Reference probe for temperature sensors - Page 1
Forum section: electronics / general

author: Personwithhats
author_rank: Contributor
timestamp: March 04, 2024, 07:13:29 pm
content: Hello there,I'm in the process of developing several temperature monitoring boards and probes, some with Class A RTD's and some withTMP119/7chips.I'd like to know, at least in ballpark, if my boards/probes perform within listed calibration class and agree with each other.Not looking to do a full span calibration for each probe. Hoping for the listed +-0.15C up to 120C, and usual class A, just hard to guarantee when I have nothing better or even comparable.Best probe I could find readily available was a1PT100KN2515CL1/10ceramic wire-wound class 1/10B RTD.Which, if I'm not wrong, falls down to Class 1/3B at 100C? Or does it drop straight to ClassB? >.>Can't use it for immersion testing which is unfortunate since I have a nice water bath I was hoping to use, but having thermowell CNC'd isn't much of an ask either. (If anyone has advice for dry-temp testing that would be good too! Plan is to just have an aluminum block with holes and a heater cartridge.)SPRT's are far far outside my budget, then you add calibration oof.

author: thephil
author_rank: Regular Contributor
timestamp: March 04, 2024, 08:12:36 pm
content: How many data points and what kind of accuracy do you have in mind? If all you need is a quick sanity check, you may get away with an ice/water bath (0°C) and some boiling distilled water (100°C). You can even compensate for your altitude:https://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.htmlThis approach is used a lot in equipment monitoring in medical and biology labs.

author: Personwithhats
author_rank: Contributor
timestamp: March 04, 2024, 08:16:31 pm
content: Yes that's basically more or less what I was aiming to do, simple sanity check.Just, I'd like to have a 'reference' thermometer/RTD for comparative purposes.And most of the RTD's will not be water immersible (used at 600C, ceramic potted)

author: thephil
author_rank: Regular Contributor
timestamp: March 04, 2024, 08:32:55 pm
content: You could probably put them in a thin plastic bag for protection. That will slow the response/equilibration time, but still work. I have seen people using small plastic tubes for that purpose, too.However, if your water bath has a known temperature, you don't really need a reference probe. If you need additional data points in between, that would be a different story...

author: mzzj
author_rank: Super Contributor
timestamp: March 06, 2024, 10:06:26 pm
content: Your best bet is sensor+display unit sold and calibrated as a combohttps://www.test-meter.co.uk/eti-pt100-precision-plus-thermometerhttps://www.gardco.com/Products/Temperature-Measurement/Thermometers/Pt100-Thermometers/c/p-99592Alternatively you could try to find calibration house to do basic 3-point calibration for ordinary A-class Pt100 but the ready made units linked above are likely cheaper.

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: March 06, 2024, 10:45:46 pm
content: Quote from: Personwithhats on March 04, 2024, 07:13:29 pmSince you've mentioned SPRTs, I take it your reference probe doesn't itself have to be an RTD.So that leaves open the option of using an interchangeable thermistor probe, guaranteed to, say, +/- 0.1 C.Here's one vendor (just an example, not a recommendation):https://www.ovenind.com/departments/temperature-sensors/one-tenth-degree/

author: enut11
author_rank: Super Contributor
timestamp: March 07, 2024, 06:35:28 am
content: For around $95AUD you can buy a 0.2C accuracy Hanna thermometerhttps://www.instrumentchoice.com.au/checktemp-1c-pocket-thermometer-hi98509?campaign=20704478587&content=678126796263&keyword=&gad_source=1

author: beanflying
author_rank: Super Contributor
timestamp: March 07, 2024, 07:44:26 am
content: There is secondary PRT's like the Fluke 5616 I got from High Voltage a few years ago. A little like yourself I want an order of magnitude better than the bits I was playing with, building and measuring.https://www.eevblog.com/forum/buysellwanted/wanted-quality-rtd-or-up-to-and-including-a-working-sprt/msg2384448/#msg2384448I am still in denial of the what I paid even for this oneA very quick search of evilbay didn't get a sensible hit but it might be worth putting a WTB post up.GL

author: TUMEMBER
author_rank: Regular Contributor
timestamp: March 07, 2024, 11:30:12 am
content: Quote from: Personwithhats on March 04, 2024, 08:16:31 pmIf you want to be sure for temperatures around 600 degrees Celsius, why do you assume that checking around 0 and 100 degrees is an indicator of accuracy beyond the physical operating point of the tested sensor? R0 is not a determinant of linear error. Extrapolation does not apply here. You don't know whether this error will be positive or negative, the sensor class is only the default manufacturing tolerance field.The 1/10 B DIN resistor class is only valid for a very small temperature range, if you use it above 120 degrees you will permanently change its characteristics (overheat) and it will "flow".

