CA1213672A - Apparatus for detecting a temperature by means of at least one temperature-responsive sensing resistor - Google Patents
Apparatus for detecting a temperature by means of at least one temperature-responsive sensing resistorInfo
- Publication number
- CA1213672A CA1213672A CA000461899A CA461899A CA1213672A CA 1213672 A CA1213672 A CA 1213672A CA 000461899 A CA000461899 A CA 000461899A CA 461899 A CA461899 A CA 461899A CA 1213672 A CA1213672 A CA 1213672A
- Authority
- CA
- Canada
- Prior art keywords
- calibration
- temperature
- voltage drop
- sensing resistor
- resistor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
- G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
- G01K7/18—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer
- G01K7/20—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a linear resistance, e.g. platinum resistance thermometer in a specially-adapted circuit, e.g. bridge circuit
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K17/00—Measuring quantity of heat
- G01K17/06—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device
- G01K17/08—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device based upon measurement of temperature difference or of a temperature
- G01K17/10—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device based upon measurement of temperature difference or of a temperature between an inlet and an outlet point, combined with measurement of rate of flow of the medium if such, by integration during a certain time-interval
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Measuring Temperature Or Quantity Of Heat (AREA)
- Measuring Volume Flow (AREA)
- Measuring And Recording Apparatus For Diagnosis (AREA)
- Details Of Flowmeters (AREA)
Abstract
Abstract An apparatus for detecting a temperature by means of at least one temmerature-responsive sensing resistor (F1,F2) comprise an evaluating circuit which processes a voltage drop depending on the temperature of the sensing resistor. The sensing resistor (F1,F2) lies at a common current source (1) in series with two fixed calibration resistors (G, D). The basic resistor (G) has a lower calibration value (Rel) which is assumed by the sensing resistor at a predetermined lower temperature. The differential resistor (D) has a differential calibration value (Rd) of such a size that the series circuit of the calibration resistors has an upper calibration value (Re2) which the sensing resistor assume at a predetermined higher temperature. The evaluating circuit determines the actual temperature from at least one measurement voltage drop (Vfl, Vf2) with regard to a characteristic calibration curve resulting from at least one calibration value (Rel, Re2, Rd) and the associated calibration voltage drop (Vel, Ve2, Vd). This leads to a very simply constructed apparatus which is easily adjustable.
Fig. 1.
Fig. 1.
Description
1213f~72 26th A~gUEt9 19~3 -~K
DAN~OSS ~S, ~ordborg (Denma~) Apparatu~ fox detectin~ a temperature ~y mean~
of at least one te~per~ture-responsive sensing resistor -The invention relate~ to an apparatus for detecting 2 temperature by mean~ of at least one temperature-responsive sensinæ
resistor and an evaluatin~ circuit which processes a voltag~ drop dependi~g on tha tempera~ur~ of the sens~ng re~istor.
In a known apparatus of this kind, the supply temperature and ~eturn temperæture of a heatin~ i~stzllation are eæch measul~d with a temperat~re-dependent Ie~istor9 A te~peratu~e measule~e~t con~ertar ~r~duoe~ a curr~t signal which ch~nge~ linearly with the te~pe~ature.
It is paYsed thI~ugh a load res~stor at which a ~olta~e drop propo~-tional to the temperature can be t~pped. In addition~ a cu-~rent ~i~nal i~ ~upplied for the flow ~uant~ty 80 that a ~oltæg~ d~op proportional to the flow qu~ntity can be t~pped at a thixd load resl~tor. ~he ~oltage drop~ are su~cessively fed to the e~aluating oircuit by means of a multipl~0r and t.here they are temporarily ~torea after analo~ue-di~ital con~ersion. ~th the aid of a tempera-dependent th~mal co~ffici~nt ~hich can be tapped from a ~tored table, the amount o~ heat transmitted to the ilow quantit~ can be oalcvlated by ~nt~gration, indicated ~nd stored by fo~mi~ thQ
~2136'^~Z
temperature difference and multiplication by the termal coefficient.
~ he temperature measurement converter which is to transmit a CV~ t 9i~lal proportional to the sensor temperature is quite e2pen--~ive. ~lso, ad~ustment is ~omplicated becau~e which two such measurement converters it is necessa~y to adj~st three potentiometers for each. Since the ~esult of the temperature difference contain~ th~
tolerances of ~oth tempera~ure meæsur~ment converters and of bo~h load resistoIs, th~ result can be quite erroneous in the case of small temperature differen¢es.
~ he invention i~ based on the problem Or providin~ an apparatu3 ofthe aforementioned kind in which the desired tQmperztur~ can ~e detected with considera~ly lower expense and adj~stment i~ also ~uch s~mpler.
~ his problem is sol~d according to the inve~tion in that the at least one ~ensing resi~tor lies at a common currest sourcc i~ ~erie3 ~ith two fixed c~3~bratio~ resi3tors, n2mely a basi¢ resistor and a aif~erential resistor, that the basi¢ resistor has a lowex calibratio~
value assumed by the sensing resi6tox at a predetermlned lower t~mperature and the diff~rential resl~tor ha~ a differential calibration valu~ of BUCh a size that the series oircuit of the callbration r2sistors has an upper calibration value assumed by the sensing resi~tor at a predetermined highar t~mperatur~, that a c~libration ~alue storage apparatus is provided, that at least one calibration voltaga drep can ba derived at lea~t at one o~ the ~libxation xesi~-tors or their s~rie~ oircult ~nd a mea~uremant voltage drop can b~
derived at each scn~ing resistor, and that the e~aluating cir~uit .
::
-3- lZ1367Z
dete~nines the actual temperature from at least one measurement voltage drop wi~h ~e~rd to a charact~istic calibration cur~T~ whlch result~ ~rom at least one callbration ValUQ and the associated calibration ~olta~e drop.
