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Fluke DVMs


I don't agree it's about current flow under LOAD.

there are problems that cannot be detected with a DVM
and an LED test lamp draws too little current to generate
a load.

Yes, they are reliable, but...

There are many times when a DVM showed the correct voltage an an LED test lamp lit, but an incandescent bulb would only come up dim, thus identifying the problem

BTW, if you have a Snap-On test light that uses the lightbulb that looks like an old style glass fuse and you are shocked by the price of a replacement bulb (if your snap-on dealer is actually willing to get you one)
you can get the replacement bulbs cheap.

Go to your nearest U-pull-it junkyard and steal the light bulbs out of the lighted vanity mirror in any gen1 or Gen2 Explorer:)

AD


The response time of the LED is much faster than the incandescent bulb.

If it's a load issue (or series resistance), the test light incandescent bulb doesn't draw enough current either.
 
But most LED's don't do "dim" there is either enough current to light'em up
or there isn't.

Ever notice how an LED flash light dies?

By the time you begin to wonder "is this dimmer than it was?" it's dead.

AD
 
But most LED's don't do "dim" there is either enough current to light'em up
or there isn't.

Ever notice how an LED flash light dies?

By the time you begin to wonder "is this dimmer than it was?" it's dead.

AD

This is due to a diode's forward biased (conducting) characteristics. As you can see, a small change in forward voltage results in a large change in current. This was taken using my Tektronix 576 curve tracer:

318557972_Ve6Jq-X2.jpg
 
Finding a "loose connection" or other intermittent problem with Any kind of meter is...
well... slightly stupid.

That's a job for something called a TEST LIGHT.

Meters are terrible at detecting high resistance or faults
that increase resistance with load.

Ever try diagnosing a problem with say... Trailer lights with a meter?

Did you comtemplate suicide from the frustration?

Doing the same diagnosis with a test light makes the job EASY.

OTOH diagnosing a Voltage regulator problem, or an alternator problem
in general with a needle type meter isn't nearly as easy as it is with a digital meter.

(My favorite test is the AC ripple test, which requires a digital meter with an AC volts range.)

I generally prefer autoranging meters for diagnostic use.

AD

I work on telephone and alarm systems(20yrs) for a living.Test lights or simple continuity sounders are out of the question but they are great for simple troubleshooting.If you use them out in the field on a regular basis(as a tech) your being lazy.It will tell you nothing about the "health" of the wiring. In my line of work,you sometimes deal with 500' or more wire runs with splices that go bad due to corrosion.A analog meter will pick up any fluctuations while a dvm(with a lot of waiting and watching the display) might pick up something.Why do you think the phone company techs use analog meters to troubleshoot?So my point was,analog still has some advantages over dvm's.
Once again Flukes meters kick arse
 
I work on telephone and alarm systems(20yrs) for a living.Test lights or simple continuity sounders are out of the question but they are great for simple troubleshooting.If you use them out in the field on a regular basis(as a tech) your being lazy.It will tell you nothing about the "health" of the wiring. In my line of work,you sometimes deal with 500' or more wire runs with splices that go bad due to corrosion.A analog meter will pick up any fluctuations while a dvm(with a lot of waiting and watching the display) might pick up something.Why do you think the phone company techs use analog meters to troubleshoot?So my point was,analog still has some advantages over dvm's.
Once again Flukes meters kick arse


You don't use a TDR meter for finding wire faults?
 
Attempting to diagnose say... a trailer light harness with a DVM is a waste of time leading only to frustration.

Remember that if your light lights the circuit will probably work.
On many occasions I've had a meter tell me the circuit was
"good" (proper voltage), but try to use that "voltage" to
power a lightbulb...

Remember how semi-conductors were originally discovered?


AND a Diode test lamp IS limited because it only works with one polarity.

So the clamp must be attached to the proper polarity, that means you need two
one to test ground based circuits another to identify switched hot circuits

Yes DVM's are invaluble, but don't disregard the lowly incandescent test light.

