CA2075034A1

CA2075034A1 - Method for determining a measurable variable and measuring arrangement

Info

Publication number: CA2075034A1
Application number: CA002075034A
Authority: CA
Inventors: Heinz Burtscher
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-12-06
Filing date: 1991-12-04
Publication date: 1992-06-07
Also published as: DE4038994A1; BR9106215A; WO1992010745A1; MX9102404A; CN1029530C; TW226438B; EP0514531A1; DE4038994C2; CN1063162A; ZA919595B; FI923537A; AU8914591A; FI923537A0; JPH05504411A

Abstract

ABSTRACT

In order to discover whether a partly or virtually completely empty container is contaminated with an unacceptable substance, as may be the case if a plastic bottle intended for mineral water has been used domestically for storing insecticides or the like, a sample of gas (G) from the container is ionised in an electric discharge path (3) and the discharge behaviour (UF) and/or the ionisation of the gas caused by the discharge is evaluated as a measurement.

Description

- la-2~7~J~3 Method for determininq a mea~urable variable and measurinq arranqement.

The present invention relates to a method for determining a measurable variable on gas from an empty or partially empty container in accor-dance with the introductory part of claim 1, a measuriDg arrangement in accordance with that of claim 16, as well as a use of the method.

From the EP-A-0 306 307, which herewith is declared an integral part of the present description, it is known, within the framework of the recycling of containers, to detect on empty containers, in particular plastic containers, e.g. plastic bottles, whether any contaminations are present inside the container.

To this end it is proposed to detect such contaminations with the aid of an ionization technique, e.g. flame ionization or photo ionization in the W -range, and if need be to eliminate the contaminated contain-ers before they are re-filled, in which connection preference is given to the W photo-ionization.

Seeing that in particular with in-line inspections a large number of containers occur rapidly and directly after one arother, and for reasons of reliability, such a process must be as simple and quick as possible.

Drauing off a gaJ ~mple from the cGntainer in question, ies flame 2~ 9 ~J~
onization for the subsequent anclyqi~, as kno~n from the EP-A-0 306 ~07, i~ a relatively slow proce~, a~d further~ore also disadvanta-geou~ from the sinplicity point of view. As a matter of fact, during the flame ionizatior with a hydrogen flame, the gaR flowing past the flame ~ay not significanely di-qturb the flame, which sets limits on the flo~ velocity and therefore the rapidity of the measuring opera-tion, and furthermore the ~upplying of flame gas is expensive.

The preferred ionization technique known from the EP-A-0 306 307, i.
by means of W -light, i~ complicated. In this connection refer to th~
information in the ebovementioned EP itself, according to which the ionization apparatus ~ust be cleaned frequently. In addition, the re-quired W -lamps are expensive. The W photo ionization is nevertheles preferred.

It is the object of the present invention to propose a method of the type specified in the introductory part of claim 1, by means of which the mentioned disadvantages of the technique according to the EP-A-Q
306 307 are eliminated.

This is achieved if one proceeds as indicated in the characterizing part of claim 1.

The providing of an electrical discharge gap, e.g. similar to the spark plug of a combustion engine, is extremely simple as this can b~
miniaturized, is not susceptible to contamirlation and, being flexibl~-2~7~J~electricity can be ~upplied to it practically any~here.

The use of electrical discharge gaps for gas ionization has been kn~r for a long time, e.g. from - the VS-A-2 550 ~98 t1951), - the US-A-3 728 615 (1~73) for fimoke detection, - the US-A-4 629 gg2 (1986) for fire detection.

~owever, with such applications the advantage of the ionization by electrical discharge, i.e. the fact that hardly any cleaning is re-quired and the apparatus is very quickly ready for use again, is of subordinate importance, whereas with the ionization of gas samples, which, as with the use according to the invention, occur quickly and directly after one another, this is of decisive importance.

~he procedure according to the invention is very quick, as it is su~
stantially independent of the flow velocity of the gas, and because certain applications, in contra~t to flame ionization, it can be use in the container itself.

With the method known from the EP-A-0 306 307, with which the gas i~
ionized, it is a cor~siderable disadvantage, from the safety point of view, that the ion density that occurs due to the ionization can only be ascertained as a whole, and no indications are possible regardinc the ion type in question.

