US2782102A - Gas analyzer - Google Patents

Gas analyzer Download PDF

Info

Publication number
US2782102A
US2782102A US453230A US45323054A US2782102A US 2782102 A US2782102 A US 2782102A US 453230 A US453230 A US 453230A US 45323054 A US45323054 A US 45323054A US 2782102 A US2782102 A US 2782102A
Authority
US
United States
Prior art keywords
bridge
measuring
alternating current
resistor
resistance
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 - Lifetime
Application number
US453230A
Inventor
Wilfred H Howe
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Schneider Electric Systems USA Inc
Original Assignee
Foxboro Co
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Foxboro Co filed Critical Foxboro Co
Priority to US453230A priority Critical patent/US2782102A/en
Priority to GB23741/55A priority patent/GB776112A/en
Application granted granted Critical
Publication of US2782102A publication Critical patent/US2782102A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
    • G01N27/16—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature caused by burning or catalytic oxidation of surrounding material to be tested, e.g. of gas

Definitions

  • VConventional apparatus operating on this ⁇ principle employs a direct current Wheatstone bridgelmeasuring circuit including in one arm a vheated ilarneiitdn 'cf tact with ythe gaseous mixture tor be measuld. 'Thisiilamentreceives heat from two sources. 1F, st, ajcons'ta'nt direct current potential is lapplied to the'bridge sufifc" nt tol maintain arcurrent through the iilam'entlwhich w,ill heat it 'to a temperature ,greater than the ignition peratureof the 'combustible gas, even withnofcombustible tgas present.
  • measuring .lilament increases exponentiallyias'the .temperature of ithis lament is'in'crea'seddue to ztlre :heat from Vthe combustible gas Isurrounding fit.' Since thereference filament is vnot heated by the lgas com- 'bustion,l deterioration tof the measuring iand reference-'fila-4 ments occurs at different rates, :particularly l'in lthe' measurement of gaseous lmixturesfapproaching the ilower explosion limit.
  • the present invention overcomes the A,prior artdiiriculties by measuring the heat of combustion without'the usual temperature risein the measuring fiilantept andby providing a combination yalternating current-direct V,current bridge circuit arrangement.
  • the present invention provides a ⁇ novel gas analyze ing system wherein the electrical resistance andhencethe temperature of 'theme'asuring filament is vin tainedlat a' substantially constant Value just "suliicient to assure'finduced combustion of the gaseous mixture. .
  • Thisr provides fonminimm deterioration of the jrneasrurihng vtilam t.V
  • siiiee both the vmeasuring an iilaments are held atsubstantially equal ,rr i retain accuracy of ybalance characteristics periods.
  • Separate alternatingfcurrent heater'po'wer circuits are used to supply Velectrical energy tol heat thel filaments .as a means -of Y'providinga constant current supply Yto ⁇ .the .reference filament and fa variable ,current supply toV the measurement,iilament
  • Thecurrent supply to the measurement iilament is constantly and vautomatically controlled so ,that the heatpro- -duced'tvhereby is reduced as the heat of induced combustion -of the gas increases, to the" end thatthe,measure- ⁇ inentiilament temperature yremains substantially constant.
  • a suitable measuring instrument circuit measures the difference in alternating current supplied to the measuring and reference fila ments. This instrument is calibrated directly in terms of composition of the mixture.
  • a particular feature of this invention is the structure and arrangement by means of which both alternating current and direct current ow is provided in the measuring and reference filaments, with each performing its separate function without appreciable interference with the other.
  • the direct current is prevented from circulating in the-alternating current filament heating circuits.
  • the alternating current is substantially blocked out of the direct current -bridge supply.
  • the circuit is designed with an instrument formeasuring the direct current balance ofthe bridge with this instrument substantially unaffected by the alternating current applied to the system.
  • an alternating current instrument is provided which measures the relationship between measuring iilament current and reference filament current, and thereby the composition of the mixture, with this latter instrument completely independent of the direct current function in the bridge.
  • the drawing is a schematic illustration of a hot wire gasanalyzer system embodying this invention, with the ⁇ system shown partly in specific electrical circuitry and partly in block diagram showings of standard or common units, power supplies, amplifiers, etc.
  • the drawing and the following description relate to a specific illustrative embodiment of a hot wire gas analyzer according to this invention.
  • This embodiment is 'based on an all resistance type of Wheatstone bridge 10 with arms 1, 2, 3, and 4, with arm 3 containing a measuring hot wire resistor filament M at which the gas under test is burned.
  • the bridge 10 is operated on direct current from a direct current source 11 through leads 12 and 13 to opposing corners 14 and 15 of the bridge, in the usual form of Wheatstone bridge excitation. As will be detailed hereinafter, portions of the bridge, i. e. arms 3 and 4, are also excited by alternating currents for resistor heating purposes.
  • circuit provisions must be made for the compatible operation of the alternating current and direct current systems. These provisions include, in the direct current bridge leads 12 and 13 from the Adirect current source 11, 500 ohm fixed resistors (16) (17).
  • the direct current source is floating with respect to ground in order not to interfere with the operation of the bridge, which is grounded at a specific point 18, namely, at the junction of theA bridge arms 3 and 4.
  • the bridge arms 1 and 2 are provided with 500 ohm fixed resistors 19 and 20, and the unbalance output of the bridge is taken from the junction point 21 of the bridge arms 1 and 2.
  • the direct current function of the bridge is not undesirably affected by the alternating current in the bridge.
  • arm 3 is the measurement arm, and is made up of a series arrangement of two one ohm resistors, M and m with resistor m adjacent the bridge ground point 18, and resistor M adjacent the bridge arm 2.
  • These low value resistors provide a path of low impedance to the alternating current, and also facilitate the measurement of current in these resistors as a factor in the operation of the gas analyzer.
  • the resistor M is the measuring hot wire resistor at which the Anlagenrtest is burned.
  • This measuring resistor M is selected to have a high coefficient with respect to temperature, using platinum for example, in order to provide good response in the form of tendency to resistance change andv consequent bridge unbalance when the heat of combustion of the gas under test is applied to the resistor Mr Further, the measuring resistor M is indicated as being ⁇ contained in a combustion chamber 22 which is so arranged that a gas sample can be continuously drawn or pushed through it.
  • the resistor m is a standard resistor selected to have a low coefficient with respect to temperature, in order to provide, for current measurement purposes, an unchanging vehicle for the alternating current changes which occur in the measuring resistor M, as will be seen hereinafter, as a result of the application thereto of the heat of combustion of the gas under test.
  • gas combustion heat results in changes in the alternating current values in the measuring resistor M, while measurement of such current Values may be made in the adjacent unchanging standard resistor m.
  • the bridge arm 4 is a duplicate of the bridge arm 3. Two one ohm resistors R and r are arranged in series in this arm.
  • the resistor R is used as a reference resistor; it is adjacent the bridge arm 1; and it is contained in a chamber 23 which is sealed, but otherwise is comparable to the combustion chamber 22 of the measuring resistor M.
  • These chambers, 22 and 23 may be connected by a passage (not shown) so that the same atmosphere of burned gas may surround both the measuring resistor M and the reference resistor R.
  • the temperatures Yof resistors M and R may be closely controlled with respect to each other since thermal conI ductivity is the same in each of the resistor ambiencies. In such an arrangement the heat of gas combustion which is applied to the reference resistor R is negligible.
  • the resistor r as the second resistor in the series of the bridge arm 4, is a standard resistor, like the resistor m of the bridge arm 3, and the resistor ris adjacent the bridge ground point 18.
  • the bridge arms 3 and 4 are provided with ⁇ 1000 cycle ⁇ alternating current for the purpose of heating the measuring and reference resistors M and R.
  • the alternating current in the reference resistor R is provided as a fixed component, while the alternating current in the measuring resistor M is provided as a controllable, variable component.
  • the source of the alternating current which is applied to the bridge 10 is indicated at the right of the drawing at 24, in block outline form.
  • This source may be used to provide all the alternating current in the whole analyzer system, as 'a means of tieing all the circuits together to prevent inaccuracies due to supply vari; ations.
  • the frequency f and phasing of alternating currents from different sources may vary undesirably, reducing the accuracy of the gas analyzer.
  • variations in hot wire resistance due to fluctuations in heating current are cancelled by similarly applying heating current to the reference resistance. Consequently, the effect of such fluctuations on the output of the'bridge is negligible.
  • the 1000 ⁇ cycle alternating current source 24 is an oscillatori which, through leads 25 and 26, provides activating alternating current zto aa distribution'ftransformer-'27. From'the distribution transformer. 21, leads 28 "and ⁇ 29 carry the alternating current'tothe .bridge 10, .by -Way-of a pair of :amplifiers 30 and $31. These amplifiers are powered from'acommon fpower supply 32. Thegan of the amplier issfixedgiand its outputis fapplied across 'the bridge arm ⁇ 4tthroughatrans former 33. The secondary 'zof theitransformer-33 is part of a circuit which includes the bridge.
  • the secondaryof thetransformer contains adirect current blocking condenser :34.'an'd ⁇ an assciatedfchoke 35 rfor relating thealternating .current to Ithe'jcon'denser 34.
  • the direct current component is conned to thebridgeand kept'from leaking lof intoalternatingcurrentl circuits, Vby the blocking condensers 34 and37 inlthelalt'ernatingcurrent circuits'which include 'the ⁇ A ⁇ bridge VarmsV l4 and 3" respectively.
  • the referencere- Ysi'stor R may be yconsidered to'be initially ⁇ heated to a predetermined temperaturer'by thejalternating current component therein.
  • the resistor 'Risi heated, 'for practical purposes, ⁇ only by the 4alternating current therein.
  • the application of'the output ⁇ of'the ⁇ fxedjgainarnplitierA 30 to' the lbridge army #presumably v provides a' fixed value alternating current rin 'the' reference 'resistorlSR, with the' result thatjtheresistor.
  • R ' ispresumably heated to :aA predeterminedxed 'temperature andy is.' presumably provided Hwith ⁇ a predetermined, fixed I resistance value. While the vstandard resistor r' is subjected to ⁇ the same alternating ⁇ current,"its co'eicient with respect to temperature islow and its temperature. and resistance values remain "essentially unchanged.
  • the yariable'gain ⁇ amplifier 31 is initially ⁇ adjustedin its application of' alternating current to ⁇ tlie'b'ridge arm.