In this &rrsngem~nt, one does not require a temperature measur~-ment converter. Instead, a ~ignal inaicativa of the sensor te~peratLre can be obtained dirsctly as a voltage d~op ab the sensin~ resistor.
~y means of a calculation ~ith the ald of the cha,racteri~tic calibr~-tion curve resulting from.the calibration ~oltage drops and the stored calibration Yalues, one obtalns ~e~y accurate ohmio values for the sen~ing resistor, from ~/hich the temperatuxa to be determined is obtalned with a cor,responding accuracy. It ~s suffici~t if initially the ohmic y~lue of the fixed reslstor~ serPlng for calibratlon, i.e.
the calibratio~ Yalue i8 accurately ~tored. In operation, one then obtains 6elf-ad~ustment of the apparatus. Since all the resistor~
are tra~ersea by the same cuxr4nt, especi~lly fluc~uations .~n ~he curr~nt producing t~e ~oltaga d20p8 ar~ immaterial.
Particul~r ad~ant2ges are obtainea ~f temperature aiffer~nGes are to be deteoted in this ~7ay, for example the difference between the æupply and return temperature. In forming the difference, one oalibration resistox is entirely or al~ost entirely eliminated from the calculation ~o that on~y the toler~nce of the other Galibration re~i6tor entexs ths regult, but o~ly at a fxaction of the ~tire tolerane~, n&mely i~ the ratio of the temperature ai~fercnce to the total temperatu~e xæn~e of this calibration I~sistor.
- .
i~3~
1~ a pIoferred em~odiment, the ev~luæting circult deteDmine~
the actual nensor temperature from the actual o~ic value of th~
~eneing xesistor calculated from the formula:
(Vfl V9) Yd ~herein Rfl i9 ~he actual ohmic value o~ the 6ensing ~e~istor, Vfl is the aa~oci~ted mains ~olta~e drop~
Re i8 the lower or upper calibration ~alue, Y~ i3 the as~ociated calibration voltago drop, Rd i8 the dlfferential ca}ibratio~ value or the difference betwee~ ~he upper and lower calibration value and Vd i~ the associated calibration ~oltaæedrop or the s~sociated calibratio~ ~olta6e drop difference.
Ih this w3y, the actual ohmic Yalue of the sensing r~istor i~
obt~ed from tm ~e ~ea~ured ~oltage drop~ and two stored oalibration ~alues. ~ro~ the thus obt ined actu~l ohmic ~alue one ¢an as usual ~alculate th~ temDerature of the sen6ing re~istor even if there i8 no linear relationship betwee~ the sensor temperature and s~nsor res~stance.
In particular, the at leas~ one se~slng xe6~stor c~n therefore be formed by a PI100 rasistor of which th~ resist~nce has a quadratic relationship to the temperature.
In simple ca~es it will be s~f~cient if the evaluatin~ circuit ~etermines the actual t~mperat~re dif~erence from ~he ohmic difference cf two ~ensin~ resistors calculatcd from the formula:
Rfl - Rf2 = (~fl ~ ~f2) Vd whereln .
~5~ ~21367Z
R i~ the actual ohmio value of the fir~t sensing resistor7 Vfl i8 th~ a~ociated measure~ent voltage drop, R~2 i~ the &ctual ohmi¢ value of the second s~n~ing resistor, V~2 i~ the associated measuremsnt voltag~ drop, Rd i9 the differential calibration value or the difference between the upper and lower oalibration value, End Yd i~ the assoc~2tsd ca~bration ~oltage drop or the a~ociatea calibration voltaga drop difference.
~ y reason of the difference formed be~Jeen the a4tual ohmic ~alues of the ~e~ing re~istors, calculation need only take pla~e with the differential calibration ~lue and the associated calibration voltage d~op or their equivalents. mis simplification i8 permissible if the sensing res~stor and the temperature do not have a linear relationship or if aepartures from such linearity do not have a ma~ked lnfluence, particularly in the ¢ase of small temperature dlfference~.
It is reconmended that a multiplexer ~uccessiv~ly Applies to tha ~nput of the evaluating circuit voltage drop tapp~ngs that are ~xo~ided at the re~istors of the ~eries cir¢ult and if the e~aluating ~cuit has an i~termediate store for the~e voltage d~ps. ~he ~easu~ed vo~tage drop~ can therafore be ~ed to the evaluatin~ oirc~it dil~otly ana ~n ~ 91mple mann~.
In an ~paratus in which the e-raluat~ng ¢ircuit comprises an nalo~ue-digital convert.er and a di~ital computer circuit which aaloulates from the dirference be~ween the supply ~ld ret~xn flow temperature of a heat eYoh&~g~r in~t~71ation the measured thL~ugh~low quantity and possibly the a~ount of heat trans~itted to a te~peratv.re-~ependent ther~al coefficient, it i9 advantageG~ if the digltal oomputer circuit al80 czlculates the actual ohmic ~alue~ of` the 6~nsing ~esistors and their con~ersion to te~perature valu~.
~ he invention will now be de~cribed in more detail ~i.th ref-erence to the drawings, wherein:-Pig. 1 ~how~ the ~erie~ ¢ircuit of ~he calibration and ~ensingresi3tors;
~ i~. 2 ls a dingramm~tic repre~entation of an evaluating d rcuit for an apparatus ~or measurlng the amount of hea~ transferrea in the heat exchanBer, and i~g. 3 1~ the ~raph of a characteri~tic calibratio~ cuurre.
