new UEI DT200 - show 1.5*c in ice :-[ ?

[piotres]

Hi

3 weeks ago I have bought a brand new UEI DT200 from bes.ltd.uk . It has 2 stock k-probes . I have tested it on glass with some melted ice cubes and both probes show 1.0-1.5 *c :mad: . So I decided to buy a new probes - I have thought that pribes are bad .

Today new K-probes arrived - 2 pcs- every from antoher manufacter (one green, one white-blue :D ) - and it's the same ... :( :eek:

Lowest I have seen in melted ice was 1.0*c with every of 4 K-probes which I have in home :( Usually 1.5*c :shakes:

I do the tests correctly, in the same way like other users, and I have tested in the same way my old CHY 502 thermocouple and it was 0.1*c with CHY in that conditions . So tests are OK .

Can I calibrate my DT200 a bit ??

Thanks a lot

Regards
Peter

[Marvin]

Hi Peter, here i insulated a small cup, filled with smashed ice and tested. I never reached 0C, but 0.1 and 0.2 C. If you tested with another thermometer, you have to send it back to calibrate.
The UEI dont have this function.:(

[IYP]

your temps are always going to be off a bit in that situation because of imperfect contact with the ice and the fact that it is melting....and the fact that the probe is going to warm it up a bit...try boiling water....should be pretty close to 100c

[piotres]

Heh as I said I have tested CHY502 in the same way and I had 0.1-0.2 *c, so it isn't needed to insulate the glass .


In higher temps all is ok - eg. Yesterday I have measured my temperature - with orginal probes I have 36.5*c under my tongue ;) so Ok

[Unknown_road]

your temps are always going to be off a bit in that situation because of imperfect contact with the ice and the fact that it is melting....and the fact that the probe is going to warm it up a bit...try boiling water....should be pretty close to 100c

no if you leave an ice water mixture standing for a while it will be exact 0*C. the ice is 0*C and the water is 0*C, when you add heat to the mixture temps won't rise untill all the ice is gone, all the heat is transformed into potential energy not thermal.

piotres, are you sure the battery is ok? if the battery is ok and the meter is set on K-type probes it probably needs to be send to the factory for calibration. Or you take the 1*C for granted.

[expansionvalve]

I am not that familiar with these meters but most of the mid to high end stuff I have seen in the past has a small screw inside the case for calibration purposes, it may be the case with your meter, it may not.. I'd rip it apart and look if there are no warrenty stickers on it that would be damaged on destruction.

[johann]

I am RMA'ing my UEI DT200 soon. Horribly bad is an understatement.

My unit I cannot run 2 probes and temps go crazy. Sometimes even with a single probe, temps are completely wrong. That is with brand new battery.

It has caused alot of work for me, even stripped a unit before because of the invalid readings. Temps are also at least 2c off even when it seems to be working OK.

Maybe its just a faulty unit, but Im not happy with it. Soon I will buy a new thermometer. So Im stuck with this one also

[s7e9h3n]

I am RMA'ing my UEI DT200 soon. Horribly bad is an understatement.

My unit I cannot run 2 probes and temps go crazy. Sometimes even with a single probe, temps are completely wrong. That is with brand new battery.

It has caused alot of work for me, even stripped a unit before because of the invalid readings. Temps are also at least 2c off even when it seems to be working OK.

Maybe its just a faulty unit, but Im not happy with it. Soon I will buy a new thermometer. So Im stuck with this one also
From personal experience, the UEI's have one of the worst "sockets" to accept the thermocouples. If you have a probe inserted and accidentally bend one of the plugs up or down, the piece inside the UEI which contacts the plug will be out of alignment. Once this happens, you're basically $hit out of luck. I've had 2 dT200's rendered useless because of this problem while my other thermometers - an Extech and a Fluke have had no issues whatsoever......

[Bergo]

crap I just bought one, maybe should have went with the fluke i was looking at o_O

[Comp-Freak]

Hehe, before I'd bought one, I heard only good things. Now I have one, this topic appears ;)

But mine seems to be fine, temps are ok around 0 degrees.