  • the operation' ofthe; bridge 10 may besuma rnarized as follows:
  • the bridge is activated by direct current, and'fthereference and measuring resistors R and Ml are initially '-heated' by alternating current in f-fsuch a ⁇ mannenthatthe"bridge is'rbalanced.
  • a sample-'of the gas funderetest is 'exposed-to 'the heated measuring resistor M, and the gas sample is burned.
  • Various-conditions inthe bridge are representative of the amount of .heat applied to the-ineasuring'resistorfM as Aa resultofthecombustion of the gas underltest.
  • A- connec- ⁇ tionV slider 41 is provided on the 50,000 ohm resistor in the mid-point area thereof, with an output lead 42 extending from the connection slider 41.V
  • the pseudo bridge 38 is not a true bridge because there is no appreciable variation of any of the resistor values. Instead, the current values are made to difer in different arms of this bridge, and the ratio between these currents is measured in potentiometric fashion.
  • the potentials at the connections between the standard resistors r and m and their respectively associated reference and measuring resistors R and M are a measure of the 1000 cycle current values in the reference and measuring resistors. Further, the potential on the slider connection 41 is a measure of the difference in potentialacross the standard resistors r and m.
  • the slider connection (41) potential is a measure of the unbalance between the measuring and the reference resistors M and R, and of the degree of combustibility of the gas under test.
  • the potential at the slider connection 41 is used to provide a record of the degree of combustibility of the gas under test, by applying this potential to a recording system which is shown in the drawing as enclosed in a dotted line box 43.
  • the lead 42 from the slider connection 41 to the recording system 43 is provided with a blocking condenser 44 to prevent any direct current from reaching the recording system, and a 1000 cycle tuned filter 45 is provided between the lead 42 and ground.
  • This filter has an impedance to 1000 cycle alternating current in the order of one-half megohm, with very much lower impedance to all other frequencies. As a result, the lter forms an effective by-pass to spurious noise frequencies.
  • a variable coupling condenser 46 is located in the slider connection lead 42 beyond the tuned filter 4S, as an imepdance for controlling the effectiveness of the hot wire bridge output voltage, and the sensitivity of the recording system 43.
  • the recording system 43 may be considered as a servo amplifier with a balanceable recorder bridge 47 therein.
  • the output of the recorder bridge 47, from the bridge unbalance point 48, is connected to the pseudo-bridge output lead 42, with the resultant voltage fed through an unbalance voltage amplifier 49 to the rest of the rebalancing servo network.
  • the remainder of the servo network comprises an unbalance voltage detector 50, a power amplifier 51 and a pen drive motor 52, with the pen drive motor producing a mechanical movement.
  • a vmechanical connection 53 is used to apply the pen drive movement to adjust a variable, rebalancing condenser 54 in the recorder bridge 47.
  • This condenser adjustment movement is applied, through a mechanical connection 55, to a recorder pen 56 as a means of moving the pen 56 generally radially over a rotating chart 57.
  • the recorder bridge 47 is formed with the upper arms thereof each having a variable coindenser therein, one of which is the previously mentioned rebalancing condenser 54; and with the lower arms thereof each provided with a fixed resistor 58, 59.
  • the output connection 48 of the recorder bridge 47 is between the two variable ⁇ condensers, and the ground connection 60 of the recorder bridge 47 is between the two fixed resistors 58, 59.
  • the recorder bridge 47 A is excited from the distribution transfonner 27, and the servo network is provided With 1000 cycle alternating current from the oscillator 24 through leads 61, 62 to the unbalance voltage detector 50.
  • the gas analyzer described herein therefore operates to supply heating, alternating current of a suitable fixed value to the reference resistor R, and heating, alternating current of a variabile value to the measuring resistor M.
  • This current to the measuring resistor M is controlled at a value such that the resistance, and hence, presumably, the temperature of the measuring resistor M, is the same as that of the reference resistor R.
  • The, recording system 43 provides a continuous record of the relation of the alternating currents in the reference and measuring resistors R and M. The difference between these currents is presumably due to the heat supplied to the measuring resistor R by the combustion of the gas under test, and hence the record shows the approach to the explosive limit of the gas.
  • the analyzer depends on a combined direct current and 1000 cycle alternating current operation of the hot wire bridge 10 and its associated structure.
  • the direct current bridge 10 circuit measures the resistance of the reference and measuring resistors R and M.
  • This control operates on the alternating current supply from the variable gain amplifier 31 to hold this supply to such a value that the resistance of the measuring resistor M is maintained equal to the resistance of the reference resistor R, which is heated by the constant 1000 cycle alternating current supply from the fixed gain amplifier 30.
  • a continuous record of the ratio of the two alternating current heating currents in the measuring and reference resistors M and R in effect represents the reduced electrical heating of the measuring resistor M as its heating current is reduced, and thereby, the amount of heat supplied by combustion of the gas sample.
  • Thisinvention therefore provides a new and improved gas analysis device of the hot wire type.
  • a direct current excited electrical bridge in combination, a reference resistance in one arm of said bridge, a measuring resistance in another arm of said bridge, means for associating gas with said measuring resistance for combustion by heat from said measuring resistance, a first alternating current supply means essenltially exclusively operatively associated with said reference resistance arm for producing a predetermined set value of alternating current in said reference resistance, a second alternating current supply means essentially exclusively operatively associated with said measuring resistance arm for producing and varying a gas combustion temperature in said measuring resistance, means operatively connecting the output of said direct current bridge to said second alternating current supply means, whereby a predetermined resistance value relation is maintained between said measuring resistance and said reference resistance, and means for making the direct current function in said bridge compatible with respect to said alternating currentcomponents.
  • a hot wire electricalrbridge circuit gas analyzer comprising, in combination, a direct current excited bridge, a reference resistor and a measuring resistor in different portions of said bridge, means for heating said reference resistor by applying a fixed alternating current essentially exclusively vto said reference resistor portion of said bridge, means for heating said measuring resistor by applying a variable alternating current essentially exclusively to said measuring resistor portion of said bridge, means for burning a gas adjacent said measuring resistor to tend to change the balance condition of said bridge by tending to change the resistance value of saisi measurina'-lr-esstor-rand; means. fory vil-frias.
  • said measuring hot wire at' a substantially ⁇ corrstantpre determined temperature suicient to assure combustion of the measured gas, circuit provisions for the compatible operation of the functions of said alternating and direct currents, including predetermined and sufcient alternating current impedance in the direct current power supply, the balancing arms of the direct current bridge, and the direct current input to the control circuit, to limit the alternating current flow in these circuit elements,
  • a lhot wire electrical gas analyzer comprising, a Wheatstone-bridge, a direct current source connected to energize said bridge, a reference resistor in one arm of said bridge, a measuring resistor in anotherk arm of said bridge for receiving heat of combustion of a gas as a means of determining the degree of combustibility of said gas, a controlled alternating current supply network arranged to provide constant heating excitation essentially exclusively to said reference resistor arm and to provide variable heating excitation essentially exclusively to said measuring resistor arm, a feedback connection from the output of the direct current bridge to the controlled alternatng current supply to provide a control of alternating current supply to the measuring resistor as a means of automatically maintaining direct current bridge balance and consequently essential equality of resistances in the measuring and reference ⁇ resistors, and means for essentially isolating the direct current function in said bridge with respect to said alternating current component whereby change in said controlled alternating current is available as a gas combustibility measurement signal forr the operation of recording, indicating and control means, singly and in any combination thereof.
  • pseudo bridge includingA an alternating.
  • a hot wire electrical bridge circuit gas analyzer wherein a gas is burned by catalytic combustion at the hot wire with the result that the heat of such combustion tends to change the electrical resistance of the hot wire to produce a bridge balance condition changing effect whichisa measure of the degree of combustibility of the gasunder test, comprising, in combination, a direct current operated bridge, ⁇ a measuring hot wire resistor and a standard resistor in series therewith in one arm of said Y bridge, with said arm heated by variable ralternating current, a control feedback from the output of said bridge to said variable alternating current, means for essentially isolating the direct current function in said bridge circuit lwith respect to said variable alternating current, and a ence resistance arm, means for associating gas withsaid l measuring resistance for burning by catalytic combustion at said measuring resistance, a first alternating current supply means for essentially exclusively heating said refl nasales' erencc arm and producing a predetermined set value in said reference resistance, a second alternating current supply means for essentially exclusively heating said measuring arm
  • a hot wire electrical bridge circuit gas analyzer wherein gas is burned by catalytic combustion at the hot wire with'the result that the heat of such combustion tends to change the electrical resistance of the hot wire to produce a bridge balance condition changing effect which is a measure of the degree of combustibility ofthe gas under test, comprising, in combination, a Wheatstone bridge, said bridge having a 500 ohm resistor in each of two adjacent arms, a one ohm reference resistor and a one ohm standard resistor in series in a third arm of said bridge and a one ohm high temperature coeicient measuring resistor and a one ohm low temperature coefficient standard resistor in series in the fourth arm of said bridge, a 100 volt direct current supply having 500 ohm resistance leads to said bridge between each of said 500 ohm arms and their respectively adjacent one ohm resistor arms, said bridge having a ground connection between said one ohm resistor arms and an output connection betweensaid 500 ohm arms, a gas sample combustion chamber

