Repair worklog : Old rusty HP 3458A

[HighVoltage]

No and no. You guys such savages  .

One local taiwanese volt-nut contacted me few days ago. After some challenging discussion with great help of google translate, it was determined that he has some nice gear, including a RAM-sick 3458A. So hopefully next month we will have a chance to meet and look on his 3458A, and perhaps get my 4920M calibrated. This is my best shot right now for AC calibration. 

How does fixing his 3458A help you to get your 4920M calibrated?

[TiN]

HighVoltage
That is to be determined. It's all I can say right now, sorry. 

[klaus11]

Another question, the Front / Rear button when pressed remains locked, or else you press and exits to stop pushing.
I need to know if so or is defective.

[Dr. Frank]

Another question, the Front / Rear button when pressed remains locked, or else you press and exits to stop pushing.
I need to know if so or is defective.

That is a purely mechanical switch, therefore stays locked in either position.
If it flips out again, the locking spring/mechanism is defect.

[klaus11]

Thank DR. Frank, the conclusion is faulty.

[TiN]

I have a question to 3458A owners. Anyone was using non-10V/non-10K standards for calibration before?
Meter actually allow 1V - 12V for DCV and 1K to 12K for OHM, but also accept -0.9 to 0.9 values and -12 to -1V, which makes me thinking

If I understand correctly, less than 10V/10K would compromise adjustment, as measurement value is more suspected by noise floor limit, reducing SNR and absolute accuracy precision. That's clear more or less.

But how about -10V calibration? Anyone tried?

[Macbeth]

If I understand correctly, less than 10V/10K would compromise adjustment, as measurement value is more suspected by noise floor limit, reducing SNR and absolute accuracy precision. That's clear more or less.

But how about -10V calibration? Anyone tried?

You can always take a backup of your SRAM and then try your experiment surely? 

I have to admit when adjusting the cal of my Keithley 2015 I have merely swapped the +/- leads around when doing the +10V and -10V DC cal. I'm sure I should be shot down as a heretic for this even though I allowed a few minutes for the lead swap to settle any thermals?

[TiN]

You can always take a backup of your SRAM and then try your experiment surely?

Aha, A5 CPU board is on it's way already. 

I'm sure I should be shot down as a heretic for this even though I allowed a few minutes for the lead swap to settle any thermals?

Why? That's what Fluke 5700A does as well, just swaps the signal with relay.

[Macbeth]

Why? That's what Fluke 5700A does as well, just swaps the signal with relay.

Ahh. I figured something more sophisticated like an actual dual rail supply +/- and using something like "lead compensation" too.

With the 3458A I was always under the impression that you only  needed an an accurate +10V DC and a 10K ohm resistor for complete calibration, no need for a negative calibration at all. But from what you are saying any accurate source of a reasonable magnitude can be used as long as you tell the meter what it is measuring? Like with the Keithleys IIRC anything from 9.9V - 10.1V are acceptable. It seems the 3458A has much more leeway if it allows negative volts to be used as a calibration reference!

[PA0PBZ]

Interesting, my Datron 1081 insists on having both + and - on all the DC calibration steps.

[View[+]Finder]

Re: reversing the filter HP3458A, HP3245A
1) Fans prefer having their 'low pressure' side in open air (vacuum is limited, but pressure isn't)
2) Filters work better when they have a little lint on them (the designers knew that)
3) Filter replacement on air entry is difficult if inside the case (someone has to do it)
4) the 'dirt' in the air is mostly human skin cells (get a HEPA filter for your lab)

Just some observations . . .

[TiN]

Since so many questions about 3458A lately popping on forums, I think it's justified to revive this worklog thread.

Another reason is that I just finished initial calibration test, using yesterday calibrated 5700A (to standards which values I know sub-ppm (maybe  ) ).

Calibration points performance report - non-traceable, using my calkit software.

Please keep in mind that verification specification is 24 hour, 95% with K=1.
It is NOT what usual accredited calibration lab data reports have. 

