Brand new Bm869s calibration

[bdunham7]

Looking at a 1V signal off the Fluke standard.   Details are important....

Fluke standard attached to my old HP, which was used to align the Fluke meter.   As I would expect, four meters yields four different answers.  I also have no idea what that standard is even good for. 

The standard was a transfer standard for obtaining a standard 10V from a Weston cell, of course.  Its from the pre-JJA days when its 2ppm transfer accuracy was as good as could reasonably be expected.  I find mine to still be occasionally useful, but as you are demonstrating with the 1V signal, only the 10V output works with anything other than high-impedance meters.  Mine is at least as accurate as any 6.5 digit meter if you watch the tempco.

[bdunham7]

Im currently developing a digital control system for an analogue poly synth and Im just finding myself needing to get a better idea of what value the components and voltages Im cobbling together actually is.

You're going to use a DAC to control a VCO?  That seems like the hard way...

[J-R]

After buying both an HP34401A and a Fluke 287 with fresh calibration and data printouts and then buying Ian's excellent PDVS2mini, I did venture down the volt-nut path a small amount.  I also sent out my DMMCheck Plus and a few of Doug's references from voltagestandard.com to get everything as up to date as possible and then ran through all my test equipment.

With all of that in mind, it is true that the BM869s is not quite stable enough to leverage the 500,000 count mode for absolute measurements unless you make allowances for temperature drift specifically.  But also the 50,000 count mode can drift a bit as well.

If I calibrate the BM869s at 5V at 73F after letting it sit for 30m or so, and then the next morning turn it on at 65F, it is 6 counts low in 50,000 count mode (about 55 counts low in 500,000 count mode), while the Fluke 287 is bang on to the very last digit under the same conditions (50,000 counts).  This result from the Brymen is in line with what can be seen in the thread I linked to: https://www.eevblog.com/forum/testgear/brymen-bm869-and-bm867-batch-calibration-check/

Given the price difference and other aspects of those two DMMs, this is completely acceptable as long as you are aware of it.

The 5V calibration point is easy to keep tabs on and if you calibrate it under the current operating conditions, the 500,000 count mode is honestly very good and completely usable in that scenario.

I also did calibrate the 50V setpoint but it wasn't very far off in my case (2 counts maybe at the worst).

So my suggestion is get the BM869s and compliment it with a good 5V reference that you can ship out every so often for calibration.

I found DCmV to be nearly perfect, far better than spec.

AC stuff is tricky.  A few seconds with a function generator and you can get pretty much any DMM to read garbage, so I think that is what a scope is for?

As you said, for resistance and capacitance something like the DE-5000 is a good companion.

[mrdave45]

Im currently developing a digital control system for an analogue poly synth and Im just finding myself needing to get a better idea of what value the components and voltages Im cobbling together actually is.

You're going to use a DAC to control a VCO?  That seems like the hard way...

Yes, Itll have 8 voices, so 16 vcos, plus filter cutoff and resonance, plus all the usual goodies like pwm and a stack load of vcas.

How else would you control something like that? You can only use a resistor ladder off a keyboard for mono synths, and maybe a duophonic synth if youre really clever. I never really looked into that. Midi is also digital, so thatll need converting.

Plus, how would you control everything else and make it patchable. The cs80 i think had duplicate rows of pots I think, but thats a very expensive way of storing patches when you can get a handful of dacs and multiplex the heck out of them.

Plus you can get much more creative with digital modulation sources which really dont need to be analogue.

[Fungus]

I just haven't bought decent test equipment before and wanted some advice over getting one of these devices stock or whether i should get them calibrated. But having seen the photos of several of these next to higher end bench measurements, I fairly sure this will meet my needs.

I'd bet money that it will easily beat the paper specification of 0.03%.

[mrdave45]

Thanks again, I've ordered one along with a de 5000.
Just need a logic analyser now. I suspect it'll be a cheapo la2016, but will have a look at a msos  but I think the one I'll really want will be far too much.

[bdunham7]

How else would you control something like that? You can only use a resistor ladder off a keyboard for mono synths, and maybe a duophonic synth if youre really clever. I never really looked into that. Midi is also digital, so thatll need converting.

For an analog hybrid like you're doing, I guess I can't really think of anything.  But you'll have to tune each note like a piano, right?  Or is is worse, where you have to tune the equivalent of 8 pianos?  I'm still trying to make a mental image of how that all maps out...

[mrdave45]

The hybrid nature of the instrument doesn't affect how its tubed. Pretty much all analogue vco polysynths use dacs.
Youll need to setup each oscilator for correct scaling and initial pitch at a given voltage. That will mean the dacs will be pretty close. For a monosynth, that would be enough. However, with multiple osc, you will need some calibration routines. But tuning every note and making note off offset would be an automated once in a blue moon procedure. Generally, check a few specific pitches on each vco would be enough.
If you look at the service manuals, all those patchable synths essentially use one dac which is multiplexed and sampled and held where it scans round 20 to 40 parameters or so.

