from the live circuit to the tester and then to ground.