Products > Test Equipment
7.5 digit bench DMMs comparison
HighVoltage:
--- Quote from: Mickle T. on September 24, 2016, 10:59:47 am ---It's a Keithley Propaganda.
--- End quote ---
I agree, most definitely propaganda by a guy that was on the 7510 design team.
But he posted a few interesting things on reddit
--- Quote ---Well, there's the fact that our primary precision, low noise, sensing FET was pulled by the manufacturer halfway through our design process. They said it's obsolete and they're not making it anymore. Cue a crazy many-month scramble to find and design in a replacement.
Or how we learned how amazingly sensitive grounds can be, when a stray few microamps flowed through a few milliohms of trace resistance, but only under certain rare conditions. That little bit extra threw off our measurements by a few digits until we found it and fixed it.
And of course, there was the time when an early firmware bug caused some bad interaction between the program pointer and the speaker output, causing looped program data to be streamed over the speaker. Loudly. Our problem report referenced units "screaming in pain".
--- End quote ---
--- Quote ---I think I can answer a few questions without giving away any trade secrets or anything:
Noise? Well, very careful grounding, for one. Also, our low-noise amplifiers are all made from discrete components rather than off-the-shelf op-amps, some of which components go through additional selection processes, matching, auto-calibration-biasing, etc. Also, said selection process is annoying as piss to handle form an engineer's perspective.
Front end? To keep it accurate while still providing all the functions and ranges, the unit tests and corrects various parts of the frontend in between measurements. That's the toggle-able "AutoZero" option on the unit.
The ADC? We actually have two different ones in this unit. If you are on a "slow" function (slower than, say, 10k sample/s), you use our custom, Keithley-built 32-bit A/D. Anything faster than that uses an Analog Devices AD7982 18-bit SAR with (again) a highly customized frontend.
--- End quote ---
Dragony:
I wonder if Keithley has addressed the complains about the fan in the meantime? How do those companies work? Is it a "fire and forget" type of development and they will just never address it, or is there a chance they will reduce the noise of the fan in future revisions? Maybe they already have done so? Thats still an annoying thing on the DMM.
And why is everyone concerned about high voltage? I have high voltage on my clothing all the time and I am fine. :-//
HighVoltage:
Actually the fan noise of the 7510 is not annoying to me at all.
May be its will get louder during high current measurements but right now it is not even noticeable.
The original fan of the Agilent 34410A DMM and some Agilent power supplies are much louder.
Dr. Frank:
The fan on the 465/470A is quite silent.
Keysight also was very agile to correct several FW bugs, (I got two fixed consecutively) so they really listen to the customer
Frank
Kjelt:
You can always replace it with low noise brands such as Noctua and BeQuiet. First thing I do with professional network equipment is replace those airplane fans.
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