Products > Test Equipment
Brand new Bm869s calibration
bdunham7:
--- Quote from: joeqsmith on February 19, 2021, 06:37:44 pm ---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.
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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:
--- Quote from: mrdave45 on February 19, 2021, 07:13:24 pm ---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.
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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:
--- Quote from: bdunham7 on February 19, 2021, 07:19:56 pm ---
--- Quote from: mrdave45 on February 19, 2021, 07:13:24 pm ---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.
--- End quote ---
You're going to use a DAC to control a VCO? That seems like the hard way...
--- End quote ---
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:
--- Quote from: mrdave45 on February 19, 2021, 07:13:24 pm ---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.
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I'd bet money that it will easily beat the paper specification of 0.03%.
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