2~ 3~
So that, ~ith a method according to claim 1, one can neverthele~
~electively ~ake conclu~ions with regard to the pre~ence or ab~ence of certain type~ of ion~, it is propo~ed to proceed a~ indicated in clai~ 2.

Thi~ procedure provide~ the advantageou~ combination of a simple and flexible u~e and a more reliable indication regarding the presence of ab~ence of ions ~ith a known mobility gradation.

In the following the invention ~ill be explained in its verious aspects, with reference to drawings.

Shese show:

Fig. 1 diagrammatically the use according to the invention of a discharge gap for the ionization and simultaneous deter~i-nation of a measurable variable which, for example, is at least co-significant for the container selection, Fig. 2 proceeding from the illustration of Fig. 1, a further embc-diment wherein the discharge current is regulated and the said measurable variable is determined from the behaviour o~

the regulating circuit, Fig. 3 diagrammatically, the use a spark gap according to the inven-tion for the ionization of the container gas in the containc~
itself, : ' ' - ': ~ ' ' - s 2~

Fig. ~ diagra~maeically, a fir~e e~bodiment for the discharge ionization of the ga~ and Jub~equent, ele~tro-~tatic ion ~eparation, for determining a mea~urable variable, Fig. 5 analogou~ly to the illustration of Fig. 4, a further embo-diment, wherein ~eparations are detected in dependence on respective ion mobilities as measurable variableQ, Fig. 6 diagrammatically, inside a to be tested container, a spark ionization device, followed by an electro-static, mobility-~electively operating ion separation device, Fig. 7 diagrammatically, the provision of a pre-selection to preve~
explosio~s in the case of certain contamination substances, for a discharge gap inside (a) or outside ~b) the container Fig. 8 diagra~matically, on a measuring arrangement according to the invention, a conveying system for containers that occur in a stream, and a ga~ sampling device provided ahead of th~
measuring arrangement with discharge gap according to the invention.

As mentioned at the outset, the present invention relates to the problem of investi~ating the state of contamination, in particular of empty containers. For example, with plastic bottles which occur i~
a stream, for re-use, there exists great uncertainty as to how they were used after their original content, e.g. mineral water, fruit n juice~, etc~, had been emptied. It ic ~rown that ~uch bottlo~ are often u~ed for other purpose~, for example in the household, e.g.
for ~toring ~oap ~ater, herbicide~, engine oil, acid~, petrol, benzene etc. If quch ~ub~tance ~ere Jtored in container~ that are nade available for re-u~e ~ith a ne~ original filling, ~ith certain categorie~ of conta~ination ~ub~tances an edverse effect on the taste of the newly filled original content can be expected, or ~uch a container can no longer be used for re-filling becau~e of the in-compatibility of the contamination or becau-~e they may be harmful to people'~ health.

For this reason it must be ascertained ~hether and ~hich residual contaminations are presene in the containers, so that a selection can be carried out bet~een containers that can no longer be u~ed for a new original filling, those that, for example, first have to undergo a special cleaning proces-~, and those that can quite safely be re-filled.

In this connection it must be borne in mind that, depending on the material of the container, in particular with plastic bottles, certain of the mentioned contamination substances are absorbed by the ~all material, and the contamination i8 slowly desorbed into a freshly filled content.

Fig. 1 no~ shows diagra~mmatically a first embodiment of a device for ascertaining a ~easurable variable which at least is co-sig-nificant as to ~hether the gas present in an empty container does 2~7~J~?,~
or do~ not contain conta~ination~ of a ~pecific ~ub~tance group.
A~ in certain case~ a1BO the content of a container may bc conta-~inated, and the ga~ lying above this i~ then cont~inated, the invention can, with regard to all its aspects, aloo be u~ed on coutainer~ that have already been filled.

By ~ay, for example, of a sampling line 1, a gas sa~ple G is draun off fro~ a to be tested, empty or partially filled container, of ~he type illustrated diagrammatically in Fig. 8, posYibly also ore from outside the container ~hich i~ in direct contact therewith or ~ith its filliug, and is ~oved past a discharge gap 3 with an elec-trode pair 5. The gap 3 iR operated by means of a current source 7.
The di~cbarge i~ produced as a corona discharge or as a spark diR-charge.

