Agilent U1186 Thermocouple +3C accuracy instead of ±1.1°C advertised - Page 1
Forum section: electronics / general

author: smile
author_rank: Regular Contributor
timestamp: September 09, 2011, 07:41:14 pm
content: Hi, I just got my new proble for Agilent U1252B DMM, tested it with mercury thermometers (two of them) show room tem at 24C, the DMM proble shows as 21C.So that gives +3 Accuaracy???The included "Operating instructions with the probe"List Accuracy of U1186A K type thermocouple as ±1.1°CSo I should get something like 25.1at high end, and 22.9 at low end if the room temp is 24C, my DMM shows 21C.Should I return the probe as faulty???

author: Unknown
author_rank: Unknown
timestamp: September 09, 2011, 07:55:23 pm
content: What are the accuracies of the mercury thermometers ? What were you measuring? That probe is tiny and the mercury thermometers are big maybe there was a difference in coupling to the heat source. For probes this tiny the air currents make a difference. Take this into account before deeming it inaccurate.

author: saturation
author_rank: Super Contributor
timestamp: September 09, 2011, 08:18:24 pm
content: Yes, to eliminate geometry errors use a water bath.

author: smile
author_rank: Regular Contributor
timestamp: September 09, 2011, 08:25:11 pm
content: Quote from: HAL-42b on September 09, 2011, 07:55:23 pmAs I said I use two lab mercury thermometers that show the same temperature, they are 1 degree accurate, I also got 0.5 degree mercury thermometer (but actually cheaper one) that shows 0.5 degree more than the two I mentioned.So at worst case there is 0.5 degree fault on mercury thermometer side.The DMM proble shows 3 degrees less, I even tried to measure human body temperature, and at 33.5 that can't be right when you add 3 degrees you get 36.5 normal body temperature.Initially I was measuring air temperature in closed vessel, no air movement there.

author: smile
author_rank: Regular Contributor
timestamp: September 09, 2011, 08:43:01 pm
content: Quote from: saturation on September 09, 2011, 08:18:24 pmOK I re tested, the error is still 3 degrees, mercury at 23 degrees, DMM at 20.2 degreesAs you know mercury doesn't measure negative temperatures so I wonder what would be negative temperature accuracy? Or is it linear?Dave could make a temperature probe shootout to review various including this model thermocouple probes !!!

author: Unknown
author_rank: Unknown
timestamp: September 09, 2011, 09:10:58 pm
content: Mercury thermometers are usually calibrated in water at a certain immersion depth. This depth is usually marked on the thermometer. Anything except measuring liquid temperature at this exact depth may be introducing error.Besides that, the way the k junction is connected to the DMM may be introducing an offset voltage which needs to be accounted for. Ideally you should make yourself an offsets table by calibrating the thermocouple at 0°C and 100°C.I am saying all these because there isn't much in a way of inaccuracy which can be attributed to a manufacturer. It is hard to manufacture a thermocouple wrongly.

author: Richard W.
author_rank: Regular Contributor
timestamp: September 09, 2011, 09:13:51 pm
content: For measurements with K-type sensors you must be shure, that the multimeter and the plugs on the leads have room temperature!If the multimeter or the plugs are hotter or colder than room temperature, the cold junction compensation doesn't work correct.(Thermocouples are measuring the temperature difference between hot and cold junction. The compensation is necessary to get the absolute temperature.)Usually there is a platinum temperature sensor in the meter to measure the temperature of the cold junction.For testing the cj-compensation you have to short circuit the input terminals of the meter.The value on the display is the actual value for the compensation. This should be room temperature.If not, wait some hours. If it's still not room temperature -> faulty meterThe procedures with the two thermal fixed points can be found in the internet. This would also be worth a try.Maybe you have to consider the height above sea level. depending where you are livingBTW: The Agilent is also capable to do measurements with J-type sensors. The resulting error when the wrong sensor is selected would only be a few degrees...

author: smile
author_rank: Regular Contributor
timestamp: September 09, 2011, 09:46:04 pm
content: Quote from: Richard W. on September 09, 2011, 09:13:51 pmYes they are is the room for a whole day so certainly room temperature.Quote from: Richard W. on September 09, 2011, 09:13:51 pmMy meter has internal thermometer displayed too, its 20.8 degreesI have short circuited the meter and the values is 20.9 - 21.0The mercury thermometer shows 23 degrees.Quote from: Richard W. on September 09, 2011, 09:13:51 pmI have the yellow probe, clearly written K on it, the default for agilent is K type probe. K symbol is displayed during measurements.

