Hi one and all,
Ever since I acquired an SDL1020X-E (now upgraded to 1030X spec) just over a week ago, I've developed a sudden and keen interest in K type thermocouples and how well Siglent have implemented their "Isothermal" cold junction reference in the SDM3065X.
Failing to find any in depth tear down videos or even just write ups, I started a more general DDG search and came upon the service manual here:
https://int.siglent.com/u_file/document/SDM3065X_ServiceManual_SM06036-E02F.pdf Which offered this little nugget hidden away on page 14 of this 36 page pdf (read it and weep).
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[3] Relative to cold junction temperature, accuracy is based on ITS-90. Built-in cold junction temperature
refers to the temperature inside the banana jack and its accuracy is ± 2.5 °C.
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That's a pretty lousy performance and suggests they're using a cold end temperature sensor well removed from the banana jacks of which they speak.
I mean
If a cheap Chinese knock off of the Hakko FG-100 can track well within 0.5*C of three separate "Weather Station"'s indoor thermometers, you'd think Siglent might have taken just a modicum of care to get this right and at least place the NTC resistor sensor in between the relevant banana jack sockets to keep the cold end junction compensation error minimised.
That statement strongly suggests they've placed it well away somewhere on the mainboard or, Gawd forbid! resorted to the one built into the main cpu with a compensatory fudge factor applied ("fudge" being rather apt if such a Half
Arsed method has actually been employed).
The fact it appears to be under-reading only by about 0.6*C as best as I can tell, using the K type TC that came with a BSIDE ACM91 I'd bought primarily for its DC clamp meter's 1mA resolution, would appear to be down to 'dumb luck' in my example.
I think most thermocouple based thermometers manage to sense the cold junction temperature to well with 0.5*C so it's rather a disappointment to see Siglent take such a lackadaisical attitude to the temperature measurement functions. This is made all the more egregious by the fact that the temperature display is irritatingly cursed with some two to four meaninglessly dancing digits to the right of the decimal point.
Right now, I've only got the one K type TC (fortuitously terminated with banana plugs) and a bunch of spare TCs for that FG-100 soldering iron temperature calibration aid. I've got a 5 metre coil of fibreglass and stainless steel insulated TC wire to make my own K type probes along with a couple more K types (another banana plug ended probe like the BSIDE one and the other with the mini TC polarised plug supplied with a cheap TM-902C Meter on order from eBay sellers. Hopefully, I'll be able to run more tests with another two K type TCs by the start of next week (the 5 metre coil of TC wire is on a slow boat from China).
BTW, what had prompted this sudden interest in K type TC probes was the fact that when I was stress testing the SDL1030X at 309W, I was reading heatsink temperatures of 90 to 92 deg C with no hint of the OTP kicking in, despite Siglent specifying the threshold temperature had been set to a mere 85*C, leaving me to ponder just what this OTP trip out temperature is actually set to (poor calibration or a design decision to go some ten degrees higher and not bother the user guide's copy writer with an update?).