121GW Thermocouple Question - Page 1
Forum section: electronics / testgear

author: JDW
author_rank: Frequent Contributor
timestamp: January 27, 2023, 09:43:31 am
content: I recently purchased a 121GW, and while comparing the included Thermocouple with that of my Fluke 116, I noticed the 121GW's thermocouple has a transparent, slidable piece and I would like to know the purpose. Please see my finger point to it in the attached photo. The Fluke meter's thermocouple doesn't have such a slidable piece, which makes me wonder why it's needed.Thanks.

author: Overspeed
author_rank: Frequent Contributor
timestamp: January 27, 2023, 10:08:34 am
content: Hellothat an open thermocouple so the weld is exposed , the plastic sleeve is used to protect the soldered bead end and also to avoid electrical contact when used on equipment under powerRegardsOS

author: JDW
author_rank: Frequent Contributor
timestamp: January 27, 2023, 01:16:20 pm
content: Thank you for explaining, although I will admit I still don't understand, for two reasons:1. I've been using my K-type sensor for years along with my Fluke 116, and never had any issues without that little transparent tube, and2. When I connect the metal tip to measure the temperature of something, the metal tip is never touching merely another wire, and therefore, that little transparent tube wouldn't be able to fit over the sensor's metal tip and the thing it's touching to measure temperature.So for now, I still don't see the need for it.

author: mendip_discovery
author_rank: Super Contributor
timestamp: January 27, 2023, 02:08:43 pm
content: Let us just say you want to check the temperature in the oven. If the metal part of the probe accidentally touches the element with 240V (110 for the luddites) heading down the wire, now its not likely to cause an issue. Still, if you were to come in contact with either of the two banana connectors at the yellow plug end you would get that voltage running through you, as someone who has been at the end of a few shocks, it is not fun or wise to repeat.So it's a bit of health and safety stuff that is there to protect you, but there is a very low risk of it happening. Some of my low temp probes have some heat shrink on the end to avoid it making contact.

author: thm_w
author_rank: Super Contributor
timestamp: January 27, 2023, 10:58:42 pm
content: Quote from: mendip_discovery on January 27, 2023, 02:08:43 pmThe heatshrink is more to prevent the braided outer fiberglass sleeve from coming loose, which could be the case here as well.

author: J-R
author_rank: Super Contributor
timestamp: January 28, 2023, 03:46:04 am
content: It's not typical heat-shrink tubing on the UEi design (121GW), it feels like silicone.This simply cannot be a safety feature as it easily slides around, which actually makes it less safe if you're trying to hold the probe next to something dangerous. From my research, due to how this style of thermocouple works, you should not use it on anything that is electrically conductive anyway, since it can affect the readings (due to current flow). This style of sensor is a very low mass design, primarily to be used for measuring air (gas) temperatures, not direct contact with materials.It also can't be anything you would use over the top of the thermocouple bead, because as an insulator it would impact the readings, or at least delay them greatly, which is the exact opposite of the entire purpose of this type of bead thermocouple design.Is it to keep the braid from coming undone? Doubtful. While there are plenty of photos online showing an actual tight piece of heat-shrink instead, there are also lots of photos of these braided types without anything on the end at all. From my testing, I do not see it being necessary for this as the braid is just not going to come undone very much and also the silicone tube is constantly sliding around, even off the end, so it's a terrible solution to that anyway.Personally, I think some good possibilities are it's an insulator for when you're holding it, or as protection for the wires if you have to clamp it in place.

author: JDW
author_rank: Frequent Contributor
timestamp: January 30, 2023, 02:35:35 am
content: Quote from: J-R on January 28, 2023, 03:46:04 amThe single best explanation thus far — THANK YOU!

author: thm_w
author_rank: Super Contributor
timestamp: January 30, 2023, 11:31:36 pm
content: Quote from: J-R on January 28, 2023, 03:46:04 amSilicone heat shrink exists:https://www.shinetsusilicone-global.com/products/type/heat_tube/index.shtmlQuote from: J-R on January 28, 2023, 03:46:04 amSure, I never said it was a good solution, just a potential one.and yeah, some thermocouples with fiberglass braid do not have heatshrink. If you've used them heavily for a few years, you'll see they start to come apart over time. Even if they don't, getting fiberglass fibers stuck into your fingers is very very unpleasant for some of us.From adafruit:https://www.adafruit.com/product/270"There's a small piece of heat shrink on the end to keep the fiberglass from fraying. If you're using at >250°C temperatures, simply remove it with a small blade." Some manufacturers will use polyamide or ceramic cement in place of the heatshrink.

