Suggestions for K-type thermocouple thermometer with  fast update rate - Page 1
Forum section: electronics / testgear

author: Signal32
author_rank: Frequent Contributor
timestamp: August 05, 2016, 02:03:52 am
content: Hello,I'm looking to buy a k-type thermocouple thermometer.One spec that is generally not mentioned is the update rate, which I'm very interested in.So, I'm wondering if anyone knows of a k-type thermocouple thermometer with fast update rate (5SPS+).The one that I have now (Barnant 600) has only about 2SPS.Accuracy is not that crucial and price would preferably be $50-$100.Thanks

author: uncle_bob
author_rank: Unknown
timestamp: August 05, 2016, 02:10:48 am
content: HiHow about building one?Bob

author: joeqsmith
author_rank: Super Contributor
timestamp: August 05, 2016, 02:15:13 am
content: Are you wanting to log the data to a PC? Does it need a stand alone display? How many channels?

author: uncle_bob
author_rank: Unknown
timestamp: August 05, 2016, 02:30:03 am
content: HiFor that matter, if accuracy is not an issue, why not just a general purpose ADC card ....into a PC.Bob

author: joeqsmith
author_rank: Super Contributor
timestamp: August 05, 2016, 02:39:57 am
content: Quote from: uncle_bob on August 05, 2016, 02:30:03 amThat's what I was thinking or a small cheap DAS like the LabJack.

author: Signal32
author_rank: Frequent Contributor
timestamp: August 05, 2016, 04:54:06 am
content: Thanks all for your replies.Yes, I would like a separate self-contained unit, with a battery & display.Preferably 2-channel but 1-channel would be OK.If I was going to go the PC-route I would probably just use my 34401A linked to my PC and do the conversion there.As for building one myself, that would be nice, but I don't think I have the time to do it.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 05, 2016, 05:57:59 am
content: So no logging then. My Brymen and UNI-T both have two temperature inputs. The UNI-T is the same update rate as what you already have but they claim the Brymen samples 5X/sec. I am not sure if that's with both probes active.The cost of is about double what you want to spend. Seems like there should be something out there.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: August 05, 2016, 07:03:46 am
content: If you want to build it yourself, an Arduino with an LCD and a MAX31856 should work a treat, and should fit your budget. By buying breakout boards you should be able to build it in an hour or so, since there are libraries for that IC.Conversion time is less than 185ms in one shot and less if kept freerunning, so 5SPS should be very well doable.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 05, 2016, 07:19:49 am
content: Are you really measuring something that can change temperaturethat quickly? Most objects in the real world have so much thermal mass that measuring more often than every second or two doesn't really buy you anything.

author: Signal32
author_rank: Frequent Contributor
timestamp: August 05, 2016, 07:27:41 am
content: Quote from: Richard Crowley on August 05, 2016, 07:19:49 amYes, you are correct about that but the reason I want a fast update rate is not to be able to accurately measure fast changing temperature in objects but to- Easily be able to observe / adjust the contact of the thermocouple using feedback from the fast updating data- Be able to tell fast if the object's temperature is rising / falling and at about what rate, even though the readings are not accurate

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: August 05, 2016, 07:50:54 am
content: Quote from: Signal32 on August 05, 2016, 07:27:41 amI have the Fluke 54 II B, it's very quick but I don't know the readings/s. Fluke just specified in the DS 'Fast" reading. However, the max internal data logging is 1 reading per second. It may log faster via the external interface but I don't have the cable to test that.Also, this meter is not cheap and it only does temperature. Well outside of your preferred price range.

author: Assafl
author_rank: Frequent Contributor
timestamp: August 05, 2016, 08:35:27 am
content: Reading speed of a K-type (or any other thermometer FWIW) depends predominantly on the thermal mass of the tip. Tiny exposed tips are the fastest, sheathed isolated immersion types are the slowest. So if you want fast response - a tiny tip (or exposed tip) is best.A nice option I use quite a bit for reading K-types is the TC4C from mlg properties and Bill Welch. It is predominantly an Arduino Board (or Shield) intended for Coffee Roasters. Athttp://www.mlgp-llc.com/arduino/public/arduino-pcb.htmlIt uses the MCP3424 4 channel Sigma Delta A/D which can be set to the following sample rates (per resolution).Programmable data rate options 3.75 SPS (18 bits)15 SPS (16 bits)60 SPS (14 bits)240 SPS (12 bits)Also has an EEPROM so you can save the calibration params if need be...