According to ~g. 1, a supply sensing resistor Fl ha~ing a temperature-dependent actual ohmi¢ ~alue Rfl and a raturn senæing resi~tor ~2 ha~ing a temperature-dependent aotual ohmic ~alue Rf2 are ~pplied to a common current ~ource 1 in a ~eries circult betw~en two calibration resisto3~, na~ely a basic re~l~tor ~ nnd a differential reæ~stor D. Ihe current I flow ~ g th~oueh the serie~ oircult c~n for e~ample be 1 ~ + 5%. Ihe basic reai~tor has a de~ined ohmio Yalue~
namaly the lowar calibration ~alue Rel which may for example æ~ount to 100 ohm ~0.01~ ~he d~Eexential re~istor ha~ a defined ohm~c ~alue, na~ely th~ direrenti~1 oalibrat~on lralue Rd which may for exæmplo amount to 50 ohm-~ 0.01S~. qhe ~erie~ circuit of the calibration xes1~tors G and D therefore likewise has a defined ohmic ~alue5 namel~
tho upper oal~bration Yalue Re2 wbich therefore amo~mts to 150 ohm. ~e 8~YlSia~ res1stor~ Fl and ~2 ar~ in thi~ embodimen~ PI100 xes~s~or~ 60 , , _7_ ~Z1367Z
that tho lower cc~libration vc~lue R~l corresponds to the QhmlC v~lue of the ~ensing xe~i~tors at 0C ana the upper calib~ation value Re2 corresponds to the ohmic ~alue of th~ ~ensing re~istoIs at a~out 130C.
.~en the current I is flo~ng~ mea3urement voltage dxops Vfl or V~2 cc~ be tapped at the sen6ing re~istor~ ~1 or F29 r~spectivel~. ~t tho calibration res~sto~ G ana D or their series circult one can tap the cali~xation ~oltc~ge drOpE Vel or ~d or ~e2. ~n operatio~l9 however, no more tha~ two of the~e ca~ratlon voltags drops are required bec~u~e the third calibration voltc~ge ~rop cc~n be cc~culat~d therefrom.
~ i8 ~:hOWrl ill ~g- 2, the inputs 2 of a multiple~{er ~ have applied to them the a~orementioncd c~libration voltc~ge drops ~el c~nd Ve2~ the measure~ent volta~e drops Vfl ~nd Vf~, as w~ll a3 a th~OU~l-flo~ ~oltags drop Vq corresponding to tne ~low throu~h tho heat e~chan~ar in~tallatio~ and a calibration volt~g~ dr~p Ve3 which effect~ its oalibration. ~he ~put~ 2 ~ con~ecutively scanned unde the ~nflusn~e of an address~ng s~gnal supplied by way of a control lr,put 4. ~br ~x?~pl~ the mea~urem~nt and throu~h~low voltage drop3 Vfl~ V~2 and Vq are led at least onca per second and thc oth~r calibration ~olta~ drop~ rel, Va2 and Ve3 pp ~econd~ to the output 5 of the multiplexex ~. Ihis output 5 i99 po3sibly by ~ay of an ampl~ier ~rot sho~m)~ conalected to a~ analogue~
digltal convorter 6, ln the 3~mpl~t ca5e a ~ol~aga-dependeI~t o~cillator which tr~ns~.tY the corra~pollding di~ital ~ al~ by ~ay of ~ optoooupler 7 to tho computgr circult 8 of a microp~ces~,or 9. '.'~c -8- lZ13~7Z
mloroproces~or al~o produces the aadressLn~ ~ignals for the ~ltipie~er 3 which ~re tx-~nsmitted to itS cont~ol input 4 by way of a furthe~
optocoupler 10. ~hu ~icroproces~or 9 compxises dif~erer.t ~tora~e ~ones, ~or exanple an inter~ediate ~tore ll ~or the intex~ediate ~tora~e of the digitalised si~nals Eupplied by way of the multiplexer 3 ana a ~tore 12 having an input 13 by way of which so~e or all calibration ~alues R~l~ Re2 or Rd can be introduc~d. ~y means of the optocouplers 7 and 10 the in~ut ~tage of the thus formed e~raluat~
ir~g cir~uit 14 is ~alvanically sep2rated from the ~e~t of the appllance. ~he microp~ocesgor 9 a180 ha3 a time base 15 ~7hich i~, ~r example, provided with a ve~y accuratel~ operative c~stal.
An a~pli~ce 17 connected to sn out~ut 15 of the m~croproce~or 9 compri~es two ~ech~ical counter~ 17 and 18 as well as an indicat~n~
app~ratus 19. The counter 17 for exa~ple continuously 6u~ates the tbroug~flow _nd the oou~ter 18 the smount of heat. Ihe indicating dpparatus 19 c_n ~e ~witched to dif~erent values wlth the P~d o~
change-over switche~ 20, for example to ~upply temperature, s~tu~n temperatur~, dsfferential temperature, minimum differential ~emperP.-ture, throu~hflow qu~ntit~, liniting scale Yalue of the thx~ughput, ~mount of heat and the like.
A further output ~ is conneoted to a digital-ana~o~uo con~aIter 22 to the output 23 of which ther~ ~ay be transmitted ps~ogrzmmable ~rrent ~i~n~ls; fox e~a~ple oonce~in~ the ~mount o~ heat, the ths~ughflow quantity, the supply flow temperature, the ret~rn flow temper~ur~ ox the diff~rent~21 tem~eratur~. lhe current output c~m fbx example ~ for~ed by an impre~sed current 8ignal of 4 to 20 ~A.
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~ noth~r output 24 of the microprocessor 9 leads to a ~lurality o~ optocouplers 25, 26, 27 and 28. Ihe optoco~pler 25 transmit~
pulse~ in synchro~m with ths counter 17, i.e. the thxoughflow quantity, and tha optocoupler 26 transmit3 pulses in gynchronism with the counter 18, i.e. th~ amou~t of heat. The optocoupler 27 can for example træns~it an alar~ if the differential t~mperatul~ is lewer th~n the eet mininum differ~nti~l temperature. Ihe optocoupler 28 can transmit an ~rror signP-l, for example ~n dependence on ~n error 8ienal, a failure in the current and the like.