author: nfmax
author_rank: Super Contributor
timestamp: March 07, 2024, 05:50:21 pm
content: It might be cheaper, and certainly easier, to send the RTDs out for calibration at their operating temperature. Otherwise you need a high temperature dry block calibrator as well as a reference thermometer. An ice point check for R0 before and after will tell you if they have shifted - and you don’t need a reference thermometer for an ice point test

author: beanflying
author_rank: Super Contributor
timestamp: March 07, 2024, 06:57:41 pm
content: Kaye Ice Point calibrator because a Triple Point Cell is ott.https://www.eevblog.com/forum/testgear/kaye-140-4-ice-point-reference/msg2412237/#msg2412237Sika 600C Dryblockhttps://www.eevblog.com/forum/testgear/sika-18600e-dryblock-temperature-calibrator-teardown-pictures-testing/msg2249781/#msg2249781Not a perfect pair but they get the job done. I am sort of back working on a variable temperature refrigerated system but that is still a way off getting to the top of the list

author: Personwithhats
author_rank: Contributor
timestamp: March 07, 2024, 09:15:04 pm
content: Quote from: nfmax on March 07, 2024, 05:50:21 pmDo you happen to know who would be able to do such a service without asking too much? xdGood to know that R0 would detect if they've shifted, even if not how/how much. Or would the shift be a fixed, correctable offset?

author: Personwithhats
author_rank: Contributor
timestamp: March 07, 2024, 09:16:06 pm
content: Quote from: TUMEMBER on March 07, 2024, 11:30:12 amReally? Even RTD's would change characteristics above their stated temp range?I was hoping with their linearity and stability, that heating them within their rated 500C etc. range wouldn't affect the measurements or have them 'flow'For clarity, the RTD's are ceramic thin films an rated upwards of 600C, mostly used at temperatures between 300 and 500C.The TMP chip is rated upwards of 150C, and will be used at temperatures between 30 to 120C.Its stated error is better than even a +-0.1C thermistors in the lower ranges, and they claim very low drift though it has only been tested via a 1000 hour burn in test.

author: Personwithhats
author_rank: Contributor
timestamp: March 07, 2024, 09:18:53 pm
content: Quote from: thermistor-guy on March 06, 2024, 10:45:46 pmYes I am considering just using a 55031 +-0.1 glass bead thermistor, would be good up to 70C and stable enough to use.The TMP states significantly more accuracy (assuming I don't screw up the board design etc.) so comparing the two can only catch large amount of error

author: Overspeed
author_rank: Frequent Contributor
timestamp: March 09, 2024, 01:35:28 pm
content: HelloIf you want to have a real calibration you need at least on fixed point as a triple water point which can be done DIY after that a bit more complicated as except Gallium you shall go the lead and Tin point be reach a temperature over the 100 deg C .Other solution to avoid to spend thousands of USD / Euro in calibration equipment is to just purchase an already calibrated probe with an official certificate and run comparison in hot bath or air ovenAfter as limitation is to assess of what level of accuracy you really need and on what range as IF you search also linearity that another level of costs / work , take in consideration than PT100 / Pt1000 request very hight quality pcb / resistor / design / connector / wires to reach real accuracy and be repeatableI use an UK made ASL thermometer which deliver real 0.01 C and I have also a similar unit from GalenkampRegardsOS

author: mycroft
author_rank: Regular Contributor
timestamp: March 09, 2024, 05:24:30 pm
content: Are Sulfur (S) with a melting point of 115.21 °C and Indium (In) at 156.60 °C good candidates for calibration points?

author: Personwithhats
author_rank: Contributor
timestamp: March 10, 2024, 06:31:30 am
content: Out of curiosity, is there a way of telling if the probe is an SPRT/etc. just by how it looks?I know of a few listings that are reasonably low enough to gamble on. Not sure how to deal with the probe(s) short of sending them out to be calibrated.Don't see pricing on calibration (and not sure if a probe can ever be 'uncalibratable'? Or if it's just a normal RTD vs SPRT)

author: TUMEMBER
author_rank: Regular Contributor
timestamp: March 10, 2024, 10:55:13 am
content: Quote from: Personwithhats on March 10, 2024, 06:31:30 amCompare the parameters of what you have and what you want. Specify what type of sensor (sensor resistor) you have as a control and what type of sensors you should check. For now, I don't know what operating temperature range do you expect - 150 or 600 degrees Celsius?It is very important what technology the resistors or wire resistors are made of? Is it thin film? The class, accuracy and permissible operating temperature range of these two types are different. It's matter.Wire W O.3 is max 660 C F O.3 is max 500 C. I came across a case where F O.3 was used in sensors used at 600 C, after reaching the temperature of 550 C they started to "flow" - unstable readings. Additionally, R0 changed with each heating-cooling cycle.Large production batch to be thrown away.Calibration against ISOTECH-SPRT 670.File 90613300TPay attention to the sensor parameters - the note in the table (550 temporarily) means that the manufacturer does not guarantee proper operation in these conditions.You can easily translate the file using Google translate to pdf "copyable" and not "graphic".Most "industrial" sensors have a stability R) of no better than 0.05% per year and this is rather a dream.The "flowing" sensors were not from JUMO, but from another company. In most cases, the measuring resistors come from the Chinese and are only packed in a "housing" from a local distributor.

author: r6502
author_rank: Regular Contributor
timestamp: March 11, 2024, 11:59:57 am
content: Hell all,when you buy PT100 RTD's, at a qualified shop, it is normally possible, to get a calibration certificate, where you specify the points of calibration, and it should also be possible to specify the measurement uncertainty of the calibration.To check the input, where the RTD's are connected to, you could use a PT100 simulator, or if you need only a few points, go and buy some precision resistors e.g. 100Ohm for zero point check and a 2nd resistor to check a 2nd temperature point. I used some Vishay S102 series resistors for this purpose.Guido