CA2074939A1

CA2074939A1 - Method for the analysis of a gas sample, analysis arrangement, uses thereof and test plant comprising the said arrangement

Info

Publication number: CA2074939A1
Application number: CA002074939A
Authority: CA
Inventors: Ulrich Matter; Rene Nuenlist; Heinz Burtscher; Michael Mukrowsky
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-12-06
Filing date: 1991-12-04
Publication date: 1992-06-07
Also published as: CN1063061A; MX9102403A; BR9106216A; FI923536A; CA2074950A1; DE4042557C2; WO1992010752A1; EP0514532A1; ZA919596B; FI923535A0; JPH05504410A; AU8914491A; EP0513276A1; MX9102402A; BR9106217A; DE4038993C2; WO1992010751A1; FI923535A; AU8928291A; CN1085660A

Abstract

ABSTRACT

Rapid sequences of gas samples (G) are taken to a semi-conductor sensor (60a,b,c) for analysis. The analysis procedure is accelerated by differentiating the semiconductor sensor output signals in time (61) and taking successive gas samples (59) to the semiconductor sensors (60a to 60c) sequentially. In cycle stages in which the semiconductor sensor concerned (60a to 60c) receives no gas samples, the lines and casing are flushed with gas (S). The effect of the flushing process on the semiconductor output signal (A) is minimised by adjusting the flushing gas and/or the flow rate ratio between the flushing gas and the gas sample in the semiconductor region.

Description

207~939 thod_for the a~lY8i~ 0~ ~ ~as_~amP-le, ~nalY~ rranqement~ U8 thereo~ a~d to~tJpL~g~gs~DI~Lh~ e 3Aid ~rranaomo~.

The prese~ inve~io~ rslates ~o 8 method in a~corda~ce ~ith the introductory part of clai~ 1, an analyais arrangement ~ccordi~g to that of claim 12 as ~ell a~ to a test plant comprising auch a~
~rr~gemen~ according to claim 22 a~d a u~e thereof sccording to claim 23.

Semi-conductor gas se~sors are known, a~ made and marketed, for example, by the company Figaro E~gineering, Osaka/Japan. Such semi-conductor ga~ ~ensors ca~ be introduced extremely ea~ily and, because of their small size, also directly into containers or along-side a flow path for gas ~ample from the co~taine.s, at any point, for the a~alysis of the gas samples. The reliability aspect can be improved even further by providing ~everal ~uch semi-conduceor gas sensors.

~o~ever, semi-conductor ~en30r9, and in particular 3emi-co~ductor gas 9e 30r~ have relatively lo~g step re ponse times, i.e. when a sudden change i~ the ga occurs on the inpu~ side, its output ~ig~al charlges similarly to that of a lo~-pas~ ~ilter, and relatively slowly moves a~ymptotically towards the corre~po~ding end value.

This problem, whe~ consideri~g the rapidity of the proce~, form an obstacle for th~ uqe of semi-conductor gas ~ensors, arLd i~ eliminated --1' :

,} one proceed~ ~ indicated i~ clQim 1. 2074939 .. . . . .
Since as output ~ignal ~ith uch ~emi-conductor ga8 8~ngor UgUal ly the output re~i~ta~ce varies, the cha~ge ~ith respoct ~o time of it3 output re~i~tahce ia, therefore, evaluated.

As the time differentiatio~ of the semi-conductor gas se~sor output signal correlates with the ~aximum value of the output sigrlal which ie trie~ to reach, already shortly af~er there occurs on the input side a change in a gas concentratio~ and/or i~ a substance, the a~alyRis ~ignal ca~ be ascertained from the said differentiation.

From the above it can now be noted, among others, that ~hen a semi-co~duc~or yas ~ensor has detested a gas component which moves its output si~nal in ~he direction of a new e~d value, this gas ~en or, because of its ~memsry", ~ill now analyse a further gas ~ample fal-sified with th~ result o~ previously deeected measurements. This would mean that a provided gas ~ensor would agai~ drastically slo~
down the process cycle, as it is necessary to wait until the effect of a previous gas a~alysis has died away.

