General > General Technical Chat

How much accuracy do YOU really need?

<< < (4/7) > >>

artag:
There's somebody here who's signature consists of a series of crossed-out remarks of the form

4.5 digits 6.5 digits 7.5 digits are enough for anyone.

Always gives me a tickle. Sometimes the precision isn't important but achieving more is fun in itself.

pqass:
I confess that I have a touch of gear acquisition syndrome; 3 bench meters in 3 years (so far). Although, my limit is 6.5 digits since 7.5 digits is right out of my $$$ range.

But I didn't really appreciate the low end (microvolts, milliohms) until I was able to do a 4-wire measurement.  It enabled me to precisely cut NiChrome shunts for my e-loads.  I couldn't do this with my hand-held [4000 count] meters.  Then it dawned on me that there is an important world of applications between 1 ohm and 2 milliohm (8" of 14AWG).  Also, having microvolt measurement capability allowed me to monitor thermocouples directly!

My latest meter, an HP3456A can do 6.5 digits but the features, moreso, just blew me away.  It doesn't directly offer current measurement but that doesn't matter because you can provide your own shunt, measure its resistance, then enter that into the "Y" register. The meter can then calculate (X-Z)/Y where X=the measured voltage drop and Z=0!  And there are many other great features like: offset compensation, choosing PLC, stats, error calc. (binning), temperature (via NTC),  etc.

mumoto:
I worked as a metrologist for nearly two decades.

With my current work,  all I can say is "not a lot" in the general electrical sphere.

I understand a good deal of the science of measurement, but sometimes (ha! I'm no long working in the field) good enough is good enough  :-//

I could start a long scientific and philosophical explanation, but it's horses for courses.   

exe:
10k counts is enough for everything I do, but for some reason I have 6.5digit dmm...

vk6zgo:

--- Quote from: TomKatt on February 09, 2023, 11:42:30 am ---
--- Quote from: tom66 on February 09, 2023, 11:34:14 am ---For day-to-day usage of a multimeter?
--- End quote ---
I'm curious about all equipment.  I agree with your sentiments about the DMM's.  But even when I pull out the scope, I'm not sure how many times I relied on it's accuracy either...  Certainly I got by for many years using my ancient HP180A cro.

While I don't do much with RF, that's one field where I suspect true accuracy might be an important spec (then again - the Shango066 tv example.  Love the way he tests caps by playing phone audio through them and listening for the filtering)

--- End quote ---

Nah!---------RF is normally specified in dB.

You'd usually be happy if you could read better than 0.5 dB on a Spectrum Analyser, & that is just under 11%.
Really "scrunching up your eyes" you might be able to "guess" 0.25dB, which is a tad under 6%.

This can be "a trap for young players".

On one occasion, we had a test where we had to input +16dBm of audio into the (600 ohm) L & R inputs of a TV stereo encoder.
"Easy peasy" we thought, the audio signal generator has a low Z (30 ohm) output, so we can just "parallel 'em up".
The error would only be a fraction of a dB, so "it's cool for cats".

Sadly, that was not the case, as the Tx spec was 50% deviation, which showed up with this setup as 47%!!

What looks like nothing with dB, soon mounts up to something quite a lot more concerning.

At another job, we had some UHF transmitters, which as is common, consisted of a bunch of individual smaller amplifiers paralleled up
via diplexers, complete with unbalanced loads.
Unfortunately, we found ourselves having multiple amplifier failures.

It turned out that the "rent an EEs" back in the dear old PRC had been fairly "laid back" both in the ratings of the unbalanced loads & the frequency response/ amplitude matching of the amplifiers.

"Meh!---- They're within a coupla dB" didn't quite hack it, the unbalance loads blew up, followed by the associated amplifiers, ending up in a mess.

In the end, I had to go through all the smaller amplifiers with an SA & tracking generator, getting their response at the operating frequency within 0.5 dB to avoid killing the unbalance loads.
I was unimpressed at having to push chip capacitors around on PCBs to get exactly the right response, something I hadn't done for around 30 years!

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod