Digital thermometer? - Page 1
Forum section: electronics / testgear

author: BillyO
author_rank: Super Contributor
timestamp: March 23, 2025, 05:17:41 pm
content: Does anyone know of a decent digital thermometer that is decently accurate and linear without costing and arm and a leg?I have dozens of DMMs here, some costing many hundreds of dollars and if I lay out the 10 best of them with the thermocouples that they came with I'll get 10 different temperature readings. Some of the most expensive meters being at the opposite ends of a +/- 15% range! Also, the linearity sucks! They all seem to get closer to each other at 0 and 100, but in between it's mayhem. I have no idea which is the one to trust.

author: KungFuJosh
author_rank: Super Contributor
timestamp: March 23, 2025, 05:55:13 pm
content: Have you tried a thermocouple wire thatdidn'tcome with any of the meters?

author: IanB
author_rank: Super Contributor
timestamp: March 23, 2025, 06:26:22 pm
content: Quote from: BillyO on March 23, 2025, 05:17:41 pmhttps://www.thermoworks.com/You can get accuracy within 0.5°F with a NIST traceable calibration certificate. There are all sorts of options for monitoring and connectivity, depending on how much you want to pay. The Thermapen ONE gives good basic accuracy for a hand-held thermometer. I use it as a cross check for thermocouple readings.

author: bdunham7
author_rank: Super Contributor
timestamp: March 23, 2025, 06:42:42 pm
content: Quote from: BillyO on March 23, 2025, 05:17:41 pmName the brands and models here. It could be that some of the meters lack cold junction compensation measurement or some are just crap. For example, the HP 34401A can be modded to read thermocouples, but it does a crap job because of the lack of cold junction measurement. You can enter the value manually, but that's pretty useless. Also, your meters have to be in a stable temperature for a while for the compensation settle.Here's 4 random meters, 5 TCs and a short. I'm missing an adapter, so one meter is using the internal measurement. I can swap the TCs around and all of my errors will be less than 0.5C after 5 minutes. This picture was taken using the TCs that came with the meters except the 189 which was retrieved from a junk bin.

author: tautech
author_rank: Super Contributor
timestamp: March 23, 2025, 07:18:29 pm
content: Quote from: BillyO on March 23, 2025, 05:17:41 pmDo you have one of the SDM3000 benchmeters Bill ?See p47 and later for tweaking thermocouples for better accuracy:https://int.siglent.com/u_file/download/23_10_10/SDM3055_UserManual_EN03B.pdf

author: IanB
author_rank: Super Contributor
timestamp: March 23, 2025, 08:05:13 pm
content: Quote from: bdunham7 on March 23, 2025, 06:42:42 pmI think reading room temperature is not a good test for a thermocouple. For a better test, you need to read a temperature far from room temperature, such as boiling water. Then you may see variations.

author: Mahagam
author_rank: Regular Contributor
timestamp: March 23, 2025, 08:33:57 pm
content: Quote from: tautech on March 23, 2025, 07:18:29 pmSDM3055 SW 1.02.01.28 Relative mode doesn`t work for temperature measurement. Why?

author: tautech
author_rank: Super Contributor
timestamp: March 23, 2025, 08:47:01 pm
content: Quote from: Mahagam on March 23, 2025, 08:33:57 pmPlease report in detail here for Siglent to investigate:https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/

