EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Lightages on May 10, 2015, 04:37:22 am
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So it looks like I won't be buying a calibrator and would like to buy a very good reference meter to use a possible transfer standard that will get calibrated regularly. I am looking for less than $800 with calibration valid or less than $600 without, I picked the Keithley 2015 and Agilent 34401A as appearing to be what I am looking for. What would you get?
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Not much difference between the two. If you don't need THD, the Keithley 2000 is also a good buy.
Watch out, as old units tend to have dim FVD displays. I bought a mint 3 year old Keithley 2000 for 300$.
You would still need a calibrator for proper DMM calibration, unless you have stable 10A 1000V AC/DC sources, to characterize all ranges.
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What do you want to measure? How many digits do you want/need?
Also it depends on where you live how much you will end up spending. Not only for shipping!
Looks like you might want to look at the long therm stability. Some products are sold as stable enough to be calibrated once every two years instead of one.
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Yes it won't be easy or even not correct to use a bench multimeter, but it is the closest I can get. I need better than 4.5 digits accuracy by 10X for my uses. a 6.5 digit class instrument is needed for longer term drift to stay within that IMHO. I am sure I can build the sources I need for short term stability as I will be only using some very specific values and not a full range fully variable values.
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I don't think there's much between them, since the Keithley 2000/2015 are a bit less sought after, you can find some cracking deals on them.
FWIW, I bought 3x used HP 34401A, all of them >15 Years old and they were more or less still within 1Y spec for 10VDC anyway (about 16-25ppm out). I can't remember what the normal cal count was out of factory, it's about 35, I hope someone else can chime in. So if it's above 35 then you know it's either been taken care of or tinkered with.... :-DD
Make sure they have good pictures so you can kinda sorta tell how the VFD displays are faring, be careful of long exposures in dimly lit areas and for the 34401A, check that it's in 6.5 digit mode because it defaults to showing 5.5. One of my meters has the last digit significantly brighter than the rest, must have only been used in 5.5 digit mode, it does annoy me slightly =P.
By the way, a replacement VFD from Keysight (well the display assembly anyway) for the 34401A runs around ~$150, but you have to have a serial number that's past a certain value. Anything US3603XXXXX is okay IIRC, some of the older #3146AXXXXX needs to be above..uhhh..okay I forgot (I want to say 57000 but I really have forgotten), but do check before you purchase a 3146A serial number, sorry! It's mentioned somewhere in the service manual update notices.
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A Keithley 2000 would be a good choice. Yes the VFD on an older unit can be dim, but a new VFD costs about 60 dollar, and it's quite simple to install. On the bright side, if the VFD is dim it has had a lot of houres. So basicly the reference has aged well. My personal meter had a dim display to, and it's reference is more stable than our work meters. There is a lot of info about these meters on this forum. A Keithley 2700 is an option too. It's basicaly an 2000 with an switching options. They might be even cheaper to get.
A decent Keysight/Agilent meter will do fine too.
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I have lots of 34401A meters in use.
The oldest one with the HP logo is going back to 1994 and it still works perfectly.
The newest one from 12/2014 is with the Keysight Logo and besides the new shaped buttons, really shows no difference.
They are just work horses and usually do not break down and the calibration is stable over many years.
And if they should fail, they can be repaired.
The lowest price I paid was just under Euro 200 and the highest was around Euro 440.
I have no experience with Keithley DMM's
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I have a 34401A which blew one of its filter Tants and took out a few zeners with it but the full circuit is available and quite a bit of help on forums (?fora).
Also a bit of a HP fanboy. Both good gear.
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I bought a Keithley 2015 THD a while back and this was mainly for the THD and SINAD functions and also the (accurate) onboard AF synthesiser.
As an everyday DMM it's a bit lame in terms of human factors so it doesn't live on my bench. I keep it in storage and normally only use it for the above features via GPIB and a netbook PC.
The reason it is lame in terms of human factors is that this is very much an ATE machine designed for use in a rack. The user interface is very annoying to use unless you want to use the default settings for AVO etc.
The display is poor with badly designed fonts but you can read it at an angle so it's better than an old school LCD DMM in this respect. The display on mine is still reasonably bright.
The meter is very deep in size and is very heavy. Much too big and heavy (IMO) if you plan to want to move it about on your workbench on a regular basis.
It is also quite thirsty in terms of power consumption.
Basically, you would need to be very keen (and forgiving?) if you wanted to use this meter as an everyday tool rather than just a calibration checker/reference. I also have a Fluke 45 meter here and it is far nicer to use with a better display. It's lighter, takes a tiny fraction of the power consumption and has a much better UI. Obviously, it can't match the 2015 for technical performance but the human factors for the Fluke 45 meter are far better so I use the Fluke in preference to the 2015.
I'm not suggesting you opt for a Fluke 45 but maybe you need to look at the human factors of the other meters on your list.
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3457A? 3478A?
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Yes I was also looking at a 3457A but it is older, bigger, and heavier to ship. The benefit is that if it is older, it should be more stable too..... They are also cheaper. Hmmmm
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You might also want to consider the differing cost of calibration between these models and how long the calibration intervals are. Some high end (but now old and cheap) meters could prove to be a false economy if they have higher calibration costs. i don't plan to send off my 2015 for calibration at any point in the future so I can't advise on calibration costs for this model.
