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Old 19th Jun 2018, 9:57 pm   #61
Superscope
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Hi Mark,

Yes, I read about the Mod regarding the Noise on the Power Rails for the 8008.
I will do that shortly and then re-test, but I thought it important to test the
Device out of the Box first.

Yes, all 3 together were expensive, but it's been many years since I invested
in any Test Equipment and the Total was a lot less than half the normal retail price. They are NOS, so out of Cal.
As I mentioned, I will put the 287 in for Cal and use it as my Bench Standard.

Now at least, I can start on my Constant Current Standard Project and have a reasonable chance of getting it right.
In addition, it's time to re-visit the AVO Meter collection.
I still love to use these Works of Art where possible.

Ian
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Old 19th Jun 2018, 10:21 pm   #62
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Unless you think you have a realistic need for the performance the extra digit offers it's probably not worth sending the Fluke 287 for calibration if it agrees with the (new) Fluke 87V. I'd recommend saving the cost of the calibration and maybe keep a lookout for a classic old bench meter from Keithley or Fluke to use as another confidence crosscheck.

One thing to watch out for is that the the 287 is very heavy on batteries. We have a few of them at work and they are always easy to find because they are always in the surplus DMM container at work with a postie note saying "Flat Battery". The 187/9 also seems to eat batteries when compared to the 87V.
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Old 19th Jun 2018, 11:28 pm   #63
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Default Re: Meter Suggestions for Basic Alignment/Calibration

I'd get the highest digit counting meter calibrated, that can be your best reference. But for calibration to mean anything you will need to do it at regular intervals. It may not need to be every year, it could be two years.
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Old 20th Jun 2018, 12:23 am   #64
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
But for calibration to mean anything you will need to do it at regular intervals.
That's partly why I think it's a complete waste of money for home/hobby use.

Unless you are running a business or have a megatastic DMM with loads of digits and you work in a physics lab it really isn't worth calibrating a modern DMM. They have been boringly brilliant for decades now and easily exceed the requirements of most professional users let alone hobbyists. I've not had to adjust any of my DMMs here at home since the 1990s. Some have never been adjusted and they are still in good agreement with each other.

Buy an old/used bench meter from one of the big names and you can expect it to retain very good accuracy for many years. If it starts to drift out of spec by a factor of two it probably isn't worth calibrating any more because it will probably be going faulty anyway.

The risk is that a hobbyist can end up (needlessly/pointlessly) calibrating a DMM every year or so like pampering a new puppy in the form of regular visits to the vet. In reality, it's the piece of test gear on a typical bench that is least likely to need any looking after or adjusting for many, many years
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Old 20th Jun 2018, 12:55 am   #65
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Default Re: Meter Suggestions for Basic Alignment/Calibration

But you can't measure someone's needs or passion for their hobby by your own opinion. You could spend an eternity telling someone they don't need to have spent the money on a Bentley when a Ford would have done.

So I dont think it's a waste of money for home hobby use, I think it's money well spent if you're serious about the measurements you're making, especially when calibration adjusting a load of Avos.

It would be entirely different if you only had a meter for checking batteries every now and then.

If one is serious about a hobby, then why not know to a traceable standard how accurately a meter is measuring?

As you say, it may not need adjusting at all, but the calibration is only a check anyway. And unless you have it calibrated, if it were to drift by a factor of two, how would you know?
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Old 20th Jun 2018, 1:10 am   #66
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
Originally Posted by Radio Wrangler View Post
Calibration is an interesting minefield.

A general certificate of calibration simply means that an instrument was checked on a specified date and was found to comply with its manufacturer's specifications.

Thereafter, several things go wrong:

1) The couriers bounce the thing down several flight of stairs on its way home from the cal lab. Maybe this affects the accuracy, maybe it doesn't. How lucky do you feel?

2) Once home, most users see the cal certificate and then treat the instrument as gospel, ignoring or unaware of the allowable amounts of error specified by the manufacturer.