If, by the not illustrated Yuction device, the gas sample G is drawn off from the empty container and moved past the discharge gap 3, its dischar~e voltage will change. This voltage UF i~ mea-sured with a voltage measuring device 11.

The output signal of the voltage measuring device 11 i5 evaluated as a measurable variable and to this end is fed to a co~parator unit 13, to which other reference signals are fed from a reference signal unit 15. Selected according to the discharge voltage UF, output ~ignals A1, A2 ... are given off as measurable variables, which are relevant for specific sub-groups of contamination substan-ces or even for specific contamination ~ubstances, or for specific 2~ ?~
contamination concentration~. The refercnce signal~ are deter~ined b~
calibration me~suremen~s and adju~te~ ba~ed on ~tandard contaminated gas ~a~ple~.

Proceeding from the illu~tration of Fig. 1, Fig. 2 ~how~ a further meaJurable variable determination on a3 discharge gap 3 according to the invention. ~ere, by mean~ of a controllable high-voltage ~ource 7a, a discharge i~ maintained between the electrodes 5 of the spark gap 3. With a current mea~uring device lla, the di~charge current iF i~ measured and compsred on a comparator unit 17 with a current reference value iFSQLL that can be ~et on a reference signal unit 19.

The difference Jignal ~ ascertained on the comparator unit 17 i6 passed on as regulating difference, possibly by ~ay of a regulator 21, as adjustment variable, to the controllable voltage source 7a ~hich now acts as an adjusting element in the current regulating circuit, in such a way that the discharge current iF follow~ the reference value that can be set on the reference signal source 19 a~ nominal value adjuster, and preferably corresponds to the constant adjusted reference value i~nLL

The regulating differerce signal 4 or the adjustment signal gu for the voltage ~ource and/or the output voltage of the voltage source 7a is evaluated a~ measurable variable. This me~surable variable can, e~ explained with reference to Fig. 1, in turn be fed to a comparator unit 13 with superposed reference signal unit 15, and depending on 3~

the Jignal range in which the mea~urable variable a~certained on the regulating circuit lies, a conclucion ie roached regarding the pre-~ence or ab~ence in the ga~ J~mple G of cont~ination~ of variou~
~ubstance groups or regarding the presence of conta~ination~ of variou~ concentrationq.

As can be noted from Fig. 1 and 2, here the di~charge behaviour of the discharge gap 3 snd its electric sctuation, i.e. the discharge gap itself, i~ used directly an a measured value recorder for the measurable variable.

With the e~bodiments according to Fig. 1 and 2, a corona-AC or DC
discharge i9 produced.

As illustrated in the Fig. 1 and 2, the gas sample G can be tapped off through a sampling line 1 from the to be tested container.

~owever, according to Fig. 3 it is also possible, seeing that the discharge gap 3 can easily be miniaturized, to introduce the dis-charge gap 3a into the to be tested container 25, e.g. ~ith the aid of a test lance 23 illustrated diagrammatically in Fig. 3, and to then proceed in accordance with the information furnished in respect of Fig. 1 and 2.

~he taps 27 on the lance 23 according to Fig. 3 correspond to the taps which in Fig. 1 and 2 are shown with the same reference numeral 27 on the discharge gaps 3 illustrated there.

., 2~ 3~

Fig. 4 ~ho~ a further e~bodiment of an arrangement according to the invention for performing the meehod accordin~ to the invention, ~herein by ~eans of the di~charge gap the ga5 i~ ionized and, in contrast to the e~bodi~ent~ of Fig. 1 and 2, the ionized ga~ i~
evaluated ~ay from the di-~charge gap.

By ~ay of the sampling line 1, the gas sample G is taken from the to be tested container or its direct vicinity and fed to the discharge gap 3, operated ~ith the current source 7. A condenser arrangement, e.g. a cylindrical condenser 29, is provided after the discharge gap 3, in the direction of flow of the gas. It compriseq the cylindrical outer conderser shell 29a and the coaxial, inside mandrel 29i.