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Investigating Or Analyzing Materials Using Thermal Means (AREA)

Description

Feb. 19, 1957 w H. How; GAS ANALYZER Filed Aug. 31, 1954 Jill xo4momwh. 40m-P200 INVENTOR. wpLFRi-:D H. HovvE mm OEEUH Y N Nw Nm mm ww l QH? w-\ 10N mpom M 5450 ooo N9 l5 l 65u50 mainz/4l I m95? 526m mozmzn /a /8 VIII AGENT United States Patent GAS ANALYZER Wilfred-H. Howe, Sharon, Mass., assigner to The Fox .boro;Company,. Foxboro, Mass.,.a corporation of Massachusetts .Application August 31, .1954, serial No. 455,230
9 Claims. (.Cl. .Z3-255) 'This invention-relates to apparatus for the analysis of mixtures of .combustible gases, especiallymixtures in such proportions below the lower explosive limit ortheiipper explosive limit such that combustion Yin the mixture is not self-sustaining. 4It particularly relates to electrical bridge apparatus which relies on the familiar principle that induced combustion of such mixtures `V will -occur in a limited area immediately adjacent to alilame'nt which is heated to a temperature above the ignition temperature of the combustible gas. The heat generated by'such induced combustion is related to the composition of lthe mixture, and such apparatus provides a measurement .of the heat generated as a measurement of lthe composition of the mixture under test.
An .important use for such apparatus is in chemical operations to measure mixtures of combustible gasand air'intorderto maintain these mixtures at an optimum composition .for the particular chemical operatioiijnd still have asafe margin below :the lower explosion limit ofthe mixture.
VConventional apparatus operating on this `principle employs a direct current Wheatstone bridgelmeasuring circuit including in one arm a vheated ilarneiitdn 'cf tact with ythe gaseous mixture tor be measuld. 'Thisiilamentreceives heat from two sources. 1F, st, ajcons'ta'nt direct current potential is lapplied to the'bridge sufifc" nt tol maintain arcurrent through the iilam'entlwhich w,ill heat it 'to a temperature ,greater than the ignition peratureof the 'combustible gas, even withnofcombustible tgas present. ,'Second, induced combustion k:of .the gaseous mixture "occurring in `the area immediately 'ajacent Lto ythe heated .lament further heats v the "lf ment to 4an extent related-.to the composition of theirnjixtlyire. In vthis' conventional arrangement ythe "Wheatstone :bridge measurement of theresistance ofthe lfila/nteut vthus gives a measure ofthe composition of the combustible 'mixture. .f Itis common practice to :include afsecoiidfdupli'- cate *filament ina secondari-m of" the 'Whea'tstoneb This duplicate `iila-ment 'resistor 'is' presumablyffiected by ambient temperature, 'by minorehan'ges in the supply lvoltage and lby aging e'eetsyexa'ctly the samelafsh the measuring lament is vaffected so that 'these conditions do lnot disturb'the relationship between thecomposition "of fthe `gaseous mixture and fthe resistance 'readings l'obtainable from the bridge.
c 1' Conventional prior artapparatusof this typetemploys a platinum iilament -asa measuring element lresistor. This filament deteriorates appreciably whenimainta'ined at the inecessary temperature just above'the ignition-'temperature forcombustible gas. Evaporation andtotheivdeterioration of the. measuring .lilament increases exponentiallyias'the .temperature of ithis lament is'in'crea'seddue to ztlre :heat from Vthe combustible gas Isurrounding fit.' Since thereference filament is vnot heated by the lgas com- 'bustion,l deterioration tof the measuring iand reference-'fila-4 ments occurs at different rates, :particularly l'in lthe' measurement of gaseous lmixturesfapproaching the ilower explosion limit. This deteriorationchangesthe :resistaA rice , 2 s ance "characteristics of the ilaments andy thus not only upsets thc, balance of they bridgeY but -lS'c upfctc .thc equalityiof characteristics between rneas'uring'and reiferencelamen'ts.
.This diiculty bcccmcs cxtreme in scmcgcSq-lcnding operations where itis important to 'maintain a mixture at a value :as closer as rpossible 'to the explosion while 'maintaining adequate vsafety .against VVactual explo? sfive mixtures. `In certainjprocesses the yield o f u sejful product increases rapidly as the composition approaches the explosion limit. lSince'the degree to which'the ex. plosjion limit can vsafely be approached Yis dependent largcly Vcron thc accuracy cf'thc measurement alid'thc stability of the vcontrol of ythe compos ition,V it becomes of ii amount impcrtancc tc p'rcvldc an accurate; ,Sta'blcY ',fl'cliable measurement. In .the 'conventional constant v potential direct current'bridge measuring system, ,the` 'staf bilitygand reliability of the measurementjfalls "short of what is 'desired in yspite of frequent extensive and costly maintenance procedures.
The present invention overcomes the A,prior artdiiriculties by measuring the heat of combustion without'the usual temperature risein the measuring fiilantept andby providing a combination yalternating current-direct V,current bridge circuit arrangement.
currentibjridge With'a measuring resi t by alternating current, with a control feedba li Yfrom the output ofthe 'bridge to control the alternating vcurrent and ,therebyjtov vcontrol its .heatingyefyecg as am 'ns' of i'rramtaining abridgebalance condition, and with ay direct current lfunction and an alternating 'current f unction'fe'ssentilly isolated with respect to each other, l
Thus the present invention provides a `novel gas analyze ing system wherein the electrical resistance andhencethe temperature of 'theme'asuring filament is vin tainedlat a' substantially constant Value just "suliicient to assure'finduced combustion of the gaseous mixture. .Thisrprovides fonminimm deterioration of the jrneasrurihng vtilam t.V Furthermore, siiiee both the vmeasuring an iilaments are held atsubstantially equal ,rr i retain accuracy of ybalance characteristics periods. This both increases the lreliability l measurement yand reduces the maintenance problems'gin checking and rebalancing the/measuring circuit/,topgamp'ensate f'fo'rrapid deterioration 'ofy the "measuring lilarne'nt and also very considerably lengtheus thcilfclful life/@f thc 'mccsics lamcht, thereby fcducia the .cccltly rcplacenre'nt 'andrecalibration at frequent interyalsrequired with' the conventional system. n f i l 'Y .An embodiment of A"the present invention,which y will be described in detail he'r'elinafter, `utilizesa direct r"current Wheatfstone'bridge 'for the measurement ofthe relative Vresistance vof the 'measuring and yreference filaments in a fr'nariner 4resembling conventional practice. However,.current limiting resistanc inthe direct'curretit supply-circuit limitsthe direct current tlow te vga relatively small value. In a preferred embodiment the directeur- 'rentbridgeccurrent provides roughelyy one percent ofthe total filament vheat1ener gy. Separate alternatingfcurrent heater'po'wer circuits are used to supply Velectrical energy tol heat thel filaments .as a means -of Y'providinga constant current supply Yto `.the .reference filament and fa variable ,current supply toV the measurement,iilament Thecurrent supply to the measurement iilament is constantly and vautomatically controlled so ,that the heatpro- -duced'tvhereby is reduced as the heat of induced combustion -of the gas increases, to the" end thatthe,measure-` inentiilament temperature yremains substantially constant.
heat energy supplied to the measuring element byinduced combustion of the gas under test. This difference is thus a measurement of the composition of the measured gaseous mixture. A suitable measuring instrument circuitmeasures the difference in alternating current supplied to the measuring and reference fila ments. This instrument is calibrated directly in terms of composition of the mixture.
A particular feature of this invention is the structure and arrangement by means of which both alternating current and direct current ow is provided in the measuring and reference filaments, with each performing its separate function without appreciable interference with the other. The direct current is prevented from circulating in the-alternating current filament heating circuits. The alternating current is substantially blocked out of the direct current -bridge supply. Finally, the circuit is designed with an instrument formeasuring the direct current balance ofthe bridge with this instrument substantially unaffected by the alternating current applied to the system. Similarly, an alternating current instrument is provided which measures the relationship between measuring iilament current and reference filament current, and thereby the composition of the mixture, with this latter instrument completely independent of the direct current function in the bridge.
It is therefore an object of this invention to provide a new and improved gas analysis device.
Other objects and advantages of this invention will be in part apparent and in part pointed out hereinafter. The objects and advantages of this invention may be appreciated by reference to the accompanying drawing.
The drawing is a schematic illustration of a hot wire gasanalyzer system embodying this invention, with the `system shown partly in specific electrical circuitry and partly in block diagram showings of standard or common units, power supplies, amplifiers, etc.
The drawing and the following description relate to a specific illustrative embodiment of a hot wire gas analyzer according to this invention. This embodiment is 'based on an all resistance type of Wheatstone bridge 10 with arms 1, 2, 3, and 4, with arm 3 containing a measuring hot wire resistor filament M at which the gas under test is burned.