3) Most users ignore or are unaware of the specified uncertainties of the cal lab they used.
Sorry to continue to be a neghead but I agree with all the above based on experience at work. We have some really nice test gear (and lots of it) but calibration is generally seen as a necessary business requirement and not something to look forward to.

The test gear (for calibration) usually goes in the back of a transit van for a couple of days then you have to hope and pray the cal house don't actually find the need to take the gear apart and meddle with it. I think it is usually away for a couple of weeks but I don't know for sure. But for at least two days it will be subject to a free shock and vibration test in the back of a transit van.

Sometimes the gear comes back scratched or damaged. My nearly 30 year old Fluke DMM at work came back with a damaged display last year from Trescal. It wasn't worth the time/cost of complaining but I've used that DMM all my time at this company. So I was quite upset about this. The fact they can take it away, calibrate it and trash the display and then their driver delivers it back unpacked yet visibly damaged tells you all you need to know about how much your test gear is cared for at these places.
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Old 20th Jun 2018, 1:25 am   #67
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Default Re: Meter Suggestions for Basic Alignment/Calibration

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Originally Posted by Radio Wrangler View Post
Calibration is an interesting minefield.
A general certificate of calibration simply means that an instrument was checked on a specified date and was found to comply with its manufacturer's specifications.
Which I why I say, it needs to be calibrated at intervals. So that there is a trend and then there can no longer be the uncertainty that it was only fine on that one day you first had it calibrated.

Quote:
Thereafter, several things go wrong:

1) The couriers bounce the thing down several flight of stairs on its way home from the cal lab. Maybe this affects the accuracy, maybe it doesn't. How lucky do you feel?
This issue isn't exclusive to calibration, but you can take it there yourself.

Quote:
2) Once home, most users see the cal certificate and then treat the instrument as gospel, ignoring or unaware of the allowable amounts of error specified by the manufacturer.
Some, not most, certainly not all.

Quote:
3) Most users ignore or are unaware of the specified uncertainties of the cal lab they used.
Some, not most, certainly not all.

Quote:
Originally Posted by G0HZU_JMR View Post
Sorry to continue to be a neghead but I agree with all the above based on experience at work. We have some really nice test gear (and lots of it) but calibration is generally seen as a necessary business requirement and not something to look forward to.

The test gear (for calibration) usually goes in the back of a transit van for a couple of days then you have to hope and pray the cal house don't actually find the need to take the gear apart and meddle with it. I think it is usually away for a couple of weeks but I don't know for sure. But for at least two days it will be subject to a free shock and vibration test in the back of a transit van.

Sometimes the gear comes back scratched or damaged. My nearly 30 year old Fluke DMM at work came back with a damaged display last year from Trescal. It wasn't worth the time/cost of complaining but I've used that DMM all my time at this company. So I was quite upset about this. The fact they can take it away, calibrate it and trash the display and then deliver it back unpacked yet visibly damaged tells you all you need to know about how much your test gear is cared for at these places.
I'd say those who see calibration as only a business requirement probably don't understand it at all.

With regards to your feelings of cal centres, I guess it depends on the cal centres, the people you choose.

We would have a company come to us and calibrate our gear, they were good, nothing got damaged. They'd come to us due to the amount of gear we had, they'd do three days here.
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Old 20th Jun 2018, 1:41 am   #68
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Default Re: Meter Suggestions for Basic Alignment/Calibration

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And unless you have it calibrated, if it were to drift by a factor of two, how would you know?
You don't know for sure it hasn't gone out of cal by the time you get it back from the cal house... or it might go out of cal weeks or month later.

The best thing to do is buy several decent DMMs and cross check them now and again if you are worried about accuracy or drift. Where I work I've never seen a single engineer show any interest when a decent DMM comes back from calibration. That would be hundreds of engineers over several decades. But on internet forums there are armies of people who seem obsessed by it.