author: smile
author_rank: Regular Contributor
timestamp: September 09, 2011, 09:53:00 pm
content: Here is photo from my test:

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 09, 2011, 10:03:01 pm
content: Quote from: smile on September 09, 2011, 08:43:01 pmHere is one made before five minutes.The gladiators : Fluke & Agilent & a 23 years old (made in Taiwan) K probe,that came with my first (Good one ) DMM.

author: saturation
author_rank: Super Contributor
timestamp: September 09, 2011, 10:05:18 pm
content: Hmmm, impressive. Test it now against water as calibration, ice bath water and boiling water. Ice water is ~ 0C while boiling is 100C. Note in real life there can be minor variations due to the contaminants in fresh water [ ideal should be distilled] and your absolute ambient pressure but for 1C degree accuracy those two should suffice. Whomwever shows the proper value is likely the right measure and the others are off.FWIW I have the same 1186a model, 2 in fact, a 1252a and several 1272a under tests; I also have a Fluke K thermocouple and a 1000F version, they are all within 1-2F of ice and boiling water. However, the Agilent models are the fastest responding of all.Quote from: smile on September 09, 2011, 08:43:01 pm

author: nukie
author_rank: Frequent Contributor
timestamp: September 10, 2011, 03:04:13 am
content: Get anOmegawith proper termination for thermocouple mini plug. With all the uncompensated adapters and connectors you are introducing thermal error. Heck even my 3x 187/9 flukes are not accurate. They only give you a ball park figure. Measuring temperature is not hard but measuring accurate temperate is another game. Your lab thermometer, do they come with a cal certificate? If not, don't even trust it.

author: smile
author_rank: Regular Contributor
timestamp: September 10, 2011, 05:30:05 pm
content: Quote from: nukie on September 10, 2011, 03:04:13 amAny direct URL to product or name please.Quote from: nukie on September 10, 2011, 03:04:13 amWell seems you did not read all thread, human body temp is 36.5 degrees so my 2 mercury thermometers measure like it should be 36.5 degrees, my DMM shows 3 degrees less.Quote from: nukie on September 10, 2011, 03:04:13 amNo I don't have measurement certificate, but thermometers are from lab hardware that cost allot of money, so they should be accurate, both show the same temp so that is alone 99% guarantee that they do not lie. Also they show human body temp OK, so seems to be accurate unlike the DMM.Also my DMM when shorted shows incorrect temperature, see attached picture, so it is faulty?The internal DMM thermometer and the value shorted however seems very close from each other.

author: Richard W.
author_rank: Regular Contributor
timestamp: September 10, 2011, 06:58:11 pm
content: QuoteThe internal thermometer IS the sensor for the cold-junction-compensation. So the values should not only be close, they should be equal.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 10, 2011, 07:13:19 pm
content: @smileIs this the way that they act in your village when some one helps them out.I do not know if it sounds crazy but I was expecting a tiny thanks word.Even so, when some one comments accuracy issues, I expect that he had clean first the banana plugs of the DMM unit,with medical alcohol or other cleaning fluid with out oil in it.

author: smile
author_rank: Regular Contributor
timestamp: September 10, 2011, 09:26:08 pm
content: Quote from: Richard W. on September 10, 2011, 06:58:11 pmWhen one values changes the other doesn't so that makes them not the same.

author: smile
author_rank: Regular Contributor
timestamp: September 10, 2011, 09:32:02 pm
content: Quote from: Kiriakos-GR on September 10, 2011, 07:13:19 pmThank you for your help, I did not notice that I have not replied to your post.You did not answer my initial question by posting different values for different probes (very likely to happen and normal because they are different brand probes).I was expecting same manufacturer and same type probe comparison, like agilent K trype 3 probes compared between each other. Then we could talk about probe accuracy, comparing different manufacturer probes that are different type K, J etc. only shows that reading can differ.Quote from: Kiriakos-GR on September 10, 2011, 07:13:19 pmThe meter and thermocouple is brand new

author: IanB
author_rank: Super Contributor
timestamp: September 10, 2011, 09:52:37 pm
content: I don't think it has been mentioned strongly enough in this thread that thermocouples measure relative temperature, not absolute temperature. There is an independent temperature sensor inside the meter using a thermistor or some other device to establish a reference point, and the thermocouple probe temperature reading is based off this reference.So if your meter's internal temperature reference says room temperature is 21 C, then the thermocouple will read room temperature as 21 C also. It can do nothing else.So if you think your room temperature is really 24 C and the meter reads it as 21 C, then the meter's internal ambient temperature sensor might be out of calibration.