The bridge 10 is operated on direct current from a direct current source 11 through leads 12 and 13 to opposing corners 14 and 15 of the bridge, in the usual form of Wheatstone bridge excitation. As will be detailed hereinafter, portions of the bridge, i. e. arms 3 and 4, are also excited by alternating currents for resistor heating purposes. In order for the direct current function of the bridge to be usable, circuit provisions must be made for the compatible operation of the alternating current and direct current systems. These provisions include, in the direct current bridge leads 12 and 13 from the Adirect current source 11, 500 ohm fixed resistors (16) (17). The direct current source is floating with respect to ground in order not to interfere with the operation of the bridge, which is grounded at a specific point 18, namely, at the junction of theA bridge arms 3 and 4.
About 100 volts are applied by the direct current source to the two 500 ohm fixed resistors 16 and'17 in the bridge leads 12 and 13, and the bridge is thus supplied with about 100 ma. of direct current. The alternating current in the -bridge is supplied at l2 volts and` 1000 cycles and at about one ampere of heating current, so that the.1 ma. of direct current has no appreciable 'effect on the alternating current function. As a further provision for making the alternating current and direct current operations compatible, the bridge arms 1 and 2 are provided with 500 ohm fixed resistors 19 and 20, and the unbalance output of the bridge is taken from the junction point 21 of the bridge arms 1 and 2. Thus.
4 the direct current function of the bridge is not undesirably affected by the alternating current in the bridge.
In the bridge 10, arm 3 is the measurement arm, and is made up of a series arrangement of two one ohm resistors, M and m with resistor m adjacent the bridge ground point 18, and resistor M adjacent the bridge arm 2. These low value resistors provide a path of low impedance to the alternating current, and also facilitate the measurement of current in these resistors as a factor in the operation of the gas analyzer. The resistor M is the measuring hot wire resistor at which the gesundertest is burned. This measuring resistor M is selected to have a high coefficient with respect to temperature, using platinum for example, in order to provide good response in the form of tendency to resistance change andv consequent bridge unbalance when the heat of combustion of the gas under test is applied to the resistor Mr Further, the measuring resistor M is indicated as being` contained in a combustion chamber 22 which is so arranged that a gas sample can be continuously drawn or pushed through it.
The resistor m is a standard resistor selected to have a low coefficient with respect to temperature, in order to provide, for current measurement purposes, an unchanging vehicle for the alternating current changes which occur in the measuring resistor M, as will be seen hereinafter, as a result of the application thereto of the heat of combustion of the gas under test.
Thus, gas combustion heat results in changes in the alternating current values in the measuring resistor M, while measurement of such current Values may be made in the adjacent unchanging standard resistor m.
The bridge arm 4 is a duplicate of the bridge arm 3. Two one ohm resistors R and r are arranged in series in this arm. The resistor R is used as a reference resistor; it is adjacent the bridge arm 1; and it is contained in a chamber 23 which is sealed, but otherwise is comparable to the combustion chamber 22 of the measuring resistor M.
These chambers, 22 and 23, may be connected by a passage (not shown) so that the same atmosphere of burned gas may surround both the measuring resistor M and the reference resistor R. In this fashion the temperatures Yof resistors M and R may be closely controlled with respect to each other since thermal conI ductivity is the same in each of the resistor ambiencies. In such an arrangement the heat of gas combustion which is applied to the reference resistor R is negligible.
The resistor r, as the second resistor in the series of the bridge arm 4, is a standard resistor, like the resistor m of the bridge arm 3, and the resistor ris adjacent the bridge ground point 18.
The bridge arms 3 and 4 are provided with `1000 cycle `alternating current for the purpose of heating the measuring and reference resistors M and R. The alternating current in the reference resistor R is provided as a fixed component, while the alternating current in the measuring resistor M is provided as a controllable, variable component.
` The source of the alternating current which is applied to the bridge 10 is indicated at the right of the drawing at 24, in block outline form. This source may be used to provide all the alternating current in the whole analyzer system, as 'a means of tieing all the circuits together to prevent inaccuracies due to supply vari; ations. For example, the frequency f and phasing of alternating currents from different sources may vary undesirably, reducing the accuracy of the gas analyzer. Further, variations in hot wire resistance due to fluctuations in heating current are cancelled by similarly applying heating current to the reference resistance. Consequently, the effect of such fluctuations on the output of the'bridge is negligible.
The 1000`cycle alternating current source 24 is an oscillatori which, through leads 25 and 26, provides activating alternating current zto aa distribution'ftransformer-'27. From'the distribution transformer. 21, leads 28 "and `29 carry the alternating current'tothe .bridge 10, .by -Way-of a pair of :amplifiers 30 and $31. These amplifiers are powered from'acommon fpower supply 32. Thegan of the amplier issfixedgiand its outputis fapplied across 'the bridge arm^4tthroughatrans former 33. The secondary 'zof theitransformer-33 is part of a circuit which includes the bridge. arm'4 and consequently 'the reference resistor .lRand `the standard resistorv r. As a pa'rt of .thisfreference resistor circuit a .connection from .the `bridge `'ground point 18.10 the secondaryof thetransformer contains adirect current blocking condenser :34.'an'd `an assciatedfchoke 35 rfor relating thealternating .current to Ithe'jcon'denser 34.
.The -variable :gain amplifier lZilfapplies alternating currentlacross the bridgefarm'.'3,2and therefore' to the measuring resistor. IM and-fits associated* standard resistor m, through f`a ftra'nsformer 36. The measuring 'resistor bridge arm '3.is partiof an alternatingcurr-cut vcircuiteincludin'g the secondary of the transformer n36 and a blocking condenser 37 Vwith an associated choke '38, inman ner and purpose comparable to vthe-alternating current circuit .of the reference resistor r.
The pattern of alternating currentadirect "zcurrent voperation compatibility `in the bridge`fisthus-complete. Undesirable 'i alternating current eifects '1 arevr kept from 'the direct vcurrent input 'by the SOOohm'resi'stors 16an`d"17, and fromthe direct current -output'byfthe i500V hmre si'stors 19fa'n'd 'ZG-inthebridge arms 'f1 and'2. jIn the alternating 'currentsectionof `the"bridg`e, the direct current component is conned to thebridgeand kept'from leaking lof intoalternatingcurrentl circuits, Vby the blocking condensers 34 and37 inlthelalt'ernatingcurrent circuits'which include 'the `A`bridge VarmsV l4 and 3" respectively.
The alternating current f components as Asupplied tto the bridged() 'are Lalsof.compatible with eachiother, that is,'-they Vare essentially isolated f'rom each "other, :since the transformer'secondary "circuits provide complete, lov/*impedance circuits which are 4essentially independent of each other. 1
ln view of the foregoing, therefore, the referencere- Ysi'stor R may be yconsidered to'be initially ``heated to a predetermined temperaturer'by thejalternating current component therein. The resistor 'Risi heated, 'for practical purposes, `only by the 4alternating current therein. The application of'the output`of'the`fxedjgainarnplitierA 30 to' the lbridge army #presumably vprovides a' fixed value alternating current rin 'the' reference 'resistorlSR, with the' result thatjtheresistor. R 'ispresumably heated to :aA predeterminedxed 'temperature andy is.' presumably provided Hwith` a predetermined, fixed I resistance value. While the vstandard resistor r' is subjected to`the same alternating `current,"its co'eicient with respect to temperature islow and its temperature. and resistance values remain "essentially unchanged.
The yariable'gain `amplifier 31 is initially` adjustedin its application of' alternating current to `tlie'b'ridge arm.
3 until the bridge 1) is balanced, usually'because .the measuring resistor` M yis provided lwith. a Vresi'stance'v'alue which is balanced against the resistance Value yofthe reference resistorlR, as heated'by Aalternating current from, the xedgainarnplier 30.
Thus the'bridge'ld is in condition for operation.y It is excited with direct current, portions .3.;.and 4..'of...it arefh'ea'ted by alternating"currennandthe-bridge. is balanced bothfwith respect .to vdirect currentfand .with 'respect to .alternating current. n
measuring resistor .combustion chamber 22and the heatezlmeasuring `resistor-1M 'atleast' initiates combustionin tl'iezgaszsample. Y The measuring resistor; Mzrnay be specially. treatdltofprouide fcatalytic combustion'fof Sthewgas; thez v'gasv 'combustionlmay beridu'e mainly 'tovthe Atthis -point..ar gas sample is introducedl intothe i fromflthe-bridge output lpointhZl 'to ground,y that is,1to
the "fbridgeground 'point ylill. 'This output fis applied through a lead 139 and 'an alternating current filter l40 to a unit i410 which isf a'direct-current voltage -d'etector and amplifier. The output of the u'nitl40' 4is vappliedlto the #variable vgain 'amplifier r431 las -a 'control feedback whichvariesthe alternating current inthe l-bridgelarm -3 in 'faccordance `with the bridge `unbalance "condition,