Last autumn I bought a Keithley 2000 bench DMM at auction for the same cost of a (new) handle/feet kit so I could fit the handle to another meter. I didn't really care if the Keithley 2000 worked because it was worth it for the handle alone and any spares for the other meter. But it did work and it was only out of cal by 1 year. I only checked it once but it agreed with the other Keithley meter within 2 or 3 LSDs. To many hobbyists this LSD error would be a stressful problem that would 'need' addressing but to me it just meant that they were probably both still healthy meters and OK to use.

The meter below probably cost me 1/3rd the cost of even a basic annual calibration on a cheaper meter. Why would I want to calibrate it when it is probably two orders of magnitude better than I will ever need in terms of absolute accuracy and unlikely to drift this much in many years? I expect this meter to fail before it ever needs calibrating for hobby use. Note that it is just connected to a basic 5V supply here to show something on the display. Buy a few cheap/used meters like this and cross check them now and again.
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Old 20th Jun 2018, 3:05 am   #69
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
You don't know for sure it hasn't gone out of cal by the time you get it back from the cal house... or it might go out of cal weeks or month later.
That's unlikely to have happened, but then you do know, the next time it's calibrated

Quote:
The best thing to do is buy several decent DMMs and cross check them now and again if you are worried about accuracy or drift.
That's probably the best way to confuse yourself.

Quote:
Where I work I've never seen a single engineer show any interest when a decent DMM comes back from calibration. That would be hundreds of engineers over several decades. But on internet forums there are armies of people who seem obsessed by it.
I wouldn't say people on forums are obsessed by calibration. What I'd say is, that forums are where people have a discussion. So if calibration is being discussed, then people are discussing calibration. It's hardly an obsession, no more so than your obsession for trying to convince us to not have a calibrated instrument and a dislike for electronics hobbyists.

Quote:
Last autumn I bought a Keithley 2000 bench DMM at auction for the same cost of a (new) handle/feet kit so I could fit the handle to another meter. I didn't really care if the Keithley 2000 worked because it was worth it for the handle alone and any spares for the other meter. But it did work and it was only out of cal by 1 year. I only checked it once but it agreed with the other Keithley meter within 2 or 3 LSDs. To many hobbyists this LSD error would be a stressful problem that would 'need' addressing but to me it just meant that they were probably both still healthy meters and OK to use.

The meter below probably cost me 1/3rd the cost of even a basic annual calibration on a cheaper meter. Why would I want to calibrate it when it is probably two orders of magnitude better than I will ever need in terms of absolute accuracy and unlikely to drift this much in many years? I expect this meter to fail before it ever needs calibrating for hobby use. Note that it is just connected to a basic 5V supply here to show something on the display. Buy a few cheap/used meters like this and cross check them now and again.
How do you know your meter is two order magnitude better, if you never have a trend to follow, such as cal checks?

If it agrees with the other meters by 2 or so lower significant digits, it may well still be within spec, so I don't think any hobbyists are going to be stressed by that.
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Old 20th Jun 2018, 7:35 am   #70
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
Originally Posted by Sinewave View Post
Quote:
Originally Posted by G0HZU_JMR View Post
Calibration is an interesting minefield.

A general certificate of calibration simply means that an instrument was checked on a specified date and was found to comply with its manufacturer's specifications.
Quote:
Originally Posted by G0HZU_JMR View Post
Thereafter, several things go wrong:

1) The couriers bounce the thing down several flight of stairs on its way home from the cal lab. Maybe this affects the accuracy, maybe it doesn't. How lucky do you feel?
This issue isn't exclusive to calibration, but you can take it there yourself.

Some, not most, certainly not all.

Quote:
Originally Posted by G0HZU_JMR View Post
3) Most users ignore or are unaware of the specified uncertainties of the cal lab they used.
Some, not most, certainly not all.

Those quotes were originally from me.