When proceeding i~ accordance with the wordi~g of claim 2, this is prevented in that at least two sets comprisi~g at least one semi-co~duc~or ~as sensor each are provided, and the tese gas from successive contai~ers is fed to dlfferent sensor sets, so ehat the individual sets are given time to re-set their output signals to a ~7~9 L~sic value ~ithout i~cre~.in~ th0 time o the proces~ cycle.
.

,, , _ So thae, ~h~n proceedi~g in thi~ ~armer, the ~upply li~es and the semi-conductor ~a~ ~en~or i~elf ca~ be cleaned, it i~ propo3ed, in accorda~ce ~ith clai~ 4, ~o rinse it arld accordingly also the supply lirles ~ith ga , a~ter the mea ureme~. With ~uch a sas rins-i~g, because of the type of the rin~ing gas andtor it3 flow along ~he se~sor, there occur~ o~ the sen30r a behaviour qimilar to that ~hich occurs during the aforemen~ioned detecting of a specific gas componen~ in the ~ample. As a re~ult thereof such a gas sensor, be-cauRe of ~he rirlsing operatio~, again car~Lo~ be used for some time for sample ~ea~urements.

It now is proposed, as indicated i~ claim 6, to adapt the type of the ri~sing gas and/or the rinsing gas flow ~o the flow of a carrier gas for the gas ~ample irl such a way that, when changing over from rirlsing to ~ea~uring or vice-versa, this charLge produces an only mi~imal, i~ any, change i~ the sigrlal at the output of the ~emi-co~ductor sen~or~ Accordi~gly, the sen~or does no~ 'lexperience" a change fro~ testing cycle to rirlsing cycle or vice-versa.

In accordance with the wording of claim 5, preferably a carrier ~as i.~ used and, in the sense of ~hat has been 3aid ~ith refere~ce to claim 6, according to claim 7 a3 rinsing gas the carrier gas is used.

With the aforemerltioned semi-conductor se~sors, in particular semi-conductor yas Rensors, ehe "memory" behaviour of which has been 2074~
_~plai~ed, there ~l~o occur~ A probl~m e~p~cially ~h~n one or several of th~ providQd ~emi-c~nductor ~ensors d~tect a high ga~ level tha~
pushe~ up it~ output ~ig~al, 80 that such a ~ensor then al~o require~
a corre~pondingly long time to ~wing back to it3 original value, As a recult thereof ~uch a ~emi-conductor ~ensor ~ould ther~ again not be ready for ~ubsequent exami~ations, and the measuring cycle ~ould be extended accordingly until the ~ai~ 3emi-conductor sensor has again reached its readines~ ~o measure.

To prevent thi~, in accordance ~ith the wording of claim 8, ehe out-put signals of the provided semi-conductor sensor se~s are checked to 3ee whether they exceed a predetermi~ed value. I~ so, the set in question is disabled at least for the i~mediately following a~alysis.
One of the other semi-conductor sensor sets which is ready to measure i9 then used.

The time differentiation of the output signals of the semi-conductor serLsor is checked ~o see ~hether it exceeds the predetermined value, so that al50 here one rleed not ~ait untll the output ignal of the ~emi-conductor 3ensor levels out on the output signal level corres-ponding to the gas sample component.

Since anyway, preferably, successive gas samples are fed sequentially to differe t 3emi-conductor sensor sets, so ~hat, for example, those that have just been u~ed can in the meantime be rinsed, in ~he cases mentioned herP preferably more than one measurirlg cycle is left out s~

2~7~93~
~ntil the set ~hich i8 over-saturAted in the indic~ted ~ i3 agairl ready eo ~es ur~, ~hich can ~a~ily be deter~irl~d by mo~i'coring its output ~ignal, in accordance ~ith claim 9, ~hilst the ~u~sequen'c mea-suring cycles ~re carried out u~affec~ed on other Bet~ .

An analy~i3 arrangemen'c according ~o the inventio~ is specified in th~
claim~ 12 to 21.