The condenqer 29 is charged to a predetermined voltage value by mean~ of an adjustable voltage source 31, 90 that an electric field E i~ formed on the condenser. Because of the gaq ionization on the discharge gap 3, depending on the polarity and strength of the electric field E, ions of the one polarity are driven to one of the condenser plates 29a, 29i, and ions of the other polarity to the -~
other plate. The balance of the ions driven to the capacitance plates 29a, 29i produces, in the external circuit connected to the cylindrical condenser 29, a current i. This is measured as current integral by a charge amplifier 32 or, as indicated by broken lines, by a current amplifier 32a.

2~;J~3~

When a chargc ~nplifier 32 is provid~d, t~e integration ti~e T, during ~hich the current flo~ing thr~ugh tb,e condenJer 29 is integrated, is pre-~et, and thi~ inte!rval T i~ set off by any signal ST defining the ~eart of the ~easuring cycle, e.g. at the start of the JuckiDg off of gas or when a specific surge front of the current i occurs.

When the integration time T hss expired, the re-setting Jwitch on the charge amplifier, illustrated diagrammatically in Fig. 4, iQ
closed.

The output signal, ~hether it corresponds to the current integral if the charge amplifier 32 is provided, or to that of the provided current amplifier 32a, i5 fed, in the ~anner already described with reference to Fig. 1, to a comparator unit 13, on the output side of which, ~elected according to the ~agnitude of the occurring input signal E, output signals Al, A2 etc. occur as measurable variable.

Here the spark gap 3 provided according to the invention, arranged either in a to be tested container itself in accordance with Fig. 3, or, as illustrated in Fig. 4, in the sampling line 1, is used for the ionization of the to be tested gas.

This procedure makes it possible, because the spark gap can be miniaturized, to provide the gas ionization in a constructionally flexible ~arlner at any point of a selection plant. The separation takes place at the same point, either along the sampling line, or Z~

in the to be teJted container it~elf, or i8 located a~Ay from the ionization.

Wherea~ the procedure de~cribed ~ith reference to Fig. ~ only per-mit~ a lu~p ~u~ determination of, a~ nea~urable variable, the charge balance of the ga~ that occurs as a re~ult of the spark ionization, to ~hich end, if the condenser arrange~ent 29 i8 arranged along~ide a sAmpling line l, the gas must be fed in at a predeter~ined flo~
velocity, Fig. 5 sho~s in principle a procedure by neans of ~hich, after ionization of the ga~ fro~ the container, by the u~e according to the invention of a spark gap, an evaluation takes places of the ions formed in the gas according to their mobility. As a result thereof contaminations of different substances or substance groups can be detected more ~electively.

To this end the ionized gas G~ i9 fed to an electro-static separator stage 35, constructed -~ubstantially as sho~n in Fig. 4, ~hich, for example, again consists of a cylindrical condenser arran~ement. This comprises, for example, a large internal mandrel 30i as ~ell as a plurality of cylindrical surfaces 30a arranged insulated behind one another. All condensers, formed by the co~mon internal ~andrel 30i and one cylindrical surface 30a each, are preferably placed under the same electro-static voltage by means of the voltage source 31, 80 that the same field strengths E prevail above the respective condensers 30i, 30a.

If the gas enters the condenser space 30z ~ith ions of a different z~7~3~

mobility. a~ illustrated diagra~atically, and the~e experionce in ~a~e, becau~e of the homogeneoug field strength E, provided that the ion~ have the same charge~, al o identical deflection force~, then the more mobile ion~ are deflected more per axially traver~ed path than the le3s mobile one~. Accordingly, the currents il, i2 ...
led off from the respective condensers are, a~ measurable variables, ~n indication for the ions deflected ~equertially in the dircction of the gas flo~, wherein ions of a decrea~ing mobility contribute sn increasing amount to the current of the conden~er arrangements posi-tioned do~tream ~ith respect to the direction of flow of the gas.

The tapped-off currents i, as explained with reference to Fig. 4, are detected by a charge amplifier or current amplifier, and pro-cessed further as measurable variables for the container selection.

Fig. 6 shows an embodiment for discharge ionization of the gas and electro-static separation measurement, directly in a to be tested container. In a further development of the arrangement described ~ith reference to Fig. 3, on the lance 23 with at its end a dis-charge gap 3, on the upper part, a plurality of metallic surfaces 33i, insulated from one another, is provided, and coaxially to same, a metallic cylindrical surface 33a.

