Question

What is there inside a neon light screw driver tester and how does it work?
I mean this thing: http://www.hunters-wholesalers.co.uk/images/710031UK.jpg

Answer 1

@ujjwal do u have ever used multimeter??????

Answer 2

If you mean this thing http://www.cbtplanet.com/images/multimeter.jpg
My answer would be no!
Never used it in high school!

I have used voltmeter and ammeter...

Answer 3

there are one point contact tester two point and no point:)

Answer 4

you have used voltmeter then what it actually reads ??

Answer 5

PD between two points in circuit!

Answer 6

yes potential difference then neon light tester has two points one with u touch and other point is grounded by your touch.
means relies on stray capacitance and current passing through the user's body to complete the circuit.The tip of the tester is touched to the conductor being tested (for instance, it can be used on a wire in a switch, or inserted into a hole of an electric socket). A neon lamp takes very little current to light, and thus can use the user's body capacitance to earth ground to complete the circuit.:)

Answer 7

so you're saying that the tester won't work if I'm wearing say...rubber gloves?

Answer 8

It will work on voltages that will ionize the neon bulb (usually in excess of 70 volts) and yes it should work even you were holding it with rubber gloves. Since stray capacitance is still there, don't know off hand what the dielectric is for rubber but it may even work better lol. It is an ideal device to just check for presence of voltage.

Answer 9

I am 100 % sure it won't work if you are wearing rubber gloves or rubber shoes or standing on something which is an insulator!

I just don't understand how it works.. When i opened one of those testers and saw what was inside i saw a spring and a bulb which lights up..

What does spring (coil) do?

Stray capacitance is totally new to me..

And yeah, why don't we get a shock? How is the amount of current flowing out controlled?

Answer 10

@ujjwal @radar is correct:)

Answer 11

Do you mean it will work even if we are wearing rubber gloves?

Answer 12

yup:)

Answer 13

Any two adjacent conductors can be considered a capacitor, although the capacitance will be small unless the conductors are close together for long distances or over a large area. This (often unwanted but here wanted) effect is termed "stray capacitance".

Answer 14

and shock can be feel only at high voltage difference not high current :)

Answer 15

I have a tester with me now and i am sitting on a plastic chair.. When i touch ground with my foot and use tester, it works fine and when i lift my foot from ground, tester doesn't work..

I don't have a rubber glove but when i touch tester i with my hands wrapped up in a plastic bag tester doesn't work!

So, i guess it shouldn't work for rubber gloves either..

Answer 16

And i get a shock if i directly touch a live wire but with tester, i don't get a shock.. Why?

Answer 17

@ujjwal the voltage drop across neon bulb is high so the voltage after the neon bulb is not so high :)

Answer 18

You can hold an ordinary flourescant (spelling?) bulb near a field of radio frequency and it too will light. The actual current flowing through your body is limited by the bulb. Now a word of caution do not use on extrememly high voltage as it may actually flash over. It is fine for normal household voltages (AC) and DC circuits less than 200 volts. If the neon bulb has dual plates that are visible, for AC you will see two ignitions, DC only ones side of the bulb will light. Now real high power radars such as the 4 megawatt (peak) long range surveillance radars will heat up and kill birds that fly to close to the antenna horn. Usually a radome will prevent this from happening, bulbs will light up if too close.

Answer 19

capacitance is inversly proportional to the distance d so glove has less d but plastic chair has d very very high which make c very very small so bulb doesn't glow:)

Answer 20

@ujjwal

Answer 21

Now i get it after this discussion and going through several sources on internet.. And the spring is actually a resistor with a high resistance which is used to lower the current!

And yeah i am sure it won't work if you put on rubber gloves!
While using a tester you are a 'part of circuit'. So you wouldn't like to put an insulator in between!
Putting on a gloves would prevent you from being a part of circuit!

Thanks @Aperogalics and @rader

Answer 22

Thanks @radar

Answer 23

I am sure there are physical restraints that prevent it from working. But from a practical standpoint, it is actually a good troubleshooting tester. Now from an engineering standpoint not too practical lol.