author: bdunham7
author_rank: Super Contributor
timestamp: March 23, 2025, 08:55:18 pm
content: Quote from: IanB on March 23, 2025, 08:05:13 pmWhy, because the TC compensation would make it nearly a null reading? AFAIK the OP was complaining specifically about room temperature readings. In any case, here's 3 TCs and a Class A 4W RTD in a kettle. The two Fluke TCs tracked the RTD perfectly all the way up even though they aren't in the exact same spot in the kettle. The Cheap-Tech meter actually was ahead of them all by a few degrees at one point. The heat from the kettle was probably affecting the cold junction compensation of the smaller Fluke but I didn't think of that until afterwards. Still, they're at +/- 0.4C from the RTD in a randomly moving pot of water.As the kettle is cooling down, the temperatures diverge a bit, but at 70-80C both Flukes and the RTD converge to +/- 0.2C if I stir the pot. The Cheap-Tech is off by a degree or so at 75C, so it might be a bit non-linear. But the decent products all agree to less than the apparent actual variation in the pot of water. IOW your typical errors in temperature measurement are not going to be dominated by TC error here.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 23, 2025, 09:52:41 pm
content: I use these platinum thermistors.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 23, 2025, 10:46:35 pm
content: Depending on the temperature change you want and how portable you want the measurement the temp/humidity measurement ICs are surprisingly good and affordable. I have used the TI HDC1010EVM, an evaluation board that you just plug into USB and use and been happy with the results. There are app notes indicating the chip itself has accuracy in the 0.1 degree range. The evaluation board has the chip on a break off section allowing you to put it remote from the power and USB interface circuits which cause a very significant amount of self heating. With the sensor broken off the results are very good.

author: Fungus
author_rank: Super Contributor
timestamp: March 23, 2025, 11:32:07 pm
content: Bottom line: K-type thermocouples are cheap and cheerful but they're not very accurate.To make them work well you need to calibrate each individual probe to their meter.Some meters (eg. The Fluke 189 in that photo) allow you to manually add an offset to the reading but you'll need a temperature reference to be able to figure out what it should be.

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 06:01:21 pm
content: Sorry for the slow reply, been busy with another snow storm.So, the two meters I'm most concerned with are my Brymen BM786 and my Siglent SDM3055. They are supposed to be my "best" two meters but they are the furthest apart in their readings. All my cheaper meters fall in between. So, I have no idea which is correct or if they are both wrong and nothing to calibrate them against.In these pictures, the two meters have been on for 30 minutes with two supposedly identical probes just dangling beside each other in the air. If I exchange the probes (or use entirely different probes) the results are the same. Maybe a .3 degree difference from what you see here.

author: IanB
author_rank: Super Contributor
timestamp: March 24, 2025, 06:13:27 pm
content: Something's wrong. Thermocouple probes are usually accurate to ±1°C or so. Your picture shows a much bigger discrepancy than that. I would say one or other of your meters is malfunctioning.

author: KungFuJosh
author_rank: Super Contributor
timestamp: March 24, 2025, 06:18:20 pm
content: Is the correct load set in the Siglent? Choosing the wrong probe type will give all kinds of wonky results.

author: Fungus
author_rank: Super Contributor
timestamp: March 24, 2025, 06:24:55 pm
content: Quote from: BillyO on March 24, 2025, 06:01:21 pmIt'snothingto do with the meters. It's100%to do with the probes.(try swapping the probes around...)

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 06:26:11 pm
content: Quote from: KungFuJosh on March 24, 2025, 06:18:20 pmThey are type "K" probes and the meter is set to KITS90.

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 06:27:11 pm
content: Quote from: Fungus on March 24, 2025, 06:24:55 pmI mentioned that. There is about a 0.3 degree difference.

author: Fungus
author_rank: Super Contributor
timestamp: March 24, 2025, 06:40:19 pm
content: Quote from: BillyO on March 24, 2025, 06:27:11 pmDo you have one with the yellow plug that comes apart. Try shortening the wire, see what happens.(it might go the wrong way...)You'll still need a temperature reference though.

author: KungFuJosh
author_rank: Super Contributor
timestamp: March 24, 2025, 06:45:29 pm
content: Quote from: BillyO on March 24, 2025, 06:26:11 pmDid you give it time to settle after switching probes? I put a type K Fluke in my SDM3065X also set to KITS90. It started off 4 degrees F too high, then settled within about .5 degrees to the digital thermometer next to it within a few minutes, with no warmup time on the meter. I think my touching the probe is maybe why it needed time to settle. 🤷

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 06:47:56 pm
content: Quote from: KungFuJosh on March 24, 2025, 06:45:29 pmYes, about 10 minutes. There is a little settling but it slows down pretty quickly.

author: KungFuJosh
author_rank: Super Contributor
timestamp: March 24, 2025, 06:53:39 pm
content: Quote from: BillyO on March 24, 2025, 06:47:56 pmHow is the meter's accuracy otherwise?

