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DMMCheck Plus Multimeter Reference(and other References) - Experiences..
Martin72:
There was a difference if I used the TL leads from fluke or the probemaster from home.
It makes also a difference depending on how the probe tips are pressed against the test points, from which side, etc.
It is simply not 100% firm contact.
As for the clips :
For current/voltage it was OK, but for resistors I had more resistance ( albeit in small form) than when I used the probe tips.
I don't think the short term soldering brings any disadvantages, differences in ambient temperature are enough to create "more" deviations.
Speaking of ambient temperature, I had refrained from performing the measurements until now.
By heatrun tests we have in the test field at present approx. 31°C... 8)
KungFuJosh:
--- Quote from: Martin72 on August 04, 2023, 07:33:01 pm ---There was a difference if I used the TL leads from fluke or the probemaster from home.
It makes also a difference depending on how the probe tips are pressed against the test points, from which side, etc.
It is simply not 100% firm contact.
As for the clips :
For current/voltage it was OK, but for resistors I had more resistance ( albeit in small form) than when I used the probe tips.
I don't think the short term soldering brings any disadvantages, differences in ambient temperature are enough to create "more" deviations.
Speaking of ambient temperature, I had refrained from performing the measurements until now.
By heatrun tests we have in the test field at present approx. 31°C... 8)
--- End quote ---
The precise value doesn't matter independently when you're comparing devices. The only thing that matters is you remove inconsistencies in the testing method. If you use the same probes/clips for all meters, you eliminate the inconsistencies of your test setup. In other words, if the clips you're using altered resistance by .001Ω, it doesn't matter, it will have the same altered value for all devices.
If you solder wires on to the reference, you (semi) permanently alter the cal values. Then if you connect with different probes to those leads, you still have an inconsistent test setup.
Martin72:
--- Quote ---Then if you connect with different probes to those leads,
--- End quote ---
Why should I do this..
By soldering I have made a better contact, this could well lead to the calibration no longer being correct, if more or less contact-safe clips were used when calibrating, that is true.
However, I will soon send the checker with these solid leads for recalibration.
Then no one has to worry about it anymore. 8)
Martin72:
--- Quote ---Speaking of ambient temperature, I had refrained from performing the measurements until now.
By heatrun tests we have in the test field at present approx. 31°C..
--- End quote ---
On Saturday we still had 25.5°C, but I was curious....
I had already measured last week with the Keysight, for this I had used the test leads from Fluke and it was loosely 4 kelvin cooler in the test field.
Here are the values I had measured at that time:
DCV: 4.9997V
DCA: 1.00049 mA
ACV: 5.0000V
ACA: 1.0001 mA
Freq.: 100.003 Hz
The pictures show the current measured values with the soldered leads and just at 25.5°C.
Now you can wonder if the deviations are caused by the temperature, by the soldered leads or by the measurement uncertainty...
J-R:
For the DMMCheck Plus voltage and current measurements, the probes or clips you use do not matter, for the reason I proved earlier using Ohm's law. You can put a decade resistance box in series with your DMM and crank up the resistance to see for yourself. A common resistance to encounter when using test leads/probes/etc. is going to be under 1 Ohm, typically around 0.1 Ohms if you're shorting them directly. The contact resistance would have to be very high such as 100 Ohms or more to be an issue.
However, for resistance measurements, YES, the type of probe and lead you use and how you hold it makes a big difference in a 2-wire configuration, but the accepted solution is a 4-wire/Kelvin connection.
Soldering on the reference invalidates the calibration, and there is just no way around that. Will all the values be different or "wrong"?? That is up for speculation and it would really require another calibration with an 8.5 digit DMM to "know" one way or another. But again the fact remains the previous calibration is no longer trustworthy.
The 34450A is not a good enough DMM for analyzing the performance of the DMMCheck Plus. One year 10V range accuracy spec is 0.015% reading + 0.005% range. So 5V could display between 4.9988V and 5.0013V.
However, I've commented before on applying too much value to published specifications, so without the calibration data we shouldn't speculate too far on the actual performance of this 34450A.
But comparing the before and after measurements, and given the performance class that the 34450A is targeted for, it would be unwise to put much trust into the last digit of the display regardless.
I recently received my DMMCheck Plus back from calibration:
34401A: 5.000,00V
34461A: 4.999,98V
K2010: 4.999,995V - 4.999,997V
For verification, I also got identical readings from my PDVS2mini @ 5V.
For 1mA DC, my calibration sheet states 1.0009mA and I observed:
34401A: 1.000,94mA
34461A: 1.000,863mA
K2010: 1.000,779mA
I would put more stock into the value provided by the 34461A since it has a 1mA range while the other two only have 10mA.
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