Products > Test Equipment
Keysight's new 34465A (6.5 digit) and 34470A (7.5 digit) bench multimeters
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HighVoltage:

--- Quote from: EEVblog on March 12, 2015, 06:37:11 am ---You'll have to wait for my teardown, rendering now... 35 minutes of waffle about the reference and A/B comparison with the 34461A board.

--- End quote ---
We wanted to order a new one today, but will wait for your teardown.
Thanks so much for all your teardowns and explanations.
It really helps in a buying decision.
EEVblog:

--- Quote from: HighVoltage on March 12, 2015, 09:07:20 am ---We wanted to order a new one today, but will wait for your teardown.

--- End quote ---

Photos are up in the usual place for those who can't wait...
Teardown wise the 34470A is as good as you could expect it to be  :-+
Dr. Frank:
Thanks Dave!

LTZ1000A, 15k / 1k divider, 95°C. For 55°C Tamb., 8ppm/year stability only.
All SMD resistors, maybe also metal foil SMD?
And a lot of PCB slots!!
PCB fully thermally and air shielded, high temperature plastic, again.
 
They just copied the errors from 1988.. could have been done better..

Obviously, they just transferred the old 3458A reference PCB to modern design / components.
Even the alternative positions for R4 and R5 are available.. for pimping to 65°C / 1ppm/yr.


Frank
EEVblog:

--- Quote from: Dr. Frank on March 12, 2015, 09:56:43 am ---They just copied the errors from 1988.. could have been done better..
Obviously, they just transferred the old 3458A reference PCB to modern design / components.
Even the alternative positions for R4 and R5 are available.. for pimping to 65°C / 1ppm/yr.

--- End quote ---

What errors?
I'm not familiar with the 3458A reference, never opened one. But isn't it the ducks guts?
Do you doubt this can meet the claimed specs?
I was impressed with the plastic enclosure design and the separation of the driver transistor (for separate cooling?).
Dr. Frank:

--- Quote from: EEVblog on March 12, 2015, 10:40:33 am ---
--- Quote from: Dr. Frank on March 12, 2015, 09:56:43 am ---They just copied the errors from 1988.. could have been done better..
Obviously, they just transferred the old 3458A reference PCB to modern design / components.
Even the alternative positions for R4 and R5 are available.. for pimping to 65°C / 1ppm/yr.

--- End quote ---

What errors?
I'm not familiar with the 3458A reference, never opened one. But isn't it the ducks guts?
Do you doubt this can meet the claimed specs?
I was impressed with the plastic enclosure design and the separation of the driver transistor (for separate cooling?).

--- End quote ---

Hi Dave,
sure, this reference is something like the Holy Grale. We discussed that in the Ultra LTZ1000 blog intensively.

But anyhow, HP engineers originally designed this circuit to run on 95°C, also due to the required ambient temperature of 55°C.
That causes a higher drift than intended originally by LT: running on 65°C instead gives typically -1.. -2ppm/year, and other designs of 8 1/2 digit DMM, standards and calibrators use 45..55°C oven temperature for around 1..2 ppm/year guaranteed stability.


In this instrument, they could have used the LTZ1000, (non A), easily reducing the oven temperature by 10°C and increasing the stability by a factor of about 2, and maybe further down to 75°C by better thermal management, giving 3..4ppm/year for sure.

Obviously, the Keysight engineers did not want to create an improved circuit, which they would have to re-qualify elaborately.
That could also be true for the rest of the circuitry, where they may have copied the Multislope IV circuit and algorithm from the 34410/11.
Frank
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