[mrdave45]

I dont suppose if any one knows whether you can log frequency against voltage with the data logger? It looks like the meter will read freq and output with VFD function but was wondering if i could graph output voltage (ac rms, preferably on a db scale, but i can always export to excel and process that) in freq domain rather than time domain to create a freq response bode plot. Just wondering whether i should have ordered the data logger after all.

Thanks

[IanB]

The meter (like almost all logging DMMs) can sample what is shown on the display at regular time intervals and record these measurements to a log (in the case of the BM869s this log is stored on a computer connected over the interface cable). Since the 869s has a dual display it can log two displayed values in each record. This would allow you to import the data log into Excel or something and then plot voltage against frequency.

[mrdave45]

Amazing. 
That's unbelievably useful and a lot cheaper than an mso with the bode plot function enabled. And as it turns out, perfectly adequate for what I need it for.
Woooooooo.
I'd better order one of those interfaces too.

[HKJ]

You may want to check TestController https://www.eevblog.com/forum/testgear/program-that-can-log-from-many-multimeters/, it is some very flexible software that can log from BM869s and a lot of other devices. The result can then be shown in charts (Log scales are possible) and/or saved as csv files.

[Martin72]

Hi,
I've decided that I need to upgrade the twenty year old maplin dmm I bought as a student. It's starting to get a bit flakey and I'm also fairly sure it's quite inaccurate. This has generally not been too much of a problem. Mostly relative measurement have been good enough. I'm now needing to be able to measure various parameters to a decent accuracy as well as better precision.
I'll probably get my self a decent lcr meter too.

Im pretty much set on a Bm869s. This seems to be a good all round meter and should be leagues better than my current one.

I've been searching round the forum about the 869s and it seems there's quite a few comments about these being far off calibration out the box.

I've also read a few posts about people doing a quick calibration. I would have thought a fairly sophisticated pice of kit is needed to calibrate a meter properly beyond checking against a 5v source or whatever.

Do I need to get a calibrated one, to what level, or should I get one stock and put that money towards an ltz1000 reference.

Im mainly needing voltage and frequency to be super duper out of this thing. I expect to get really good capacitance (tightly matching pf caps) or resistance measurements I want an lcr meter. Probably a de 5000.

I think a high end bench meter is a bit beyond budget and probably overkill for what I need so just a good solid dmm should be just the ticket.

One of the first thing I´ve done after buying the 869 was to calibrate it external, according to ISO standard.
Had cost me 79€ plus shipping and didn´t regret it so far.
A dedicated calibration lab have unlike better references to calibrate like hobbyists got.

[mrdave45]

Thanks for the test software link, that looks like it'll be just the ticket.
As I've already ordered the meter and the spec is an extra 2 decimal places at 0.02%+2d over 1.5%+4d, I'll worry about the calibration a bit later. 2000 count to 50,000 (500,000 at a push) It'll do for the time being (more than do).
I knew my old meter wasn't much cop, but I hadn't realised quite how bad it was. Even though when I bought it it was one of the betters ones they had.

[mrdave45]

Meter arrived today, and so far it's so much better than my old one it's not even funny. It begs one of 2 questions.
1. How can meters be made this good (I know there are plenty better).
2. Being as they can be made to be this good, how can they be made as badly as my old one. Which was still a lot better than many others I've used over the years.

Thanks for everyone's help and input. I feel sure I've got the right tool for me at this time.

I'll post some pictures once I've compared the meters on the output of my dacs.

[larsdenmark]

I bought my BM869s 5 years ago and the DMMChecker 3 years ago and today I get the reading in the image. I'm quite happy!

[J-R]

I bought my BM869s 5 years ago and the DMMChecker 3 years ago and today I get the reading in the image. I'm quite happy!

But have either been checked against something with a current calibration?  My DMMCheck Plus drifted quite a bit within the first year but has been much better since then.

[larsdenmark]

I bought my BM869s 5 years ago and the DMMChecker 3 years ago and today I get the reading in the image. I'm quite happy!

But have either been checked against something with a current calibration?  My DMMCheck Plus drifted quite a bit within the first year but has been much better since then.

No. Neither have been checked since purchase. I guess both could have been drifting since I got them.

[miro123]

...
I've been searching round the forum about the 869s and it seems there's quite a few comments about these being far off calibration out the box.

Seems?  Please post the the links.  I would like to read them for myself.   
 

Hi Joe,
see attached picture of my BM869s - 2 years old , before calibration + adjustment @ 50V range.
In general my BM869s is extremally linear . The voltage reference seems to be the weakest point in terms of TC and mid-long term stability.
He was off directly by the purchase but it get worst to the point that I adjusted it.
I'm rising question why youtube reviewers check 50,000/500,000 meters at 20% of full scale - 1v,10,100v?