Author Topic: newbie problems with KX-board ( LTZ 1000A )  (Read 4849 times)

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Offline voltampereTopic starter

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Re: newbie problems with KX-board ( LTZ 1000A )
« Reply #25 on: February 19, 2018, 09:17:26 pm »
Of course there is a possibilty that the meter is noisy and drifting!

But how can they keep it within 5ppm/year when it is drifting 2ppm in 84 hrs already?!

I really hope to prove this wrong some day  :-\

Joerg
 

Offline voltampereTopic starter

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Re: newbie problems with KX-board ( LTZ 1000A )
« Reply #26 on: February 20, 2018, 06:54:26 am »
And they do even claim a 24hr stability of 0,5 ppm.

So i will stop blaming the meter for now and continue to improve my KX build.

Shielding, guarding, cabling, insulation, ....

Regards

Joerg



 

Offline Andreas

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Re: newbie problems with KX-board ( LTZ 1000A )
« Reply #27 on: February 20, 2018, 07:35:24 am »
Hello,

there is only one way out of the dilemma:
- more references or
- more DMMs
or both  >:D

by the way: a LM399 reference needs no precision resistors to deliver stable 7V output.

with best regards

Andreas
 

Offline voltampereTopic starter

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Re: newbie problems with KX-board ( LTZ 1000A )
« Reply #28 on: February 20, 2018, 08:49:00 am »
Hello,

there is only one way out of the dilemma:
- more references or
- more DMMs
or both  >:D

by the way: a LM399 reference needs no precision resistors to deliver stable 7V output.

with best regards

Andreas



... and more time!!!  :palm:

 

Offline Magnificent Bastard

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Re: newbie problems with KX-board ( LTZ 1000A )
« Reply #29 on: February 20, 2018, 01:36:25 pm »
By the way...
How can you achieve the noise spec of a HP3458A in the 10 Volt Range ( 0,01 ppm RMS ) if your LTZ inside the HP3458A has a noise of 1.0 - 1.6 uV?
Or am i doing wrong calculations here?

The 1.0~1.2 uV spec is in Vpp not Vrms.  Vrms will be (roughly) 1/6 of the Vpp value.  So, an LTZ1K is good for around 0.2uVrms, which at the 10V scale on the 3458A is 0.02 ppm; that's +/-2 digits in the right-most position of the display.  The 0.02 ppm DNL spec comes from this noise limitation.  I think you will find that thermal EMF's from the leads you are using will often exceed that number. For low thermal EMFs, I have found that the leads with the best performance are a simple single twisted pair of "freshly stripped" bare copper; either #26 Bell Telephone wire, or #24 CAT/5 or #23 CAT/6 Ethernet cable; and I have had the best luck with the Bell Telephone wire (which is cheap, fortunately).
 


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