Siglent Bench DMMs SDM3065X, SDM3055 and SDM3045X

[KungFuJosh]

Following up from the other thread talking about SDM3065X stability:

After 1 hour warm up time with both the meter and the reference on.

10.00460 (claimed by reference seller - not certified)
10.0039? on SDM3065X



I will post again after some hours.

ETA: TestController log rate is set at 0.1s.

[TheDefpom]

It is FAIRLY settled after an hour, it is still warming up for about 4 hours, after that although there is still some movement but it is small.

[KungFuJosh]

Okay then. I've passed the 4 hour mark now. So I'll post the info now, then reset the data and let it run for 4 more hours and see if there's a difference.



Note that there were some minor changes in temp and RH.

[bdunham7]

ETA: If we pretend to believe the stated value of 10.0046, then the bottom number to stay within would be 10.000197976. Seems safe. 🤷

10.0046 would be displayed as 10.00460 on a 6.5-digit DMM and is 4.6mV or 460ppm over the nominal 10V.  If your combined tolerance is specified as 48ppm of 10V or 480µV (40ppm  * 10V + 4ppm * 20V) then your lower reading limit would be 10.00460 - .000480 or 10.00412. 

[KungFuJosh]

ETA: If we pretend to believe the stated value of 10.0046, then the bottom number to stay within would be 10.000197976. Seems safe. 🤷

10.0046 would be displayed as 10.00460 on a 6.5-digit DMM and is 4.6mV or 460ppm over the nominal 10V.  If your combined tolerance is specified as 48ppm of 10V or 480µV (40ppm  * 10V + 4ppm * 20V) then your lower reading limit would be 10.00460 - .000480 or 10.00412.

Apparently I'm still confused. If the resulting accuracy for this range is:
0.0040 + 0.0004 = 10 x (0.0040 / 100) + 10 x (0.0004 / 100) = +/-0.00044

So you're saying that the specified .00044 is an offset number instead of a percentage number? Damn it. Okay, I guess that makes more sense than another percentage.

Thank you. Learning is fun? lol

I guess there's no point in worrying about the 10.00460 since it's a bullshit number. Still pretty close anyway.

[Martin72]

You can imagine why I want to have my reference (yes, it's not forgotten) calibrated externally...
And even then it wouldn't be “perfect”.
In the calibration protocol of my SDM3065X, the measurements were done like this:
Fluke voltage reference set to the range, measured the actual current value with a Keysight 8.5 digit meter, then measured with the SDM3065X and its displayed value is compared to that from the Keysight.
That would be the way.
Then the reference value would be almost irrelevant, as you measure with a much more accurate meter.

[KungFuJosh]

Weeeeeeellll, I think this test is pointless. My ref isn't stable enough, nor is the environment. PP was solid at 3ppm for the first two hours. Then after I sat in the room for a bit, it jumped to 3.6ppm. Then when the air conditioner shut off, it jumped again up to 4.2ppm.

None of that is bad of course, but for a tighter tolerance I'd need an enclosed ref and better environment control.

You can see the jump in the chart after the AC shut off.

[mawyatt]

Okay then. I've passed the 4 hour mark now. So I'll post the info now, then reset the data and let it run for 4 more hours and see if there's a difference.



Note that there were some minor changes in temp and RH.

Think you are showing the same long term plot twice, they both look identical!!

Best,

[KungFuJosh]

Think you are showing the same long term plot twice, they both look identical!!

Nuh uh! 😉

The air conditioner came back on, and the voltage went back down (or at least started to before I shut it off).