RTD linearization
in [Design]
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From: John Larkin on 14 Dec 2009 19:24 On Mon, 14 Dec 2009 22:54:55 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Mon, 14 Dec 2009 14:40:42 -0800) it happened John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in ><ocfdi55vqof40ba34eu8efe47ntn5vgrqp(a)4ax.com>: > >>But I am an artiste! >> >Are not we all? >Designing is an artistic action. > > >>>And I want to add something to that. >>>All that talk about measuring to .x digits temperature (substitute for 'x' >>>what you had in mind), will really look funny when: >>> The sun shines on your outside sensor, and the temp is all of the sudden 20 degrees to high. >>> Hail falls on it, and starts melting, and it insists it is zero C. >>>Snow, rain, so: >>> You need a very good place, shielded from wind, sun, away from hot walls, >>> other radiating objects, at the correct height. >>> >>>I have been measuring outside temp now for many years, and seen some very funny readings. >> >>I plan to put the outdoor sensor (1K RTD in a plastic tube,\ > >Well, at least you can exchange it anytime for a LM135 in that same circuit, >without needing linearisation, only a software update. > I'm not a big fan of the National LM35 family. They aren't very accurate, have EMI sensitivity, and all the ones I've used have nasty latchup problems. Not a good choice for outdoors at the end of a long cable. Platinum RTDs don't latch up and don't rectify RF and don't oscillate into capacitive loads and are accurate to a fraction of a degree C. John
From: Joerg on 14 Dec 2009 20:30 Nico Coesel wrote: > Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: > >> On a sunny day (Mon, 14 Dec 2009 15:07:57 -0800 (PST)) it happened >> "langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote in >> <58449058-bc64-4418-8392-8ed79dd5023d(a)m25g2000yqc.googlegroups.com>: >> >>>> that wil lgenerate, and how to handle that. >>>> I find this a bit primitive. >>> Here we normally use pt1000 so copper resistance is not such a big >>> issue, and driving it with >>> a current source has caused lots of issues, because the common mode >>> noise rejection sucks >>> when one wire sees ground the other a high impedance current source >>> it is possible to get around it with a much more complex circuit but >>> why bother if you can >>> correct in software >>> >>> -Lasse >> Why not use LM135 or similar? > > A pt1000 element is available in industrial bolt-on versions and no > polarity issues. IOW any fool can install a pt1000 element. > That's what the guys at one shop said. Until I torque'd off a 16mm crane hook ... screeee ... *POP* -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jan Panteltje on 15 Dec 2009 06:43 On a sunny day (Tue, 15 Dec 2009 00:18:56 GMT) it happened nico(a)puntnl.niks (Nico Coesel) wrote in <4b26d588.449188812(a)news.planet.nl>: >Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: > >>On a sunny day (Mon, 14 Dec 2009 15:07:57 -0800 (PST)) it happened >>"langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote in >><58449058-bc64-4418-8392-8ed79dd5023d(a)m25g2000yqc.googlegroups.com>: >> >>>> that wil lgenerate, and how to handle that. >>>> I find this a bit primitive. >>> >>>Here we normally use pt1000 so copper resistance is not such a big >>>issue, and driving it with >>>a current source has caused lots of issues, because the common mode >>>noise rejection sucks >>>when one wire sees ground the other a high impedance current source >>>it is possible to get around it with a much more complex circuit but >>>why bother if you can >>>correct in software >>> >>>-Lasse >> >>Why not use LM135 or similar? > >A pt1000 element is available in industrial bolt-on versions and no >polarity issues. IOW any fool can install a pt1000 element. Yes I know, I have designed input circuit for PT1000. But I actually used constant current. But in many cases you do not need something like a PT1000, I have done industrial temp sensing with a Si diode too... hehe And, usually things like PT1000 are not installed by fools, but qualified technicians. Who know about 4 wire systems for example.
