Why do voltage detectors ......

[iwire]

Re: Why do voltage detectors ......

Originally posted by Mega VAR:
Wow, looks like all of you got mad.

I doubt anyone is mad, more likely they are amused by your arrogance.

Why not tell us your qualifications?

 

[George Stolz]

Re: Why do voltage detectors ......

Originally posted by Mega VAR:
Electromagnetic waves (present around AC circuits) consist of oscillating electric and magnetic fields, which are at right angles to each other and also at right angles to the direction of wave propagation.

Relating to an AC circuit, which changes potential in relation to a time variable, thus the sinusoidal waveform, the electric field produced by the conductor is changing and the above applies.

Oh, so that's how a tick tracer works.

 

[roger]

Re: Why do voltage detectors ......

Originally posted by physis:
Do you know the right hand rule too?

 

[jwelectric]

Re: Why do voltage detectors ......

After reading this thread I am so confused that I put coffee in my milk this morning.

 

[Mega VAR]

Re: Why do voltage detectors ......

The main point I am getting at is, a tic-tracer is not a reliable source for working on a conductor. You should always check the conductor with a probe-type meter. The tic-tracers are wonderful tools to make you get a probe-type meter to verify the circuit has been de-energized.

 

[physis]

Re: Why do voltage detectors ......

Well that's a nicer way of putting it. And we know that.

Edit: You have some physics knowledge Mega VAR, do you want to get JW's question? I can only answer about half of it. I still don't know how the things work.

[ July 28, 2005, 11:58 AM: Message edited by: physis ]

 

[physis]

Re: Why do voltage detectors ......

By me:

What was I saying anyway? EMF is electro-magnetic.

I see why you were telling me what EMF is now Rattus. Some days I just don't know what's going on.

 

[rattus]

Re: Why do voltage detectors ......

The way I see it, there is a small capacitance between the hot wire and the tester, and this cap is in series with another capacitor between one's body and ground. The AC voltage causes a tiny current in these caps therefore we have a voltage divider. The tester senses this divided voltage.

Although a tiny current is present, the tester senses voltage--probably a CMOS op-amp.

I have a tester which looks like a fat fountain pen, and it is very useful in IDing hot wires, etc., but it is no substitute for a real voltmeter.

For example, it can be used to find an open lamp in a string of Xmas tree lights--if only if you can separate the hots from the neutrals.

 

[physis]

Re: Why do voltage detectors ......

A very tiny amount of capacitance. Very sensitive amp. Filter to focus on 60 hz.

You don't need anyones body. I use mine to find which breaker to turn off all the time.

I hope I don't have to take one apart cause I will.

[ July 28, 2005, 01:17 PM: Message edited by: physis ]

 

[Mega VAR]

Re: Why do voltage detectors ......

Electric fields and magnetic fields can exist without the other, when I wrote in one of my previous threads I was talking about AC. I did not state that. There has to be a change in one or the other (time variable) for the other to be present at the same time. I do not know all of the specifics without consulting my text book of how to explain this pheneomenon.

The thing that gets me, (I have not researched the tic-tracers) is how the meter detects voltage in an unenergized conductor if it does not detect voltage in DC circuits.

None of this information is not quoted.

I would be interested to find out if the non-contact voltmeter that was used in the original posting remained lit, or just blipped when coming in contact with the conductor, or blipped when coming close to the conductor.

I do not want to come accross as arrogant. I just wanted to know if anyone in here has the qualifications to back up their information, or if everyone is posting hypotheses based on past experiences.

 

[Mega VAR]

Re: Why do voltage detectors ......

I had a double negative in the previous posting and would like to correct that. I did not quote or obtain any of the information I stated from a qualified source.

 

[physis]

Re: Why do voltage detectors ......

The thing that gets me, (I have not researched the tic-tracers) is how the meter detects voltage in an unenergized conductor if it does not detect voltage in DC circuits

I would guess that DC is intentionally ignored because it's easy to do and it would cause false triggering.

Edit: I'm thinking by it's very nature it's a decoupling capacitor and ignores DC just because of that.

[ July 28, 2005, 01:27 PM: Message edited by: physis ]

 

[rattus]

Re: Why do voltage detectors ......

Sam, these testers do not work on DC because the reactance of the cap to DC is infinite. It is a simple capacitive voltage divider which works with AC only. Neither will it work on very low frequencies or very low voltages.

 

[physis]

Re: Why do voltage detectors ......

That's what is meant by decoupling Rattus. Unless my terminology is slipping from lack of use.

 

[Mega VAR]

Re: Why do voltage detectors ......

Rattus are you in the military?

