T 0856/92 08-02-1995

1. The appeal is admissible.

2. The independent Claims 3 and 7 together with dependent Claims 4 to 6 and 8 to 11 essentially correspond to the set of Claims 1 to 9 (auxiliary request) on the basis of which the Opposition Division has decided to maintain the patent in amended form. Since no appeal was filed against the maintenance of these claims (the Proprietor of the patent is the sole Appellant), neither the Board nor the Opponent may challenge the maintenance of the patent on the basis of these claims (see decision of the Enlarged Board of Appeal G 9/92, OJ EPO 94, 875; in particular first paragraph of the headnote). No comment is therefore required with respect to these claims.

3. Claims 1 and 2, allowability of the amendments

Claim 1 is based on the original Claim 1 and contains the additional features that control means are provided for controlling the valve means and the measurement of streaming potential with the aid of the electrodes, and that these control means are programmed to perform a measuring cycle in which stock enters the measuring cell through the lower port to build a pad of particles on the underside of the filter mesh subsequent to the formation of the pad, a pulse of substantially constant pressure difference is applied across the pad, said pulse being shaped such that there is negligible accumulation of further particles to the pad, a measurement of streaming potential is performed while said pressure pulse is applied, and the pad is subsequently flushed from the filter mesh to drain through the lower port.

There is no controversy about the fact that a control circuit controlling the valves and the measurement is disclosed in the application as filed (see eg reference number 140 in Figure 1; page 10, lines 17/18 and page 14, lines 13 to 19). It is also undisputed that a pad of particles is built on the underside of the filter mesh, subsequently a pulse of substantially constant pressure difference causing negligible accumulation of further particles is applied across the pad while a measurement of streaming potential is made (eg page 8, line 35; page 9, line 33 to page 10, line 5; page 21, lines 13, 16, 21 and 31/32), and subsequently the pad is flushed from the filter mesh (eg page 9, lines 28 to 32). However, the Respondent argues that the control means and their operation leading to the above events are only disclosed (see original Claim 11) in the context of specific operations of specific valves and in particular only for a cycle including a low pressure reference condition (between steps (a) and (b) and/or between steps (b) and (c)), which further features are not included in the present Claim 1.

There is no simple rule indicating which combinations of features can, and which cannot, be considered as independently disclosed. Certainly, the whole of the content of the original application has to be taken into account, and each case has to be individually checked as to the information a skilled reader would gain from the application at its filing date. In the present case, from the above-cited passages of the original application and from the comments in the description regarding the disadvantages of the prior art (page 3, lines 10 to 25; "the measurement is not made with the same plug"), the reader gains the information that one of the main points of the invention (besides the spatial uniformity of the pad) is the maintenance of the properties of the pad during the measurement, which is achieved by inserting a pulse of pressure difference between the steps of forming and of flushing the pad, and by measuring the streaming potential during this pulse. The fact that in an apparatus for such measurements the necessary steps are automatically controlled by control means is understood by the reader to be the usual way of operating a measuring apparatus performing several steps and being applicable in an industrial plant, so that the reader understands the disclosed control means (140) to generally serve the purpose of controlling the necessary sequence of operations, independent of which steps might be required according to the one or the other embodiment.

For these reasons, the Board does not see a contravention of Article 123(2) EPC in the formulation of present Claim 1.

The additional feature of Claim 2 is disclosed on original page 10, lines 3/4 and in Figure 4. Claim 2 is therefore also allowable under Article 123(2) EPC.

The above-mentioned features of Claim 1 (as far as added after grant) do not extend, but rather restrict the scope of protection conferred. The requirements of Article 123(3) EPC are therefore also fulfilled.

4. Novelty

4.1. In correspondence with the subject-matter of Claim 1, D5 (see in particular page V43, right-hand column, paragraph 2 to page V44, right-hand column, paragraph 1 and Figures 2 and 3) describes a measuring apparatus for use in the measurement of an electrical characteristic, ie streaming potential, of a fibrous dispersion. The measuring cell of this known apparatus has a housing, first and second ports for fluid to be passed through the housing, a filter mesh between the ports and a respective electrode in each compartment on both sides of the filter mesh to measure the streaming potential. Naturally, first and second conduit arrangements for introducing particle-bearing stock and flushing water to the ports are provided. The first conduit arrangement includes connections for a source of particle bearing stock and drain. Moreover, it is implicitly disclosed that the known apparatus comprises control means for the valve means and for the measurement of streaming potential (see German "abstract", lines 4/5; page V43, right-hand column, lines 8/9 and 34 to 39; page V44, left-hand column, line 2; and page V45, left-hand column, lines 40/41), the control including the flushing of the pad subsequent to the measurement.

The apparatus according to Claim 1 is distinguished from this known apparatus by the fact that the cell is oriented to have the filter mesh essentially horizontally disposed with the first and second ports respectively below and above the filter mesh allowing a generally vertical flow direction and formation of the pad on the underside of the filter mesh, that valve means are provided in the first conduit arrangement, and that the control means are programmed so that subsequent to the formation of the pad a pulse of substantially constant pressure difference is applied across the pad, said pulse being shaped such that there is negligible accumulation of further particles to the pad, and a measurement of streaming potential is performed while said pressure pulse is applied.