[johann]

Im just working with this UEI and if anyone was thinking of buying one then DONT, its a piece of :banana::banana::banana::banana:

[Unknown_road]

Im just working with this UEI and if anyone was thinking of buying one then DONT, its a piece of :banana::banana::banana::banana:

because you have a faulty unit doesn't mean nobody should buy one. I never had problems with mine. I think they're very good bang/buck. problems happen just send it back and it will be fixed.

[johann]

even when it works, temps are off. reading 1.5c in icewater is bad and its not just mine, piotres started this thread because his is exactly the same as mine.

I think for £70 you can do better, thats my opinion

[Revv23]

yeah mine reads like 2c off in a bath..


annoying but i dont really care, got it used for pretty cheap


if i were buying new fluke would be my brand.

[Unknown_road]

even when it works, temps are off. reading 1.5c in icewater is bad and its not just mine, piotres started this thread because his is exactly the same as mine.

I think for £70 you can do better, thats my opinion

Although I doubt if everybody here makes a good ice bath, calibration errors occur with every brand but most people here have uei's so we see calibration errors with those more often. When you get it back and the unit you get is still off then you have a reason to complain about the company.

btw. to be 100% sure that your ice bath is 0*C, put only ice cubes in a glass. Wait till you have a good water/ice mixture and then put the probe in the water.

[Jort]

maybe due the global warming the ice is hotter LOL:D

[catkicker]

maybe due the global warming the ice is hotter LOL:D

Ah, another sign there out to get us.

[[XC] Jaco]

I just received my DT200.

Mine's showing 0,2 - 0,4 °C in ice water .
I guess it's not the most accurate device , but it's good enough for me.

[marvt74]

The only thing is, if its 0.5-1C out at 0C is it likely to always be out by that much or is it likely to get far more innacurrate at lower temps

[Weee]

Mine was showing anywhere between 60-100*C at room temperatures depending and fluctuated wildly after about a month... probably would have shown about 35-75*C in ice water.. needless to say i played the warranty card there.

[kayl]

to do the test properly ya need to put the ice in a rag or something and then crush it with a hammer.
then place the ice in a glass with a tad of water
ypu really need the ice and water situation to get proper temps.

In saying this, after 8months mine went faulty, read -36c at 24c room temp.
just happened one day?? seems a few ppl are having issues with their UEI dt200



this pic was for the autocascade compertition when the temp probe was working sweet.
http://www.xtremesystems.org/forums/attachment.php?attachmentid=23905&stc=1

[\Karting_freak]

ice CAN be 1.5C and snow too :)

[johann]

I dont mind for mu DT200 to be a little off, but sometimes it goes completely crazy. It is very difficult to charge without a solid temp. When I arrive home I will upload a video clip of an example to explain hat I mean.

[Unknown_road]

Does everbody know that the couples have a + and a - ? :D

[yngndrw]

They can usually only be plugged in one way though. Unless someone pulled the plug off and swapped it over. :P

[johann]

Does everbody know that the couples have a + and a - ? :D

They can only go in one way :)

[wdrzal]

Although I doubt if everybody here makes a good ice bath, calibration errors occur with every brand but most people here have uei's so we see calibration errors with those more often. When you get it back and the unit you get is still off then you have a reason to complain about the company.

btw. to be 100% sure that your ice bath is 0*C, put only ice cubes in a glass. Wait till you have a good water/ice mixture and then put the probe in the water.


80% crushed ice 20% h2o, ice and water should be distilled to be accurate.

[Comp-Freak]

I think most of the time, the cause beiing off in an icebath is indeed the icebath itself. When I moved the probe a bit, temps fluctuate because it hits the icecubes, or the little bit warmer side of the glass.