A test plant accordi~g to the i~ve~tion comprising a~ analy3is arrangC
ment according to the invention is 4pecified i~ claim 22, with which c conveyor arrangement is provided for plastic bottles that are conveye~
as cor~tainers i~ streamline fashio~ to and from the analysis arrange-ment, and ~ith which every bot~le can be tested at a fast rate, unlik~
spot checks which, i~ particular i~ connectio~ with the re-use of fooc co~tainers ~ can~ot be used for reasons of safety.

In the followi~g the invention ~ill be explained, by way of example, with reference to figure~.

These ~how:

Fig. 1 a signal flow/fu~ctio~ block diagram of an analysis unit accordi~g to the inventio~ with semi-co~ductor sensors, in particular semi-conductor gas sensors, operating by the ~e~hod accordi~g to the irlYerLtion, ~ 207~39 kig. 2a ~he qualitati~0 respon~e behaviour o a ~emi~onductor gas ~en~or ~o ri~ g gas/te~t ya~ cycl~

Fig. 2b the adju4ted behaviour of ~he ~e~i-corlductor ga3 s2~sor, ~i~. 3 diagr~mmatically, the block diagram of a preferred gas 5amp-ling unit on the a~alysi~ unit according to the invention.

The present inv~tio~ relate~ to the problem of irlvestigating, in particular ~ith e~pty container~, ehe ~tate of ~heir con~ami~atio~
with the aid of gas ~amples. For example, with plastic bottles which are received for re-use, there exists great uncereairlty as to how they ~ere u~ed after their original content, e.g. mineral water, fruit juice , etc., had bçen emptied. It is krLown that such bottles are ofeen used for other purposes, for example in the household, e.g. for stori~g oap ~ater, herbicides, engine oil, acids, petrol, benze~e, etc. If such 3ub~tances were stored in contai~ers that are made available for re-u~e with a new original filli~g, wieh certain categories of contami~ation substances an adverse effect on the taste of the newly filled original content can be expected, or such a corLtairer carA no lorlger be used for re-filling because of the in-compatibility of the contamirlation or because they may be harmful to people' A health.

For this reason i~ must be ascertained whèther and which residual contaninations are present in the containers, so that a selec~ion ~7 ~07~9 ~a~ be casried out be~ee~ co~t~in~r~ th~t ca~ ~o lo~ger be u~ed for a ne~ original fillin~, tho~e that, for exa~ple, firs~ have to u~dergo a ~pecial cleani~g proce~, a~d those that ca~ quite ~afely be re-filled.

As in certain cases also the content of a container may be conta-minated, and the gas lying above thi4 i~ ~he~ contaminated, the i~vention can, ~ith regard to all it~ aspects, also be u3ed on containers that have already bee~ filled.

The analysis technique ~hich i5 0~ interest i~ the prese~t connection i5 ehe or~e by mean~ of se~i-conductor sensors, e.g. for infrared absorption ~easur~ments on the gas, infrared ~emi-corlductor sensors, or also, and in particular, by means of semi-conductor gas sensors which directly detect gas components on the ~as sample. Semi-con-duc~or gas ~eu~or~ suitable for irLfrared absorption measurements are marketed, for example, by the company Kohl SerL~ors Inc., 70W
Barham Ave~ue, US-Santa Rosa. Semi-co~ductor gas sensors which are of particular ineerest here, are marketed by ~he company Figaro Erlgi~eeri:~lg, Osaka/Japan.

Whe~ u~ing such ~emi-co~ductor compone~ts there e~ists a problem i~
that their step response i5 relativ.ely slow. If, duri~g the flowing pa~t of contaminated gas as gas sample, a co~tamination pulse or gas co~ponent pulse i~ produced o~ the input side of such a sensor, the semi-conductor ~e~sor output sig~al will move up relatively 510wly to a corresponding maximum value, to then drop again just as ~lowly.

