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Old 6th Jun 2018, 3:52 pm   #41
Superscope
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Hi David,

Guilty as Charged your Honor!

All I wanted was suggestions for a Accurate uA Meter!

However, to be fair, I think all parties to this Thread have brought valuable information to the Table, and for me (who started this Thread) it has been
invaluable.

Mark,

I must admit, my first thoughts on your suggestion were that I would never
trust implicitly any Chinese equipment at any price without a recognized
Western Brand Name behind it.
This comes from many Years in Industry where I have seen just how Bad some very well known Professional Chinese Branded Equipment has been.

However, as you pointed out, at that price, you can't really go wrong.

I think it was you that hit the Nail on the Head, saying you should have an order of magnitude higher on the Test Equipment you are using over the Test Equipment you are repairing. I agree here 100%.
Great Web Site by the way! you have a lot of interesting stuff there.

The suggestions of using a Voltage Reference, and Resisters makes perfect
sense, especially if a fixed value of Current (37.5uA in this case) is required
often.
I will be going down this route and thank everybody for their input.

However, my original question is still relevant, because any HomeBrew
Equipment would still need to be checked against a known Standard before use. No matter how well planned or calculated, you can't guarantee any New component 100%.
So an accurate Meter is still needed.
How accurate, obviously depends on what your doing, and for an AVO
meter my Target of 0.1uA accuracy I thought was quite acceptable.

Sinewaves last message sums it all up nicely and the suggestion of a Fluke 87V looks like the way I'm going for the Meter, in addition to some Voltage references.

Mark,

I ordered one of those AN8008's!

At that price, I want to test it out against a Fluke.


Ian
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Old 6th Jun 2018, 4:19 pm   #42
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Thanks for post #38 Mark, i knew there would be inherent factors skewing the result, that has shed extra light on it.
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Old 6th Jun 2018, 4:45 pm   #43
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
Originally Posted by mhennessy View Post
Quote:
Originally Posted by Radio1950 View Post
If it was me, I would do what some others have suggested, use a 10 Volt precision IC, and use some 0.1% resistors to generate a calculated 37.50 uA source, then check with say a good Fluke 4.5 bench style DVM or similar, or even another known good AVO 8, as also suggested previously.
My own workshop reference is based on a 2.5 Volt reference IC, and the concept works well.
The only caution I'd add is this: sometimes you need to account for the internal resistance of the multimeter as this will be in series with the precision resistor, so will reduce the current flowing.

From 2.5V, you need a 66.67k resistor. On the uA range, the AN8008 has a 100 ohm shunt resistor - which is nice and low because the measurement IC has a 1uV resolution - other meters might need to use 1k to measure uA to the same resolution.

Adding 100 ohms to your 66.67k resistor will reduce the current to 37.444uA. Not a huge change, and not anything to worry about here

But, re-do the numbers for a higher current. Let's say 100mA. The milliamp shunt for most multimeters will be 1 ohm. From 2.5V, you need 25 ohms, but with the added 1 ohm of the meter, you'll now have 96mA.

Obviously, that's an extreme example just to make the point, but it's easy to overlook when aiming for high precision. It also causes fun when you put addition meters in series to verify the reading of the DUT. If you know that the additional meter is accurate, then take that as the reference and ignore the fact it's a bit lower than expected. But if your 2.5V reference and the resistors are the basis of the current measurement, beware of this trap

In addition to the shunt resistors, the fuse will add something to the total resistance, as will PCB tracks and leads, of course. And different meters might use different shunts. All in all, it's why I favour measuring the voltage across a known resistance to determine the current - it removes the internal resistance of the meter from the equation

Oh, I have a Fluke 45 - nice meter to use, but only has 100nA resolution. The Fluke 87V/187/189/287/289 (and Aneng AN8008 ) hand-held meters manage 10nA. But the 45 is usually better VFM on the s/h market.

Cheers,

Mark
Maybe something like precision pot like what's on the Time Electronics 1030? Then one can adjust the current to bring it back to what's required with one or two meters in seires.
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Old 6th Jun 2018, 5:06 pm   #44
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Default Re: Meter Suggestions for Basic Alignment/Calibration

As a fringe benefit of this thread i found that the seldom used 50uA, 300uA and 1mA ranges on my 'decent' AVO Model 9 are completely up the creek, with an intermittent under-read.

Thanks Ian!
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Old 6th Jun 2018, 5:19 pm   #45
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Hi Ian,

Glad to have been of some help

One possible solution to the problem: do you know anyone locally that has "posh" multimeters at work? If so, they almost certainly have them routinely calibrated, and perhaps they would be able to check your meters against theirs?

Alternatively, if you wanted to build yourself (or buy) a simple voltage reference, several of us on here have decent multimeters and can measure your reference for you. I did that a while back for a forum member - actually I went slightly further than that by building an LM4040 into a box with a PP3 and an LM317 current source, complete with a label that recorded the voltage my Keithley 2015THD stated - it was to check some old Fluke 70-series meters, so more than adequate for that task.