[jinu117]

Another thing... you need to electrically insulate the probe itself. Use something like artic ceramique around it once :)

[[XC] Jaco]

Another thing... you need to electrically insulate the probe itself. Use something like artic ceramique around it once :)

interesting. are you saying the electrical conductivity of plain water causes incorrect readings ? (I was never great in physics at school ;) )

[jinu117]

I've noticed some rapid fluctuation of temp on evap head before when there was moisture on testing surface. Put some thermal paste to at least cover the probe and all no more wild fluctation of 5c. (could be some electricity going through copper evap too but oh well)
Well, thermocouple works like this.
2 dissimilar metal joined under different temperature gives different voltage out in mili volts. This is translated into temperature by thermometer.
See... 2 metals joined... producing voltage... drop it in the water... yes... the potential is so low as to impact the reading hugely... :P But why take chance :)

[Unknown_road]

I've noticed some rapid fluctuation of temp on evap head before when there was moisture on testing surface. Put some thermal paste to at least cover the probe and all no more wild fluctation of 5c. (could be some electricity going through copper evap too but oh well)
Well, thermocouple works like this.
2 dissimilar metal joined under different temperature gives different voltage out in mili volts. This is translated into temperature by thermometer.
See... 2 metals joined... producing voltage... drop it in the water... yes... the potential is so low as to impact the reading hugely... :P But why take chance :)

or just use distilled water like wdrzal says.

[kayl]

do the Dt200 come with K-type or j-type probes??
maybe selecting wrong setting for probe using?

[Comp-Freak]

do the Dt200 come with K-type or j-type probes??
maybe selecting wrong setting for probe using?K-type.

[Waus-mod]

Well the best thing to take a look of its accurate... put the probe in dry ice or ln2 (prefer ln2 over dry ice) if it doesnt shows -196 you know it :)

[Waus-mod]

Well the best thing to take a look of its accurate... put the probe in dry ice or ln2 (prefer ln2 over dry ice) if it doesnt shows -196 you know it :)

@ compfreak... what do you meassure with youre dt200?

[Comp-Freak]

@ compfreak... what do you meassure with youre dt200?Not much until my single stage is finished ;) Have measured icewater, and put it under my tongue ;) Also tried things like outside temp and temp of a central heating radiator @ school. Temps according to the DT200 did look fine.

[piotres]

I have sold my DT200, and this weekI will buy Voltcraft K102 thermo (2 probes, to -200*c, just like UEI, but costs 70 eur :) )

Regards
Peter

[wdrzal]

Another thing... you need to electrically insulate the probe itself. Use something like artic ceramique around it once :)


Not all probes can be submersed, you need the correct probe,"submersion" probe to put directly into liquid.

[piotres]

Ok I have a Voltcraft K102 now ...and this time I have a good thermometer :)

K102 vs DT200

http://www.members.lycos.co.uk/piotres1/thermo/uei0.jpg
http://www.members.lycos.co.uk/piotres1/thermo/volt0.jpg

http://www.members.lycos.co.uk/piotres1/thermo/uei-48.jpg
http://www.members.lycos.co.uk/piotres1/thermo/volt-51.jpg

Measuring in the same moment :slobber:

No comments needed in my opinion :stick: :D

[marvt74]

Good call i also have the K102, terrific especially for the price did you get it from Conrad in the UK or find a local supplier?

[piotres]

I get it from Conrad in Poland :)

[Gray Mole]

Nice one, that's the next probe I'd like to get myself, though I might go for the 4 probe version to make the multi evaps easier to work with.

I'm glad you were able to get a nice new probe though, that should make life a little easier :toast:

Gray

[MaxxxRacer]

Guys if you want a REALLY kick as thermouple reader, the Omega HH506 cant be beat. For 145 dollars u get the accuracy of a Fluke 52 series with dual input and data logging. It even comes with the RS232 cable to hook up to the computer as welll as the software to make it work...

http://www.omega.com/ppt/pptsc.asp?ref=HH506A_HH506RA&Nav=teml04

[Waus-mod]

Well... you just cant say the dt200 meussures fault... mayb the probes didnt got in good contact. On the other hand. When we go deep down the voltcraft doesnt have that accurance that the dt200 have under -100°C!