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 07:00:53 pm
content: Quote from: KungFuJosh on March 24, 2025, 06:53:39 pmGreat. Both of those meters agree with each other well withing their specifications. The both also agree likewise with my Fluke 8840AF.However, they don't even agree on the cold junction temperature. In that case the Siglent is much (6 degrees) lower than the Brymen. The Brymen, at least, is fairly close to the temperature measured by the probe (room temp) (yes, it a cold room).

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 07:07:08 pm
content: Quote from: Fungus on March 24, 2025, 06:40:19 pmSeveral, but they are crimped connections. I don't have any spare terminals.

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2025, 07:11:27 pm
content: Show us the "cheap" meters as well. Low power meters probably do the best with TCs and bench meters tend to be the worst. The issue is thermal gradients and cold junction compensation accuracy are much harder to control in devices that use more power. As I was playing with TCs and the RTD yesterday to post those photos, I did notice that the Fluke 289 was noticeably worse than the 117 and 189 in random deviations from the RTD, but still well within spec. IDK what to expect from the Siglent bench meters with TCs, my bench meters either don't read them at all or do a terrible job. I've no idea why the 786 would be off, how far is it from the other units?IDK how you can sort this out without getting some very good reference device of some kind, as you mentioned in your OP. I got a Class A 4W RTD385 Pt100 probe from Evolution Sensors for $60USD and with the bench meter I should be accurate to less than 0.2C without any need to characterize it. I would assume your Siglent would be able to do something similar with an RTD, perhaps not 0.2C but certainly better than 0.5C, without too much doubt or variance.https://evosensors.com/collections/rtd-sensors?srsltid=AfmBOopP2mRcsTX_v6JRe1AQXu7ew_gawkoMEcF5cn8Jm1VI8G9Yn9dYCan you use the "ALL" readings mode for the Siglent? This will give you the actual voltage measured and then using the ITS-90 table you can deduce the cold junction compensation value that it is using. Also, make sure you are actally using the internal measurement. See pp 48-49 of your manual.https://www.thermocoupleinfo.com/type-k-thermocouple.htm

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2025, 07:13:42 pm
content: Quote from: BillyO on March 24, 2025, 07:00:53 pmHow are you getting that value on each of them?

author: Fungus
author_rank: Super Contributor
timestamp: March 24, 2025, 07:28:21 pm
content: Quote from: BillyO on March 24, 2025, 07:07:08 pmFor playing around you can probably just wind the wire around the connector a bit to make it shorter.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 24, 2025, 07:31:47 pm
content: One gets the cold junction temperaure with a copper wire as a short. A bit higher than room temperature can be correct for a meter that runs a bit warm and this way heats the terminals / connectors.The extra heat from the bench DMM can effect the cold junction compensation. So bench DMMs can be a bit problematic with thermcouples.A TC with 4 mm plugs is not a great solution to start with as the cold junction temperature is measured at the wrong place.For some uses one can also use NTC thermistors - some of them are reasonable accurate / selected.

author: Fungus
author_rank: Super Contributor
timestamp: March 24, 2025, 08:16:08 pm
content: Yep, as noted in Dave's video; the cold junction temperature is usually measured quite a long way from the actual cold junction.I'd expect bench meters to be more affected by this than handhelds simply because they're warmer inside.

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 08:28:03 pm
content: Here's the Brymen with 4 of the better cheapies. It agrees fairly well with these ones. Is this evidence that I need to work with adjusting the Siglent?Also shown is the shorting block I use for cold junction testing.