author: JDW
author_rank: Frequent Contributor
timestamp: January 31, 2023, 01:05:12 am
content: Quote from: thm_w on January 30, 2023, 11:31:36 pmPlease define "fraying" and "frayed." Because if you look at the full resolution photo I attached to my opening post, right at the very tip you can see it came "frayed" (to my eyes) straight out of the box. This is a 121GW that I purchased this month and received this month. I doubt that's just a one-off. Probably most thermocouples included with the 121GW are like that.There are two more things that require consideration.First, the transparent silicone heatshrink gizmo (or whatever it is), would get in the way if it were placed near the metal tip because there are times when you want to fit the tip in a tight spot, like between fins on a heatsink, and that transparent silicone gizmo would prevent me from doing that in many situations.Second, if you once again take a look at the full resolution photo I attached in my opening post, you will see the thermocouple included with the Fluke 116 meter. I have no idea what the material is, but it certainly is NOT because it is very thin, smooth to the touch, feels like plastic of some sort, and therefore it will never fray at all. Maybe that puts an upper limit on the maximum temperature it can handle versus the thermocouple of the 121GW, I don't know, but I do like the Fluke's wire simply because it cannot at all. I am guessing that is perhaps why it did not come with that transparent gizmo too.All said, if the 121GW documentation would have mentioned that transparent gizmo and explained its purpose and proper usage, I probably would have had no need to even start this thread.

author: thm_w
author_rank: Super Contributor
timestamp: January 31, 2023, 01:53:15 am
content: The Fluke wire is coated with PFA sleeve (or similar PTFE), which is a smooth high cost material, but, cannot stand as high a temperature as the fiberglass (260C vs 450C+).Yeah any kind of sleeving or coating will increase the diameter and make it harder to get it into small spots. I also would prefer the Fluke style for most general purpose use. Its sold for $55 though..

author: J-R
author_rank: Super Contributor
timestamp: January 31, 2023, 08:15:35 am
content: Found some photos here of a UEi bead thermocouple where it seems to suggest any tubing is not for keeping the ends from fraying.In one photo it's not in the right position, and in the other it's not there at all:https://www.grainger.com/product/UEI-TEST-INSTRUMENTS-Bead-Wire-Temperature-Probe-6CMU0Then also an interesting photo showing the tubing being used as protection while the end is clamped.Perhaps the type manufactured for the 121GW is also used in other configurations and they didn't want to bother changing things.

author: JDW
author_rank: Frequent Contributor
timestamp: April 27, 2023, 08:24:41 am
content: Quote from: J-R on January 31, 2023, 08:15:35 amSorry to jump back into this thread, but I'm doing thermal testing today.The UEI ATT29 you linked isn't the exact shape of the Type-K thermocouple that came with my 121GW, so I am wondering of what comes with the 121GW has the same maximum temperature spec or something else? That ATT29 says it can measure up to 510°C (and the 121GW meter can measure higher still). But is that correct?I know for a fact that my Fluke's Type-K thermocouple (photo posted earlier in this thread), can only measure a measly -40 to 260ºC. When coupled to a Fluke 116 and placed on a Hakko soldering iron tip set to 350°C, it measures about 270°C, which shows the limits of what that Fluke Type-K thermocouple can measure.I also have a UNI-T UTi260B Thermal Imager (set to Low Gain to measure temps above 150°C), but I really don't know the correct Emissivity setting for soldering iron tips. That is why I was hoping to do a check with a Type-K so as to choose the best Emissivity setting on the thermal imager.So to repeat my question, is the Type-K thermocouple included with the 121GW really able to measure up to 510°C?I wish this important info was printed in the 121GW manual! But I can only find what the meter is capable of (a max of 1350°C), not the max temp. of the included Type-K thermocouple.

author: thm_w
author_rank: Super Contributor
timestamp: April 28, 2023, 12:10:50 am
content: Quote from: JDW on April 27, 2023, 08:24:41 amIt wasn't making good enough contact with the thermocouple. Its not easy to do, you'll need a very large blob of solder and a wider tip.The temperature limitations of a type K, below 1200°C, are generally due to the insulation used and its lower maximum temperature. You can find similarly designed thermocouples with fiberglass insulation rated for around 400C.

author: JDW
author_rank: Frequent Contributor
timestamp: April 28, 2023, 01:51:40 am
content: Quote from: thm_w on April 28, 2023, 12:10:50 amWhen I used a larger tip and applied a large solder blob, I was then able to get between 348°C and 349°C on both Type-K thermocouples on both my 121GW and Fluke 116 meters. Thanks. But getting a thermal imager to properly read is truly challenging. It seems that the darkness of the object matters quite a bit. I have to set Emissivity to 0.46 to measure roughly 349°C on the solder blob, but that measurement changes as more black cruft appears on the solder blob. And further down the neck, it reads over 400°C, which of course is not right, but such is due to the tip being shinier and lower down the neck being a medium to dark gray. Interesting.My main intent is to measure heat across components on a PCB, most of them being thru-hole -- large 5W resistors, massive electrolytic caps, etc. It's not practical to have multiple meters and multiple Type-K connections, which is why my intent is to take a wire-tie and strap my Type-K to a given 5W resistor to measure it's temperature, then adjust my thermal imager's emissivity to match. Then hopefully, I can get meaningful thermal measurements on other components on the board when it is powered.

author: Overspeed
author_rank: Frequent Contributor
timestamp: April 28, 2023, 05:01:38 am
content: HelloSo to repeat my question, is the Type-K thermocouple included with the 121GW really able to measure up to 510°C?Any K thermocouple can measure up to 1370 deg C but in the real word that limited to 800 deg C as the alloy used in K thermocouple go oxided over 800 deg CBUTthe acquisition circuit can limit this as low cost circuit don t have linearization circuit as K output voltage is not linearhttps://www.analog.com/en/app-notes/an-1087.htmlRegardsOS