In article , no- snipped-for-privacy@nowhere.net says...>=20
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Not quite. The other side of the coin is that he knows he's the=20 one who screwed up when things don't go right. Hackers have no=20 clue, so blame the tools.
=20
- 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.
Indeed and engineers *are* toolmakers, in every sense of the word.
And hence the disgreement between the users of tools and the Creators of Tools.
claims *over*
impedance" or "HI-Z"
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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.
*over*
"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.
I
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.
Cincinnati Milacron. Tolerances to one one hundred thousandth of an inch.
Their machines used to be what made America. Everything from unibody car frame machining to the M1A1 Turret way and gear. All the vocational schools were filled up with old Cincinnati machines that companies parted with as they bought newer, larger machines. America used to be about fabricated goods. Automation did kill us. The computers that operate automation machinery are the only jobs left for those folks.
As we globalized the world's economy, we took a hit, and it ain't over yet. We need to close out borders except to paying customers. They treat us as tourists when we go there. We should give them the same treatment.
Whay comes around, goes around, and we will be getting our prosperity back eventually. Likely be after I'm long dead though.
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.
Absolutely correctly worded.
The same with ANY measurement instrument, nothing unique here at all.
Crippled? Hardly the right term, try purposely designed. Just like you wouldn't go around saying a meters DC range is "crippled" because it's 0.5% when they could have made it 0.1%. Or a meters current range is "crippled" because it has a burden voltage of 10mV/mA instead of 1mV/mA. etc.
Usually, with meters, a lower spec is done to meet a lower price point. But in the case in question it is done for the purpose of meeting a (niche) market need. A tool is not crippled just because it doesn't meet YOUR job spec.
Dave.
Spehro Pefhany wrote in news: snipped-for-privacy@4ax.com:
Cool. Someone gets it. krw isn't wrong, but he said only what I already said. An inevitable logical derivation isn't a new unmade point.
"David L. Jones" wrote in news:9f33ec2f-7412-4832-bcb5- snipped-for-privacy@b38g2000prf.googlegroups.com:
Makes sense but do you concede that understanding the conditions matters more than the meter? What matters in wiring that is capacitatively or inductively coupled but not directly so, is that some kind of light load is placed on the line, and the voltage measured across that load. Only when that load needs to be a simple resistance can it be assumed that it is the meter's job to include it. In all other cases it can be assumed that the meter should tax the circuit as lightly as possible while analysing an external load chosen to fit the analysis needed. Which in turn directly implies that in the hands of someone who knows electricity, especially AC and frequency dependent behaviour, the high impedance meter is the way to go. Ideally with a plug-in load module or two, just as meters used to come with plug-in current shunts.
I don't test for live circuits with a DMM. I use test lamps or a low(er) impedance voltmeter. If you worked for me I would sack your arse if I caught you using a DMM to test for live.
Who said anything about it being *analogue* ?
Impedance is a property of the input of the meter not the display type.
I've used high and low impedance analogue meters and the same in digital form.
No, you carry the correct tools. You use a load to test for live/dead circuits, not a DMM. (I use test lamps with fuse protected leads). If you need to measure voltage, then you use a voltmeter...how hard is that to understand????
Hi guys, why does it seem "you are writing aloud"? There are no reasons for that: I think that we should be here just to discuss our opinions without pretend to be the owner of the absolute knowledge, don't you?
The original thread was concerning a problem of capacitor charge sustainment due to the DMM high Z input. I guessed it's due to the latest methods used to perform the analog to digital conversion. The older one methods always used to get the input voltage on a comparator, this should give a good certainty that no currents flow out from the ADC input to the device connected to it. It is my opinion, that the capacitive DAC method instead could inject a current backward to the DUT due to the switching operations of the inner capacitances of that ADC frontend. I don't know whether I'm right or not, but (if I am right) we should consider this behaviour of that kind of ADC in future applications where Hi-Z analog to digital conversion is required.
Of course (always if I'm right), this states that this kind of DMMs should never be used for the purpose of determine the parallel parasitic resistance of a capacitor, because their input Z could be "so high" to become "negative".
Massimo
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