%~7~3~

~lne~ problems ~ay ~180 occur ~i~h oth¢r ~e~suring eeshniques, e.g.
~ieh the i~fr~r~d absorptio~ mea~ure~e~t ~ith sami-co~ductor i~frared ~en ors, ~o that the follo~ing explanatio~ also spply to these.

A~ can be rloted from Fig. 1, the output ~ignal~ of the set3 60a, 60b and 60c, respeceively, illustrated there and each comprising at least OLe se~i~conduc~or s~nsor ~L, are ~uch ehat, depending on the occur-ring co~ta~i~ation, they move toward3 the maximum value A~x, which take3 a relatively long time.

To now shorten the measuri~g cycle time, use is made of the ~act tha~
the climb of the output signal increases when the reached maximum out-put signal value A~x beco~es higher. For this reason, the sensor output sig~al is not evaluated directly, but its ~i~e differentiation i~ e~aluated as the ~easurable variable A~, as illustrated in Fig. 1.

Since with semi-conductor sensors the variable i5 its resistance, A
corre~ponds ~o the ree~ista~ce pattern.

A can furthermore be ~oted, the time which the output sig~al of such 3ensors requires ~o agai~ a~elume its initial value is the longer, ehe higher the reached maximum value A~ax. To now nevertheless ~e able, indepe~denely of this, to drastically shorten the measuri~g cycle time, according to Fig. 1, two or much uch se~sors or ~ets of such sen~ors are u3ed, e.g. cyclically, for succe~si~e gas sample analyses.
This is controlled by a control u~it, e.g. with a cyclic register 62 ~ ~v 2 ~ 7 ~

~ ay of ~ontrol input~ ~' o~ flo~ ~itche-~ 59. Pr0fer~bly it i3 ~onitored, e.g. with co~parator units 64, ~hether the output ~ignal of o~e of the ~en80r8 or set o~ se~sors a~sume3 a~ inadmi3~ibly high value, and this one se~sor or set of Ren~or~ i~ then taken out of the cycle for a predeter~ined time ~.

A~cordi~gl7, ~t~ 60a, b ... with at least one ~emi-conductor sensor each are provided, ~hich are used ~equentially for ~ucce~sive gas ~amples G. If the output signal o~ a semi-conductor ~ensor or its time differe~tiation moves beyond a threshold value pre-set on com-parator units 64, then the 3ensor or set of ~ensor~ in question will be ~wi~ched o_f for a predetermined number of subsequent sample gas ~easuring cycles.

Aq indicated by broken lines, in this connection it is readily possible to monitor the output signal values A, e.g. ~ith a furt~er comparator 65, and as illustrated for set 60c, as a~ example, to determine, in accordance with the momentary output signal value, the time during which a semi-conductor ~as sensor set must remain out of action. In oeher ~ords, such a sensor set will only again start to m~asure ~hen its output signal value again drops below the threshold value set o~ the ehreshold value u~it 65.

A further problem ~ith ~emi-conductor gas sensors or possibly also radiation semi-conductor sen~ors, as used for the in~rared absorption -- lU
%07~3~

.
mea-~uri~g, i~ that on the one hand ~upply lines for the 3ampl~ g~s G
and hou~ing arrangeme~t~, in ~hich the sen~ors are arrarlged, mu~t be rin3ed to ~inimize the influe~ce of a preceding ~ea~uremen~ on ~ su~-sequ0nt measurement, but that on ~he other hand such semi-conductor en~ors react tc a ri~ing ~as flow S with a 310~ output si~nal, of the eype a~ illustrated at A in Fig. 9. This would mean, therefore, ~ha~ when uch semi-conductor sen~ors are rinsed, in particular ri~sed with ga~, preferably ~ith purified air, after such a rinsing cycle they ~u~t remain out of operation for ju~t as long as after a ~easuring cycle, i.e. the nu~ber of provided semi-conductor sensor sets 60 according to Fig. 1 would have to be doubled ~o obtain the same throughputs.