lThe operation' ofthe; bridge 10, therefore, may besuma rnarized as follows: The bridge is activated by direct current, and'fthereference and measuring resistors R and Ml are initially '-heated' by alternating current in f-fsuch a `mannenthatthe"bridge is'rbalanced. A sample-'of the gas funderetest is 'exposed-to 'the heated measuring resistor M, and the gas sample is burned. The I.heatof combustion Aof zthefffgas Tis applied' to 'the measuring resistorMs'withtherresult that the resistance `value ofthe 'measuringjresistor M is increased. This/increased resistanceunbalances the'bridge and through-the detector and amplifier-Iunit740',l -brings Ithe control 'feedback'into OperatOn'toreduCc the -gain of vthe `variableffga-in arnplifier '31, with fthe v-zresultl 'that 'the :alternating current fin the#lmeasuringresistor M is reduced.Y Consequentlyfthe heating? effect of Vthe alternating currentvis reduced and the -resistance value.v of --the measuring resistor`M is reduced toits initial value, and the bridgel isrebalanced. he effect off'theabove .faction von the measuring resister 'M\is'to'fsubstitute? heat from the gas combustion for heat from the alternating current, with Athe resulting current vreductionavailable as afactor in thevrneasurementofthe-.degre'e of combustibility of the vgas-urider test. lnftheoperation'of thebridge AEdi, therefore, 'the temperatures :and` resistance values of the reference and measuringaresistorsR and M are maintained essentially equal, with the Variant/being the alternating current-value in the measuring resistor Vi. f
Various-conditions inthe bridge are representative of the amount of .heat applied to the-ineasuring'resistorfM as Aa resultofthecombustion of the gas underltest. The tendency toward-bridge unbalance is one such condition, an'clthe resultant change in thehea'tin'g alternating cu-rrent in the fvrneasu'rin'g resistor Yisv another, IHowever, the factor whichis used as ameasurableicondition ini-representation ofv the 'degree of'combustibility of the =gas under test, i.-` c in representation of 'the heat .of combustion-of the gas under test, is the ratio between the'alternatingcurrentin the reference'resi'stori?` and the alternating current in the measuring'resistor M. "For practical purposes.y
circuit 3S. VThe reference and measuring resistorsRV andV M are not included -in this measuring circuit.
The pseudo'bridge circuit-comprises the standardv resisters rand m as two adjacent bridge arms withthe ground point 18 therebetween, a pair of 100,000 ohm resistors connected to the midpoints of the measuringjan'd reference bridge arms 3 and 4, between the standard resistor and Athe measuring or reference resistor `-as vthe k case may be,z and''a'50,000 ohm resistor4 connecting the outerends ofthe two'1`00,000'ohm resistors. A- connec- `tionV slider 41 is provided on the 50,000 ohm resistor in the mid-point area thereof, with an output lead 42 extending from the connection slider 41.V
The pseudo bridge 38 is not a true bridge because there is no appreciable variation of any of the resistor values. Instead, the current values are made to difer in different arms of this bridge, and the ratio between these currents is measured in potentiometric fashion. The potentials at the connections between the standard resistors r and m and their respectively associated reference and measuring resistors R and M are a measure of the 1000 cycle current values in the reference and measuring resistors. Further, the potential on the slider connection 41 is a measure of the difference in potentialacross the standard resistors r and m. Since this slider connection difference voltage is proportional to the ratio between the current in the reference standard resistor r and the current in the measuring standard resistor m, the slider connection (41) potential is a measure of the unbalance between the measuring and the reference resistors M and R, and of the degree of combustibility of the gas under test.
The potential at the slider connection 41 is used to provide a record of the degree of combustibility of the gas under test, by applying this potential to a recording system which is shown in the drawing as enclosed in a dotted line box 43.
The lead 42 from the slider connection 41 to the recording system 43 is provided with a blocking condenser 44 to prevent any direct current from reaching the recording system, and a 1000 cycle tuned filter 45 is provided between the lead 42 and ground. This filter has an impedance to 1000 cycle alternating current in the order of one-half megohm, with very much lower impedance to all other frequencies. As a result, the lter forms an effective by-pass to spurious noise frequencies. A variable coupling condenser 46 is located in the slider connection lead 42 beyond the tuned filter 4S, as an imepdance for controlling the effectiveness of the hot wire bridge output voltage, and the sensitivity of the recording system 43.
The recording system 43 may be considered as a servo amplifier with a balanceable recorder bridge 47 therein. The output of the recorder bridge 47, from the bridge unbalance point 48, is connected to the pseudo-bridge output lead 42, with the resultant voltage fed through an unbalance voltage amplifier 49 to the rest of the rebalancing servo network.
The remainder of the servo network comprises an unbalance voltage detector 50, a power amplifier 51 and a pen drive motor 52, with the pen drive motor producing a mechanical movement. A vmechanical connection 53 is used to apply the pen drive movement to adjust a variable, rebalancing condenser 54 in the recorder bridge 47. I
This condenser adjustment movement is applied, through a mechanical connection 55, to a recorder pen 56 as a means of moving the pen 56 generally radially over a rotating chart 57.
The recorder bridge 47 is formed with the upper arms thereof each having a variable coindenser therein, one of which is the previously mentioned rebalancing condenser 54; and with the lower arms thereof each provided with a fixed resistor 58, 59. The output connection 48 of the recorder bridge 47 is between the two variable` condensers, and the ground connection 60 of the recorder bridge 47 is between the two fixed resistors 58, 59. The recorder bridge 47 Ais excited from the distribution transfonner 27, and the servo network is provided With 1000 cycle alternating current from the oscillator 24 through leads 61, 62 to the unbalance voltage detector 50.
The gas analyzer described herein therefore operates to supply heating, alternating current of a suitable fixed value to the reference resistor R, and heating, alternating current of a variabile value to the measuring resistor M.
This current to the measuring resistor M is controlled at a value such that the resistance, and hence, presumably, the temperature of the measuring resistor M, is the same as that of the reference resistor R. The, recording system 43 provides a continuous record of the relation of the alternating currents in the reference and measuring resistors R and M. The difference between these currents is presumably due to the heat supplied to the measuring resistor R by the combustion of the gas under test, and hence the record shows the approach to the explosive limit of the gas. The analyzer depends on a combined direct current and 1000 cycle alternating current operation of the hot wire bridge 10 and its associated structure. The direct current bridge 10 circuit measures the resistance of the reference and measuring resistors R and M. Unbalance of this bridge 10, operating through the direct current amplifier 40', provides a direct current controlto the 1000 cycle variable gain amplifier 31 and consequently to the alternating current in the measuring resistor M. This control operates on the alternating current supply from the variable gain amplifier 31 to hold this supply to such a value that the resistance of the measuring resistor M is maintained equal to the resistance of the reference resistor R, which is heated by the constant 1000 cycle alternating current supply from the fixed gain amplifier 30.` A continuous record of the ratio of the two alternating current heating currents in the measuring and reference resistors M and R in effect represents the reduced electrical heating of the measuring resistor M as its heating current is reduced, and thereby, the amount of heat supplied by combustion of the gas sample.
Thisinvention therefore provides a new and improved gas analysis device of the hot wire type.
As many embodiments may be made of the above invention, and as changes may be made in the embodiments set forth above, without departing from the scope of the invention, it is to be understood that al1 matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative only and not in a limiting sense.
I claim:
1. In an electrical bridge gas combustibility measuring system, in combination, a direct current excited electrical bridge, a reference resistance in one arm of said bridge, a measuring resistance in another arm of said bridge, means for associating gas with said measuring resistance for combustion by heat from said measuring resistance, a first alternating current supply means essenltially exclusively operatively associated with said reference resistance arm for producing a predetermined set value of alternating current in said reference resistance, a second alternating current supply means essentially exclusively operatively associated with said measuring resistance arm for producing and varying a gas combustion temperature in said measuring resistance, means operatively connecting the output of said direct current bridge to said second alternating current supply means, whereby a predetermined resistance value relation is maintained between said measuring resistance and said reference resistance, and means for making the direct current function in said bridge compatible with respect to said alternating currentcomponents.
