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Strange readings when measuring current.

DMM7510 7½-Digit Graphical Sampling Multimeter
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Ilya Grudovik
Posts: 25
Joined: October 30th, 2018, 1:54 pm
Country: Belarus

Strange readings when measuring current.

Post by Ilya Grudovik » November 26th, 2018, 1:20 am

Measure the current with open inputs:

10µA range - 1.4 pA
100uA range - 24 pA
1 mA range - 127 pA
range 10 mA - 647 pA

These are excellent numbers around 0.1 ... 0.2ppm

Measure the current with shorted inputs:

10µA range - 33nA (3300ppm !!!)
100 uA range - 330nA (3300ppm !!!)
1mA range - 3.3mkA (3300ppm !!!)
10mA range - 28mkA (2800ppm !!!)

These figures are possible in the presence of thermal EMF = 33 µV at the input (28 µV for the last range)

And this is not a thermo emf jumper. After measuring the DCV, I see nanovolts.

This is something internally.

Moreover, this displacement does not create any problem if we measure the "current source".

But it creates problems when measuring the current that generates a voltage source and series resistance. And a two-year error of 20 ppm we get at a voltage of just 1.65V and less. Unfortunately, I have nothing to test this hypothesis.

Kiriakos
Posts: 25
Joined: September 1st, 2018, 11:27 am
Country: Greece
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Re: Strange readings when measuring current.

Post by Kiriakos » April 10th, 2019, 11:16 am

For calibration comparisons if you do not own a proper manufactured short plug, any comparisons using DIY toys they are not considered as valid.
But you can not be blamed when TEK it self, does not offer pricing and product information for their own 4X short plug, there is no photograph of it anywhere.

https://www.ittsb.eu/forum/index.php?topic=1452.0

Ilya Grudovik
Posts: 25
Joined: October 30th, 2018, 1:54 pm
Country: Belarus

Re: Strange readings when measuring current.

Post by Ilya Grudovik » April 11th, 2019, 6:22 am

Kiriakos wrote:
April 10th, 2019, 11:16 am
For calibration comparisons if you do not own a proper manufactured short plug, any comparisons using DIY toys they are not considered as valid.
This is a great way to protect yourself from questions. Well, my short circuit is bad. Let's close the inputs with the test leads that come with DMM. Hope they are okay?

P.S. I am sure that even if I spend $ 100 and buy the right short, it will not change anything. Nor the measurement results. Neither the Keithley reaction.

Most likely, an electrometer stands at these limits, and this behavior with closed inputs is quite expected. But I have to read this in the documentation. I do not do my research. This behavior is described by reference. https://www.tek.com/support/faqs/volts- ... rt-applied

But whether my assumption is true, I also do not know. Because Keithley does not want to support his customers.

Kiriakos
Posts: 25
Joined: September 1st, 2018, 11:27 am
Country: Greece
Contact:

Re: Strange readings when measuring current.

Post by Kiriakos » April 25th, 2019, 1:59 am

Ilya Grudovik wrote:
April 11th, 2019, 6:22 am
Kiriakos wrote:
April 10th, 2019, 11:16 am
For calibration comparisons if you do not own a proper manufactured short plug, any comparisons using DIY toys they are not considered as valid.
This is a great way to protect yourself from questions.
According my views, they are answers which I own nowadays, and they did not come from Google search, but from personal engagement and testing which this included use of very expensive made in Japan measuring equipment too, and lots of personal time of a knowledgeable technician.
I can share that if I get paid, but not for FREE.

I do not feel so far as Tektronix / Keithley customer, neither expecting reactions from this forum support team.

If you insist staying in denial at getting a short plug this is recognized as trouble free, and a measuring standard, then just pay the bill about shipping back your DMM for quality control verification at Tektronix / Keithley lab in Germany.

If your complain this stands in the eyes of real CAL Lab technicians’ you will get a replacement DMM.
If your own complain does not stand as fact? Then you will pay and shipping back costs, and entire adventure will cost you around 80~90 Euros shipping, plus a flat fee for equipment inspection.

Here it is your next destination …
Franck Cocheteux
Customer Service Representative
[email protected]ktronix.com

Ilya Grudovik
Posts: 25
Joined: October 30th, 2018, 1:54 pm
Country: Belarus

Re: Strange readings when measuring current.

Post by Ilya Grudovik » May 20th, 2019, 6:25 am

Kiriakos wrote:
April 10th, 2019, 11:16 am
For calibration comparisons if you do not own a proper manufactured short plug, any comparisons using DIY toys they are not considered as valid.
But you can not be blamed when TEK it self, does not offer pricing and product information for their own 4X short plug, there is no photograph of it anywhere.
Keithley short plug can not be connected to the connectors for current measurement :(

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