[runmc]

Walt gave me a great explanation on calabration a couple of days ago. I saved it Walt.:D

As you know probes are 2 dis-similiar metals that put out a current, This changes with tempature.A temperature meter is just a milli-volt meter that reads the current and dispays it as a tempature. Different probes types use different metals because there is less "drift" in the "preferred range", but the calibration (zero) voltage is different for the types. so they must start at the correct point. set to the wrong scale the reading will be wrong. I can't remember the calbration voltages but we will make some up for a example.a k probe produces 12.05 millvolt at 0c ,and a T probe produces 11.62 at 0c. as the probes gets colder they produces less voltage. after all that ranting I hope you understand the "simple" answer is if the starting point is wrong so will any reading along the way.

you should also know meters not only have a "zero" calbriation point but low,high and mid points. just because a meter reads 0cin a ice bath is no gaurentee that it is correct at -50c or -100c. there is a "standard calibration scale" for each probe type and each fraction of a degee has a specific voltage that probe should put out.

When calibrating not only does the meter have to be calibrated correctly so the voltage it reads dispaly the temp for the voltage but the probe needs to be checked also to be sure it produces the correct voltages for the "standard". either the meter or the probe itself can cause a calibration error.

probes that are not "immersion type" can give false readings just by putting them in water, you really need acalibration meter to accuratly set them but for our purposes a degee or two is close enough.in fact most meters have that much error.

All credit goes to wdzral:woot:

[kayl]

Ok I have a Voltcraft K102 now ...and this time I have a good thermometer :)

K102 vs DT200

http://www.members.lycos.co.uk/piotres1/thermo/uei0.jpg
http://www.members.lycos.co.uk/piotres1/thermo/volt0.jpg

Measuring in the same moment :slobber:

No comments needed in my opinion :stick: :D

from that pic i would say the DT200 is more accrate than the K102
you need to crush the ice and have a ice liquid solution. You need heaps of crushed ice and a tad of distilled water.:toast:

[kayl]

this is how i do my ice tests.to do it properly it would also need to be check at 100c (boiling water) and maybe like Waus-mod said with 1n2 at -196c:toast:
hatiem also did his with co2 straight out of a fire extinguisher (spot on hey)



http://www.xtremesystems.org/forums/attachment.php?attachmentid=43571&stc=1&d=1140182337
http://www.xtremesystems.org/forums/attachment.php?attachmentid=43572&stc=1&d=1140182337
http://www.xtremesystems.org/forums/attachment.php?attachmentid=43573&stc=1&d=1140182337
http://www.xtremesystems.org/forums/attachment.php?attachmentid=43574&stc=1&d=1140182337
http://www.xtremesystems.org/forums/attachment.php?attachmentid=43575&stc=1&d=1140182337

[Fhqwhgads6680]

@ maxx yeah that omega looks REALLY nice for that price...I need to get a something like that....arg I hate money!!!

[piotres]

I have also tested DT200 with a glass full in half with water from melted ice so 0*c for sure ..show 1.5*c, so the same.

[wdrzal]

Great example Kayle :clap: :clap:


Here the mv calibration voltages for K type thermocouple.s

[Revv23]

hmm now that i think about it, i didnt use distilled water or insulate the probe.

my DT200 may have been right on.

[johann]

Voltcraft K102 on the way... I need to see face to face what temps both give, my DT200 I believe is way off now. I get odd readings and it doesnt correspond to pressure readings. Cant be rigth

[wdrzal]

Voltcraft K102 on the way... I need to see face to face what temps both give, my DT200 I believe is way off now. I get odd readings and it doesnt correspond to pressure readings. Cant be rigth


did you try a differnt thermacouple?

[johann]

I always use both on the evap for in case there is bad contact. Both give similar readings

[johann]

lol another fault to buy something from conrad uk.

I phoned today to find out where my Thermometer is and some person who could barely speak English explained to me that its going to take 7 working days for it to arrive from Germany.

WTF This is supposed to be a UK shop????

Also they claim they cant refund it which is illegal in the UK

[Athens[2004]]

K-102 Voltcraft seems good choice , any1 know whats the rate/measurment [2per sec , 1? ect] ?