author: Richard W.
author_rank: Regular Contributor
timestamp: September 10, 2011, 10:26:12 pm
content: Quote from: smile on September 10, 2011, 09:26:08 pmQuote from: smile on September 09, 2011, 09:46:04 pmThats a deviation of 0.2°C, caused by 8 microvolts on the input terminals. Thats negligible.(measuring microvolts with a handheld DMM is not the best idea, but that's what you are doing when you measure with k-type sesors)As IanB said:The internal measured temperature is the reference for the k-Type measurement. Wrong reference, wrong k-type measurement.By the way:Please have a look at the second table on page 6. 0,3% + 3°C accuracy of the meterYou have to add this to the +/- 1,1°C accuracy of the sensor.If the real temperature is 24,0°C the displayed value can be from about20 to 28°C(approximately)Problem solved (maybe)

author: Zero999
author_rank: Super Contributor
timestamp: September 11, 2011, 07:18:09 pm
content: just one question: why are thermocouples used?Surely a thermistor or temperature sensing IC are better options?

author: IanB
author_rank: Super Contributor
timestamp: September 11, 2011, 07:31:50 pm
content: Quote from: Hero999 on September 11, 2011, 07:18:09 pmI think because a thermocouple probe is small and robust and has a fast time constant. You can put the probe in hostile or hard to reach places on the end of a long wire. The probe can withstand temperatures of several hundred degrees. When suitably encased the probe can be placed in hot liquids or in corrosive environments. The reasons are many...

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 11, 2011, 08:12:52 pm
content: Its true that for every type of application, there is specialized thermal probes.And according to that rule, the basic K type probe that come with the DMM, or you additionally get,it serves basic measurements that high accuracy and fast temperature changes its not important.The topic was looking fishy from the start, because the expectations was not logical if we think that some one expects the ultimate accuracy by a 10$ probe.Lets hope that Agilent will offer to me the true professional K type probe for review.It retails about 180$ , and yes this one it supposed to be accurate all the way for a Year time.The low cost basic probe it supposed to be used for heatsink temperature measurements,somewhere between 30 to 80C .No one cares if the heatsink would be hot as 51 or 53C, and there is no critical difference to that,and so the low cost K type probes are good enough about this task.And now I will offer one practically valuable tip.And this called as K type probe matching.You need to have a minimum set of three identical K-Probes,You test all three , and by this comparison, you accept as best the one who gives the middle reading.And you mark the difference with a permanent marker on the other probes like ( example at 20C) +1 ( 21) and - 0.5 ( 19.5).And now you can use any of the three, and you known what to expect from its one.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 11, 2011, 10:01:51 pm
content: Quote from: Hero999 on September 11, 2011, 07:18:09 pmThermocouples have much bigger temperature range than NTC thermistors and temperature sensing ICs. They can be dunked in a liquid (even a conductive liquid) and still work, and they are almost indestructable due to their welded construction. Platinum PTC thermistors have a similarly large operating temperature range, but they require an excitation current and often a 4-wire resistance measurement due to their low dR/dT (around 0.4 ohm/kelvin for a Pt100).The only disadvantage of thermocouples is that they have relatively low accuracy, especially when using sub-optimal cold junction compensation that you will find in many DMMs. This is usually not as big of a problem as people think. In measurements of gases or solids, other factors will often dominate. Temperature gradients and fluctuations mean the temperature at the probe tip may not be particularly meaningful, and direct heating or cooling of the probe tip by evaporation, air currents, light absorption, or conduction along the probe body can all create intrinsic errors in the measurement. PTCs and ICs can have their otherwise better accuracy compromised by self heating due to the operating current. Liquid measurements are much better behaved, at least if the bath is stirred sufficiently, but can still be problematic.

author: greatseo
author_rank: Newbie
timestamp: September 12, 2011, 10:18:28 am
content: Is this the way that they act in your village when some one helps them out.I do not know if it sounds crazy but I was expecting a tiny thanks word.Even so, when some one comments accuracy issues, I expect that he had clean first the banana plugs of the DMM unit,with medical alcohol or other cleaning fluid with out oil in it.