2. A hot wire electricalrbridge circuit gas analyzer comprising, in combination, a direct current excited bridge, a reference resistor and a measuring resistor in different portions of said bridge, means for heating said reference resistor by applying a fixed alternating current essentially exclusively vto said reference resistor portion of said bridge, means for heating said measuring resistor by applying a variable alternating current essentially exclusively to said measuring resistor portion of said bridge, means for burning a gas adjacent said measuring resistor to tend to change the balance condition of said bridge by tending to change the resistance value of saisi measurina'-lr-esstor-rand; means. fory vil-frias. Said vari ble altriia n g current to.ch ange, the heatinggcle@ th ,eofv 1 accordance with imbalance conditiorrsmof,` said fgeandfy nrep'resentation;ofrthe degree of;y combusti.-y blity oflfsaid. gas, saidmeansfforvarying saidvariable alternating current including an electrical connection,
fromtle outputfof said bridge tosaid,variablevalternatingwcurrentfap lyinglmean's.. i
3,v hotfw'ireelectrical gas. analyzer wherein-thetemr pe'raturejotffthe measuring hot wireresults. fromthe addi-4 tivejeltectof the heatl 'generated' by electric current flow as, saidftemperature beingmaintainedl 'ntfrallj constantlby, automatically. increasing, orV de;`
crea lng; trieeiearr'iearneaung current, as. the heat ror l co us 1o ofthe gas decreases orincreases, comprising iniV combination, vafdirect'current` system with` a bridge maintained' substantially constant thereby" maintaining,
said measuring hot wire at' a substantially `corrstantpre determined temperature suicient to assure combustion of the measured gas, circuit provisions for the compatible operation of the functions of said alternating and direct currents, including predetermined and sufcient alternating current impedance in the direct current power supply, the balancing arms of the direct current bridge, and the direct current input to the control circuit, to limit the alternating current flow in these circuit elements,
and predetermined and suilicient direct current imped-V ance in the tixed and variable alternating current sources and in the alternating current comparison circuit to limit the direct current therein, means for comparing the variable alternating current in said measuring hot wire and the substantially fixed alternating current in said reference hot wire, and means operable from said comparison of the variable and substantially fixed alternating currents to provide a measurement of the heat of combustion and hence of the composition of the measured gas for the operation of indicating, recording and control means singly and in any combination thereof.
4. A lhot wire electrical gas analyzer comprising, a Wheatstone-bridge, a direct current source connected to energize said bridge, a reference resistor in one arm of said bridge, a measuring resistor in anotherk arm of said bridge for receiving heat of combustion of a gas as a means of determining the degree of combustibility of said gas, a controlled alternating current supply network arranged to provide constant heating excitation essentially exclusively to said reference resistor arm and to provide variable heating excitation essentially exclusively to said measuring resistor arm, a feedback connection from the output of the direct current bridge to the controlled alternatng current supply to provide a control of alternating current supply to the measuring resistor as a means of automatically maintaining direct current bridge balance and consequently essential equality of resistances in the measuring and reference` resistors, and means for essentially isolating the direct current function in said bridge with respect to said alternating current component whereby change in said controlled alternating current is available as a gas combustibility measurement signal forr the operation of recording, indicating and control means, singly and in any combination thereof. Y
d from heat frorninducedcombustion v i@ l5?, Inahot wireeleetrical bridge circuit gas analyzer,- whereip afgasrisburnedat thechot wire with the` resultthat the heat ofY sue-hcombustionv tends to. change; t he electrical resistance ofl the' hotfwire toV producey a bridgev 'reslgrect to {said-,variable alternating current, andl an alter.-
natjng current; pseudo bridge includingA an alternating.
current portiono said direct current bridge for? potenti-v ometrically measuring alternating currentchange in saidbridge.l Y
6;. In a: gas analyzer; wherein the electrical condition of.4 at nannten-bla electrical' bridge is; inauencedby inny ofycombustiomofa sample offthefgas undertest in representationofthe degree ocombustibility` of the gas-under testg'adirecta= current excitedl and balanceable bridge, al reference-resisten inone arm ot said bridge, a measuring resist rinanotherjarmof Saidl bridge for responsive associationwithsaidfheat ocombustion of said gass'ample, meanaforgapplyingaxedvalue alternating `current clicclyA to saidreference-resistor bridge arm as ,n y v f tdcstablishga resistance value in said referenc resior,- means forapplyi-ng-a variable value alternatingfjcurrent etectivelyexclusively to said measuring;resistorl bridge, arm as,a;heating; action to establish a resistance value in said measuring resistor'as a balancing action with respect to said reference resistor, control feedback means from the output of said bridge for varying said variable'alternating current with direct current in accordance with unbalance conditions of said bridge, whereby a tendency to change the balance condition of said bridge isautomatically counteracted by a change in said variable alternating current as representative of the degree of combustibility of the gas under test and with a consequent change in the resistance value producing heating eitect of the variable alternating current, whereby said variable alternating current change is available as a gas combustibility measurement signal for the operation of recording, indicating, and control means, singly and in any combination thereof.
7. A hot wire electrical bridge circuit gas analyzer, wherein a gas is burned by catalytic combustion at the hot wire with the result that the heat of such combustion tends to change the electrical resistance of the hot wire to produce a bridge balance condition changing effect whichisa measure of the degree of combustibility of the gasunder test, comprising, in combination, a direct current operated bridge,` a measuring hot wire resistor and a standard resistor in series therewith in one arm of said Y bridge, with said arm heated by variable ralternating current, a control feedback from the output of said bridge to said variable alternating current, means for essentially isolating the direct current function in said bridge circuit lwith respect to said variable alternating current, and a ence resistance arm, means for associating gas withsaid l measuring resistance for burning by catalytic combustion at said measuring resistance, a first alternating current supply means for essentially exclusively heating said refl nasales' erencc arm and producing a predetermined set value in said reference resistance, a second alternating current supply means for essentially exclusively heating said measuring arm and for producing and varying a gas combustion temperature in said measuring resistance, means operatively connecting the output of said direct current bridge to said second alternating current supply means, whereby a predetermined resistance value relation is maintained between said measuring resistance and said reference resistance, means for essentially isolating the direct current function in said bridge with respect to said alternating current components, and a pseudo bridge for potentiometrically measuring the ratio between alternating current in said measuring resistance arm and alternating current in said reference resistance arm, said pseudo bridge including said standard resistances.
9. A hot wire electrical bridge circuit gas analyzer, wherein gas is burned by catalytic combustion at the hot wire with'the result that the heat of such combustion tends to change the electrical resistance of the hot wire to produce a bridge balance condition changing effect which is a measure of the degree of combustibility ofthe gas under test, comprising, in combination, a Wheatstone bridge, said bridge having a 500 ohm resistor in each of two adjacent arms, a one ohm reference resistor and a one ohm standard resistor in series in a third arm of said bridge and a one ohm high temperature coeicient measuring resistor and a one ohm low temperature coefficient standard resistor in series in the fourth arm of said bridge, a 100 volt direct current supply having 500 ohm resistance leads to said bridge between each of said 500 ohm arms and their respectively adjacent one ohm resistor arms, said bridge having a ground connection between said one ohm resistor arms and an output connection betweensaid 500 ohm arms, a gas sample combustion chamber containing said measuring resistor, a controlled 1000 cycle, 12 volt, alternating current supply network arranged to provide constant heating excitation to said reference resistor arm and to provide variable heating excitation to said measuring resistor arm, a direct current blocking condenser arrangement between said bridge and said alternating current supply network, a control feedback connection from the output of the direct current bridge to the controlled alternating current supply to provide a control of alternating current supply to the measuring resistor as a means of automatically maintaining direct current bridge balance, and a pseudo bridge for potentiometrically measuring the ratio between alternating current in said measuring resistance arm and alternating current in said reference resistance arm, said pseudo bridge including said standard resistors.
References Cited in the tile of this patent UNITED STATES PATENTS 2,219,540 Miller Oct. 29, 1940 2,467,856 Rich Apr. 19, 1949 2,617,716 Hartline Nov. 11, 1952 2,650,496 Middleton Sept. 1, 1953 OTHER REFERENCES Munch: Ind. and Eng. Chem, vol. 42, No. 2, February 1950, pages 69A and 70A.