I have buy one and waiting 4 the shipment.

[marvt74]

Athens[2004] it seems to be every 2 seconds.

Johann thats pretty poor i received mine in about 2 days i think

[johann]

Athens[2004] it seems to be every 2 seconds.

Johann thats pretty poor i received mine in about 2 days i think

From Conrad? Did it say 5-7 working days on the website?

[vapb400]

That thermometer looks good Maxx. Does anybody know what Hipro uses? the one with the huge bright display?

[marvt74]

From Conrad? Did it say 5-7 working days on the website?

I dont remember it was just before christmas i think now, they seemed very quick as i remember getting an email about 2 hours after about a free gift and tried to ring to get it included but it had already been packaged :)

Maybe i was just lucky with stock levels

[Bergo]

well, I got screwed, Just received my UEI DT200 which I bought on Ebay Jan 22nd (over a month shipping) and it is HORRIBLY out of calibration, it's reading -2.9 t1 and -2.1 t2 @ room temperature (abuot 22 degrees) I was wondering if anyone here has the ability to calibrate these units, or if anyone knows if UEI will calibrate them for a fee, I've already been overcharged for shipipng and had to pay border duties, so I'm not particularily excited about another expenditure, should have bought a new ones :(

[wdrzal]

Voltcraft K102 on the way... I need to see face to face what temps both give, my DT200 I believe is way off now. I get odd readings and it doesnt correspond to pressure readings. Cant be rigth

johann I just happened to catch your statement about temperature not corresponding to pressure readings.

Your aware in a running system you have superheat and they don't match the p/t chart;)

[johann]

Hi,

Example of what I observed then people can tell me if it is correct or not...

Fully charged system with R402, Danfoss sc21, idle lowside pressure -15psi

evap temp -45c

Loaded with 160 watts lowside -5psi

evap temp -35c

That I believe is way of or not?

I would think with -15psi on lowside evap would be more like -60c at least and loaded -5psi would be -50c, that is my guess.

Also it is not the system, the other one I have here using Danfoss NL11f and chilly rev e evap is the same.

Both systems are stable running sweet..

[Athens[2004]]

That thermometer looks good Maxx. Does anybody know what Hipro uses? the one with the huge bright display?

its not thermometer i think its a controller-thermometer shimaden (http://www.shimaden.co.jp/english/products/index.html) but i dont remember excatly the model :mad:

[PoL]

I have sold my DT200, and this weekI will buy Voltcraft K102 thermo (2 probes, to -200*c, just like UEI, but costs 70 eur :) )

Regards
Peter

Hey guys! It was me who bought this DT200, and got to say it's working great for me. I have another digital thermometer which has always worked great, and did always show 0.0º in water+ice, and this DT200 is showing 0.3º, so man, I think it's sooo accurate. :toast:

Actually, the temp in the water has only a 0.3º difference, while the atmosphere one is exactly the same. :)

http://img516.imageshack.us/img516/3172/img7409copia8xa.jpg

http://img517.imageshack.us/img517/9522/img7414copia2oy.jpg

http://img517.imageshack.us/img517/9158/img7412copia6vs.jpg

[johann]

Mine is most proppably just faulty, Ill send it for RMA.

[cold_ice]

I have either a Voltcraft and a UEI thermometer. I made a test today, in my opinion both meters have the same accuracy, as my test shows. The only disadvantage is that the UEI needs longer to show the temp when you start it, and the batteries don't last long at all in comparison to the Voltcraft.

I used the same probe for the test, the same conditions:
http://www.xtremesystems.org/forums/attachment.php?attachmentid=43974&stc=1&d=1140904708

http://www.xtremesystems.org/forums/attachment.php?attachmentid=43975&stc=1&d=1140904708

So both are a bit off when the probe is in LN2. But it's fine when you think the probes are only rated for -50°.