author: SgtRock
author_rank: Unknown
timestamp: September 12, 2011, 11:26:27 pm
content: Dear Smile:--You might want to generate plotted curves showing the Agilent reading vs your Mercury reading. If the space between the two curves is relatively consistent, adjusting the calibrated temperature should help. If the lines diverge or cross you will just have to do the best curve fitting you can, making the part of the range you use the most as accurate as you can, and using a fudge factor for the rest.--You might also consider getting one of these "Temperature range: -58 to 482 °F(-50 to 250 °C); Accuracy: +/- 1C (between -20, 80 °C), or +/- 2 ° (out side of -20, 80 °C)", see below. They are quite handy in the kitchen. BTW, I am betting DJ uses a Fluke to check the baby bottle temperature. :http://www.ebay.com/itm/Digital-Thermometer-SS-Sensor-Memory-Kitchen-Food-HVAC-/370378620912?pt=LH_DefaultDomain_0&hash=item563c493ff0To Greatseo:--"immigration attorney"--Welcome to the EEVBLOG Parade Grounds. I just wanted to tell you, that you are starting off on the right foot, that is, the wrong foot. In the Air Force we used to make troops that started of on the right foot carry a 5 pound rock in their left hand for a day or two. In other words Sir or Ma'am as the case may be, please try to get with the program.--This is truly an international forum. Many of the people posting here are Electrical Engineers and Electronics Professionals for whom English is a second or third language. Now DJ, Simon and the other administrators are not likely to censor you, but you are not going to make many friends, belittling folks for their nationality or ethnic origins. I will let it go this time and wish you a hearty "- - - - . - - . -"Best RegardsClear Ether

author: IanB
author_rank: Super Contributor
timestamp: September 12, 2011, 11:34:22 pm
content: Quote from: SgtRock on September 12, 2011, 11:26:27 pmDid you notice that this post was a spam post? It is an exact copy-and-paste of what Kiriakos wrote a few posts back...

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 13, 2011, 01:10:37 am
content: With off topic gossip the post counter rises fast UV.Keep up the good work. LOL

author: SgtRock
author_rank: Unknown
timestamp: September 13, 2011, 01:26:26 am
content: Dear IanB:--No I did not realize it was a spam post. Now I see that you could be correct. Just how does that work anyway. Do they have a Spambot that looks for imperfect English grammar and syntax and the joins forums in order to post spam links. Or do the have humans posting spam for a dollar a lick or what. Just how do they do this sort of thing. I am not being sarcastic. It certainly looks like spam, now that I think about it, but I cannot figure out how they do it profitably.--Back on topic; I have two Fluke 87s with no temperature capability, that is why I bought a kitchen thermometer with remote sensing probe. They are cheap, reasonably accurate, and free up your DMM to do something else at the same time. And most of them even have an alarm to let you know when you have reached the temperature. Most also function as stopwatches and alarm timers. One should be very helpful on any bench."Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP LabsBest RegardsClear Ether

author: smile
author_rank: Regular Contributor
timestamp: September 13, 2011, 08:31:36 am
content: Thanks for everyone help, I try to get some more thermometers to compare to.Quote from: Richard W. on September 10, 2011, 10:26:12 pmYes the deviation of the meter is like you said 0,3% + 3°C + +/- 1,1°C accuracy of the sensor, that really is crap for such an expensive meter that is. And what is the point of using expensive (like @Kiriakos-GR said) probe for 180$ if the meter will be the bottleneck then ?Still better to use mercury thermometers to measure accurately thenwhat a nonsense in 21st century, and inconvenience.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 13, 2011, 09:06:14 am
content: Quote from: smile on September 13, 2011, 08:31:36 amDamn. I knew that thermocouple measurement was a bit of a 'we can do that free' feature on DMMs, but I didn't expect a 3C offset. An omega temperature controller will do a much better job, of course at a cost. If you want to measure temperature more accurately on your DMM you could get a Pt1000 and measure it on ohms mode. You will have to look up the conversion yourself. Pt100 is more common but when measured with a standard DMM will have larger errors due to contact resistance. Even a Pt100 will be good to 0.5 C or so.

author: Unknown
author_rank: Unknown
timestamp: September 13, 2011, 09:11:18 am
content: Quote from: smile on September 13, 2011, 08:31:36 amYeah, temperature measurement is crap, even in expensive meters. Same for capacitance, actually. Or frequency. Or inductance, if available at all. Basically anything except the classic VDC/VAC (low frequency)/R/IDC/IAC/diode/continuity features.Fluke (and some others) also make dedicated thermometers, my guess is that those are better, although K-type has always been the cheap, not so accurate option.