A plurality of ~ett~ng switche~ 29 ~er~e~ to ~et the heat m~a~uring apparz~u3 to different ~pplioation~- ~br example, one oan ~et the min~mum dif~erential temperature, the c~rxent outpv.t in the aigltal-analogue co~verter 22 or the ~ltiplication factor for ~he counters 17 and 18. Four change-over switches 30 for binary coded dec~7 aigits permit the t~m~al zone of the t~ ou~flow quænt~ty sc~le to b~ set from 0 to 9999 m3~ .
~ ig. 3 ~how~ the ohmic value or c~libration value R a~air.st the ~oltage drop V. m e illustrat~d characteristio curve K is o~tained, a~ i~ sho~ by th~ entered parti~ularst ~hen two of thepQi~ of cal~bration values R~l/Vl or R~,~V2 or Rd ~ d ar~ enteIed. If, in addition, th~ measurement ~olta~e drops Vf1 or Yf2 are knolm, the a~sociated ohmlc valua Rfl or R~2 ~ the sensing r~si~tors ~1 or ~2 can bo oalculated without difficult3r. If the ch~racteristic curve vs~es throug~ some exte:~nal in`luenc~ uch as æ chan.~e in the current;
I, th~ ohmic v&lu~s~ of the ~en~ilg res:lstors n~vertheles~ retain th~
correct v~lue.
. .
~Z~367'2 i3y way of e~ ple~ one ca71 ~orm from the clata ~ve~l in ~g, 3 ~he following e~uation conco~ ng the gradient of the characteristic cu~
R~ ~ Rd ~ ~ ) ~ hrou,~h a ~imple co~Yersion, thi{l give~ tho equation of claim 2.
~ en ~ ; a difference, one can &lso fo~ulate L;he follow-~n~ equation _ fl Rf2 ~ Ra '2) fl Vfl vd ~ i.~ pe~ts on0 to derive ths equatlon of c~a~m 4.
W~en fonn~ng a c~fference, the~rore, lt i8 now onl the ~adicnt of th~ characteristic cur~e ~ that i8 important ~nd for thif~
c~nly the differe~tia' reeistor D m~t b~ monitorea. q~e ba~ic resistor G has been eliminatea. Consequently it i~ only ths tolerancc o~ the ~er~n~ial resi~tor D that must b~ ~aXe~2 in'Go account and ev~m this onl~ i~ the ra1;io of the dif~.erence oï tne m~ure~cnt voltaga drops ~ Vr~ to tha oalibxation volt~e dxop ~rd at the dif~r~ntial re~istor.
I~, for ex~mp~e, the differential calibxation ~ ue in a ~1100 resistor is 50 ohm ~ 0.01 ~' ~d the differential zone ~oe~ ~ro O to 130Ct the~ 1C co~c:3ponds to about 330 millios~. Tne tot~l tolora~ce of the differential xG~l~.tor D ~mounts to - 5 ~illi.on~ .is corresponds to 0.013C with a l~O~C differenc~. ~.e aCcux~o~Y ~er l~C of the difference is th~refore O.OC~01C~ No m~ed elrors th~ ore occur e~en wîth ~-exy small tempera~re difference~.
qhe ap~ar~tus as ~e^cr~bed c~n also be used for other purpos~s than te~per~ture ;e~sure~.e-n~9 for ~x~ple to ~nonitor or re~lzte pxoce3se~ in ma~ t~me a~d industrial .;mstall~tions.
It i~ al~o possible to use dif~ere~t temperat~re-depsndent resistors, for exa~ple nicl;el sensors.
~ ~..
DAN~OSS ~S, ~ordborg (Denma~) Apparatu~ fox detectin~ a temperature ~y mean~
of at least one te~per~ture-responsive sensing resistor -The invention relate~ to an apparatus for detecting 2 temperature by mean~ of at least one temperature-responsive sensinæ
resistor and an evaluatin~ circuit which processes a voltag~ drop dependi~g on tha tempera~ur~ of the sens~ng re~istor.
In a known apparatus of this kind, the supply temperature and ~eturn temperæture of a heatin~ i~stzllation are eæch measul~d with a temperat~re-dependent Ie~istor9 A te~peratu~e measule~e~t con~ertar ~r~duoe~ a curr~t signal which ch~nge~ linearly with the te~pe~ature.
It is paYsed thI~ugh a load res~stor at which a ~olta~e drop propo~-tional to the temperature can be t~pped. In addition~ a cu-~rent ~i~nal i~ ~upplied for the flow ~uant~ty 80 that a ~oltæg~ d~op proportional to the flow qu~ntity can be t~pped at a thixd load resl~tor. ~he ~oltage drop~ are su~cessively fed to the e~aluating oircuit by means of a multipl~0r and t.here they are temporarily ~torea after analo~ue-di~ital con~ersion. ~th the aid of a tempera-dependent th~mal co~ffici~nt ~hich can be tapped from a ~tored table, the amount o~ heat transmitted to the ilow quantit~ can be oalcvlated by ~nt~gration, indicated ~nd stored by fo~mi~ thQ
~2136'^~Z
temperature difference and multiplication by the termal coefficient.
~ he temperature measurement converter which is to transmit a CV~ t 9i~lal proportional to the sensor temperature is quite e2pen--~ive. ~lso, ad~ustment is ~omplicated becau~e which two such measurement converters it is necessa~y to adj~st three potentiometers for each. Since the ~esult of the temperature difference contain~ th~
tolerances of ~oth tempera~ure meæsur~ment converters and of bo~h load resistoIs, th~ result can be quite erroneous in the case of small temperature differen¢es.