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If you could get a 8846A for those prices I would jump on it. At 24 ppm it would be more accurate than the meters mentioned so far. Also an extremely nice meter in general. (Yes I am a fanboy)
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Is it important if you have a known transfer accuracy from the manufacturer? I see that the 34401A has a transfer accuracy listed in the meter's specifications for all ranges.
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Yes I was also looking at a 3457A but it is older, bigger, and heavier to ship. The benefit is that if it is older, it should be more stable too..... They are also cheaper. Hmmmm
Two 3457A's would give you better confidence in your meter as a transfer standard.
Having one meter, even though it's "calibrated" technically that doesn't mean anything, you have to build up confidence in that meter that it doesn't drift. How can you really do that when it get cal'd once a year and you have nothing else to compare it too in the mean time?
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Is it important if you have a known transfer accuracy from the manufacturer? I see that the 34401A has a transfer accuracy listed in the meter's specifications for all ranges.
Transfer accuracy is usually only valid for 24 hours, and often a tighter temp range.
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Yeah, like I said, it really isn't the correct way of doing it but it should be close enough for me. I won't be calling anything I do a calibration rather an accuracy check against a calibrated meter.
Two meters? Maybe a good idea but I don't think that is going to happen. I do have a Keithley 197 that is probably OK as a drift reference as it is still within 1 year cal when I received it a couple of months ago. Maybe it was calibrated recently but there were no cal stickers on it.
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Yes I was also looking at a 3457A but it is older, bigger, and heavier to ship. The benefit is that if it is older, it should be more stable too..... They are also cheaper. Hmmmm
Just be aware that you'll have to replace the backup battery when you get it, and also the IEC socket before you power it up because they sometimes blow up releasing super smelly gas that lingers around for a week (especially if it lived its life in a country on 110V mains and you have 220V mains). I swear I can still smell it even though it's been a few months....
You can occasionally find them for $100, not too bad at that price. Though after shipping and stuff, a K2000/HP34401A isn't that much more and is a fair bit more accurate...
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Two meters?
The first one is the most difficult one to get.
Suddenly you have 3 or more and wonder what happened.
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Either the Keithley or the Agilent will meet your needs. I'd get a couple of reasonable 10V references just as a sanity check. I've rarely found a meter a little off, it's either drifted very little, usually much less than its drift spec, or it's changed significantly.
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So it looks like I won't be buying a calibrator and would like to buy a very good reference meter to use a possible transfer standard that will get calibrated regularly. I am looking for less than $800 with calibration valid or less than $600 without, I picked the Keithley 2015 and Agilent 34401A as appearing to be what I am looking for. What would you get?
I was in a similar situation 2 months ago.
At 800 U.S. $, your are close to the price of a brand new, waranted and calibrated 34461A.
I got mine in France at http://www.es-france.com/. (http://www.es-france.com/.) I asked and got a quote together with a contact name, had a call, and after a few minutes of negotiation, got a 15% discount.
So, finally, 877 Euros (984 U.S. $), on stock, free shipment, 3 years warranty, and a bunch of nice features that are not present on older models.
O.K., that's above your $800 target, but close enough to consider this alternative to my humble opinion.
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I have two 3457a and three 3456a as well as many older HP meters. I find the 3456a meters to be very stable. I hate the settling time of the 3457a but they hold calibration. At first I though my 3457a meters had a noise problem but they both do it. Turning on the filter helps, shielded leads are important, of course, when you are working over 5.5 digits.
I also love the big red display of the 3455a but they all break at this late date and even though many use good calibration references, they drift a little and take forever to warm up.
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Though big the 3456A's are quite stable, though going with a more modern meter +1 for the 34401A.
BTW: I had my 3456A running for 4 weeks, almost 24/7 after recapping the psu, still need to order that screw...
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OK, thanks for all the replies and information. I am going to have to hold off for a bit because circumstances have changed for me. FYI, I will probably go for the HP 34401A or the new model.
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Though big the 3456A's are quite stable, though going with a more modern meter +1 for the 34401A.
BTW: I had my 3456A running for 4 weeks, almost 24/7 after recapping the psu, still need to order that screw...
You're talking about the captured cover screw we debated a few months ago, correct? Did you ever find someone that had it in stock? I just went down and looked at it. That is a very unique screw. It is a 4 x .75 pitch with an unthreaded and slotted section near the philips head. The threaded section is about 8mm long with another 3-4mm of unthreaded where the slot that holds the keeper c-clip is grooved. I'll bet that screw is not the least expensive part on that meter.
In order to make one, I would start with an 8mm x .75 philips head screw, take the temper out, turn down the threads to the correct size which is about 3.4mm and rethread following whatever is left of the original threads, if any. That would leave a shoulder where you could cut the groove. The problem would be holding onto the little puppy while turning down the thread. Maybe super glue it to an old philips head screwdriver and take light passes on it. Then you heat it up and that breaks the super glue while making your eyes burn. Drop it into acetone after it cools to remove all the glue.
Next time I am in the hardware store I'll grab an 8 x .75 and see if I can get it to stick to an old philips for machining. If so I will make you one for the price of postage.
Of all the parts on that meter, that is the one you don't want to lose.
Jerry