4.2. D1 and D2 do not relate to the measurement of streaming potential, but to freeness testing. Consequently, there is not an electrode in each of the compartments before and after the filter mesh and no measurement of the potential between the compartments is made while the fluid is streaming through the pad.

D3 describes an apparatus for measuring the streaming potential in which the direction of fluid flow is vertical and the pad is horizontal.

However, the fluid is not a fibrous dispersion (but a solution of dye), the pad is not formed on a filter mesh during the flow of the fluid, but prefabricated and stuffed into the cell, and the pad is not flushed after the measurement. Since the fluid is not a fibrous dispersion, there is no necessary connection between the accumulation of particles on the pad and the pressure difference (ie velocity of flow). How the chosen pressure difference changes as a function of time during the measurement, is not mentioned.

D4 relates to the automatic measurement of streaming potential in a fibrous dispersion. A pad is built up on a filter mesh and flushed after the measurement. However, the arrangement is quite different from that according to the patent in suit since there are actually two filter meshes which are both not horizontal but vertical and between which the flow of the dispersion enters through a further port for forming the pad. The flows for building the pad and for making the measurement are not directed through the same ports of the measuring cell. Neither a separate pulse of pressure difference nor avoidance of further accumulation of particles during measurement are mentioned.

4.3. For these reasons, the subject-matter of Claim 1 is novel in the sense of Article 54 EPC.

5. Inventive step

5.1. It is undisputed that D5 represents the prior art closest to the subject-matter of the patent in suit since this document describes the principle of automatic measurement of streaming potential in a fibrous dispersion comprising the step of building the pad and measuring the streaming potential by using the same flow of dispersion through the filter mesh/pad (caused by a pressure difference across the pad).

As compared with this prior art, the subject-matter of Claim 1 aims at better reliability of the measurement (cf page 3, lines 22 to 25 of the original description) and, more specifically, at avoiding non-uniformity (cf page 3, lines 1 to 3) and temporal changes (cf page 3, lines 10 to 13, 16 and 17) of the pad while the measurement is made.

These goals are achieved on the one hand by choosing a horizontal orientation of the filter mesh, and on the other hand by employing a separate pulse of pressure difference (= fluid flow) across the pad shaped such that substantially no further accumulation of particles occurs (according to D5 the measurement is made while the pad is being built up).

5.2. It may be true that changing the filter orientation from vertical to horizontal (and consequently the direction of flow from horizontal to vertical) is a simple modification which a skilled person would always consider and the effects of which (reduction of the effects of sedimentation on the uniformity of the pad) could be seen beforehand.

However, the idea of temporally separating the build-up of the pad from the measurement of the streaming potential, while nevertheless using the same flow of dispersion for generating the streaming potential, and of ensuring the constancy of the precedingly formed pad during the measurement by shaping the separate pulse of pressure difference across the pad (ie the velocity and duration of flow of the dispersion generating the streaming potential) such that the amount of dispersion passing through the pad is not sufficient to provide substantial accumulation of further particles on the pad, is neither derivable from the teaching of D5 nor from the general experience of the skilled person.

5.3. Moreover, the idea of performing a measuring cycle of this kind could not be derived from any of the other cited documents.

In the apparatus for measuring streaming potential according to D4, the step of passing fluid through the pad is separated from the step of forming the pad. However, the measuring fluid flow in this apparatus (comprising three ports and two filter meshes) is quite different from the pad forming flow, and the composition of the fluid used for generating the streaming potential is more or less undefined. No teaching is given regarding further accumulation of particles or a corresponding shape of a pressure pulse.

In the apparatus according to D3, the step of streaming potential measurement is also separated from the fabrication of the pad. However, the pad is not even fabricated in the measuring apparatus itself, and no teaching regarding the accumulation of further particles on the filter mesh could be derived since the fluid is not even a fibrous dispersion.

Finally, D1 and D2 do not relate to streaming potential measurement but to freeness testing, and consequently the measurement (of the amount of flow through the pad) is not separated from the formation of the pad.

5.4. Since for these reasons the above-mentioned idea is not obvious for a person skilled in the art, the subject-matter of Claim 1 involves an inventive step in the sense of Article 56 EPC. Claim 1 is therefore allowable under Article 52(1) EPC.

Claim 2 is allowable due to its dependence on Claim 1.

6. This decision relates to Claims 1 and 2 amended during the oral proceedings in the absence of the Respondent. Nevertheless, the Board does not consider this to be in conflict with Article 113(1) EPC and the decision of the Enlarged Board of Appeal G 04/92 (OJ EPO 1994, 149) since as compared with Claim 1 according to the former first auxiliary request known to the Respondent the present Claim 1 has in substance only been amended in such a way as to clarify those points already mentioned, as lacking clarity, in a communication of the Board accompanying the summons to the oral proceedings and to supplement features already pointed out in the said communication as appearing to be essential for the invention. Thus, the Respondent had the opportunity to comment on these facts (cf. the similar findings in the unpublished decision T 202/92). Claim 2 essentially corresponds to Claim 1 according to the former third auxiliary request which is known to the Respondent.

7. Since the patent requires an adaptation of the description to the set of claims forming the basis for the maintenance of the patent, the Board remits the case to the Opposition Division in accordance with Article 111(1) EPC.