~ he invention i~ based on the problem Or providin~ an apparatu3 ofthe aforementioned kind in which the desired tQmperztur~ can ~e detected with considera~ly lower expense and adj~stment i~ also ~uch s~mpler.
~ his problem is sol~d according to the inve~tion in that the at least one ~ensing resi~tor lies at a common currest sourcc i~ ~erie3 ~ith two fixed c~3~bratio~ resi3tors, n2mely a basi¢ resistor and a aif~erential resistor, that the basi¢ resistor has a lowex calibratio~
value assumed by the sensing resi6tox at a predetermlned lower t~mperature and the diff~rential resl~tor ha~ a differential calibration valu~ of BUCh a size that the series oircuit of the callbration r2sistors has an upper calibration value assumed by the sensing resi~tor at a predetermined highar t~mperatur~, that a c~libration ~alue storage apparatus is provided, that at least one calibration voltaga drep can ba derived at lea~t at one o~ the ~libxation xesi~-tors or their s~rie~ oircult ~nd a mea~uremant voltage drop can b~
derived at each scn~ing resistor, and that the e~aluating cir~uit .
::
-3- lZ1367Z
dete~nines the actual temperature from at least one measurement voltage drop wi~h ~e~rd to a charact~istic calibration cur~T~ whlch result~ ~rom at least one callbration ValUQ and the associated calibration ~olta~e drop.
In this &rrsngem~nt, one does not require a temperature measur~-ment converter. Instead, a ~ignal inaicativa of the sensor te~peratLre can be obtained dirsctly as a voltage d~op ab the sensin~ resistor.
~y means of a calculation ~ith the ald of the cha,racteri~tic calibr~-tion curve resulting from.the calibration ~oltage drops and the stored calibration Yalues, one obtalns ~e~y accurate ohmio values for the sen~ing resistor, from ~/hich the temperatuxa to be determined is obtalned with a cor,responding accuracy. It ~s suffici~t if initially the ohmic y~lue of the fixed reslstor~ serPlng for calibratlon, i.e.
the calibratio~ Yalue i8 accurately ~tored. In operation, one then obtains 6elf-ad~ustment of the apparatus. Since all the resistor~
are tra~ersea by the same cuxr4nt, especi~lly fluc~uations .~n ~he curr~nt producing t~e ~oltaga d20p8 ar~ immaterial.
Particul~r ad~ant2ges are obtainea ~f temperature aiffer~nGes are to be deteoted in this ~7ay, for example the difference between the æupply and return temperature. In forming the difference, one oalibration resistox is entirely or al~ost entirely eliminated from the calculation ~o that on~y the toler~nce of the other Galibration re~i6tor entexs ths regult, but o~ly at a fxaction of the ~tire tolerane~, n&mely i~ the ratio of the temperature ai~fercnce to the total temperatu~e xæn~e of this calibration I~sistor.
- .
i~3~
1~ a pIoferred em~odiment, the ev~luæting circult deteDmine~
the actual nensor temperature from the actual o~ic value of th~
~eneing xesistor calculated from the formula:
(Vfl V9) Yd ~herein Rfl i9 ~he actual ohmic value o~ the 6ensing ~e~istor, Vfl is the aa~oci~ted mains ~olta~e drop~
Re i8 the lower or upper calibration ~alue, Y~ i3 the as~ociated calibration voltago drop, Rd i8 the dlfferential ca}ibratio~ value or the difference betwee~ ~he upper and lower calibration value and Vd i~ the associated calibration ~oltaæedrop or the s~sociated calibratio~ ~olta6e drop difference.
Ih this w3y, the actual ohmic Yalue of the sensing r~istor i~
obt~ed from tm ~e ~ea~ured ~oltage drop~ and two stored oalibration ~alues. ~ro~ the thus obt ined actu~l ohmic ~alue one ¢an as usual ~alculate th~ temDerature of the sen6ing re~istor even if there i8 no linear relationship betwee~ the sensor temperature and s~nsor res~stance.
In particular, the at leas~ one se~slng xe6~stor c~n therefore be formed by a PI100 rasistor of which th~ resist~nce has a quadratic relationship to the temperature.
In simple ca~es it will be s~f~cient if the evaluatin~ circuit ~etermines the actual t~mperat~re dif~erence from ~he ohmic difference cf two ~ensin~ resistors calculatcd from the formula:
Rfl - Rf2 = (~fl ~ ~f2) Vd whereln .
~5~ ~21367Z
R i~ the actual ohmio value of the fir~t sensing resistor7 Vfl i8 th~ a~ociated measure~ent voltage drop, R~2 i~ the &ctual ohmi¢ value of the second s~n~ing resistor, V~2 i~ the associated measuremsnt voltag~ drop, Rd i9 the differential calibration value or the difference between the upper and lower oalibration value, End Yd i~ the assoc~2tsd ca~bration ~oltage drop or the a~ociatea calibration voltaga drop difference.
~ y reason of the difference formed be~Jeen the a4tual ohmic ~alues of the ~e~ing re~istors, calculation need only take pla~e with the differential calibration ~lue and the associated calibration voltage d~op or their equivalents. mis simplification i8 permissible if the sensing res~stor and the temperature do not have a linear relationship or if aepartures from such linearity do not have a ma~ked lnfluence, particularly in the ¢ase of small temperature dlfference~.
It is reconmended that a multiplexer ~uccessiv~ly Applies to tha ~nput of the evaluating circuit voltage drop tapp~ngs that are ~xo~ided at the re~istors of the ~eries cir¢ult and if the e~aluating ~cuit has an i~termediate store for the~e voltage d~ps. ~he ~easu~ed vo~tage drop~ can therafore be ~ed to the evaluatin~ oirc~it dil~otly ana ~n ~ 91mple mann~.