[Bergo]

Bump

anyone here know where I can get this calibrated? couldn't fnid a link for out of warranty work on UEI's website, says I need a copy of the original purchase receipt, which I don't have :(

[wdrzal]

Uei will still calibrate it, just for a fee

[MaxxxRacer]

cold_ice, the method of checking the LN2 your using isnt exactly completely accurate. I say this because the temperature of the LN2 will change with the pressure in the room.. if the pressure dips below 1ATM the temp of the LN2 will icrease and vise versa

[cold_ice]

But this was measured at the same time. I just wanted to show, that the UEI and the Voltcraft meters are as accurate.

[kayl]

But this was measured at the same time. I just wanted to show, that the UEI and the Voltcraft meters are as accurate.


:toast: adn what better way to show it hey.
The supco meters seem to look exactly the same as the Voltcraft
except they take J probes as well. mine only takes k's

[MaxxxRacer]

alot of meters are manufactured by a 3rd party and distributed under several companies names. Omega does this with most of their products. I have found that alot of Omega products can be found under the "Sper Scientific" name, but at much better prices.


Fluke and UEI do not do this though.

[johann]

OK my voltcraft meter arrived and Im still having problems. Both meters read the same.

The voltcraft came with no probes so I had to use the UEI probes.

Problem is below -45c it becomes dodgy. It hits -50c but no matter what I do I cant get a reading below that and I am 100% sure that its colder than that, more in the region of -60 to -65

The k type probes are only rated -40c I think. should I try different probes?

Anyone had problems like this before?

The probes do not look like the probes on the pic above, its got a yellow plug that closes with 3 screws

[wdrzal]

probes can be faulty, also you need to get a probe with the correct range, They make K probes to -200 they are just more expensive. The plug doesn't matter,its just some are molded on .

[Waus-mod]

I had same problem.. i had blue probes with my dt200.. and could only meassure -170. now i have some yellow probes i can meassure -192 :D so the probes aint good!

[johann]

I had same problem.. i had blue probes with my dt200.. and could only meassure -170. now i have some yellow probes i can meassure -192 :D so the probes aint good!

For £70 they could have at least provide decent probes

[Waus-mod]

For £70 they could have at least provide decent probes

yes youre right..... but when you look into the uei page you see they only have probes that will do -40. so you cant blaim them. Otherwise i bought the dt from bes in uk and i think they put the probes into the package and not uei!

So buy some fluke probes or probes that are good for -200 and youre done :)

[johann]

yes youre right..... but when you look into the uei page you see they only have probes that will do -40. so you cant blaim them. Otherwise i bought the dt from bes in uk and i think they put the probes into the package and not uei!

So buy some fluke probes or probes that are good for -200 and youre done :)

Im getting 1 probe from Gray to test it, then I will buy more :)

[Comp-Freak]

Anyone got a good address to buy probes?

[PoL]

Yes, the UEI probes and the ones that came with the thermometer you see in the pictures I posted in the page before, are told to work til -40º.
But both read -195º (more or less) with both thermometers in LN2. :toast:

[Marvin]

Here the probes worked under -40 C. I think they lost accuracy, but they read under low temps.

[Marvin]

The temps :

[Marvin]

Crappy Uei, a month ago ,4 months after buying from chilly, the thermometer became completely crazy. Even without probes inserted, it reads wrong temperatures.Also, change the battery, and tested with new probes :
http://www.forumpcs.com.br/galeria/albums/userpics/10827/normal_22-06-06_0914.jpg

[Xeon th MG Pony]

sounds like the Transisters they use for the current mirror have a huge temp swing, if some one where to find the cluster and insulate the one half of the mirror it may solve that issue or add filter caps to the end of the power rail if they haven't.

[ak_47_boy]

Is there no calibration pot inside? I would have thought there would be one...

[jinu117]

Crappy Uei, a month ago ,4 months after buying from chilly, the thermometer became completely crazy. Even without probes inserted, it reads wrong temperatures.Also, change the battery, and tested with new probes :
http://www.forumpcs.com.br/galeria/albums/userpics/10827/normal_22-06-06_0914.jpg

RMA :)

[jinu117]

RMA :)

Oh and probes... it doesn't matter. it is more of UEI caliberation inside that gets massed up it seems.