From: Jan Panteltje on 15 Dec 2009 06:44 On a sunny day (Mon, 14 Dec 2009 16:01:08 -0800 (PST)) it happened "langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote in <a46c6326-b414-45a7-8785-1ab60f9ef8af(a)v30g2000yqm.googlegroups.com>: >On 15 Dec., 00:18, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: >> On a sunny day (Mon, 14 Dec 2009 15:07:57 -0800 (PST)) it happened >> "langw...(a)fonz.dk" <langw...(a)fonz.dk> wrote in >> <58449058-bc64-4418-8392-8ed79dd50...(a)m25g2000yqc.googlegroups.com>: >> >> >> >> >On 13 Dec., 18:54, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: >> >> On a sunny day (Sun, 13 Dec 2009 09:28:53 -0800) it happened John Larkin >> >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in >> >> <8k7ai51i2m2us5a8nl49cb0llls0lq4...(a)4ax.com>: >> >> >> >On Sun, 13 Dec 2009 12:20:05 GMT, n...(a)puntnl.niks (Nico Coesel) >> >> >wrote: >> >> >> >>John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> >> >>>On Sat, 12 Dec 2009 12:46:37 -0800, Joerg <inva...(a)invalid.invalid> >> >> >>>wrote: >> >> >> >>>>John Larkin wrote: >> >> >> >>>>> Does anybody remember the value of negative resistance that linearizes >> >> >>>>> a 100 ohm platinum RTD? >> >> >> >>>>No uC at hand for this job? Maybe this helps: >> >> >> >>>>http://pdfserv.maxim-ic.com/en/an/AN3450.pdf >> >> >> >>>>But you don't have to use a Maxim opamp :-) >> >> >> >>>I'm thinking I'll use 1K RTDs for the automation project, and lay out >> >> >>>an interface board... easier than hand wiring. The little RS232 widget >> >> >> >>1k RTDs are easier to interface. I used one to control my floor >> >> >>heating. 2k2 (IIRC) in series from 3.3V and then fed directly into an >> >> >>ADC. In a limited temperature range, the output is quite linear so >> >> >>there is not really a need for fancy math. >> >> >> >I'm thinking along these lines... >> >> >> >ftp://jjlarkin.lmi.net/RTD.jpg >> >> >> >All the 1Ks will be 0.1%. >> >> >> >The opamp will have a gain of about 8, input and output centered on >> >> >+2.5. This should be accurate to a fraction of a degree C, so we'll >> >> >know how to dress. The Z-wave home automation systems have a combined >> >> >motion detector and temperature sensor (no temp-only nodes I know of), >> >> >but I don't trust their accuracy and they only go down to 40F, not >> >> >good for outdoors. >> >> >> >I can run RG174 to the RTDs. No EMI/ESD hazards as with semiconductor >> >> >sensors. >> >> >> >John >> >> >> For a reasonable long cable to the sensor, a 4 wire system with current source would be better. >> >> Else you will have to include the variance of the resistance of the copper, >> >> plus the voltage drop in the cable. >> >> You will also have to take into account cut or shorted cables, and the sort of signals >> >> that wil lgenerate, and how to handle that. >> >> I find this a bit primitive. >> >> >Here we normally use pt1000 so copper resistance is not such a big >> >issue, and driving it with >> >a current source has caused lots of issues, because the common mode >> >noise rejection sucks >> >when one wire sees ground the other a high impedance current source >> >it is possible to get around it with a much more complex circuit but >> >why bother if you can >> >correct in software >> >> >-Lasse >> >> Why not use LM135 or similar? > >might be simpler electrically, but generally the inductrial type >temperature sensors in stainless steel meant to screw into e.g. >pressuretanks pipes etc. are pt1000/pt100 types > >-Lasse True, but this started about J.L's outside temperature sensor for his home automation IIRC.
From: JosephKK on 19 Dec 2009 17:36
On Tue, 15 Dec 2009 11:43:31 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Tue, 15 Dec 2009 00:18:56 GMT) it happened nico(a)puntnl.niks >(Nico Coesel) wrote in <4b26d588.449188812(a)news.planet.nl>: > >>Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >> >>>On a sunny day (Mon, 14 Dec 2009 15:07:57 -0800 (PST)) it happened >>>"langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote in >>><58449058-bc64-4418-8392-8ed79dd5023d(a)m25g2000yqc.googlegroups.com>: >>> >>>>> that wil lgenerate, and how to handle that. >>>>> I find this a bit primitive. >>>> >>>>Here we normally use pt1000 so copper resistance is not such a big >>>>issue, and driving it with >>>>a current source has caused lots of issues, because the common mode >>>>noise rejection sucks >>>>when one wire sees ground the other a high impedance current source >>>>it is possible to get around it with a much more complex circuit but >>>>why bother if you can >>>>correct in software >>>> >>>>-Lasse >>> >>>Why not use LM135 or similar? >> >>A pt1000 element is available in industrial bolt-on versions and no >>polarity issues. IOW any fool can install a pt1000 element. > >Yes I know, I have designed input circuit for PT1000. >But I actually used constant current. >But in many cases you do not need something like a PT1000, >I have done industrial temp sensing with a Si diode too... >hehe >And, usually things like PT1000 are not installed by fools, >but qualified technicians. >Who know about 4 wire systems for example. Give it another few years of immigration and trade unionism. You will be lucky if they ever learn the local language usefully, or much else. |