Each has it's place.
No toolbox is complete without BOTH.

Just like I own simple wire end crimpers because there are times and places
where I can't make my expensive controlled cycle crimpers fit.


TDR? sure I keep it in the glovebox of my Ferrari...

AD
 
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AND a Diode test lamp IS limited because it only works with one polarity.

Not true, they make dual LEDs (back to back) in the same package, that are polarity independent. They even put 2 different color LEDs in the same package that will be one color with one polarity, and the color changes with the opposite polarity!! Besides that, unless you are working on a positive ground electrical system, all the voltages should be between GROUND and +12V (> +14V with a bad voltage regulator).

There are also single LEDs that are polarity independent:

http://pubs.acs.org/cgi-bin/abstract.cgi/jpcbfk/2003/107/i30/abs/jp034020+.html



TDR? sure I keep it in the glovebox of my Ferrari...


Sounds like you have never heard of using TDR to find wiring faults:

http://www.tessco.com/products/displayProductInfo.do?sku=474610&eventPage=1
 
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Indeed, we used TDR's in the USAF for years. They work well and are not all that expensive anymore if you work in a job where you do that kind of stuff a lot.
 
Handheld Time Delay Reflectometers are relatively new.

I'm only suprised to seem them priced as low as $800

I remember when a Benchtop model from HP or Dranitz was
several thousand dollars.

Using one to find a trailer light wiring fault on a pickup truck
is like using a $30,000 Phase Angle Volt meter to diagnose
an alternator problem on the same truck...

Or a 50Mhz Oscilliscope to monitor a 60Hz AC line.

AD
 
Handheld Time Delay Reflectometers are relatively new.

I'm only suprised to seem them priced as low as $800

I remember when a Benchtop model from HP or Dranitz was
several thousand dollars.

Using one to find a trailer light wiring fault on a pickup truck
is like using a $30,000 Phase Angle Volt meter to diagnose
an alternator problem on the same truck...

Or a 50Mhz Oscilliscope to monitor a 60Hz AC line.

AD

I guess you haven't been keeping up with electronics technology!

Here is a TDR meter for $200:

http://cableorganizer.com/triplett/network-testers-lan/tdr-3271.htm

They have been out for many years!!!


If you are trying to find a RF noise source, that may be coming in on a 60Hz AC line, you probably need a scope much better than 50Mhz!!:haha::haha:
 
If there's a line noise in my neighborhood >50Mhz I'm not searching
for it I'm probably making it...

I've been out of the electroncs biz since the early-90's
so I haven't really kept up on the prices of test equipment.


AD
 
If there's a line noise in my neighborhood >50Mhz I'm not searching
for it I'm probably making it...

I've been out of the electroncs biz since the early-90's
so I haven't really kept up on the prices of test equipment.


AD


Dual LEDs were also available before early-90's!


Handheld Time Delay Reflectometers are relatively new.

TDR is Time Domain Reflectometry
 
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Dual LEDs were also available before early-90's!




TDR is Time Domain Reflectometry

Is it your goal in life to start as many pointless arguments as possible? It's an embarassment to the entire forum that you trash so many threads with your bickering.
 
Is it your goal in life to start as many pointless arguments as possible? It's an embarassment to the entire forum that you trash so many threads with your bickering.

If you notice, I was just correcting AD's mistakes, NOT bickering!!
 
and an LED test lamp draws too little current to generate
a load.
AD

This could be solved by adding a 47 ohm (2 watt or so) resistor in parallel with the LED light circuit. This would make it draw about what an incandescent bulb would (if not a tad more), and wouldn't be as fragile as an incandescent bulb should you ever drop it.
But then the challenge here would likely be... fitting that resistor inside the test light lol.



(and yes, I do realize 47Ω on 12V will produce 3 watts, it's only for a short moment that it will be in use. 2W resistors are almost half the size of 3W ones, making the chance of fitting it slightly possible :) )
 
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