author: uncle_bob
author_rank: Unknown
timestamp: August 05, 2016, 01:27:00 pm
content: Quote from: Assafl on August 05, 2016, 08:35:27 amHiSimply put:If you can *see* the thermocouple without magnification, it's not going to settle in < 0.2 seconds.....(Yes, I have tired old eyes, but you get the idea).Bob

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2016, 03:08:26 pm
content: You could use analog cold-junction compensators, such ashttp://www.omega.com/pptst/SMCJ.htmlor cheaper units ahead of a normal analog input device with appropriate update rate.

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: August 05, 2016, 11:38:57 pm
content: Quote from: uncle_bob on August 05, 2016, 01:27:00 pmI guess "fine" is a relative term, A 0.1mm thermocouple would be in that ball park.As I understood the post the OP was more interested in change and not settling time.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 06, 2016, 03:55:26 am
content: Quote from: blacksheeplogic on August 05, 2016, 11:38:57 pmThis article describes a continuous Pasteurizing processor where they use a T-type thermocouple with a settling time of ~4 seconds, and they are quite happy with a practical response time of 0.5 sec (2 samples/sec).http://www.mstarlabs.com/sensors/thermocouple-example.html

author: Signal32
author_rank: Frequent Contributor
timestamp: August 06, 2016, 08:45:17 am
content: Surprising that there are no decent options for this.I've discovered that my Keithley 2001 supports K-Type thermocouple temperature measurements so I'll have to do with that.Though I think the cold junction temperature compensation is not based on real data since it doesn't have a built-in temp sensor.Side question, anyone know what is the material that is used to isolate thermocouple wire :The white stuff with blue stripes.

author: TiN
author_rank: Super Contributor
timestamp: August 06, 2016, 10:24:57 am
content: K2001 TC readings are compensated based on programmed in reference point or from manually measured CJC temperature (there is function in thermocouple config to do this).Also that thermocouple on photo does not seem to be good accuracy one. You can do own thermocouples using wire (plenty on eBay). I had this donebeforeand K2001. Accuracy was well enough <1%.

author: Assafl
author_rank: Frequent Contributor
timestamp: August 06, 2016, 12:50:50 pm
content: Quote from: Signal32 on August 06, 2016, 08:45:17 amIt looks like cloth (or fiberglass) fiber which depending on the fiber would do well for high temp measurement.However, the short length of the cable and especially the shrink tubing (I assume to prevent Fraying) means it isn't really for the kinds of extreme temperatures that a K type should be able to measure (nor even a home oven...).All my K-Type (and other TC) have CJC - The Thermoworks handheld, the Omega HH806, Even the inexpensive TC4C Arduino Shield has CJC. Heck - even the Gossen Metrahit 29S (the older Energy) and the OLED Agilent have an internal reference thermistor for CJC (or can accept a fixed value), though I have never used them with the K-Types....So it seems illogical - Are you sure the Keithley doesn't have CJC (perhaps named Ambient Temp Compensation or other non-standard term)?

author: uncle_bob
author_rank: Unknown
timestamp: August 06, 2016, 04:16:43 pm
content: Quote from: blacksheeplogic on August 05, 2016, 11:38:57 pmHiThere seems to be a lot of confusion over the update rate and response time of the thermocouple its self.... Five samples a second is faster than your eye can follow, but logging does not seem to be a concern.Bob

author: joeqsmith
author_rank: Super Contributor
timestamp: August 06, 2016, 04:39:43 pm
content: Quote from: uncle_bob on August 06, 2016, 04:16:43 pmThey posted their reason but I didn't understand as well.

author: TiN
author_rank: Super Contributor
timestamp: August 06, 2016, 05:46:36 pm
content: Quote from: Assafl on August 06, 2016, 12:50:50 pmHere's quote from UM:QuoteTCSCAN-2001 scan card have CJC sensor and copper bar around terminals, so that will work too. So it's not supposed to have direct thermocouple connections at DMM terminals, but you can do so with reduced accuracy and without real CJC. There is no sensor on DMM's terminals.

author: DP53
author_rank: Newbie
timestamp: November 16, 2016, 07:46:57 pm
content: A lot of information on thermocouples, temperature measurement, etc.:http://senphys.com/seebeck-effect-27.html