author: baljemmett
author_rank: Unknown
timestamp: September 13, 2011, 10:43:33 am
content: Quote from: SgtRock on September 13, 2011, 01:26:26 amThere's no 'could' about it -- it's a spam post. The bot algorithm is (roughly) join forum, find active discussion, copy an extract from a little way back in the thread, post it as fresh reply with spammer's link in the footer. It works because people don't always notice it's just parroting something already said, since (usually!) the 'new' contribution will be related to the subject being discussed, and so the link gets to sit there gathering search engine legitimacy and maybe even the odd click. Setting 'nofollow' on links helps with the search engine bit but I don't think SMF implements that.Unfortunately in this case the bot happened to pick a tasty piece of flamebait instead of anything with any particular relevance, and so stood out like a sore thumb -- your reaction to "greatseo"'s perceived rudeness is ample demonstration of that! Come to think of it, that's a bloody daft choice of name for a spambot, rather gives the game away... I would imagine if there was a human in the feedback loop they might have chosen a less obvious section of text to copy.Back to thermocouples, huh?

author: SgtRock
author_rank: Unknown
timestamp: September 13, 2011, 12:22:40 pm
content: Dear Baljemmet:--Thank for the informative post. I guess I did get the hook caught in my lip on that one. The depth of my ignorance is very great in this area. I was unable find a meaning for SMF except for the obvious crude one, which is not what you meant, I do not think. I promise to keep my next post, strictly on topic."Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP LabsBest RegardsClear Ether

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 13, 2011, 01:08:48 pm
content: Quote from: baljemmett on September 13, 2011, 10:43:33 amI had no idea that it was a bot, I had just think that some one was attacking to me. LOLNow about the flame-bait, I love this forum so much, and I do not use this tactics,but some times the small misunderstandings its not avoidable.Yes back to the thermocouples.The U1272A has 1% +1C accuracy.If this thread helped me in a way, was that from now and on I will just add this damn 1C at every temperature measurement of my.

author: SgtRock
author_rank: Unknown
timestamp: September 13, 2011, 01:12:43 pm
content: Dear Smile:--Please disregard the erroneous comments that were previously in this post. See below for the links to the specifications of your meter and thermocouple.--Agilent U1252B specifications:http://cp.literature.agilent.com/litweb/pdf/5989-5509EN.pdf--U1186A Thermocouple (K-Type) and Temperature Probe Adapter specifications:http://www.home.agilent.com/agilent/product.jspx?cc=US&lc=eng&nid=-536902467.714195&pageMode=OV--Let us assume for the moment that your mercury thermometer is completely accurate and measures 24.0 C. The temperature accuracy specifications for the U1252B are +- (0.3% + 3) degrees C. The temperature accuracy specifications for the U1186A K-type Thermocouple are +- 1.1%.--The worst case senario analysis of the above specifications, assuming a true temperature of 24.0 C, gives the following range of possible readings that are within specifications: 19.8 to 28.1. So you meter would appear to be within specification with regard to temperature.--Many thanks to ejeffery for pointing out the errors that were previously in this post."Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP LabsBest RegardsClear Ether

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 13, 2011, 01:21:55 pm
content: Hey give a hand to the poor electrician ..My DMM specifications : Accuracy: ±1% +1°CAnd the same goes for the thermocouple ±1% +1°CIs it logical to assume that I had to add 1C ( DMM side) + 1C ( K-probe) = total compensation +2C ?

author: ejeffrey
author_rank: Super Contributor
timestamp: September 13, 2011, 01:41:08 pm
content: Quote from: SgtRock on September 13, 2011, 01:12:43 pmNo, you are misreading it. The error specified is the magnitude, it can be off in either direction. The "+" means that you have to add the fractional uncertainty (1%) with the offset error (3C) to get the maximum magnitude of the error.

author: SgtRock
author_rank: Unknown
timestamp: September 13, 2011, 02:13:05 pm
content: Dear Ejeffery:I see upon review that you are nearly completely correct. I will be correcting my erroneous post immediatly. Agilent should have stated +-(0.3% +3C). My Fluke 87 manual is even harder to read and refers to the "lease" significant digit. Thank for catching my egregious error so soon.Best RegardsClear Ether

author: saturation
author_rank: Super Contributor
timestamp: September 13, 2011, 03:57:31 pm
content: I took a quick ice water photo, I presume you know what errors can occur if its not ice shavings; the temp is not homogenous as it equilibrates accross the cubes and the container, so spots are warmer than others. However, this shows at least 2 meters including a separate IR reading independent of the thermocouple, read ~ 1C of each other.Likewise, the ambient reading of the 2 Agilent's are within 1C of each other.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 13, 2011, 05:24:47 pm
content: Agilent is very clear about temperature measurements in the user manual of the U1272A .It forbids the immersion in water of the Teflon yellow K probe.For temperature measurements of Air / liquids / metals, there is special made probes.The mini probe in the device, needs a minimum of 60 min, so to adjust at the environmental temperature..More info page 66 .