Claims (1)

1. IN AN ELECTRICAL BRIDGE GAS COMBUSTIBILITY MEASURING SYSTEM, IN COMBINATION, A DIRECT CURRENT EXCITED ELECTRICAL BRIDGE, A REFERENCE RESISTANCE IN ONE ARM OF SAID BRIDGE, A MEASURING RESISTANCE IN ANOTHER ARM OF SAID BRIDGE, MEANS FOR ASSOCIATING GAS WITH SAID MEASURING RESISTANCE FOR COMBUSTION BY HEAT FROM SAID MEASURING RESISTANC, A FIRST ALTERNATING CURRENT SUPPLY MEANS ESSENTIALLY EXCLUSIVELY OPERATIVELY ASSOCIATED WITH SAID REFERENCE RESISTANCE ARM FOR PRODUCING A PREDETERMINED SET VALUE OF ALTERNATING CURRENT IN SAID REFERENCE RESISTANCE, A SECOND ALTERNATING CURRENT SUPPLY MEANS ESSENTIALLY EXCLUSIVELY OPERATIVELY ASSOCIATED WITH SAID MEASURING RESISTANCE ARM FOR PRODUCING AND VARYING A GAS COMBUSTION TEMPERATURE IN SAID MEASURING RESISTANCE, MEANS OPERATIVELY CONNECTING THE OUTPUT OF SAID DIRECT CURRENT BRIDGE TO SAID SECOND ALTERNATING CURRENT SUPPLY MEANS, WHEREBY A PREDETERMINED RESISTANCE VALUE RELATION IS MAINTAINED BETWEEN SAID MEASURING RESISTANCE AND SAID REFERENCE RESISTANCE, AND MEANS FOR MAKING THE DIRECT CURRENT FUNCTION IN SAID BRIDGE COMPATIBLE WITH RESPECT TO SAID ALTERNATING CURRENT COMPONENTS.
US453230A 1954-08-31 1954-08-31 Gas analyzer Expired - Lifetime US2782102A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US453230A US2782102A (en) 1954-08-31 1954-08-31 Gas analyzer
GB23741/55A GB776112A (en) 1954-08-31 1955-08-17 Gas analyzer

