Products > Test Equipment
OWON XDM1041 the unknown multimeter...
Kleinstein:
The performance looks really good for a 50000 count meter. There is quite a bit extra resolution for the PC, though not clear about the stability and accuracy. The battery may actually show some drift.
The 1 sample per second mode may have good hum suppression even if the integration time is no matching full multiples of 20 ms. To get a good response on the screen, more than 1 SPS (midium speed mode) may be the more relevant case. This would be more sensitive to hum and thus the better mode for a test to hum sensitivity.
The example with the batteries is likely low hum anyway.
The high resistance case would be an example that can be sensitive to hum, but here things can even get nonlinear, especially relatively close to the end of the range.
To judge how good or bad the 50/60 suppresion is would better use a defined identional 50 Hz part. So maybe look at 1 V RMS 50 Hz int the 5 V DC range and record the data to see if there is some beat frequency / residual AC visible.
A SD ADC can have a different filter from the SINC response one gets for simple integration over a fixed time (e.g. dual slope ADC). It still helps to have the frequency about right. Looking at the hum suppression at different frequencies could give an idea about the fitler used and how much a different clock could change. Loosing the calibration is still a good reason not to change the HW.
BugCatcher:
Voltage drift is most likely dominated by temperature of battery.
Beside TC and PTxx a third method for temperature measurement ;-)
Additional information regarding high impedance measurement:
before adding the 20MOhm resistor
- switched mode to ACV
- could measure 450mV AC-voltage
-> that's an indication for 50Hz attenuation ... at least sufficient for normal use cases!
The Owon app has pros and cons
pro
- extended resolution
- unlimited recording length
con
- sampling rate heavily impacted by jitter (see the two diagrams)
the XDM internal recording
pro
- more precise sampling rate
- faster sampling
con
- limited number of samples
- only "original resolution"
Johnny B Good:
--- Quote from: theHWcave on June 13, 2021, 09:32:23 am ---Yeah, same here. After I saw Misk's post, I send an email to OWON asking about it.... but no response (so far). I'll post if I hear anything
I did an interesting test yesterday using a Peltier element cooling an old heat sink = chunk of aluminium. I had a PT100, the unknown K-type I normally use for the XDM1041 and a known (RS-components) K-type which I use for my BM869S all attached to the same area on that heat sink. Long story short, it seems as if the XDM1041 was much closer tracking the PT100 when it used the RS-components K-type. That one, RS stock# 409-4920 costs nearly £8 (incl. VAT) and is still only rated as +- 1.5 degC, so I'd imagine the unknown one to be much worse. Side note. To use the RS K-type (or other more professional sensors) you need a K-type adapter. I use the Brymen BKB32 for around £5 from Telonic
--- End quote ---
I've been trying, without any success, to obtain K-type to 4mm 19mm spaced banana plug adaptors that do actually use chromel and alumel pins as per a set of four cheap mini K-Type plugs I'd bought to upgrade my collection of K type TCs and was wondering if that BKB32 adaptor would be worth buying.
I tried to track down information regarding the proper use of chromel/alumel pins in the BKB32 without any success. The only ones I've seen that boast the use of chromel/alumel pins are the rather ubiquitous cheap Chinese ones of which I'd purchased two on the strength of this claim (shown in the attached image below). Unfortunately, they both failed the magnet test rendering this boast a work of fiction. >:( :( :palm:
I suspect that, since there is no significant temperature differential with battery powered hand held meters, the BKB32 adaptor will very likely not be using chromel/alumel pins so I was wondering if you'd care to verify whether this is the case or not with a magnet test? ;D
Incidentally, I've just discovered that the HI socket runs 0.5K cooler than the LO socket which seems to be about 1.5K above ambient (the SDM3065X sockets both run within 0.1K of each other, about another 1.5K higher again).
Neither of these meters can really do any justice to K type thermocouples, the Owon because of its reliance on the meter behaving like a mW powered hand held with hopefully, some sort of calibration offset applied to approximate the difference between its internal temperature and ambient, and the expensive 6 1/2 digit Siglent for its reliance on seemingly very rare chromel/alumen K to banana plug adaptors to ensure that the isothermal reference extends all the way into the socket where it measures the reference temperature at the back of the LO banana jack inside of the meter's significantly warmer interior.
The Owon, once warmed up, performs almost as well as the Siglent in regard of K type thermocouple sensors. The Siglent has the potential for better accuracy if only a chromel/alumel adapter could be found to maximise the benefit of chromel/alumel mini K-type plug ended thermocouples. :palm:
If you need a very fast response thermometer with better accuracy, those cheap Chinese TM-902C K type thermometers seem a cost effective way to go regardless of whether you use chrome/alumel mini-K plug ended thermocouples or not.
The later versions which use a pair of AAA cells, only draw 0,35mA from the battery, a mere 1.5mW, barely enough to raise the temperature by more than a few tens of mK which significantly simplifies the issue of reference end compensation and any need to use chromel/alumel in the mini K type socket or the thermocouple plug. The biggest source of uncertainty will most likely come from the warmth of your hands but you can always get round that issue by wearing winter weather gloves or an oven mitt, :)
Kleinstein:
The material in the adapter plugs does not have to be actually Alumel / Chromel like a type K thermoelement. The temperature difference over that adapter part is quite small (e.g. < 1 K) and the temperature range is small. So a different alloy with similar thermal EMF is OK. This also applied to thermo couple extension cables. With type K this may still be lower grade Alumel / Chromel, but for something like the plugs other materials that are easier to machine can be a justified alternative.
If the adapter / plug part is small and thermally isolated the temperature difference over the plug is very small (e.g. < 0.1 K) and the material does not really matter. Littel heat flow also helps with the meter internal temperature gradients. So a good thermal design can be more important than the "correct" material.
If higher accuracy is needed, the option would be to use an external electronic cold junction compensation. That is a small external circuit to correct for the cold juntion and give the TC voltage as if the cold junction temperature would be 0 C. The meter would than measure voltage and the conversion would be done on the PC side or as a math function. I have used such small yellow units from Omega, that were powered by a single Li cell and worked quite well together with HP3478 / 3457. For some reason they seem to be no longer available and alternative one are quite expensive.
If multiple channels are needed, an external DIY cold junction box with a sensor could be an alternative. The temperature may be stable enough to only need a single reading. The scanner cards for DMMs often include a reasonable cold junction sensor, much better than via the normal inputs.
For the SDM1041 the slight problem is that there is no really good low voltage range and the resolution may be limited. There may still be enough resolution via the PC interface.
piit79:
--- Quote from: UniSoft on January 08, 2022, 08:14:10 pm ---I am working on reversing firmware...
--- End quote ---
I'm very glad to hear that! Out of curiosity, any progress? The ONE thing I'd like to see fixed/patched somehow is the LONG delay on startup - it's very annoying. I wish I could just short-press the power button to put the meter on :/
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