Freaky Amazing DMM?!

Doesn't need to get into the innards directly, you can screen that, but you've got a pair of leads forming an aerial and most likely a diode at the junction of the test lead and the DVM socket. A low impedance input attenuator will load that down to something insignificant compared with what you are measuring.

Late at night, by candle light, "David L. Jones" penned this immortal opus:

"HI-Z"

The circuits are loaded, so any bad contacts will certainly affect the reading. Which is the way I like it. Any funny readings, move up to the next point in the line and check there.

I do know better than to measure an unloaded line without sticking some suitable load across it.

Anyways, AIUI, this started with a meter with Hi-Z in the mV range, most DVMs use a 10M or 1M divider at higher ranges.

- YD.

In article , snipped-for-privacy@argonet.co.uk says...>

Nonsense. There are many things that can be done to eliminate any external factors. Add a shunt resistor and you have your low impedance meter.

Nonsense. If an input resistor will load down your circuit so will your low impedance meter. It's *exactly* the same thing, except the user gets the choice.

Go get some practical experience.

In article , snipped-for-privacy@argonet.co.uk says...>

I certainly have more than you.

r*

-Z"

This is an oft used but seldom understood saying. The reason a craftsman supposedly never blames his tools is because a craftsman tends to buy quality tools in the first place.

claims *over*

or "HI-Z"

Keithley has

a bit

will

what

Yes, electricians generally just do just the one similar job. That's why they make meters designed for just such specific purposes. Giving your average electrician say a Fluke 289 is a bit overkill and would likely not be as productive as a more job specific instrument.

That's why many good meters have selectable Low-Z and High-Z modes.

Dave.

Safely, in a dangerous situation? What part of using the right tool for the job don't you understand?

Yes, High-Z meters are good (more useful in more cases), but Low-Z meters have their place too. There simply isn't any argument here, if you need a Low-Z meter, use one. If you need a High-Z meter, use one. "Making do" without the right tool in serious situations is stupid.

Agreed. That's why if you have serious needs you either have a dual purpose meter, with Low-Z and High-Z modes, or you have two meters.

Dave.

Daniel wrote in news:e8f56b53-9c0c-49cd-b6b5- snipped-for-privacy@i24g2000prf.googlegroups.com:

I thought it was to do with a craftsman knowing the limits of his tools, thus not blaming them for over-reaching.

Related to that, I find the best definition of a toolmaker is one who achieves greater accuracy than was provided, and makes a system to easily repeat that gain.

- I

It's easy to do safely.

What part of understanding electricity don't you understand?

If you're a sparky and all you do is wiring, sure. There is no reason to have a high impedance meter. That doesn't mean that a high impedance meter can't be used safely and accurately.

If you have a meter for every job, sure. If you don't, a little knowledge goes long way.

Nice snip. That's known as a lie in many corners.

No, you understand what you have and use it appropriately. ...something there is an obvious shortage around here.

claims *over*

impedance" or "HI-Z"

Keithley has

is a bit

they will

the

of

the

that I

what

more

That wasn't at issue here. The statement was made that a high impedance meter couldn't be used and that a low impedance *ANALOG* meter was a necessity. It's certainly not true, though one has to understand what one is doing, again a rarity in this group.

Most *good* meters don't. Many sparky meters might.

The antenna I get. A diode? Are you sure that you are familiar with modern multi-meter construction?

Low Z meters are dumbed down so that dopes can artificially SUPPRESS what they term as "noise" when reading power sources in an EMI rich environment, such that they can take "reasonably reliable" readings on a power source. They are NOT made for getting true reading on small signal sources in any way shape or form. The same thing can be accomplished by changing the sample rate or chop the input and average. The same canceling can also be gotten by twisting the meter leads together. Note that nearly all "sense line" attachments are of the twisted pair variety. There is a reason for that, and it is not so that the wires stay bundled together.

The Fluke Low Z model has the capacity to REMOVE the low Z shunt from the meter's lead-in circuit, giving the user back an actual, accurate, high Z meter.

Placing a shunt across your voltage measurement cannot be done on a source where such a low impedance will load the source. Either way, you get a flawed reading.

High impedance metrology is akin to actually getting the test data without touching or modifying the circuit. As we all know, this is a very hard thing to accomplish. High Z meters are a GOOD thing. Anyone that thinks they are not needs their head examined.

"HI-Z"

Most modern meters are high Z on nearly every range.

Loaded...

Unloaded...

Something stinks in here either way.

You have been out of the loop too long. Even your feedback has been self attenuated. No gain whatsoever.

"HI-Z"

Metallic?

Who said anything about a dangerous situation? If a pro is taking a reading, his chosen job is not dangerous to him, and he knows how to take the reading properly. That is why certain skills are taught.

All low Z meters simply have their low Z rated value utilized as a direct shunt across the input leads. That is ALL low Z meters. That is how it is done... in EVERY CASE. SO it is NOT unsafe to CREATE your own low Z input by doing the same thing. You simply must ALSO be sure to observe and obey all proximity rules and exposed node precautions, like any pro would do anyway.

Low Z meters ARE high Z meters with a shunt. In almost every case, but the cheap Harbor Frieght crap.

Going from having high Z and getting low is not a problem. The other way is simple too. All you need to do is go buy a high Z meter.

A good "low Z meter" will allow turning the shunt off. Shitty brands do not.

Get a good, High Z meter, and if you need Low Z input impedance, set it up right and perform you measurements. It really is that simple. Proper set-up.. proper reading.

Ok, I haven't followed the entire silly thread. From my side I've only been proposing that high impedance meters can be a problem, and the solution is using the right tool for the job.

Dave.

No, that's the backhand side of the expression. He doesn't blame his tools because he understands when he makes a mistake it's his. Hackers blame everyone else, and the tools (even if they have the best).

Yes, they can be a problem if YOU DON'T UNDERSTAND WHAT YOU'RE DOING. If you know what you're doing you can get the right reading form a high impedance meter just as well as one that has been crippled by the manufacturer. If necessary, you can cripple it yourself, though that is rarely needed.