Fiq. 2a illustr~tes qualitatively, over ~he time axis t, a rinsing gas flow S, hatched, and by dot-dash lines the resultant pa~tern of the output sigrLal A of a emi-conductor gas sensor. From this it can be noted that only after expiry of a fall time, a new measuring cycle with the test ~as supply G can be started on the ~emi-conductor gas se~sor i~ question. However, for time-economy rea~ns one should aim at lettins measurin~ cycles immediately follow rinsing cycles and vice-ver~a.

According to Fig. 2b in conjunction with Fig. 1, this now b~comes pos~ible accordi~g to the inve~tion in that the test gas flow G a~d the rinsing ga~ flow S are adapted to o~e another by means of flow adjustme~t elemen~s, as il}us~rated diagramma~ically in Fig. 1 at ~ o ~

~ G and Vs, in ~uch a ~a~ that ~he 3emi-co~ductor gas ~e~or expe-rie~ce~ a ~ubsta~tially continuou~, co~sta~t ~low. With ~hi3, th~
tese ga~ flo~ i~ preferably produced by the flo~ o~ a carri~r ga~, to which i~ added gaq ~rom the container that is being tested. Pr~-ferably, a~ rinning ga~ ~he 3ame ga4 i8 then used a3 the carrier gas, for exa~ple and preferably dry, puri~ied air is used for both. If differe~ gases are u~ed for the rinsing and as carrier ga4 ~ it has been fou~d thae by changing the flow ratio of the test gas G and the rinsin~ gas 5, the influence of the different gas types can to a large extent b~ compensated.

Fig. 2 b illustrates dia~rammatically, for identical carrier and rinsin~ gases, rinsing cycles S, a measuring cycle G with uncon-taminated gas, i.e. carrier gas, then a measurin~ cycle G with co~taminated saS. Taking into account the ~emi-conductor output sig~aln, the adjustment is carried out such that during the successive cycles ri~sing gas/carrier gas, or u~contaminated ~est gas, esserltially no output signal or possibly a substantially time-constant output qignal appears o~ the semi-conductor gas sensors, which makes it possible to test and rinse successi~ely in the sense indicated above.

The use of a carrier gas takes place, for example, as illustrated in Fig. 3, by con~ecting, e.g. by mea~s of a sealing con~ection 74, a carrier gas ta~k 70 to the container 71, whi~h is shown positioned o~

- -- lG -~
2~749~

a conveyin~ device 72 . By ~ean~3 of a pump 76, . carri~r ~a3 together ~ith ~as eoEltai~led i~ ~che ce)~tai~r i3 ~od to- tho measuri~g arrange-me~t, a~ illu~trated at 78. Naturally, it i~ al~o po~sible to utilize the ~a~er jet pu~np pri~ciple b7ith the carrier gas a~ pU~Qp gas.

The u3e of the carrier gas aa rirlsirlg ga~; ca~ eake place, for exa;nple, i~ an extremely simple ~ar-rLer by provi~i~g a co~trollable cha~ge-over valve Ve s, by allean~ of ~hich the con~ainer i3 bridged durin~ rir~sing pha~es.

.~ ~ . .. . ...

Claims

Patent claims:

1. Method for the aanalysis of at least one gas sample, with an analysis arrangement which comprises at least one semi-conductor sensor, characterized in that the output signal of the sensor is differentiated with respect to time, and its time differentiation is used as an analysis output signal.

2. Method according to claim 1 for the analysis of gas samples that rapidly succeed one another, characterized in that at least two sets each comprising at least one of the sensors are provided, and successive gas samples are analysed sequentially by one of the sets each.

3. Method according to claim 2, characterized in that more than two sets are provided.

4. Method according to any one of the claims 1 to 3, characterized in that, after feeding a gas sample to a sensor, the sensor and the associated sample feed lines are rinsed with a gas.

5. Method according to any one of the claims 1 to 3, characterized in that the gas sample is fed to the sensor by means of a carrier gas.

6. Method according to claim 5 when dependent on claim 4, characterized in that the carrier gas as well as the rinsing gas and/or the flows of carrier gas and rinsing gas in the area of the sensor are adapted one another in such a way that as a result of the change-over from carrier gas to rinsing gas, at least no significant signal change occurs on the output of the sensor.