This meter was DIY calibrated in January 2017. It was 24/7/365 since.
I'm happy with stability, no adjustment calibration is necessary. She is stable! 

[Zucca]

95% with K=1

I don't know what to google, what does it means?  (Imbarassed)

[TiN]

Confidence level is optimistic 95% (most of specs are confidence level 99%). K number is guardband ratio. I use own guardband , so this multiplier is not used in test reports.

  Most real calibration certificates are at K=2.

[HighVoltage]

95% with K=1

I don't know what to google, what does it means?  (Imbarassed)

Read the beginners guide to uncertainties...

[TiN]

Since it's time to recalibrate my newer 3458A it is time to take some photos of the process.
This unit had long overdue needed replacement for front binding posts, so it will be received new replacement today (expensive connectors, ouch)



It's pity that to replace front and rear terminal blocks you pretty much have to take apart whole inguard section, as there is no other way to gain access. Photo below also have rare sight of modified 3458A A9 reference for lower temperature and better annual drift.



And today living room looks like a little mess  .



Ignore the drill on background, it's there just for intimidation.

[martinr33]

 I don't see the replacement keypad buttons in the new color...

(Keysight has them, but you have  to call as they are not on  the parts list - they only list the old color).

[TiN]

I realized this yesterday, but it's no big deal Only trained volt-nut eye can pick a difference 

[VK5RC]

Thank for the close up of the A9 reference - Just noted the 111 resistor -I will need to look at other 03458-66509 - I have always assumed they all had 120 

[Dr. Frank]

Sure, the 3458A reference has always 111 Ohm, as its temperature is 95°C, therefore the Ube is about 70mV lower than intended , so to maintain the nominal zener current, the resistor has to be lower than the nominal 120 Ohm, also.
By pimping the standard ref to 65°C (100k || 15k), this increases the zener current and decreases noise.
Maybe that's the reason, why my instrument seems to perform better than others in in the Noise Performance Testing, we've done a few years back.

Greetings from Madeira
Frank

[TiN]

I got my rubber-bumper for 3458A. Looks kinda strange, what you guys think?

[Zucca]

Father:

There is a room in Taiwan full of expensive big and small toys. Hell expensive toys, with a lot of numbers and colored small lights creating an unique atmosphere.
In this room a russian man is always improving and fixing those toys.
Sometime he writes his incredible stories about chasing that failure or that strange ppm jump.
Few people in this world can understand him and his complicated games, but a lot of people just admire him for his passion and talent.
One day he even protected one of his favorite 8,5 DMM with a long and soft rubber-bumper.

The almost sleeping son looks at his dad with big eyes.

Father:

Yeah, it's too strange to be true. You are right.
Good night son, I tell you the rest of the story tomorrow.

I smoked too much, don't ask me what

[hwj-d]

Father:

There is a room in Taiwan full of expensive big and small toys. Hell expensive toys, with a lot of numbers and colored small lights creating an unique atmosphere.
In this room a russian man is always improving and fixing those toys.
Sometime he writes his incredible stories about chasing that failure or that strange ppm jump.
Few people in this world can understand him and his complicated games, but a lot of people just admire him for his passion and talent.
One day he even protected one of his favorite 8,5 DMM with a long and soft rubber-bumper.

The almost sleeping son looks at his dad with big eyes.

Father:

Yeah, it's too strange to be true. You are right.
Good night son, I tell you the rest of the story tomorrow.

I smoked too much, don't ask me what

 

[Dr. Frank]

I got my rubber-bumper for 3458A. Looks kinda strange, what you guys think?

Looks like a stretched 34401A..

On mine I've got the handles, but your bumper handles with care .. 

Frank

[TheSteve]

I don't think TiN really like that boot. I think he just put it on there to tease me. I have boots on nearly all my gear - even a Keithley 2400 has one. My 3458A's have rack handles though. With the boot on the 3458A it doesn't look like a serious piece of gear anymore.