In an ~paratus in which the e-raluat~ng ¢ircuit comprises an nalo~ue-digital convert.er and a di~ital computer circuit which aaloulates from the dirference be~ween the supply ~ld ret~xn flow temperature of a heat eYoh&~g~r in~t~71ation the measured thL~ugh~low quantity and possibly the a~ount of heat trans~itted to a te~peratv.re-~ependent ther~al coefficient, it i9 advantageG~ if the digltal oomputer circuit al80 czlculates the actual ohmic ~alue~ of` the 6~nsing ~esistors and their con~ersion to te~perature valu~.
~ he invention will now be de~cribed in more detail ~i.th ref-erence to the drawings, wherein:-Pig. 1 ~how~ the ~erie~ ¢ircuit of ~he calibration and ~ensingresi3tors;
~ i~. 2 ls a dingramm~tic repre~entation of an evaluating d rcuit for an apparatus ~or measurlng the amount of hea~ transferrea in the heat exchanBer, and i~g. 3 1~ the ~raph of a characteri~tic calibratio~ cuurre.
According to ~g. 1, a supply sensing resistor Fl ha~ing a temperature-dependent actual ohmi¢ ~alue Rfl and a raturn senæing resi~tor ~2 ha~ing a temperature-dependent aotual ohmic ~alue Rf2 are ~pplied to a common current ~ource 1 in a ~eries circult betw~en two calibration resisto3~, na~ely a basic re~l~tor ~ nnd a differential reæ~stor D. Ihe current I flow ~ g th~oueh the serie~ oircult c~n for e~ample be 1 ~ + 5%. Ihe basic reai~tor has a de~ined ohmio Yalue~
namaly the lowar calibration ~alue Rel which may for example æ~ount to 100 ohm ~0.01~ ~he d~Eexential re~istor ha~ a defined ohm~c ~alue, na~ely th~ direrenti~1 oalibrat~on lralue Rd which may for exæmplo amount to 50 ohm-~ 0.01S~. qhe ~erie~ circuit of the calibration xes1~tors G and D therefore likewise has a defined ohmic ~alue5 namel~
tho upper oal~bration Yalue Re2 wbich therefore amo~mts to 150 ohm. ~e 8~YlSia~ res1stor~ Fl and ~2 ar~ in thi~ embodimen~ PI100 xes~s~or~ 60 , , _7_ ~Z1367Z
that tho lower cc~libration vc~lue R~l corresponds to the QhmlC v~lue of the ~ensing xe~i~tors at 0C ana the upper calib~ation value Re2 corresponds to the ohmic ~alue of th~ ~ensing re~istoIs at a~out 130C.
.~en the current I is flo~ng~ mea3urement voltage dxops Vfl or V~2 cc~ be tapped at the sen6ing re~istor~ ~1 or F29 r~spectivel~. ~t tho calibration res~sto~ G ana D or their series circult one can tap the cali~xation ~oltc~ge drOpE Vel or ~d or ~e2. ~n operatio~l9 however, no more tha~ two of the~e ca~ratlon voltags drops are required bec~u~e the third calibration voltc~ge ~rop cc~n be cc~culat~d therefrom.
~ i8 ~:hOWrl ill ~g- 2, the inputs 2 of a multiple~{er ~ have applied to them the a~orementioncd c~libration voltc~ge drops ~el c~nd Ve2~ the measure~ent volta~e drops Vfl ~nd Vf~, as w~ll a3 a th~OU~l-flo~ ~oltags drop Vq corresponding to tne ~low throu~h tho heat e~chan~ar in~tallatio~ and a calibration volt~g~ dr~p Ve3 which effect~ its oalibration. ~he ~put~ 2 ~ con~ecutively scanned unde the ~nflusn~e of an address~ng s~gnal supplied by way of a control lr,put 4. ~br ~x?~pl~ the mea~urem~nt and throu~h~low voltage drop3 Vfl~ V~2 and Vq are led at least onca per second and thc oth~r calibration ~olta~ drop~ rel, Va2 and Ve3 pp ~econd~ to the output 5 of the multiplexex ~. Ihis output 5 i99 po3sibly by ~ay of an ampl~ier ~rot sho~m)~ conalected to a~ analogue~
digltal convorter 6, ln the 3~mpl~t ca5e a ~ol~aga-dependeI~t o~cillator which tr~ns~.tY the corra~pollding di~ital ~ al~ by ~ay of ~ optoooupler 7 to tho computgr circult 8 of a microp~ces~,or 9. '.'~c -8- lZ13~7Z
mloroproces~or al~o produces the aadressLn~ ~ignals for the ~ltipie~er 3 which ~re tx-~nsmitted to itS cont~ol input 4 by way of a furthe~
optocoupler 10. ~hu ~icroproces~or 9 compxises dif~erer.t ~tora~e ~ones, ~or exanple an inter~ediate ~tore ll ~or the intex~ediate ~tora~e of the digitalised si~nals Eupplied by way of the multiplexer 3 ana a ~tore 12 having an input 13 by way of which so~e or all calibration ~alues R~l~ Re2 or Rd can be introduc~d. ~y means of the optocouplers 7 and 10 the in~ut ~tage of the thus formed e~raluat~
ir~g cir~uit 14 is ~alvanically sep2rated from the ~e~t of the appllance. ~he microp~ocesgor 9 a180 ha3 a time base 15 ~7hich i~, ~r example, provided with a ve~y accuratel~ operative c~stal.
