[volt-nuts] 3458A HFL Question

[Tom Knox]

Thanks Frank, I had always assumed the HFL option was simply a select A9 reference like option 002, but I recently read that HFL instruments have/had improved A1 boards. I worked on an Agilent Branded meter with the HFL Key overlay and a HFL A9 but did not notice if the unit had a different part number on the A1 board. (that was before I was aware of a possible difference). I know the H01 1000 VAC option has a different A103458-91002 , A2 03458-91000, board and A10 03458-91001 switch all with distinct part numbers. That said I have never seen anyone mention a HFL A1 part number, which  would make sense if as you pointed out the units later then mid 90's all had the superior parts. I wonder if the early HFL units had unique A1 part numbers? What is also interesting is all the attention paid to the A9 reference when in my humble opinion the A3 boards has a wider (huge) range of performance with some far exceeding spec. Yes, you can easily A-Cal out the A/d drift but I have several meter in my lab that have virtually no A/D drift. I am surprised that Keysight/Agilent/HP  has never offered select A3 boards paired with select Option 002 A9 boards (offered as perhaps option 003). In addition I have wondered why Keysight have not done some sort of an update when redesigning the processor board to add a better user interface such as a color touch screen with GUI and advanced on screen data logging and math functions. I guess we Volt-Nuts are a smaller market then I would like to think. That said what other product of any type designed in the late 80"s is still State of the Art? Truly amazing!!!!

Cheers;

Thomas Knox
1-303-554-0307
actast at hotmail.com


________________________________
From: volt-nuts <volt-nuts-bounces at febo.com> on behalf of Frank Stellmach <frank.stellmach at freenet.de>
Sent: Friday, July 21, 2017 1:15 AM
To: volt-nuts at febo.com
Subject: [volt-nuts] 3458A HFL Question

Thomas,

that has been discussed recently on eevblog, and another volt-nuts
stated, that the only difference was the implementation of a VHP101, 40k
resistor for R207. This information was supposed to come directly from
keysight, but has been deleted by the user.

The VHP101 has a T.C. < 0.3ppm/K, and is oil filled, so 2ppm/6yr drift
might be assumed, according to the Vishay datasheets.

This resistor was routinely assembled in the standard instruments since
about 1996, so 3458As younger than that should also be more stable,
although HPAK never adapted the specification. These resistors were all
marked by hand, i.e. an individual code on top of the housing, so a
selection may have taken part.

This VHP101 may improve the ACAL OHM T.C. and OHM 1-year-drift over the
original b.m.f. resistor, but the ACAL T.C. is not specified in the HFL
datasheet. The transfer accuracy also does not reflect correctly this
improvement, as the drift over 10min and 0.5°C for 10kOhm and 100kOhm
would only be related to the Ohm mode resistor array, RP300, which
obviously was not changed, and has a T.C. of about 3ppm/K, which would
yield a transfer stability of 1.5ppm for a 0.5°C change.

I think, the HFL specification is a hoax, especially, as nobody ever has
seen a real HFL instrument.

Frank


 > Does anyone know how to identify a 3458A HFL A1 board?
 >The HFL A9 is part number 03458-66529, but I have never seen a part
number for the A1 board with superior resistance measurement.
 >And does the A1 use select parts like the A9 or different parts?
Thanks: Thomas Knox

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