Electric pen tester - how do they work??

[Colin]

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

 

[[email protected]]

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

Look up "induction".

 

[Colin]

Blimey that was quick for boxing day!!!

Thanks

Col

 

[[email protected]]

Blimey that was quick for boxing day!!!

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?

 

[Colin]

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

 

[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

 

[Greg Neill]

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..

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.

 

[Palinurus]

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.

-
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.

http://www.electronicsforu.com/efylinux/circuit/cir114.htm

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

 

[Luhan]

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??

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

 

[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.

http://www.electronicsforu.com/efylinux/circuit/cir114.htm

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

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