It’s difficult to tell exactly as this part of your video is so time compressed, and is perhaps the overlayed chamber camera not really in sync, but:
121gw showing 0.899mV at -8.9c, control program (chamber temp) is shoving about 20c:
121gw showing 0.871mV at 20.9c, control program (chamber temp) is shoving about 43c:
121gw showing 0.997mV after 2h in 20.2c “room temperature”
so I get 0.899mV when chamber temp is shoving about 20c and then 0.997mV at 20c “room temperature”, why the big difference?
That temperature drift from -10 to 60C is very concerning, and what the hell is causing it.
...
I just don't get it.
Different parts inside the meter are changing at different rates when I ramp the box, even at this slow rate. With this meter, it causes a fair bit of error. I allow it to sit at the two extremes for a half hour to stabilize. There's not a lot of room in that box and there is a decent sized fan. At -10 we had 1.003mV, 20ish 0.997mV and 60C 0.928mV.
But if you leave it in your car overnight in the dead of winter (much colder here than -10C) and bring it inside to use it, expect there to be a fair bit of error until it settles. Normally we would test something like this with a shock chamber but in my home lab, you have to settle for my cardboard box.
Yes it's VERY compressed. There's about 6 hours of data, maybe more. It takes several hours for that peltier setup to cool down to -10. You get to see the last half hour, the ramp and the hold at high temp. About 2 hours, compresses into a few seconds.
I have a sinking feeling that you feel that if you took a 1lb metal block, placed it in your freezer, left it overnight, take it out the next day and held it in your hand that it would be warm because it was no longer in the freezer. You don't seem to understand that there is a lag and it will take time for it to settle. We need to consider the thermal mass of the meter. The meter's case will provide some insulation.
If you watched Part 5, where I was talking about the filters and showing some resistors that I had measured, I compared the 121 with some other meters. Two meters in particular you should note were the UT181A and the highly modified UT61E. These two meters were not allowed any warmup time before I began to log the data. Compare them with meters that were allowed minutes to warm up prior to starting the test. That UT61E would have normally wandered all over the place....
If I wanted to say look at the drift with temperature, where we would compare the internal sensor, I would step the chamber every 2 degs or so, and allow it to settle at each temperature for a half hour or so. Maybe place a TC inside the meter near it's ambient sensor that we could monitor as well. Then we could plot all of this data. We would need to make sure we can record the 121GW's ambient sensor first.
Someone had posted about how fast I ramp the temperature. To them, -10 to 60 in an hour is a fast ramp. It's interesting to hear different perspectives. We would ramp -40 to 85 or -40 to 125C in seconds. Basically the mass of the DUT and the chamber where the limiting factor. Look up a thermal shock chamber where we have two chambers running at two temperatures and a dumbwaiter running between them.