7. Method according to claim 6, characterized in that as rinsing gas the carrier gas is used.

8. Method according to any one of the claims 3 to 7, characterized in that the analysis output signals of the sets are checked to see whether they exceed a predetermined limit value, and if so the set in question is disabled for a given time which in each case depends of by how far the limit value was exceeded.

9. Method according to claim 8, characterized in that, the output signals of the sets are checked to see whether and when they again drop below a predetermined limit value, and thereupon the set in question is again enabled for the analysis.

10. Method according to any one of the claims 1 to 9, characterized in that the semi-conductor sensor is a semi-conductor gas sensor which responds directly to gas components and their concentration in the gas sample.

11. Method according to claim 5, characterized in that as carrier gas air is chosen.

12. Analysis arrangement for gas samples comprising at least one semi-conductor sensor for at least one variable that co-iden-tifies the gas, characterized in that the output of the sensor leads to a differentiation unit (61), the output (A?) of which leads to an evaluation unit.

13. Arrangement according to claim 12, characterized in that at least two sets (60a, b) are provided, comprising at least one of the sensors each, and feed lines (G) for gas samples to each of the sets with a controllable flow switch arrangement (59), by means of which the gas samples can be fed selectively to the sets, furthermore a cycle unit (62) which controls the flow switch elements (59) in such a way that the sets alternately receive the successive gas samples.

14. Arrangement according to claim 13, characterized in that more than two sets (60a, b, c) are provided to which gas samples are fed sequentially.

15. Arrangement according to one of the claims 13 or 14, characte-rized in that feed lines for a rinsing gas (5) are connected to the feed lines for gas samples (G) by way of controllable swit-ching elements (59), and in the the cycle unit (62), after actuating (G') a flow switching element for connecting a set to the feed line for a gas sample (G), connects (D') this set by way of the associated switching element (59) to the feed line for the rinising gas (S).

16. Arrangement according to any one of the claims 12 to 15, charac-terized in that a carrier gas soure (70) is provided, which is connected to a container (71) for the gas sample and to the feed lines for the gas sample (G).

17. Arrangement according to claim 15 or 16, charac-terized in that flow adjusting elements (VG, VS) are provided in the feed lines for the gas sample (G) and/or for the rinsing gas (5) to adjust the ratio of flow of gas from these feed lines to a respective set.

18. Arrangement according to claim 16 or 17, cha-racterized in that the feed lines for the rinsing gas (S) are connected to a rinsing gas source (70) which gives off the same gas as the carrier gas source (70).

19. Arrangement according to any one of the claims 14 to 18, cha-racterized in that the outputs of the differentiation units (61) of the sets (60) lead to a threshold value sensitive unit (64), the output of which acts on the cycle unit (62) and by way of same and the flow switching elements (59) blocks the gas sample feed line to a set for a predetermined period, in case the at least one output of the differentiation unit (61) of this set exceeds the threshold value (64).

20. Arrangement according to claim 19, characterized in that the out-puts of the sets are led to a further threshold value sensitive unit (65), which by way of the cycle unit (62) as well as the flow switching elements (59) again opens up the gas sample fed line to a blocked set after the output of this set has again dropped below the threshold value of the further threshold value sensitive unit.

21. Arrangement according to any one of the claims 12 to 20, cha-racterized in that the semi-conductor sensor is a semi-conductor gas sensor which responds directly to gas components and their concentration.

22. Test plant comprising an analysis arrangement according to any one of the claims 12 to 21 and a conveying system for plastic bottles conveyed in a streamline fashion, the gas inside which bottles must be analysed as gas sample.

23. Use of the method according to any one of the claims 1 to 11 and of the arrangement according to any one of the claims 12 to 21 for the analysis of gas samples from containers that rapidly succeed one another.

24. Use according to claim 23 for the analysis of gas samples from plastic bottles that rapidly succeed one another before they are filled with a beverage.