An a~pli~ce 17 connected to sn out~ut 15 of the m~croproce~or 9 compri~es two ~ech~ical counter~ 17 and 18 as well as an indicat~n~
app~ratus 19. The counter 17 for exa~ple continuously 6u~ates the tbroug~flow _nd the oou~ter 18 the smount of heat. Ihe indicating dpparatus 19 c_n ~e ~witched to dif~erent values wlth the P~d o~
change-over switche~ 20, for example to ~upply temperature, s~tu~n temperatur~, dsfferential temperature, minimum differential ~emperP.-ture, throu~hflow qu~ntit~, liniting scale Yalue of the thx~ughput, ~mount of heat and the like.
A further output ~ is conneoted to a digital-ana~o~uo con~aIter 22 to the output 23 of which ther~ ~ay be transmitted ps~ogrzmmable ~rrent ~i~n~ls; fox e~a~ple oonce~in~ the ~mount o~ heat, the ths~ughflow quantity, the supply flow temperature, the ret~rn flow temper~ur~ ox the diff~rent~21 tem~eratur~. lhe current output c~m fbx example ~ for~ed by an impre~sed current 8ignal of 4 to 20 ~A.
-9- lZ1367Z
~ noth~r output 24 of the microprocessor 9 leads to a ~lurality o~ optocouplers 25, 26, 27 and 28. Ihe optoco~pler 25 transmit~
pulse~ in synchro~m with ths counter 17, i.e. the thxoughflow quantity, and tha optocoupler 26 transmit3 pulses in gynchronism with the counter 18, i.e. th~ amou~t of heat. The optocoupler 27 can for example træns~it an alar~ if the differential t~mperatul~ is lewer th~n the eet mininum differ~nti~l temperature. Ihe optocoupler 28 can transmit an ~rror signP-l, for example ~n dependence on ~n error 8ienal, a failure in the current and the like.
A plurality of ~ett~ng switche~ 29 ~er~e~ to ~et the heat m~a~uring apparz~u3 to different ~pplioation~- ~br example, one oan ~et the min~mum dif~erential temperature, the c~rxent outpv.t in the aigltal-analogue co~verter 22 or the ~ltiplication factor for ~he counters 17 and 18. Four change-over switches 30 for binary coded dec~7 aigits permit the t~m~al zone of the t~ ou~flow quænt~ty sc~le to b~ set from 0 to 9999 m3~ .
~ ig. 3 ~how~ the ohmic value or c~libration value R a~air.st the ~oltage drop V. m e illustrat~d characteristio curve K is o~tained, a~ i~ sho~ by th~ entered parti~ularst ~hen two of thepQi~ of cal~bration values R~l/Vl or R~,~V2 or Rd ~ d ar~ enteIed. If, in addition, th~ measurement ~olta~e drops Vf1 or Yf2 are knolm, the a~sociated ohmlc valua Rfl or R~2 ~ the sensing r~si~tors ~1 or ~2 can bo oalculated without difficult3r. If the ch~racteristic curve vs~es throug~ some exte:~nal in`luenc~ uch as æ chan.~e in the current;
I, th~ ohmic v&lu~s~ of the ~en~ilg res:lstors n~vertheles~ retain th~
correct v~lue.
. .
~Z~367'2 i3y way of e~ ple~ one ca71 ~orm from the clata ~ve~l in ~g, 3 ~he following e~uation conco~ ng the gradient of the characteristic cu~
R~ ~ Rd ~ ~ ) ~ hrou,~h a ~imple co~Yersion, thi{l give~ tho equation of claim 2.
~ en ~ ; a difference, one can &lso fo~ulate L;he follow-~n~ equation _ fl Rf2 ~ Ra '2) fl Vfl vd ~ i.~ pe~ts on0 to derive ths equatlon of c~a~m 4.
W~en fonn~ng a c~fference, the~rore, lt i8 now onl the ~adicnt of th~ characteristic cur~e ~ that i8 important ~nd for thif~
c~nly the differe~tia' reeistor D m~t b~ monitorea. q~e ba~ic resistor G has been eliminatea. Consequently it i~ only ths tolerancc o~ the ~er~n~ial resi~tor D that must b~ ~aXe~2 in'Go account and ev~m this onl~ i~ the ra1;io of the dif~.erence oï tne m~ure~cnt voltaga drops ~ Vr~ to tha oalibxation volt~e dxop ~rd at the dif~r~ntial re~istor.
I~, for ex~mp~e, the differential calibxation ~ ue in a ~1100 resistor is 50 ohm ~ 0.01 ~' ~d the differential zone ~oe~ ~ro O to 130Ct the~ 1C co~c:3ponds to about 330 millios~. Tne tot~l tolora~ce of the differential xG~l~.tor D ~mounts to - 5 ~illi.on~ .is corresponds to 0.013C with a l~O~C differenc~. ~.e aCcux~o~Y ~er l~C of the difference is th~refore O.OC~01C~ No m~ed elrors th~ ore occur e~en wîth ~-exy small tempera~re difference~.
qhe ap~ar~tus as ~e^cr~bed c~n also be used for other purpos~s than te~per~ture ;e~sure~.e-n~9 for ~x~ple to ~nonitor or re~lzte pxoce3se~ in ma~ t~me a~d industrial .;mstall~tions.
It i~ al~o possible to use dif~ere~t temperat~re-depsndent resistors, for exa~ple nicl;el sensors.
~ ~..