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 08:32:24 pm
content: Quote from: Kleinstein on March 24, 2025, 07:31:47 pmI can't see it making that much difference. Unless the meter has a "K" type connector socket you are going to have to go through some sort of adapter with 4mm plugs.BTW, after several hours of being on, the Siglent is now actually measuring the cold junctionhigherthan the Brymen.

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2025, 08:54:28 pm
content: Quote from: Kleinstein on March 24, 2025, 07:31:47 pmThat seems obvious in retrospect, especially since I already know that it works on various Fluke meters as I'm doing with the 189 in the previous photos. It never occurred to me til just now that it should always work that way, partly because I've seen examples where it doesn't seem to. But the only example I have here now is a 34401A and I know why it doesn't work on those. The reason I asked how he had gotten the value was to explore how and where those errors were introduced. I'm thinking the Siglent bench meter has a calibration adjustment that may change that displayed cold junction value. It has a user adjustment as well, but that's separate AFAIK.Every meter using TC actually depends on a calibrated NTC thermistor or similar device anyway, so using one directly seems to make perfect sense. It's just that getting a direct readout in degrees C or F takes bit more work.

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2025, 09:02:40 pm
content: Quote from: BillyO on March 24, 2025, 08:32:24 pmA miniature thermocouple connector right on the meter would be ideal, but that apparently runs afoul of safety ratings. A standalone TC thermometer might be the best solution for TCs. I believe the better adapters are constructed to minimize junction errors, but I've no idea of the details.A bench metershouldhave a higher-than-ambient cold junction. I don't see how it could be 6C lower than ambient unless it had been in a colder environment immediately before testing. Are you measuring this just by shorting the inputs? Can you try what I suggested earlier? Also, you might try putting a probe in a glass of water to guarantee a stable temperature. Then take a reading with the Brymen and your best "cheap meter" and record both the temperature displayed and the voltage in mVDC. Then do the same with the Siglent, using the "ALL" display in the temp mode to display the mVDC and then using the mVDC range to read voltage directly. Then install a short and again read temperature and mVDC on the same range as used with the probe.

author: BillyO
author_rank: Super Contributor
timestamp: March 24, 2025, 10:05:35 pm
content: Quote from: bdunham7 on March 24, 2025, 09:02:40 pmYes.Quote from: bdunham7 on March 24, 2025, 09:02:40 pmYes, but it will take a couple of days. Band practice tonight and out of town tomorrow.

author: bdunham7
author_rank: Super Contributor
timestamp: March 25, 2025, 03:40:19 pm
content: Quote from: BillyO on March 24, 2025, 08:28:03 pmI missed this post, it might have saved me a bit of typing!By all means do the additional tests so we can figure out how it all adds up. However, I'll take a preliminary guess that the discrepancy is due to the difficulty of doing a proper CJ comp in a bench meter. I'm thinking that they made some tweaks in software regarding the CJ comp and those were sorted out for normal room temperatures--say 18-28C--but don't work so well in your environment.

author: G0HZU
author_rank: Super Contributor
timestamp: March 25, 2025, 04:06:09 pm
content: I've always compared my two temperature meters by putting both probe tips in the same cup of water. Maybe there are reasons this method is not ideal but it's a lot better than doing it with the probes left in free air. If one probe has been touched and has moisture on it, the temperature will be lower for quite a while due to evaporation etc. So it's easy to get confusing results in free air.I've used the ice fragments in water method to get close to 0 degC and used boiling water to get close to 100degC.The water can also be any temperature inbetween when comparing. I generally get very good agreement with these methods.One meter is a Digitron 2751K and the other is a DMM that came with its own thermocouple.

author: bdunham7
author_rank: Super Contributor
timestamp: March 25, 2025, 04:18:47 pm
content: Quote from: G0HZU on March 25, 2025, 04:06:09 pmClose to room temperature that works well, but colder or hotter you'll see significant differences unless you stir. In the previous post, as the kettle was cooling I'd see >5C differences that went away when I gave it a good stir.QuoteDistilled, degassed (boil before freezing) water and ice improve on that. As for boiling, you should be able to guess my altitude within 50M.

