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Old 19th June 2015, 06:38 PM   #1
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Default Test and Meassurement Issues

This is a very straightforward statement from Chris,
and I think it is of interest to anyone who is interested
in equipment and tools:

Quote:
Originally Posted by anatech View Post
Well guys ...
It's like this. You ask for information in hopes an expert in the field answers with the technically correct answer using the industry accepted materials and supplies. Don't turn around and complain that you don't like the answer. That's what many of you are doing.

Myself and others have also given alternatives and guidelines, and you can't complain about being that open about things. The sad truth is that the amateur tech is the one who will believe the meter is accurate to all visible digits (admit it) when some of those meters a lying about the last two digits. Then, measurements on low resistance items like speaker voice coils or load resistors, even at 8 ohms, with two leads. No consideration given for temperature effects of the meter and it's internal voltage reference or thermocouple effects from dissimilar metallic contacts. Did anyone who made measurements of heating elements state the ambient temperature and load temperatures? Where the measurements made two wire, or Kelvin connected? Kelvin leads or at least two lead sets? How about the meter make and model listed?

None that I have seen. A professional would create an error budget for everything and combine the results to give a figure to a realistic number of significant digits, then add the uncertainty term as + or - x ohms. I'll state the obvious for some of us. These resistance measurements need to be made with a 4 wire (Kelvin) connection to begin with. If not, your accuracy is so low that you may as well just quote the spec as worst case (the most error you can find). Then figure out the tempco and attempt to measure output power.

Nasty surprise time. How far up in frequency is your true rms meter good for and at what spec? Most meters are in trouble from 200Hz up. Mine is good to 100 KHz, and the bench meter for 300 KHz - exceptional performance. The LCR meter I use will go up to 100 KHz test frequency as well. It also uses Kelvin clips (4 wire).

Many of you will still quote the power to one decimal at least using a meter outside its bandwidth, peak indicating. A hopelessly indefensible reading. But, by gosh, that is the number they will stick to.

If you want to get a rough idea of output, or you simply want to heat an amplifier up to set or check bias current stability - fine. If you are preparing to quote a number, you had better have done your homework and used good testing and measurement practices to arrive at a number that can be verified by someone else should the need ever arise.

Like it or not, that is the answer. Proper resistors are not that expensive and will last a lifetime (barring accidents). Either get those, or quote your numbers as very rough, or imprecise. At the bottom of all this is a meter that is half decent. Many are available used in various places, even new decent ones starting around $220~250 (Keysight or Fluke). but read the specs for the different models so you know what you are giving up with a lower cost meter. That meter will also last you a lifetime - mine have so far. (new in 1968).

-Chris
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Old 22nd June 2015, 04:39 PM   #2
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There are some good points in that text, but the most important one is missing, with out receiving first, true technical education, there is no chance to have proper understanding of the world of measurements.

At 1988 I did graduate as electrician, among the classes was one dedicated to electrical measurements, but this was related to analog world.
I had to catch up all details about the new digital world all by my self, by using as sources all sort of user guides, from old Fluke multimeter up to recent ones and even from other vendors too.

In those documents which some lazy persons throw away at first unpacking of new product, there is a small treasure in every one.

Do you need to know of what is important in a good handheld LCR meter ?
Just read user guides of Agilent U1733C and of DER EE DE-5000.
Will you really print them and read them down to a true understanding level? This is your challenge, and the true question here is how much determination you have in your self as character.

The lazy one will fail.
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Old 23rd June 2015, 02:18 AM   #3
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The DER EE DE-5000 That came with the meter
has very little English as option.

I'll have to check out the Agilent U1733C manual.

Always appreciate your write ups and recommendations.
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Old 23rd June 2015, 02:34 AM   #4
infinia is offline infinia  United States
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1st year chem. lab teaches you this
measurement of mass, volumes etc > significant digits was hammered home.
course this before digital read outs, so the theory was in place when they did come out.
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Last edited by infinia; 23rd June 2015 at 02:36 AM.
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Old 23rd June 2015, 03:34 AM   #5
jcx is offline jcx  United States
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or it could be seen as a rant ignoring the starting premise of the original thread and the highly qualified point that you don't need NIST traceable accuracy to learn valuable things about audio power amps with cheap loads

yes, know your equipment limits

no, don't throw up your hands if you don't have the perfect meter or load

work out what you can learn within your equipment's limits, use clever workarounds to get more than many may expect is possible

I do like and own good equipment but I don't have a 1% kW load and would have to hack together something like room or water heater cal rods, measure I and V separately

but I and few diy-ers really need to know the load to single digit %
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Old 23rd June 2015, 01:07 PM   #6
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Quote:
Originally Posted by jcx View Post
use clever workarounds to get more than many may expect is possible
I am a 46 years old and expert, I do that all the time, but there is RED lines.
Do you create a toy for your son?
Do you create a sound system for your ears only?
Then yes, use even carton and woods and bricks, who cares.

But from the other hand, DIY electronics and DIY audio is a competition, and is not enough to just wish to win.
The award is the satisfaction that you did make a well performing electronic sound system .
Which this is actually a copy of work that some one else did before you, this must to comply to original design, so to really deliver the what ever expected performance.

I just finished my very own DC Load, while this is DIY, the 46 years old fellow who made it, is an expert and trained as to be a Japanese Ninja.
Therefore there is a feeling of joy but among with it there is the reinsurance that this gadget is not an experimental item.

Supacell digital alkaline battery cells review and testing at ITTSB Blog 2015

Last edited by Kiriakos; 23rd June 2015 at 01:10 PM.
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Old 24th June 2015, 12:52 AM   #7
infinia is offline infinia  United States
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^WTH ,
consider automated data collection and electronic loads.
there are better bloggers doing the same type of thing that know what theyre doing.
AND don't appear to be jr. corporate shills.
no expert detected im afraid

Re the link >are you psycho or something, talking in third person?
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Last edited by infinia; 24th June 2015 at 01:11 AM.
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Old 24th June 2015, 02:19 AM   #8
SY is offline SY  United States
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Quote:
Originally Posted by Kiriakos View Post
I am a 46 years old and expert, I do that all the time...
I just finished my very own DC Load, while this is DIY, the 46 years old fellow who made it, is an expert and trained as to be a Japanese Ninja.
We are all very impressed.
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Old 24th June 2015, 10:57 AM   #9
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Quote:
Originally Posted by infinia View Post
^WTH ,
consider automated data collection and electronic loads.
there are better Bloggers doing the same type of thing that know what theyre doing.
AND don't appear to be jr. corporate shills.
no expert detected im afraid

Re the link >are you psycho or something, talking in third person?
You must be in some emotional pain.
FYI I have blue eyes, and skills in communication so to talk with people like me who work professionally in products design and production.
Their appreciation and opinion about how much I worth to them, is what it matters to me the most, compared to anonymous comments.

From the other hand it seems reasonable to me for you to feel hate for branded products, because your home made ones these never come close in performance of products designed and produced by truly educated and hard working people.

In conclusion there is even better forum members than you, these are open minded and also these have the capacity to demonstrate appreciation for others people work.

Note: Your better Blogger is using a cheap 150$ Chinese charger as test bed.
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Old 24th June 2015, 11:34 AM   #10
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Kiriakos,

Always so negative with your responses. We are here to help each other and provide positive support. You are not very positive.

Maybe it is time to logoff and meet some nice ladies...that will help your outlook on life.
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