I'd be happy to measure a reference for you, but I must confess that my 2015 is no longer "officially" in cal. Good meters rarely drift, so I'm confident that it's fine for my purposes, but if someone else has a meter that is still in cal, it might be "better".

Of course, calibration is just a procedure to record what the meter says in response to a range of known stimuli - a lot of people assume that the instrument will be adjusted to match the stimulus, but unless specially requested, that's never done - that's often the last thing you want in practice.

Regarding the 87V, I mentioned earlier that I don't think it's great VFM - and I say that as someone who owns several and uses them daily. Mine were very careful and patient s/h purchases, but bargains are relatively rare. The 187 or 189 is a better meter IMHO if you don't mind the battery consumption (s/h only though). New, I'd also consider models from Brymen and Keysight - both of whom offer better functionality for the price compared to Fluke. I am a Fluke fan; it's just that they have got a bit uncompetitive in recent years.

Good luck with the AN8008; for the money it's hard to beat!

Cheers,

Mark
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Old 6th Jun 2018, 6:22 pm   #46
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
Originally Posted by mhennessy View Post
Hi Ian,

Glad to have been of some help

One possible solution to the problem: do you know anyone locally that has "posh" multimeters at work? If so, they almost certainly have them routinely calibrated, and perhaps they would be able to check your meters against
I did that once against an in calibration Agilent bench top meter with a price tag of about £900 and compared my old 80s bench top Fluke 8000A.

The fluke which has never seen a cal lab ever in its life was reading spot on.
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Old 6th Jun 2018, 6:50 pm   #47
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Default Re: Meter Suggestions for Basic Alignment/Calibration

I'm really not surprised

Attachment 155100

Cheers,

Mark
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Old 9th Jun 2018, 12:00 pm   #48
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Default Re: Meter Suggestions for Basic Alignment/Calibration

A comment on purchase of pre-wired Precision Reference Circuits in general: In order to assess the validity of a calibration certificate it is worthwhile looking for online reviews (particularly video reviews) in order to confirm the certificate is a genuine 'one off' rather than a mere photocopy of one which does not necessarily relate to the circuit/item you are purchasing.

Dave
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Old 9th Jun 2018, 12:36 pm   #49
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Yes, I've written about that on my website. It seems the KKMOON models are believable, but there is one specific model that sends out exactly the same cal-sheet with every unit if ships!
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Old 9th Jun 2018, 12:40 pm   #50
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Default Re: Meter Suggestions for Basic Alignment/Calibration

I bought three references (All AD584L) from different sellers.

Suprisingly the calibration documents were identical

Measured against my own 6.5 digit auto cal (not in calibration) and all three were different...but within specifications.

So they are good components (not fake) but ignore the "calibration" document (scrap of paper).

Also be aware a lot of the ones on e-bay are not the high spec "L" version, but 1% basic versions, which is only good enough for checking voltmeters.
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Old 9th Jun 2018, 3:05 pm   #51
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Default Re: Meter Suggestions for Basic Alignment/Calibration

https://www.vintage-radio.net/forum/...d.php?t=123305
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Old 9th Jun 2018, 9:57 pm   #52
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Ah, thankyou, several questions answered there without me even having to ask.
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Old 10th Jun 2018, 6:22 am   #53
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Default Re: Meter Suggestions for Basic Alignment/Calibration

The benefit of an instrument having a lot more resolution than it has accuracy is in knowing that the accuracy isn't being limited by the resolution. Accuracy is a lot harder to achieve than resolution.

This makes it seem ridiculous to people who don't understand this. A 4.5 digit meter with 0.1% accuracy? well, try it the other way round: A 2.5 digit meter with 0.1% accuracy is clearly missing out on its potential.

Ultra-high resolution voltmeters, even if not calibrated have their uses. With 5 and 6 digit machines you can usually see down to microvolt levels. I use this to debug boards with a shorted component on them. I map the potentials across groundplanes and measure the drop along IC legs (even surface mount). This saves an awful lot of component swapping, and if you want the boards to look nice and undisturbed, it's a valuable trick.

I now have three fairly high resolution DVMs and they all agree closely. They haven't been adjusted, they are all different models, so I'm inclined to think they can't be far off.

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Old 11th Jun 2018, 10:48 pm   #54
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Default Re: Meter Suggestions for Basic Alignment/Calibration

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The benefit of an instrument having a lot more resolution than it has accuracy is in knowing that the accuracy isn't being limited by the resolution. Accuracy is a lot harder to achieve than resolution.
Absolutely agree. A lot harder and very much more expensive!
Equaly it is important to understand that the accuracy is not limiting the usefulness of the reasolution (precision) of any measurements.