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for detecting temperature by means of at least one temperature-responsive sensing resistor and a signal processing circuit responsive to a voltage drop variable with the temperature of the sensing resistor, characterised in that at least one sensing resistor (F1, F2) is connected to a common current source (1) in series with two fixed calibration resistors, including a basic resistor (G) and a differential resistor (D), with the basic resistor having a lower calibration value (Re1) corresponding to that of the sensing resistor at a predetermined lower temperature and the differential resistor has a differential calibration value (Rd) of such value that the series circuit of the calibration resistors has an upper calibration value (Re2) corresponding to that of the sensing resistor at a predetermined higher temperature, further including calibration value storage apparatus (12), so that at least one calibration voltage drop (Ve1, Ve2, Vd) can be derived from at least one of the cali-bration resistors or their series circuit and a measurement voltage drop (Vf1, Vf2) can be derived at each sensing resistor, and the evaluating circuit (14) determines the actual temperature from at least one measurement voltage drop with regard to a characteristic calibration curve (K) based on at least one calibration value and the associated calibration voltage drop.
2. Apparatus according to claim 1, characterised in that the evaluating circuit (14) determines the actual sensor temperature from the aotual ohmic value of the sensing resistor (F1) calculated from the formula wherein Rf1 is the actual ohmic value of the sensing resistor, Vf1 is the associated mains voltage drop, Re is the lower or upper calibration value, Ve is the associated calibration voltage drop, Rd is the differential calibration value or the difference between the upper and lower calibration value and Vd is the associated calibration voltage drop or the associated calibration voltage drop difference.
3. Apparatus according to claim 2, characterised in that the at least one sensing resistor (F1, F2) is a PT100 resistor.
4. Apparatus according to claim 1, characterised in that the evaluating circuit (14) determines the actual temperature difference from the ohmic difference of two sensing resistors (F1, F2) calculated from the formula wherein Rf1 is the actual ohmic value of the first sensing resistor, Vf1 is the associated measurement voltage drop, Rf2 is the actual ohmic value of the second sensing resistor, Vf2 is the associated measurement voltage drop, Rd is the differential calibration value or the difference between the upper and lower calibration value, and Vd is the associated calibration voltage drop or the associated calibration voltage drop difference.
5. Apparatus according to one of claims 1 to 3 characterised in that a multiplexer (3) successively applies to the input of the evaluating circuit (14) voltage drop tappings provided at the resistors (G, D, F1, F2) of the series circuit and the evaluating circuit has an intermediate store (11) for these voltage drops.
6. Apparatus according to one of claims 1 to 3 in which the evaluating circuit comprises an analogue-digital converter and a digital computer circuit which calculates from the difference between the supply and return temperature of a heat exchanger installation the amount of heat transmitted to the flow medium and possibly to a temperature-dependent thermal coefficient, characterised in that the digital computer circuit (8) also carries out the calculation of the actual ohmic values of the sensing resistors (F1, F2) and their conversion to temperature values.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3330915.9 | 1983-08-27 | ||
| DE19833330915 DE3330915C2 (en) | 1983-08-27 | 1983-08-27 | Device for determining a temperature value by means of at least one temperature-dependent sensor resistor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1213672A true CA1213672A (en) | 1986-11-04 |
Family
ID=6207574
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000461899A Expired CA1213672A (en) | 1983-08-27 | 1984-08-27 | Apparatus for detecting a temperature by means of at least one temperature-responsive sensing resistor |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS6071925A (en) |
| CA (1) | CA1213672A (en) |
| DE (1) | DE3330915C2 (en) |
| DK (1) | DK163610C (en) |
| SE (1) | SE8403843L (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3808475A1 (en) * | 1988-03-14 | 1989-10-19 | Friedhelm Meyer | Method and device to measure a temperature |
| DE19637561C1 (en) * | 1996-09-14 | 1998-02-26 | Dienes Apparatebau Gmbh | Sensorless temperature control of a heating device |
| FR2874692B1 (en) * | 2004-08-27 | 2006-10-13 | Actaris Sas Soc Par Actions Si | DEVICE FOR MEASURING TEMPERATURE IN A THERMAL ENERGY COUNTER |
| DE102005029319A1 (en) * | 2005-06-24 | 2006-12-28 | Abb Patent Gmbh | Circuit arrangement, for determining temperature difference between two sensors, has digital microprocessor to determine temperature difference from digitized signals of analog-to-digital converter and provide temperature difference signal |
| JP5579097B2 (en) * | 2011-02-16 | 2014-08-27 | アズビル株式会社 | 4-wire RTD input circuit |
| DE102017130135A1 (en) * | 2017-12-15 | 2019-06-19 | Endress + Hauser Wetzer Gmbh + Co. Kg | Condition monitoring of a temperature sensor |
| CN110220606B (en) * | 2019-06-24 | 2021-09-14 | 宁波华仪宁创智能科技有限公司 | Temperature measuring device with calibration function and method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DD206176A3 (en) * | 1981-04-22 | 1984-01-18 | METHOD AND CIRCUIT ARRANGEMENT FOR TEMPERATURE MEASUREMENT |
-
1983
- 1983-08-27 DE DE19833330915 patent/DE3330915C2/en not_active Expired
-
1984
- 1984-07-24 SE SE8403843A patent/SE8403843L/en not_active Application Discontinuation
- 1984-08-22 DK DK400784A patent/DK163610C/en not_active IP Right Cessation
- 1984-08-27 JP JP17690384A patent/JPS6071925A/en active Granted
- 1984-08-27 CA CA000461899A patent/CA1213672A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SE8403843L (en) | 1985-02-28 |
| DK163610C (en) | 1992-08-10 |
| SE8403843D0 (en) | 1984-07-24 |
| DE3330915C2 (en) | 1986-09-04 |
| JPH0338535B2 (en) | 1991-06-11 |
| JPS6071925A (en) | 1985-04-23 |
| DE3330915A1 (en) | 1985-03-14 |
| DK400784D0 (en) | 1984-08-22 |
| DK163610B (en) | 1992-03-16 |
| DK400784A (en) | 1985-02-28 |
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