author: G0HZU
author_rank: Super Contributor
timestamp: March 25, 2025, 04:31:52 pm
content: I usually hold the two tiny thermocouple probe tips so they are face to face in the cup of water and are virtually kissing each other when using the (cold or ambient or warm) cup of water. This gives repeatable results as they are occupying the same droplet sized area of water in the cup.

author: BillyO
author_rank: Super Contributor
timestamp: March 26, 2025, 07:46:42 pm
content: Quote from: bdunham7 on March 24, 2025, 09:02:40 pmThe mug of water was left out over night. Same probe was used with all and was taped in place. I have not turned the Siglent off since I took the first picture.For some reason the Kaiweets is not in as close agreement with the Brymen as before.

author: bdunham7
author_rank: Super Contributor
timestamp: March 26, 2025, 08:18:55 pm
content: Quote from: BillyO on March 26, 2025, 07:46:42 pmYou'll see variations like that which is why even though you might often see closer agreement, you have to figure +/-1C as reasonable tolerance. Things just move around a bit.I assume from what I'm seeing that your room air temperature is about 13.8C, give or take a bit? So what we're seeing is that the Siglent agrees with the Brymen as to the measured voltage and the short is effective enough, but there's a bit discrepancy between the internally measured cold junction temperature and the actual effective cold junction temp--the latter being a bit of a complex topic. In your cold room, the internal measurement is probably correct for where it is but then there is likely a large temperature gradient between that point and the actual terminals. I think this will be more pronounced in a cold environment and your results seem to indicate that the actual effective cold junction temp is about 14C. Try putting some insulating materials--cloth, bubble wrap, some masking tape--to cover and insulate the entire right front quarter of the meter including top and bottom. Seal it up as best you can and wait a few hours. I'll bet that if you put two probes in your cup tied together near the end, one to the Siglent and one to the Brymen, that after a few hours your readings will be much closer.

author: Poroit
author_rank: Frequent Contributor
timestamp: March 27, 2025, 08:00:33 am
content: I assume you are aware of the Brymen's & Siglent's accuracy specs.Temperature (Models 789, 786 only) RANGE -200.0C to 1090C Accuracy 1) 2) 1.0%+1.0CType K Siglent -100 °C ~ 1372 °C 0.5 °C .(Page 7 of the attached).It looks like your Siglent needs a tweek. It looks a reasonably good unit so worth doing it you want it as your Reference Meter.Your Siglent also has a 4 Wire RTD Input. That is much more accurate for low temperature measurements.

author: BillyO
author_rank: Super Contributor
timestamp: March 27, 2025, 01:52:24 pm
content: Quote from: bdunham7 on March 26, 2025, 08:18:55 pmYes, around about that this time of year. I'll try what you suggest sometime, bt for now I'll just reply on the Brymen and/or tweak the Siglent.

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2025, 02:11:35 pm
content: Quote from: Poroit on March 27, 2025, 08:00:33 amPlease refer to note 3 below that spec: Relative to cold junction temperature, accuracy is based on ITS-90. Built-in cold junction temperature refers to thetemperature inside the banana jack and its accuracy is ± 3.5 ℃The Siglent is only going to be the reference meter here if he gets a 4W RTD. The TC accuracy won't ever be consistent over any range of ambient temperatures.

author: bdunham7
author_rank: Super Contributor
timestamp: March 27, 2025, 02:19:52 pm
content: Quote from: BillyO on March 27, 2025, 01:52:24 pmYou can do it if you want to satisfy your curiosity and verify that it will do what I said, but I don't think there's much you can actually do to fix the issue. I would not "tweak" it because that can't fix the issue of varying temp gradients. I thought that perhaps Siglent already had a "tweak", but it looks like they just calibrate it using the Ext Ref setting and avoid the problem entirely. That seems pointless for regular bench use. Either just forget about using the bench meter with a TC or get the 4W platinum RTD I mentioned earlier.

author: BillyO
author_rank: Super Contributor
timestamp: March 27, 2025, 02:57:49 pm
content: Quote from: bdunham7 on March 27, 2025, 02:19:52 pmFor now I'll forget it, but will eventually look into the 4W RTD.

author: hpw
author_rank: Frequent Contributor
timestamp: March 27, 2025, 04:20:30 pm
content: Quote from: bdunham7 on March 27, 2025, 02:19:52 pmI use with my SDM3065 & plot over time using a chip PT1000 resistor at up to 100°c and glue them on the surface...Note on PT100 V PT1000:The main difference between Pt100s and Pt1000s in general is the electrical resistance at 0⁰C, which is the number in the name: a Pt100 is 100Ω at 0⁰C and a Pt1000 is 1000Ω at ⁰C. This makes Pt1000s more accurate for small temperature changes as they would result in larger changes in resistance when compared to Pt100s

author: David Hess
author_rank: Super Contributor
timestamp: March 27, 2025, 08:21:41 pm
content: My experience is that uncalibrated thermocouple measurements have horrible accuracy. The specification given for the meter represents the best case with a perfect thermocouple.I have been calibrating my own home-built thermocouple probes and thermocouple converters in pairs, but this requires a thermocouple converter which allows user calibration, like an old Fluke 80TK. B&K used to have a multimeter with thermocouple socket and offset adjustment built in.I measure absolute atmospheric pressure with my sensor GPS unit so that I can use a boiling water bath as a 100C reference.

author: tautech
author_rank: Super Contributor
timestamp: March 27, 2025, 10:09:42 pm
content: Quote from: David Hess on March 27, 2025, 08:21:41 pmWho'd have guessed Temp measurements are another rabbit hole ?

author: David Hess
author_rank: Super Contributor
timestamp: March 27, 2025, 10:40:07 pm
content: Quote from: tautech on March 27, 2025, 10:09:42 pmI know not what you speak of.I estimate that my calibration was good to within 0.25 degrees Fahrenheit, where I doubt that I was previously within even 5 degrees.I needed the baffle because with the thermocouple tip exposed, the response was so fast that it was measuring the temperature of the steam bubbles in the water.

author: IanB
author_rank: Super Contributor
timestamp: March 27, 2025, 11:48:16 pm
content: Quote from: David Hess on March 27, 2025, 10:40:07 pmWhere did you get those red plastic probe supports? Are they a standard kitchen item for sugar thermometers, possibly?

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 12:31:51 am
content: Quote from: tautech on March 27, 2025, 10:09:42 pmI'll have to add a gallium standard to the USA Cal Club equipment collection...https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nbsspecialpublication481.pdf

author: Poroit
author_rank: Frequent Contributor
timestamp: March 28, 2025, 03:07:06 am
content: Have you double checked the K Type configuration of the SDM3055?Refer Pages 48,49,94

author: BillyO
author_rank: Super Contributor
timestamp: March 28, 2025, 03:13:29 am
content: Quote from: Poroit on March 28, 2025, 03:07:06 amOf course.

author: David Hess
author_rank: Super Contributor
timestamp: March 28, 2025, 03:14:14 am
content: Quote from: IanB on March 27, 2025, 11:48:16 pmThat is exactly what they are.https://www.amazon.com/dp/B089KT2245