Quote:
This makes it seem ridiculous to people who don't understand this. A 4.5 digit meter with 0.1% accuracy? well, try it the other way round: A 2.5 digit meter with 0.1% accuracy is clearly missing out on its potential.
Yes, but your 2.5 digit meter at 0.1% accuracy, while missing out on its potential, will give extremely accurate measurements with 100% certainty!

All my comments were in response to the OP (Superscope) asking for recomendations for a meter that could be used to Accuratly measure 37.5uA
My original suggestion was to determin the accuracy and precision of the measurement required. That would then determin the meter specifications.
The resulting discussion of Resolution V Accuracy was of a consequence of certain meters being suggested as suitable to accuratly measure 37.5uA, as they had a resolution down to 100nA or even 10nA, but with a measurement tollerance of over +/-0.8%

Hopefully I have demonstrated that resolution is not a substitute for accuracy, when making measurements. It is too easy to confuse resolution (precision) with accuracy (and i guess some makers prefare it this way!)

Quote:
Ultra-high resolution voltmeters, even if not calibrated have their uses. With 5 and 6 digit machines you can usually see down to microvolt levels. I use this to debug boards with a shorted component on them. I map the potentials across groundplanes and measure the drop along IC legs (even surface mount). This saves an awful lot of component swapping, and if you want the boards to look nice and undisturbed, it's a valuable trick.
Resolution without necessity for accuracy is perfect for this kind of use. Even low accuracy 6000 count multimeters, have lots of uses in fault finding, especialy for comparing values, matching components and detecting small changes.

I use a "Toneohm" type instrument for finding short circuits and high resistance via's. It doesnt display any meaningful value, just a display from 000 to 999 depending on resistance, along with a variable-pitch tone depending on resistance. Absolutely no accuracy, but an effectively infinate resolution (as good as my ears and the analogue tone circuit in the instrument)

Quote:
I now have three fairly high resolution DVMs and they all agree closely. They haven't been adjusted, they are all different models, so I'm inclined to think they can't be far off.
Exactly what I do, with two auto-cals, and two 6.5 digit DVM's

At the moment they all agree to 4.5 digits. This is the limit of my Voltage accuracy (for the time being )
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Old 12th Jun 2018, 5:14 pm   #55
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Default Re: Meter Suggestions for Basic Alignment/Calibration

I like the way 0.1% accuracy is said, surly it is 0.1% error?
 
Old 12th Jun 2018, 9:54 pm   #56
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Default Re: Meter Suggestions for Basic Alignment/Calibration

It basically amounts to the same thing!

Same as "Is the Glass Half Empty or Half Full"

Different ways of saying the same thing.




Ian
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Old 13th Jun 2018, 5:35 pm   #57
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Surely, accuracy cannot exceed resolution for a digital meter measuring an analog system ?

dc
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Old 13th Jun 2018, 11:24 pm   #58
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Dave, that makes sense to me...

As already mentioned, resolution is a substitute for (weapons grade) accuracy if we are making several measurements which should all be around the same ballpark. This assumes the DMM is not wandering between tests and the same range is used for all the measurements.

For (most of) our purposes 3 is the magic number- 1 meter generates a number, 2 meters usually disagree, and (you hope) the 3rd meter has the casting vote.
My 3.5 digit DMM measures things quite well, my 4.5 digit DMM gives me too much information for much of the time.
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Old 19th Jun 2018, 7:50 pm   #59
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Default Re: Meter Suggestions for Basic Alignment/Calibration

As an update, I was lucky enough to get hold of a NOS Fluke 287
for a very good price.
Calibration is out of Date though, so I will put this one in for Cal and
only use this as my Bench Standard. Unless I need it's advanced functions.
This is a really nice Meter, but a bit over the top for most work.

For normal use, I went for the Fluke 87V, again, I managed to get
a New one for a pretty good price.

I also bought one of those Aneng AN8008 as suggested by Mark.
At such a low price I wanted to test it out.

So I had a Blitz on updating my Test Equipment!
After initial testing, there is really no discernible difference between
the Fluke 87V and 287, they were pretty much the same apart from
the extra Digit of resolution on the 287.

The surprise though, was the Aneng 8008, which for the most part
agreed very closely if not exactly with the Flukes.

The only issue I found with the Aneng, was that on very low readings
it drifted about it's measured value to the point where in all honesty,
I would not be using it for precision work, but! Wow! that is some Meter
for the Money. On higher readings it was more than good enough.

As an aside, my old faithful Fluke 79 was also spot on within it's Resolution
limits when compared with the 287 & 87V.
Not bad for a 30 year old DMM


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Old 19th Jun 2018, 8:41 pm   #60
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Wow - what did your bank manager say about that?

As someone who has examples of all those meters, I'm not surprised. The Aneng is especially impressive, as you say. There are some simple mods that might improve things: https://www.jackenhack.com/aneng-an8...ster-readings/

Enjoy your new meters
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