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Electric pen tester - how do they work??

Hi all,,

Can anyone expalin how those pen type testers work, the ones that glow red when a Live feed is detected through the PVC coating of cables?? I took one apart and all that was inside was a couple of resisters and a coiled spring with a thin metal rod down the center. I am wondering how it actully works?

Seems very simple but cannot explain what the coil is for??

Thanks Col

Reply to
Colin
Loading thread data ...

Look up "induction".

Reply to
mike.j.harvey

Blimey that was quick for boxing day!!!

Thanks

Col snipped-for-privacy@gmail.com wrote:

Reply to
Colin

There's bugger all on the telly. I think you'll find there's a bit more than a couple of resistors in a pen tester. The coil gets a small current 'induced' in it when it is brought near to a cable which is carrying current. There will be a chip which detects this small current and turn on the lamp. There'll be a battery too, to provide power I'd have thought?

Reply to
mike.j.harvey

So after a quick google search, it would seem that the coil spring would be pulled by the magnetic field and contact the center thin rod making the circuit?? Is that right?

Didn't think there would be that much magnetic fied around a live wire...

As you can tell I am new to electronics..

Thanks Col

Col> Blimey that was quick for boxing day!!!

Reply to
Colin

Thanks Mike ignore my last post.. I will go back and have a look at the components again. I need to identify the components as I need to recreate the whole setup within a different structure for a project I am doing.

I will need to study induction a fair bit then...

The pen I took apart was from china and I sourced the resisitors but were difficult to get hold off so was wanting to redo the whole thing with readily available parts.. It does have a single 1.5v battery for the LED... I was also wanting to change the LED for a buzzer.. which I hope will be feasible.

Thanks very much for your help today... emmerdale and corrie are finishing soon :-)

Col

Col> So after a quick google search, it would seem that the coil spring

Reply to
Colin

No, the alternating field around the wire induces a current in the coil (transformer action). This current if it passes a given threshold value, causes a circuit in the tester to light the indicator.

Reply to
Greg Neill

- Nope. It's electrostatic induction, not magnetic. There are also AC/DC versions of these gadgets, though the DC ranges are more complex and a lot less sensitive, for obvious reasons. Here's a rather cute example.

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As described, it only works on AC, but a little delta-C can be applied by hand motion. A manual chopper, if you will.

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Reply to
Palinurus

The coil is for inductive pickup (probably).

Look for a small black blob on the circuit board, that is the actual circuit epoxied in.

Luhan

Reply to
Luhan

The OP indicated that his unit employed a coil. I am aware that there are electrostatic models.

Reply to
Greg Neill

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