As illustrated diagrammatically, the lance which has been developed further in this manrler is let into a to be tested container, and near the bottom thereof the gas is ionized by means of the discharge gap 3. Already because of the resultant heating of the gas inside 2~ 3~

the container, there occura a gas flow i~ the directiorl of the con-tainer opening, in ~hicb nection lies the ~eparator ~t~ge formed by the conden~er~ 33i, 33a.

~referably, in addition to thi~, a forccd flow of the ionizing ga8 G~ i~ brought about by feeding in a further gas, e.g. through dia-grammatically illustrated opening3 37.

~he electricity supply to the spark gap 3a and the condenser arrenge-Dent as ~ell as the current taps for tapping off the currentC il, i2 etc. are passed through the lance 23, and the same applies to a line to the ga~ outlets 37.

As mentioned, with the embodiments according to Fig. 1 to 3 pre-ferably a corona discharge i9 produced. With those according to Fig. 4 to 6 both a corona discharge as well as a spark discharge can be produced, i.e. ~hen the ionization of the gas is measured.
When operating ~ith spark discharge, for a measurement, preferably a series of a predetermined number of sparks is produced, and in the flo~ing gas G~ ionized by this the ion density is measured and averaged over a predetermined period, so as to obtain, in particu-lar, more reliable results.

With certain contamination substances the discharge ionization ac-cording to the invention, or also a known flame ionization, may cause an explosion. Because of this, for reasons of safety, when using these ionization techniques on the occurring empty containers, .3~

a pre-selection must be carried out. This i~, for a m~uring in~ide the Container, illustrated diagrac~atically in Fig. 7a. ~ccording to thia the to be te~ted container~, eg. pla~tic bottleJ, are noved on a conveying Jyste~, either a conveyor belt or a carrousel ~y~ten, paqt a first mea~uring ~tation 40, where, either by the taking of gas ~amples, a~ illustrated, or by i~ersiDg a probe into the con-tainer in que~tion, the presence of ~pecific, explo~ive contamina-tions ia detected.

To thiq end, preferably ~emi-conductor gaq 3ensor~ or electro-chemical cells ere used, adapted to the detecting of known exploaive contaminations. If a container ~ith explosive contaminations is detected, then, as illustrated diagrammatically, e.g. by means of a conveyor shunt, the container in question iq removed 60 that it ~ill not be tested further. Container~ that are recoRnized as safe in this respect are pasqed on to the ionization ~eaquring station 42 ~ith the lance 23.

Based on the ascertaining of further contaminations and a correspon-ding evaluation of the relevant measuring signals on an evaluation unit 44, a further conveyor shunt i5 actuated, and inadmissibly con-taminated containers are removed or passed on to a special cleaning process, ~hilst only containerq with contaminationq of an admissible type are passed on for re-filling.

Aq was mentioned at the outset, certain conta~ination substance~
are absorbed by certain ~all materials of the containers, and in ~ 7~~3~

particular by pla~tic, and are only ~lo~ly released agai~ into eh.
inside of the con~ainer. Without special measureJ the cont~ination concentration inside the container, vie~ed at a given time, may be difficult to measure. Ho~ever, if the container haR been filled snd ~aq been stored for quite a long time, there occurs, for example, sn adversc effect on the taste of the content of the container.

It i8, therefore, furthermore proposed, as illuQtrated diagra~mati-cally in Fig. 7 at 46, that prior to carrying out the contamination detection, contamination substances that have been absorbed by the ~alls of the containers should be expelled. According to the inven-tion, this is done by heating the container~, as illu~trated by the heat flow Q, ~hich can be done by infrared radiation, with plastic containers in particular al~o by microwave heating, by vaporization or gasification of the inside of the container and/or from the out-~ide, e.g. by letting in normal hot air.

In certain cases it is anyway indicated to rinse the contaiDers ~ith a gas, preferably ~ith air, and to rinse out certain amounts of resi-dual gas stemming from specific original contents, which other~ise could conceal other contaminations during the contamination detec-tion.

If a gas sample G* ic taken from the container according to Fig. 7b, the testing for explosive contaminations preferably takec place on the gas sample in question before it is passed on to the unit 41 for 2~7-~3~
~he discharge or fl~oe ionization. The otation then control~, for exa~plc, a valve 45 provided ahead o~E thé unit ~1.