[Marvin]

RMA :)
I will wait chilly´s reply, i bought from him, without any paper or order...

[froudeg]

Ice bath calibrations have always had little meaning to me.

No thermal probe, beit a thermocouple, thermistor, or RTD sensor has a linear relationship with temperature. Just because its accurate at 0 celcius, doesn't means its accurate at -100 or +100 celcius.

Thermocouple accuracy at lower temp's is greatly determined by the resolution and noise performance of the signal conditioning and a/d circuitry. The cold junction reference is also critical in thermocouple accuracy - cheaper thermocouple meters don't use a proper isothermal block, with an accurate RTD sensor....but instead rely on a simple thermisitor stuck on the pcb near the connectors. This can skew results by a degree or more.

Also the linearisation algorithm's used by the microcontrollers/control chips can have a big impact on accuracy across the range.

The same applies to thermisitors and RTD's. For thermisitors and RTD's, the initial accuracy of the probe also plays a significant part in the overall accuracy.

I've not trusted DT200 temperatures, neither do i trust most other thermocouple thermometers. I've seen some serious inaccuracies in various thermometers.....the only thing i trust is a fluke - and then one that aint old, whose calibration is shot.

[Ssilencer]

Totally agree. it is almost impossible that all the different thermometer from dif brands, and dif probe behaves the same at all the temperature range. There always be at least a small difference in measures

[froudeg]

sounds like the Transisters they use for the current mirror have a huge temp swing, if some one where to find the cluster and insulate the one half of the mirror it may solve that issue or add filter caps to the end of the power rail if they haven't.

Thermocouple circuits don't directly use current mirrors (constant current generators) for the thermocouple sensing - current mirrors are used in thermisitor and RTD circuits. However depending on what they have used for the cold junction compensation, a current mirror may have been deployed for that.

It's unlikely this would be a discrete solution anyway, any meter worth its salt would never use discrete transistors for their CC generator, it's more likely thats integrated into a A/D chip designed for signal conditioning, or if it is seperate it would probably be a dedicated chip or an opamp solution.

Also a K-type probe rating doesnt mean it wont work colder than what its rated, it just means it has not been tested for colder than that, and the initial accuracy of the probe is not accurate enough for extremely low temperatures (as the temperature drops, the output voltage drops with it - and the zero offset error of the probe can be become significant)

[froudeg]

probes can be faulty, also you need to get a probe with the correct range, They make K probes to -200 they are just more expensive. The plug doesn't matter,its just some are molded on .

The plug's do matter to some extent. They can contribute to zero offset errors, depending on what metals are used for the contacts and how well they thermally connect to the meter and its isothermal block (if present).

[Gray Mole]

Well I'm certainly not impressed with the way this UEI I have works.

It's decent and all that, but with 2 probes it's incredibly inaccurate no matter what probes are used.

-40 is -25 when you have 2 probes connected.

I may RMA if I can find the time, I just haven't bothered as I really don't and it still works well enough to get the job done. Would just be nice to have the dual input work the way it should.

Next one will likely be another fluke, maybe a 52-II or something.

I was looking at the 4 probe logging Voltcraft for evap testing but lately I haven't had the time to get into the full testing I'd like to do, and after this UEI I'm hesitant to buy anything other than another Fluke.

Cheers

Gray

[froudeg]

Yep ya can't beat a fluke for accuracy and more importantly repeatability.

They cost a bunch, but they can be trusted...which is more than i can say for the UEI's!

[Xeon th MG Pony]

Ya I thought about the current mirror and referencing unit being in a single chip after submitting lol Ah well haven't don any low level stuff in a long time, getting rusty lol In fact I'm thinking of tossing all my horded parts for it, but not sure, it's hard to let go of the PCB parts pile

[johann]

I bought a voltacraft and have never looked back, all in all 10 times better and half the price of the UEI. I get about 3 motnhs battery life from it as opposed to 3 days from the UEI. Temps wise, works great with two probes and never had any problems like the UEI when 2 probes connected.

I have rebuilt systems thinking they are dodgy because of readings from my old UEI