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

--- Quote from: Dr. Frank on March 12, 2015, 11:14:13 am ---
--- 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

--- End quote ---

Its probably more about protecting sales of 3458As or its replacement - the 33470A already has 8 1/2 digits resolution so there must be a limited market for a significantly more expensive 'true 8 1/2 digit' meter with an inferior reference. Ok, there are other reasons for buying a 3458A but an almost as good 34470A (for DC measurements at least) would make that decision harder to justify for many.

Splin
kwass:

--- Quote from: Dr. Frank on March 12, 2015, 11:14:13 am ---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.

--- End quote ---

If this is the case, why is the fan needed for normal lab environments.  It seems to me the this 61a/65a/70a should work just fine without the fan.  Has anyone here just pulled the plug on the fan in their unit and run it that way?



6thimage:
I was wrong about the model number being derived from the serial number, in the manual, under SCPI errors, there is this:

--- Quote ---+821,"Controller and measurement board model numbers do not match"
+822,"Controller and measurement board serial numbers do not match"

--- End quote ---

So both the model and serial number are stored separately in two places. The controller here is referring to the front panel - so swapping displays will cause the multimeter to error.

Interestingly, there is also this error:

--- Quote ---+820,"Model and serial numbers not restored"

--- End quote ---

So I think it is safe to assume that the model numbers are stored in at least three places across the two boards (likely twice on each board).

The main processor (the spear320) has a 32 kB boot-rom and an 8 kB sram. So I think it is unlikely the serial & model number are stored in there. The processor has a flash and ram chip above and below it. The serial/model might be stored in there but I'm guessing that it isn't - it makes more sense for that just to hold the windows ce image, as then a firmware update can't make the multimeter forget its identity.

The front panel has an NXP LPC932 - an 80C51 microcontroller with 8 kB flash, 768 bytes rom and 512 bytes eeprom. If I was designing this, I would have placed the serial and model in that eeprom (their are no other external memories on the front panel), as you could update the microcontroller's firmware without the eeprom data being lost.

With the measurement board, I think it is unlikely they would store the serial & model in the FPGA as it hinders firmware updates. There is the TI cortex-m3 on the bottom of the board, but for the same reasons as above, I think it is unlikely they would store them in there. So the question then is, where do they store serial/model and also where do they store the calibration constants? My guess is U904 in this image https://www.flickr.com/photos/eevblog/16171847343/ - it looks like the right size package for an I2C eeprom, and it has pins 2 & 3 tied together (suggesting they might be address pins). Unfortunately I can't find any details on it.
6thimage:

--- Quote from: kwass on March 13, 2015, 03:03:28 pm ---
--- Quote from: Dr. Frank on March 12, 2015, 11:14:13 am ---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.

--- End quote ---

If this is the case, why is the fan needed for normal lab environments.  It seems to me the this 61a/65a/70a should work just fine without the fan.  Has anyone here just pulled the plug on the fan in their unit and run it that way?

--- End quote ---

I asked this question to someone in the know and they said that the fan moves very little air in normal lab conditions, but ramps up when the internal temperature rises (I'm guessing PWM). They also said that the drop in accuracy between the 34461A and the 34460A (the cheapest model without rear connectors and a fan) was largely due to the lack of a fan - with the 60A varying if the side holes are blocked by the handle.
TiN:
U904 looks like ATMEL 34 I2C EEPROM. And U101 on front board looks EEPROMish too. Maybe Dave can use his MiniProg for them  :=\
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