Products > Test Equipment

OWON XDM1041 the unknown multimeter...

<< < (17/50) > >>

davebb:
Hi I have had my meter on for some time, it is reading 32.5c with input shorted , real temp in the room is 25c
i am now going to switch the meter of to cool down and then run a test with the easy dmm software recording
but it does look as this part of the meter is duff,
Thanks Dave

Kleinstein:
The part around the connects would warm up somewhat. So 6 degree higher than room temperature may be actually right.
Even with a seprate sensor near the ground therminal there is still the problem if the other terminal is the same temperature. From the design good TC probes would have to have low thermal conductivity to the outside, so that the assuption of a temperature relatively close to the meter internal temperature is not that bad.

davebb:
Hi
I do not think it is correct , it reads correct when cold, and with the probe it reads correct until it jumps after about 10-20 mins , i will log when it has been off for some time,
I will post the log soon,
Thanks Dave

davebb:

--- Quote from: theHWcave on June 06, 2021, 01:39:42 pm ---The OWON XDM1041 temperature weirdness
I did a few measurements this morning and here are the results. Note that all this about firmware version 1.2. The graphs were taken by polling the measured value via SCPI every second into a spreadsheet.
From the cold-start and warmed-up graph you can see that the meter looks at the internal temperature sensor every 600 seconds (10 minutes). During that time (about 3 seconds) the meter does not respond to SCPI polls, i.e. 3 polls time out but at the 4th one you get 4 results (i.e. it buffered the responses internally).  Note that this “pause” on SCPI every 600 seconds only happens if you are in temperature mode. If you are in millivolts for example there is no pause.

Interestingly, the very first temperature measurement after it updated the value it holds as cold-junction temperature is always a bit high. Not sure why. This you can clearly see in the warmed-up graph.

In temperature mode, the meter displays the “measured” value at the bottom of the display (what a brilliant idea! Seriously why don’t other meters copy that).  This allows an easy check if it is “doing the right thing”.
Example: With just cables to my millivolt source plugged in, but no external voltage applied, it reads 28 deg. and -0.02 mV Using the NIST tables / polynomials for K-type, 28 deg. corresponds to 1.122 mV.  This it stores as the cold junction offset (for the next 10 minutes).

If I now apply +1 mV to the input, the meter shows 52.7 deg.C and 0.98 mV.  The meter adds the 0.98 to the stored 1.122mV and gets 2.102 mV. According to the NIST polynomial equation that would be 51.9 deg.C. Ok so its off by 0.8 deg.  Maybe they use lookup tables instead of the reasonably complex maths. 

If I apply -1 mV to the input, the meter shows 2.8 deg. C and -1.03mV. Doing the same calculation, the resulting voltage is 0.092mV and the NIST value 2.3 deg C. Again, 0.5 deg. off  but I think in principle the meter is doing the right thing.

@davebb: If your meter shows the right value at startup but not some time afterwards, it seems it may not do its 600s refresh of the cold-junction temperature.  The best way to find out is to repeat the same test I have done for the cold-start graph and see if you get that staircase (or the spikes in the warmed-up) graph. You could use the OWON software and its recording function but I am not sure how it responds to the “pause” after 10mins. Better to use a small script and simply send every second: “MEAS1?<LF> “ and store the response

--- End quote ---
My be they messed mine up with  firmware version 1.3.0 that mine has ?
Dave

davebb:
Hi i have attached the log of the meter of the internal reading front ports shorted at the meter,
Thanks Dave

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod