Temp meters, thermocouple K check - Page 1
Forum section: electronics / testgear

author: jonpaul
author_rank: Super Contributor
timestamp: November 12, 2021, 08:04:55 am
content: Bonjour a tous: We use thermocouples to check power dissipation in SMPS, and to calibrate SMD solder pots with RoHS solder like SAC100.have old KEITHLEY 871 DIGITAL TC meters and a newer Fluke type 51, with type K Chromel-Alumel TC (yellow Fluke plugs)Anyone have experience with these old Fluke meters?Our Fluke probes are#30 ga Kynar wire and the thin straight SS probe.We have made many type K fine ga TC decades ago with a spot welder.How do you check or compare temp meters and thermocouples for accuracy can calibration of the TC meters?Boiling water (but depends on Baro pressure)Ice?Triple point cells?many thanksJon

author: Kleinstein
author_rank: Super Contributor
timestamp: November 12, 2021, 09:15:07 am
content: For high grade thermometers tripple point cells are used. Lower grades often are calibrated to an oil bath with a precision thermometer.Thermocouples (or more the cold junction compensation) are usually not that accurate and especially for a DIY solution a check to an ice bath is often good enough. To actually check the thermcouple it would also need a higher temperature. One can measure the barometric pressure to compensate. Still boiling water is not that practical.

author: jonpaul
author_rank: Super Contributor
timestamp: November 12, 2021, 10:05:40 am
content: Kleinstein BRAVO for your fine expertise and the fast reply!Is the Type K TC Accuracy normally 3 dec C ?My concern is not the TC accuracy as much as the consistency between different ages and type of meter.Besides the handheld Fluke and Keithley mentioned,For my Keysight 34465A DVM, I wonder about a TC function?I also have an ancient Yokogawa DCV/DCI calibrator (2601?) with the cold junct type K TC adapter.But no idea the procedure to use it!Many thanks againJon

author: Kleinstein
author_rank: Super Contributor
timestamp: November 12, 2021, 12:24:07 pm
content: The thermcouples should have an uncertainty not as a fixed +- x K, but more like +- 0.x%. The absolute error part is usually from the cold junction compensation and not the TC itself. The specs given are sometimes a bit confusing and not always logical.3 K would already be a relatively large error. This may apply to meters like the 34465 that are not really made for TC as they have very poor cold junction compensation and no really suitable plugs (e.g. use the internal temperature and normal 4 mm banana plugs).For testing the cold junction compensation of such meters with just the 4 mm plugs a simple ice bath should be good enough. Normally an Ice bath is good to +-0.5 C, with more care also +-0.2 C.To get a good TC reading from a normal DMM without a special connection it would need some external cold junction compensator (electronic ice point). I remember using nice small battery powered ones from Omega (flat type K connector in and 4 mm out), that worked very well, a litte similar to these:https://www.omega.nl/Temperature/pdf/CJ_MODULE.pdfThe question than remains if the DMM supports an electronic ice point or one would have to do the conversion from mV to K by hand.Changes are it could be worth to figure out how the cold junction TC adapter from the yokogawa works. This may be essentially the same as the external compensators for measuring.

author: jonpaul
author_rank: Super Contributor
timestamp: November 12, 2021, 05:26:41 pm
content: Klienstein 34465A has Thermo Couple J, K, also E, T, N, R types.internal reference junction, but there is an accessory TC socket to 4 mm plug adapter, several models type J and K U1180...4...6..7Ahttps://www.keysight.com/fr/en/product/U1186A/thermocouple-k-type-temperature-probe-adapter.htmlsee page 8https://www.keysight.com/fr/en/assets/7018-01627/data-sheets/5989-7040.pdfI wonder the materials of the connectors and if a jnct comp is built in? Jon

author: Kleinstein
author_rank: Super Contributor
timestamp: November 12, 2021, 05:45:35 pm
content: The HP adapters seem to be just passive plug adapters from the proper TC plugs to the 4 mm plugs. Ideally the material should be similar thermal EMF as the type K thermocouple and relatively thin to keep the heat flow low. It is still a sub optimal solution, as it is not clear if the meter actually measured the temperature of the input connectors. Especially in the 34465 the accuracy may be not as good as with the handheld, as the bench top meters often get a bit warm inside and thus tend to have heat flow via the connectors. I find 1.1 K rather optimistic for the passive solution.

author: mawyatt
author_rank: Super Contributor
timestamp: November 12, 2021, 06:36:19 pm
content: We just used a glass of crushed ice and tap water wrapped in a towel and allowed to set for an hour for 0 C calibration of the KS34465A and DM6500 using a K thermocouple and "K" plug to banana adapter plug. Using internal reference for KS34465A required an offset of -0.9C and DM6500 used a reference temp of 30.5C.We are not looking for extreme accuracy, just some relative temp measurements (rise above ambient type measurements). Later when we get access to an accurate temperature probe we'll do a better calibration.Anyway, this crude method agrees within ~1 degree with a 1% 10K thermistor we have and with ~2C with our room thermometer which is set to 25C (also another room thermometer also reading 25C).Best,

author: mawyatt
author_rank: Super Contributor
timestamp: November 13, 2021, 02:54:36 am
content: Grabbed a couple 10K 1% thermistors we had, these are hermetically sealed types.https://datasheet.lcsc.com/lcsc/1811142211_Nanjing-Shiheng-Elec-MF58-103F3950_C123393.pdfConnected them with just standard clip leads to the KS34465A and DM6500. Also connected the K thermocouple to a SDM3065X. The two thermistors and thermocouple were placed in the center of 3 spools on solder wire for high thermal mass, one for each and tops covered to keep air flow down. There is a lot of air flow from AC in my home lab and the air blows right over my setup, so not a good stable thermal environment.Let this setup run for a couple hours (still running) and the average readings were 26.207 C KS, 26.169 C DMM and 26.307 C SDM (K Thermocouple). The room reading is 78 F (25.556 C) and RH of 44%. I'm surprised they were that close in reading, considering the setup and 3 different DMMs. Note the thermistors were not calibrated just connected up, and the thermocouple used the SDM3065X built-in "K" file whatever those parameters are, have no idea as they are not displayed.Anyway, looks like I can take some confidence in readings around 25C, but 200C is going to require an accurate thermometer for other reference for verification. Think I'll order a few more thermistors and thermocouples to check out when time permits.Best,

author: jonpaul
author_rank: Super Contributor
timestamp: November 13, 2021, 10:12:00 am
content: mawyatt mille mercis! Your readings are much better than I would have expected !1/ Type K TC are Chromel-Alumel other popular type is Iron-Constantan but those can rust.We use type K.Good ref:https://www.thermocoupleinfo.com/thermocouple-types.htm2/ For Calibration check, ice water and boiling water were suggested, rather than a room temp air test as you have done.3/ We have some Keithley an Fluke K TC and KS also selles them, ready made with the yellow type K plug. There is an adapter from KS from TC socket to 4 mm plugs.4/ Will return to the lab soon and make further tests.Bon Journee,Jon

author: Kleinstein
author_rank: Super Contributor
timestamp: November 13, 2021, 10:34:10 am
content: If one has a good thermometer a check at room temperaure can be done as well. With modern meters it is very unlikely that the scale factor for voltage readings is off so much to cause trouble. For testing medical thermometers there are also reference points near 39 C (using the meting point of gallium as a reference point).

author: tautech
author_rank: Super Contributor
timestamp: November 13, 2021, 12:47:54 pm
content: Quote from: mawyatt on November 13, 2021, 02:54:36 amMike, SDM have a Custom Sensor feature where you can trim the sensor values in the UI to have it measure more accurately.A bit about it here and it seems an updated manual is coming with it properly documented.https://www.eevblog.com/forum/testgear/sdm3045x-versus-dm3058e-sensor-input-4-20ma/msg3793610/#msg3793610

author: mawyatt
author_rank: Super Contributor
timestamp: November 13, 2021, 01:55:09 pm
content: Quote from: jonpaul on November 13, 2021, 10:12:00 amAgree much better than expectedQuoteUsed an ice bath, no boiling water since the ice bath was easiest to do quickly.QuoteHave a type K with the yellow "K" adapter (Extech), this mates with a K to 4mm "Banana" adapter (Extech) for use with DMMs. Just ordered a few more type K Thermocouples and 1% 10K ohm Thermistors.Did a measurement using the 10K 1% thermistor with the Keysight U1233A Handheld DMM, 24.9 C, DM6500 24.821 C and room temp 24.44 CBest,