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US453230A US2782102A (en) 1954-08-31 1954-08-31 Gas analyzer

Publications (1)

Publication Number Publication Date
US2782102A true US2782102A (en) 1957-02-19

Family

ID=23799697

Family Applications (1)

Application Number Title Priority Date Filing Date
US453230A Expired - Lifetime US2782102A (en) 1954-08-31 1954-08-31 Gas analyzer

Country Status (2)

Country Link
US (1) US2782102A (en)
GB (1) GB776112A (en)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2879142A (en) * 1955-09-21 1959-03-24 Mine Safety Appliances Co Combustible gas detector
US3061826A (en) * 1957-04-29 1962-10-30 Jabez Burns & Sons Inc Flammable vapor detector
US3210657A (en) * 1960-08-12 1965-10-05 Texas Instruments Inc Resistance-change temperature sensing apparatus for a.c. motor windings having a.c. and d.c. sources in series
US3226636A (en) * 1960-12-21 1965-12-28 Fenwal Inc Dual function circuit
US3435662A (en) * 1965-07-27 1969-04-01 Mine Safety Appliances Co Measuring circuit for a paramagnetic gas analyzer
US3445763A (en) * 1965-10-06 1969-05-20 Gen Electric Digital reading impedance measuring arrangement
US3478579A (en) * 1968-08-08 1969-11-18 Cambridge Instr Co Air/fuel ratio indicator
US3868846A (en) * 1973-07-02 1975-03-04 Ford Motor Co Circuit for converting a temperature dependent input signal to a temperature independent output signal
US3964315A (en) * 1974-01-11 1976-06-22 The Anaconda Company Apparatus including novel bridge circuit
US4140396A (en) * 1976-06-25 1979-02-20 Instrumentation Specialties Company Measuring instrument
US4258002A (en) * 1978-03-27 1981-03-24 Barr Thomas A Explosive gas detector
US4317796A (en) * 1979-07-16 1982-03-02 Barr Thomas A Explosive gas detector
US4541988A (en) * 1983-12-13 1985-09-17 Bacharach Instrument Company Constant temperature catalytic gas detection instrument
US5269170A (en) * 1992-11-25 1993-12-14 Panametrics, Inc. Measuring system and process using zero shift compensation circuit
US5616850A (en) * 1995-12-29 1997-04-01 Gas Research Institute Emissions measuring system and method
CN111579725A (en) * 2020-06-04 2020-08-25 衢州康润智能控制系统有限公司 Gas analyzer device capable of automatically adjusting temperature

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2219540A (en) * 1939-01-25 1940-10-29 Power Patents Co Gas analysis method and apparatus
US2467856A (en) * 1945-10-31 1949-04-19 Gen Electric Control system
US2617716A (en) * 1950-01-17 1952-11-11 Stanolind Oil & Gas Co Combustible gas analyzing apparatus
US2650496A (en) * 1948-05-17 1953-09-01 Phillips Petroleum Co Fluid flowmeter with heated resistance bridge circuit

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2219540A (en) * 1939-01-25 1940-10-29 Power Patents Co Gas analysis method and apparatus
US2467856A (en) * 1945-10-31 1949-04-19 Gen Electric Control system
US2650496A (en) * 1948-05-17 1953-09-01 Phillips Petroleum Co Fluid flowmeter with heated resistance bridge circuit
US2617716A (en) * 1950-01-17 1952-11-11 Stanolind Oil & Gas Co Combustible gas analyzing apparatus

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2879142A (en) * 1955-09-21 1959-03-24 Mine Safety Appliances Co Combustible gas detector
US3061826A (en) * 1957-04-29 1962-10-30 Jabez Burns & Sons Inc Flammable vapor detector
US3210657A (en) * 1960-08-12 1965-10-05 Texas Instruments Inc Resistance-change temperature sensing apparatus for a.c. motor windings having a.c. and d.c. sources in series
US3226636A (en) * 1960-12-21 1965-12-28 Fenwal Inc Dual function circuit
US3435662A (en) * 1965-07-27 1969-04-01 Mine Safety Appliances Co Measuring circuit for a paramagnetic gas analyzer
US3445763A (en) * 1965-10-06 1969-05-20 Gen Electric Digital reading impedance measuring arrangement
US3478579A (en) * 1968-08-08 1969-11-18 Cambridge Instr Co Air/fuel ratio indicator
US3868846A (en) * 1973-07-02 1975-03-04 Ford Motor Co Circuit for converting a temperature dependent input signal to a temperature independent output signal
US3964315A (en) * 1974-01-11 1976-06-22 The Anaconda Company Apparatus including novel bridge circuit
US4140396A (en) * 1976-06-25 1979-02-20 Instrumentation Specialties Company Measuring instrument
US4258002A (en) * 1978-03-27 1981-03-24 Barr Thomas A Explosive gas detector
US4317796A (en) * 1979-07-16 1982-03-02 Barr Thomas A Explosive gas detector
US4541988A (en) * 1983-12-13 1985-09-17 Bacharach Instrument Company Constant temperature catalytic gas detection instrument
US5269170A (en) * 1992-11-25 1993-12-14 Panametrics, Inc. Measuring system and process using zero shift compensation circuit
US5616850A (en) * 1995-12-29 1997-04-01 Gas Research Institute Emissions measuring system and method
CN111579725A (en) * 2020-06-04 2020-08-25 衢州康润智能控制系统有限公司 Gas analyzer device capable of automatically adjusting temperature
CN111579725B (en) * 2020-06-04 2020-12-11 浙江特富发展股份有限公司 Gas analyzer device capable of automatically adjusting temperature

Also Published As

Publication number Publication date
GB776112A (en) 1957-06-05

Similar Documents

Publication Publication Date Title
US2782102A (en) Gas analyzer
CA1149635A (en) Humidity measuring method
US3922550A (en) Radiometric system
US5450015A (en) Apparatus for measuring impedance to determine a property of a material
US2787904A (en) Constituent potential measuring apparatus
US2550052A (en) Viscosity meter
US2517455A (en) Temperature recorder
US4198849A (en) Pyrometric temperature measurements in flameless atomic absorption spectroscopy
US3643491A (en) Derivative differential scanning microcalorimeter
US2407075A (en) Ultra high frequency power measurement
US2841765A (en) Electric ohmmeter
US2393220A (en) Combustible gas indicator
US2219540A (en) Gas analysis method and apparatus
US2879142A (en) Combustible gas detector
US3480397A (en) Gas analysis method for determining the oxygen content of a gas containing carbon dioxide
US4345204A (en) Bridgeless dielectric measurement
GB625023A (en) Improvements in or relating to wheatstone bridge measuring and computing devices
GB625024A (en) Improvements in or relating to instruments for measuring moisture content in wool and other substances
US2673465A (en) Tempeature responsive instrument
GB1109210A (en) Measuring circuit for a paramagnetic gas analyzer
US3109137A (en) Bridge circuit
US2995703A (en) Thermistor matching
US3080745A (en) Compensated bridge circuit
US2830252A (en) Arrangements for providing standardized voltage or current
US3341757A (en) Bridge circuit for determining the inverse of resistance