I currently work in the aviation industry where calibration certificates (and other certificates) are very important indeed. Calibration is backwards-looking. A shiny new cal certificate gives me no guarantee that the equipment won't go wrong in the coming year, or that it wasn't knocked out of kilter on the way home from its annual holiday at the cal lab. What the certificate certifies is that the measurements over the previous year were within the manufacturer's spec. If we get notified of a calibration failure, we want to know which parameter is off and by how much. Then we need to calculate whether the error would allow anything tested by this instrument to have been unknowingly outside it's spec. It could be innocuous if the test gear is found to still be good enough for what it has been used to do. Worst case, we may have to redo some design verification tests, or recall products for re-test. A lot hinges on calibration. A calibration failure notification could initiate an avalanche of necessary work. You don't know when, since the previous cal, the fault occurred so recalls would implicate a full year's production.

Previously, I worked in R&D at HP/Agilent for a bit over 30 years, designing test and measurement equipment. One luxury there was not just a full in-house calibration facility just a five minute trolley push away, it was backed up with a full standards lab with traceability links to multiple national standards organisations. The risk of damage due to mis-handling was a universe away from handing something to a courier firm.

I said that most users of equipment just trusted it absolutely and didn't even think of the tolerances and error budgets in its spec. I stand by my use of the word 'most'. I met a lot of customers and saw how a lot of equipment got used in anger. Some organisations went into things properly and built test equipment uncertainties into the specs of what they were testing, others just trusted it "It's calibrated, innit?" Over time you can form an opinion on the relative numbers taking each approach. Some of my stuff has wound up at JPL, Bell labs, NPL, NIST etc. and specs had to be proven following ISO TAG4 methodologies. Some of my stuff has wound up bouncing around the countryside in post-office vans. The high-falutin organisations may have procedures in place to take measurement uncertainty into account, but equipment as used on the bench in less controlled organisations just gets trusted. And the highly controlled environments are somewhat in the minority. So, I stick by 'Most'

possibly the worst measurement you could ever make is Noise Figure. A typical measurement setup using brand new, best quality test gear is going to have an uncertainty between 0.12 and 0.2dB if it is used correctly.

People are selling low noise RF amplifiers with noise figure specs (the value, not the uncertainty) down around 0.06dB. Those are the numbers indicated when one is connected between a 346 noise source and an 8970 noise figure meter. Sure, it shows the low number repeatably, but you cannot prove that the uncertainty is less than 0.12dB. It could be perfectly accurate, but it can't be proven any better than around twice the mean figure.

Many people don't enter the ENR table for the noise source they're using, they use whatever table was left in the noise fig meter. Many people aren't aware that the uncertainty figures are individual for every frequency point of every noise source and different for every cal lab they trace back to. Many people don't have a thermometer handy. 6C error in guessing the temp turns into 0.1dB further error in noise fig. Ian White and myself did a presentation on errors in noise figure measurement at a conference in Cambridge in 2012. It caused a bit of a stir This was to people who used very low noise systems, and we'd just shaken their foundations.

Other things like network analysers and spectrum analysers have their specs in the form of several factors which get combined differently depending how you use it. Conspiracy theorists may think this is a way of disguising the total uncertainty, well, it certainly works that way though that wasn't the intent.

I designed some new noise sources to go with the new noise figure analyser in 1997-2000. They download their cal factors automatically from an eeprom in the noise source, so no more wrong tables and typing errors. I included a digital thermometer in the noise source which the analyser can read, and the definition of ENR was changed slightly so temperature correction was a little better. So now users are protected better from user errors, but that keeps the uncertainty down to cal lab uncertainties. It's still people measuring 0.0something dB amplifiers with 0.something dB uncertainty test gear, though.

DVMs are a bit easier, and as Jeremy says they deliver what they promise and they prove very reliable and very stable. This is good, isn't it? because most people trust them.