I could understand the charge and dischare of a capacitor at a high rate (60 hz) for the purpose of detecting AC voltage, and I would agree that this would be an effective method. Still I wonder how the person in the first posting was detecting voltage then in a de-energized conductor? If the charge on the conductor was mearly a capacitive charge or static charge the tic-tracer should not continually light. The thing I find a little odd about the tic-tracer is if you were to tap it on a DC source the light blips (this also works if you tap it to skin or rub it on carpet), but if you tap the tic-tracer further back from the tip the light does not blip. This makes me believe there is some sort of switch that possibly opperates through magnetic induction. Whether it be from the conductor or after a capacitor in the tic-tracer. Also I took the tic-tracer to a 125V DC source on the positve side then quickly moved it to the negative conductor and there was no blip. So the phenomenon of a quickly disipating capactor seems very likely. Another thing that makes me wonder about the tic-tracer is that when moved close to the conductor there is no blip. In a coupled capacitor usually you have a grounded probe to complete the circuit. In the event that you were to put a coupled capacitor in the electric field of an AC conductor that is energized the capacitor would charge, discharge to the other circuit making it one polarity, then when the other half of the cycle comes the capacitor would charge and discharge causing the rest of the circuit to again change polarity. This would generate some sort of current within the tic-tracer, as was posted earlier in the discussion. My question then is, how did the tic-tracer detect voltage if there was no AC voltage present? Was it verified there was no voltage present, even by induction? I have heard of tic-tracers detecting voltage as low as 17 volts. Tic-tracers use a battery to illuminate the light, vibrate, or make a sound, so somehow the induced voltage must be capable of operating a switch, this is why I beleive it does not work on DC voltages. I have not seen a DC non-contact voltmeter either. Again this posting is mearly theory or my opinion, I have not backed any of the information.

 

[rattus]

Re: Why do voltage detectors ......

Mega, not any more, I have been out since 1954 and never looked back, but the motto is still a good one, although in the real world the wording was a bit more colorful.

I don't think any of these devices will detect a de-energized conductor. They only detect a change in voltage.

Imagine a series string as follows, C1, R1, C2, & C3 where:

C1: Capacitance between the wire and probe tip.

R1: Very large resistance, say 10Meg or so connected between probe tip and insulated metal shell.

C2: Capacitance between metal shell and human body.

C3: Capacitance between human body and ground.

An AC signal causes a tiny current through R1 which creates an IxR voltage which is sensed by an op-amp and perhaps rectified. This signal can turn on an audible tick or an LED.

Withdraw the probe and the IxR voltage goes to zero, and the LED goes out.

Moving the probe rapidly to and from a DC voltage could trigger the light momentarily.

I would imagine the units are a bit more sophisticated than this, but I think this is the basis for any proximity tester. Sounds like a fun project for anyone so inclined.

It is clear that a magnetic field is not required, just a changing electrostatic field.

 

[iwire]

Re: Why do voltage detectors ......

Originally posted by Mega VAR:
The main point I am getting at is, a tic-tracer is not a reliable source for working on a conductor. You should always check the conductor with a probe-type meter.

Why do you feel this way?

Do you have any evidence they do not work?

What do you think the intended purpose is of these tools?

Why are the electronics in a tic tracer any less reliable than the digital meters many people use for this every day?

By simply rubbing the tic tracer on my clothes I can check my tic tracers operation before and after I check the conductor I want to work on?

I often get false positives but I have never received a false negative.

I should add that you must know the tracers limitations, knowing it will not read through MC, AC, EMT, etc.

Considering you can not troubleshoot or measure voltage with these tools what are they for if not for checking a conductor before touching it?

I would like to add that I have watched the utility workers use non contact voltage checkers on the end of a hot stick before working on conductors.

If they can trust it why can't I?

 

[EEPeder]

Re: Why do voltage detectors ......

At my company "if it's not grounded, it's not dead."

 

[iwire]

Re: Why do voltage detectors ......

Originally posted by EEPeder:
At my company "if it's not grounded, it's not dead."

Very safe.

Grounding every circuit is not a possibility in building construction.

 

[jwelectric]

Re: Why do voltage detectors ......

Bob,
Let me start by saying that each person has a right to use any meter they feel safe with. Not knowing the function of a meter could lead to pain or death. I would like to answer a couple of your questions.

Do you have any evidence they do not work?

Yes, I see several of these each semester and at least one out of every class did not work properly especially the cheaper ones.

What do you think the intended purpose is of these tools?

To get some one that is not familiar with the way these meters work HURT!

I often get false positives but I have never received a false negative.

I have seen these meters give false negative readings even the fluke volt alert tested on a known circuit then on an unknown circuit and lied. A high humidity and low battery will get you hurt.

Why are the electronics in a tic tracer any less reliable than the digital meters many people use for this every day?

Due to the many recalls of the digital meters I personally have no use for any of them. When trouble shooting a cheap analog will walk circles around a digital meter especially when detecting a spike in the system.
With any digital meter there is a time delay before the correct reading is given but with an analog the reading is instantaneous.

As some of my students say, ?old schooled?

[ July 29, 2005, 11:30 AM: Message edited by: jwelectric ]