author: G0HZU
author_rank: Super Contributor
timestamp: March 28, 2025, 01:53:51 pm
content: At work, I have access to a Pico thermocouple meter. I think it's the TC-08 model as in the link below.https://www.picotech.com/data-logger/tc-08/thermocouple-data-loggerThese are quite useful although you need to connect it up to a PC. It allows up to 8 thermocouoples and it has an internal cold junction that can be logged along with the 8 thermocouples. The price is quite good so if you want to monitor several temperatures and log the results, then this is a good option.It comes bundled with some (fairly clunky) logging software but I would recommend downloading the drivers and then write something in MS Excel to log it remotely. That's what I do at work.QuoteHere at home I use an old Digitron 2751 K meter and this has an analogue output at the back that can be logged with a DVM. This seems to work really well and it is mains powered. I've also got a H/H meter and a couple of Keithley 2000 2015 meters that support T/Cs. However, they use a simulated cold junction so they are of limited use unless great care is used to set up the CJC manually. Even then they drift over time.Another tip I can offer if you have an ESD mat on your bench is to tuck the probe tips under the ESD mat for maybe 10 minutes and this should give a more steady reading compared to having the probes in free air. My workbench is made of solid wood material and the temperature changes very slowly. The disadvantage of putting the probe tips in water is that once they get removed from the water they will give erratic readings until they fully dry out.

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 03:22:31 pm
content: Quote from: G0HZU on March 28, 2025, 01:53:51 pmAnd somehow that takes longer than you'd think--I had to toast all of my exposed bead types with a hot air pencil after doing the boiling water comparison above before they would read anything reasonable.

author: G0HZU
author_rank: Super Contributor
timestamp: March 28, 2025, 03:34:58 pm
content: Quote from: bdunham7 on March 28, 2025, 03:22:31 pmIt's even worse if they have the braided outer material around the thermocouple wires. On one of my probes this can remain wet for ages.One thing worth mentioning about the Pico is that I recall that it takes about 100ms to read each channel. I think there may be a workaround to speed things up but this limits how quickly you can read from several thermocouples that are connected to it. This isn't a problem for 1-3 probes but when all 8 are connected to it you might only be able to get about one reading a second for each channel.The little Digitron unit I use at home has an analogue recorder output at the back and it is possible to read and log this many, many times a second to a resolution set by the external DVM.

author: ColinB
author_rank: Contributor
timestamp: March 28, 2025, 06:36:01 pm
content: The bare junction thermocouples are not designed to be submerged in water, and I wonder if a small current leakage due to the conductivity of the water could introduce error into the voltage measured by the meter? I haven't found much information on the topic, however.Maybe even the amount of error would vary depending on the input impedance of the meter, so the error would vary between meters.

author: G0HZU
author_rank: Super Contributor
timestamp: March 28, 2025, 07:05:17 pm
content: Quote from: ColinB on March 28, 2025, 06:36:01 pmI can't give a definitive answer on this, but I always assumed that you can put them in water for short periods of time. I don't think they are designed to be left in water all the time where the aim would be to measure the water temperature for weeks or months or years. I'd expect some form of degradation over time especially if the water had additives or impurities in it. But I'm really just guessing...

author: Njk
author_rank: Frequent Contributor
timestamp: March 28, 2025, 07:11:44 pm
content: Thermocouples are fine, but for really high temperatures, other methods are better. Looks like an IR meters that can measure up to 1000-18000C are relatively cheap. But I'd like to measure up to 30000C. That instruments costs above $2k. What makes them so expensive? After all, it's the same IR method.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: March 29, 2025, 08:40:48 pm
content: For most temperature aspect where I need a certain tolerance.. I tend to use these rather advanced process meters/calibrators that usually have a decent tolerance.and gives you numerous settings for cold junction compensation.. [internal, external & custom].While on spec, I recall it's 0.05% on most of the thermocouple standards (in) while out its 0.05% on a few and a tad higher on some of the other TC-standards.It's this unit below, which is a multi calibrator/process meter from Hongrun Precision Instrument.. a unit that can both source & measure.It also has a 9pin USB3 socket at the bottom intended for its "external-cjc" that seems to correspond to a cjc-USB3 dongle that comes incl.Programming, logging, and its Bluetooth ability, that the manual mentions.. I'm not sure how that all works in practice, if at all.It got quite a granular +/- voltage range down 1uV on its 110mV range in source & measure and gives fine control on many of the temperature-related standards..