I have a trio of high resolution DVMs. They are long out of cal, but they agree amongst themselves. They have NOT been adjusted to do so, so I trust them to not be very far from where they were when they were used in their respective cal labs.

If I wanted to make a calibrated measurement, I would use a calibrated meter and the afterwards I would send the calibrated meter off for cal. Provably calibrated measurements are only those made in the period between two calibration passes.

This is probably overkill for checking an avometer movement, I suspect.

David
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Old 20th Jun 2018, 7:53 am   #71
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Yes, don't forget this thread is mainly about suggestions about calibrating an AVO 8. Presumably this puts things in the ballpark of +/-1% even before temperature and linearity are considered. The calibrating meter probably needs to be several times more accurate than this and 0.1% is probably overdoing it.

My old Maplin 3.5 digit DMM I bought in the 1980s isn't a professional grade DMM but if it went out of cal by 1% I'd consider binning it. I think the spec for my Fluke 45 is 0.025% plus a couple of LSDs and the Keithley meters are something like an order of magnitude better than this. If any of them ever drift by double their spec I'd be surprised and a bit disappointed. But the Keithley could drift 10 times out of spec and still be way too good for my needs.

If I'd calibrated my Keithley 2015 meter every year I'd probably have spent over a thousand pounds on 'calibration' by now! That would be several times the initial cost of the meter.

That's why I offered the advice not to bother with calibrating the Fluke 287. Unless it develops a fault it is going to be way better than an ageing AVO 8 meter movement.
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Old 20th Jun 2018, 8:18 am   #72
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Good point about solid results only confirmed when chronologically between calibrations.

Laws of chance dictate that coincidences and statistical clusters will happen, so there is also the potential for confusion when two or more faults come into bloom at the same time (but i don't need to tell this to anyone on the aviation industry)

Like Jeremy i have a 3.5 digit DMM from the '80's, but mine has been unacceptably 'low' from day one and i somehow never got round to tweaking until this year. Wasted effort; the chip is such that you can have a good 2vDC range or good 20vDC range- but not both. It's a shame because the mouldings used for the exterior and the switch are very robust.

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Old 20th Jun 2018, 1:36 pm   #73
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Default Re: Meter Suggestions for Basic Alignment/Calibration

For what it's worth I just checked my 1980s Maplin (Precision Gold?) model DMM on a PSU and set the PSU to just trip the meter LSD to 19.00V. The Keithley meter measured 18.997V.

1.900V on the Maplin meter showed 1.8999V on the Keithley. This was one of the early Maplin PG series meters and they were very solidly built with decent resistor networks etc. This meter hasn't been adjusted in many years and I'm not sure I've ever adjusted the DC voltage range. My cheapo yellow TMK meter I bought as a 1 factory reject at a radio rally in the mid 1990s was just as good at 1.900V and measured 18.99V at 19.000V on the Keithley. It has never been adjusted since about 1995 and just needed to have the display connection cleaned to get it working back then.

The Fluke 45 measured 5.000V on the ref195 based test PSU I have here and both the Keithleys were within 10uV of each other here.

The sensible advice (given many times already on this thread) is to pursue the approach using the precision resistor plus a 4.5 DMM that can manage maybe 0.2% accuracy. Check the DMM with a new 0.05% voltage reference if there is still a doubt. But it would be extremely unlikely that a decent Fluke meter would drift this far out anyway.

Note that most DMMs tend to get bugged by uncertainty if you use them towards the lower end of their lowest ranges. Also the current ranges are often not as accurate. I always assumed the x10 resolution extension on the 87 meter came at the (same) cost of uncertainty so the LSD error magnifies by 10. Otherwise how can you claim back 0.4uA of uncertainty just by changing the resolution?