According to Fig. 8, in a preferred e~bodi~ent, the ga~ to be te~ted i~ taken, ~ith the aid of a carrier ga~ from a carrier ga~ tan~ 70, from one of the containers poJitioned on the conveying ~yste~ 72, e.g. by Venturi-Juction through a ~ealing connection 74. ~y ~eans of the pu~p 76 carrier gas together ~ith the gas fro~ the container is fed to the ~easuring arrange~ent 78 ~ith the discharge gap. With the aid of a s~itch-over valve Vts the container connection can be bridged, and the arrangement 78 rinsed ~ith pure carrier gas, e.g.
purified air.

Claims

Patent claims:

1. Method for determining a measurable variable on gas from an empty or partially empty container, with which method gas from the con-tainer is ionized, characterized in that for the determination or containers that occur in a substantially uninterrupted stream, the gas is exposed to an electrical discharge gap (3), and the discharge behaviour (UF) of the gap and/or, set away from the gap, the discharge-related ionization (1) of the gas is evaluated as measurable variable.

2. Method according to claim 1, characterized in that the gas is ionized and subsequently measuring signals that depend on the mobility of the ions are evaluated.

3. Method according to claim 1 or 2, characterized in that in the ionized gas, by means of electro-static ion sepa-ration, a measurable variable is determined.

4. Method according to claim 3, characterized in that by pre-setting electro-static ion deflection stages of different lengths and the determination of stage section specific ion separation rates measurable variable are formed.

5. Method according to claim 1, characterized in that a selection is carried out beforehand, and explosive gases are not exposed to the discharge.

6. Method according to any one of the claims 1 to 5, characterized in that prior to determining the measured values, the containers are rinsed, e.g. with water, steam, as gas, in particular with air.

7. Method according to any one of the claims 1 to 6, characterized in that prior to determining the measured values, the containers are heated, e.g. by means of infrared, steam, water, a gas, in particular with air, or with microwave energy.

8. Method according to any one of the claims 1 to 7, characterized in that the discharge is produced as a corona discharge or as a spark discharge.

9. Method according to any one of the claims 1 to 8, characterized in that the gas from the container is made to flow past the gap.

10. Method according to any one of the claims 1 to 9, characterized in that a spark discharge series is produced.

11. Method according to claim 10, characterized in that the ioniza-tion of the gas produced by a pre-set series is evaluated.

12. Method according to any one of the claims 1 to 11, characterized in that the discharge is produced inside the container.

13. Method according to claim 12, characterized in that the deter-mination of the measurable variable takes place on the gas inside the container.

14. Method according to any one of the claims 1 to 12, characterized in that the discharge is produced outside the container.

15. Method according to any one of the claims 1 to 14, characterized in that the discharge current or voltage is regulated, and a regulating difference or, correspondingly, a discharge voltage or discharge current is measured.

16. Measuring arrangement for determining components in a gas from containers conveyed in a stream, comprising a conveying system for the containers to and from a measuring arrangement with an ionization device for the gas, characterized in that the ioni-zation device comprises at least one electrical discharge gap that can be brought in contact with the gas from each of the containers.

17. Measuring arrangement according to claim 16, characterized in that the discharge gap is discharge current or discharge voltage regulated.

18. Measuring arrangement according to claim 16, characterized in that the discharge gap is followed by at least one electro-static ion separation stage.

19. Measuring arrangement according to any one of the claims 16 to 18, characterized in that the discharge gap is arranged on a driven measuring lance which can be moved into and out of a container on the conveying system.

20. Measuring arrangement according to any one of the claims 16 to 19, characterized in that a device for taking gas samples from a container on the conveying system is provided on the input side of the discharge gap.

21. Measuring arrangement according to any one of the claims 16 to 20, characterized in that the discharge gap is preceded by a selection unit which detects explosive gas components in the gas and blocks a bringing into contact of the explosive gases with the discharge gap.

22. Use of the method according to any one of the claims 1 to 15 or of the arrangement according to any one of the claims 16 to 21 for the selection of containers which are to be re-filled.

23. Use according to claim 22 for plastic bottles for foodstuffs.