So this could be 0.01uA x 40 = the same 0.4uA of uncertainty on the 600uA range with the standard 0.1uA resolution. If so then it's hard to understand why this approach hasn't already died a death. Can anyone confirm if the 87 meter has something like 20-40LSD uncertainty on the 4.5 digit extended range on the 600uA range?
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Old 20th Jun 2018, 2:39 pm   #74
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Default Re: Meter Suggestions for Basic Alignment/Calibration

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DVMs are a bit easier, and as Jeremy says they deliver what they promise and they prove very reliable and very stable. This is good, isn't it? because most people trust them.

I have a trio of high resolution DVMs. They are long out of cal, but they agree amongst themselves. They have NOT been adjusted to do so, so I trust them to not be very far from where they were when they were used in their respective cal labs.

If I wanted to make a calibrated measurement, I would use a calibrated meter and the afterwards I would send the calibrated meter off for cal. Provably calibrated measurements are only those made in the period between two calibration passes.

This is probably overkill for checking an avometer movement, I suspect.

David
Earlier in the thread I'd mentioned an 80s bench Fluke I have was reading spot on what an good Agilent was reading and it's never been adjusted at all. I've got a few Flukes which are like this.

I've been using an Agilent at work (different Agilent to the previously mentioned) which has more drift than a snow storm, so putting that against something else can cause confusion.

How 'overkill' something is depends on how certain you want to be, or how accessible you want for a nationally traceable standard to be.

If you want to set an Avometer movement to FSD, then how overkill is overkill to know that it's reading correctly at FSD? If I adjust the shunt on a model 7, shouldn't I know it's where it should be? How overkill is knowing that it's right?

It all comes down to what one wants, how serious someone is about a task, if it's a hobby then it comes down to how serious someone wants to take the hobby, whether or not they're in the electrical/electronics field for employment.

Even if someone takes a good meter to a cal lab and just pays for a 'report of readings' or something to that effect, rather than spending on cal each year. That could be an idea, but apart from testing at intervals I'm not sure what the cal lab would see the difference to be.
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Old 20th Jun 2018, 3:24 pm   #75
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Like myself, Sinewave, & many others, you're a keen AVO collector, Ian. You will need a reliable voltage source for testing fsd. Not just AVO's 37.5uA, but any MC meter.
I would recommend a Time Electronics Ltd 2003N Voltage Potentiometer. Plenty of info on the net. Gives out from 0.01uV to 9.9999V pure DC. Try BVWS Swapmeets, put out a Forum request, or try eBay(make sure you get a cast-iron assurance & return arrangement). Mains AC is only used for charging the internal battery.
Any of the other guys recommendations for a good DMM for reading uA is spot-on. Me - I use a NEWLEC(AVO) NLDMM1 which has a switched 200uA DC range. Or a Sch/Solartron 7040 Automatic Ranging DMM which goes down to 10uA Range.

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Old 20th Jun 2018, 7:40 pm   #76
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Default Re: Meter Suggestions for Basic Alignment/Calibration

To try and answer my own question about the uncertainty on the Fluke 87V uA range I went on the official Fluke website and downloaded various docs about this meter. In the User Manual the spec for uA on the lower range is given for the standard setting (not 4 1/2 digits)

This is +/-0.2% and 4LSDs. So this implies +/-0.2% with 0.4uA uncertainty if the LSD is 0.1uA. I don't see how changing the resolution can improve this uncertainty and I read the specs from start to finish and found this on another page:

Quote:
Detailed Specifications
For all detailed specifications:
Accuracy is given as ([% of reading] + [number of least significant digits]) at 18 C to 28 C, with relative humidity up to
90 %, for a period of one year after calibration.

For Model 87 in the 4 -digit mode, multiply the number of least significant digits (counts) by 10.
So does this make sense? You still end up with 0.4uA LSD uncertainty even on the 4 1/2 digit range because 0.01 x 40LSD = 0.4uA? Have I read this correctly?

So it would appear unwise to attempt to use this meter on the uA mode if your target spec was 37.5uA +/- 0.1uA. The accuracy for DC current is already degraded to +/- 0.2% but then there is 0.4uA of LSD uncertainty on top of this.

So even if you had it calibrated you can't escape the uncertainty limitations and it doesn't seem wise to use this meter on this DC uA function setting (for the 37.5uA +/- 0.1uA requirement) even with a freshly calibrated meter straight out of the box from Fluke. It would be much better to use the other method with a precision resistor and a cheapo 0.05% voltage reference to add confidence to the measurement?
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Old 20th Jun 2018, 8:37 pm   #77
Sinewave
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Default Re: Meter Suggestions for Basic Alignment/Calibration

I'd use a 6 1/2 digit ideally or the voltage reference with resistor.

Then get that calibrated
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Old 21st Jun 2018, 12:00 am   #78
Radio Wrangler
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Default Re: Meter Suggestions for Basic Alignment/Calibration

Quote:
Originally Posted by Sinewave View Post
If you want to set an Avometer movement to FSD, then how overkill is overkill to know that it's reading correctly at FSD? If I adjust the shunt on a model 7, shouldn't I know it's where it should be? How overkill is knowing that it's right?
If 'right' means zero error, then it never can be right. There will always be some finite amount of uncertainty.

If 'right' means within the maker's spec, then it can be done, provided the uncertainty on the standard is small enough. Effectively the measureent uncertainty uses up pat of the mker's spec error allowance. If the avo movement spec is say+/-1% and your standard has 0.1% uncertainty, then you want the avo to read within +/-0.9% when the current shows exactly the correct value on the standard.

For hobby use, for fixing radios you don't need much accuracy. But if metrology is your hobby, then that's a wholly different game. I don't suppose anyone deeply into metrology would use an avo.

David
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Old 21st Jun 2018, 10:52 am   #79
David Simpson
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Default Re: Meter Suggestions for Basic Alignment/Calibration

I remember, some time ago, when a similar thread query was raised, that I suggested the possibility of folk who own a NPL Standard Cell or Resistance taking them along to BVWS Swapmeets for folk to have their MM's & DMM's checked out calibration-wise. Also, if there are folk who own,(or can scrounge from work) a laboratory standard 2003N or Cropico Resistance Bridge, or similar Lab Grade equipment, they could take them along. There would be no issues, I suspect, with BVWS Officials, as they are purely battery operated.
50p or a quid a shot could go to the Museum or a chosen charity. Folk could then return to their UK locality, & their MM or DMM(along with its known accuracy, or discrepancy), could be used to check other VR enthusiast's test equipment nearby.
As David says - you don't need lab accuracy for testing vintage radios. They're full of 10% or 20% carbon resistors(old body/tip/spot) for example.
If folk are test equipment buffs, then maybe more accuracy is required. But then, take AVO CT160's & VCM's - their tabulations of voltage tolerances are laughable, for example.

Regards, David

Last edited by David Simpson; 21st Jun 2018 at 10:54 am. Reason: Spelling
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Old 21st Jun 2018, 11:24 am   #80
Sinewave
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Default Re: Meter Suggestions for Basic Alignment/Calibration

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Originally Posted by Radio Wrangler View Post
If 'right' means zero error, then it never can be right. There will always be some finite amount of uncertainty.

If 'right' means within the maker's spec, then it can be done, provided the uncertainty on the standard is small enough. Effectively the measureent uncertainty uses up pat of the mker's spec error allowance. If the avo movement spec is say+/-1% and your standard has 0.1% uncertainty, then you want the avo to read within +/-0.9% when the current shows exactly the correct value on the standard.

For hobby use, for fixing radios you don't need much accuracy. But if metrology is your hobby, then that's a wholly different game. I don't suppose anyone deeply into metrology would use an avo.
I said similar earlier, regarding basic checking.

But, if you're working on test equipment, you'd better be sure of your measurements, otherwise things could degenerate.

Interested in you comment regarding the interest in Avos and metrology. How do you draw that conclusion?
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