T 0172/82 (Particle analyzer) 19-05-1983

1. The appeal complies with Articles 106 to 108 and Rule 64 EPC and is therefore admissible.

2. Leaving aside amendments made merely for purposes of greater accuracy and clarity of formulation, the claim as it stood when the application was refused corresponds to the present claim according to the main request, whereas the original published claim contains in the characterising portion the further feature: "means (6) for delaying the output signal on the lead (12) from the first comparator (1)". This feature was represented in figure 3, but not clarified further in the description. The omission of this feature was considered by the Examining Division as an inadmissible amendment to the documents and thus a contravention of Article 123(2) EPC. The Board cannot subscribe to this for the following reasons: The principal items in the claimed auxiliary device are the narrow adjustable threshold interval (V2-V1) for the particle size and the determination of the minimum plus rate in that interval as a function of the adjustment (characterising features (a), (b), (c), (f) and (g)). It is quite clear for the skilled reader of the original documents that the delay circuit (6) is without importance for establishing the adjustable threshold interval and for registering the number of particles in this interval; indeed it even raises a question regarding the whole purpose of the circuitry, since the number of particles can be ascertained with complete accuracy only if the count pulses coming from the two comparators (1, 2) pass into the anti-coincidence circuit (7) simultaneously. The omission of the delay circuit lies therefore within the realm of clarifying an obscurity or resolving an inconsistency, which the Guidelines for Examination allow (cf. C-VI 5.3). The Board is aware that cases can arise in which the removal of a feature leads to an inadmissible alteration of the subject-matter of the application, a fact illustrated by the example given in the Guidelines for Examination under C-VI, 5.8. In that case deletion of the outer-layer feature would result in a different laminated panel to that originally claimed. A decision therefore has to be made according to the circumstances of each case as to whether (a) the sole purpose of omitting a feature is to clarify and/or resolve an inconsistency or (b) whether it inadmissibly amends the subject- matter. The Guidelines for Examination even permit, in some cases, the inclusion of features not originally disclosed, insofar as they are intended to provide an obvious clarification and can be shown to be well known to the person skilled in the art, cf. C-VI, 5.6. What applies to the insertion of features must apply mutatis mutandis in equal measure to the deletion of features. In the given circumstances the deletion of the delay circuit in the claim and in the other documents is considered admissible and indeed advisable. The claim cannot therefore be objected to on formal grounds.

3. The Examining Division raised no objections as to novelty and inventive step. Nor did it introduce any publications into the proceedings, so that the state of the art cited by the appellant in the application description can be relied upon. The publications cited there (and only those publications) are indicated in the search report.

3.1 According to these citations, apart from particle counting devices with a fixed count threshold, particle counting devices with one or more adjustable count thresholds, e.g. with the aid of an oscilloscopic display of the particle distribution curve, are also known. This state of the art is reflected in the precharacterising portion of the claim. In the case of the device described in US-A-3 638 227 for ascertaining the size distribution of particles, the count rate is plotted in a single analytical run as a function of the threshold voltage. From this plot the threshold setting for the particle system to be analysed can be determined. US-A-3 557 352 also concerns a particle counting device using a circuit for setting a count threshold. In this case the count threshold does not serve to separate two adjacent particle classes but to divide one class into two sub-classes, in particular to ascertain the median of mass distribution. The subject-matter of FR-A-2 097 763 is a special computing system for detecting a class with low probability of occurrence in a histogram formed from optical signals. The system is based on the comparison of signals with a series of pre-set values. Its main area of application is the automatic navigation of space vehicles. A narrow adjustable count interval for establishing in conjunction with a counter the minimum pulse rate when the interval is adjusted is no more present in the case of the last-mentioned system than it is in the actual particle analyzers according to US-A-3 638 227 and 3 557 352. Accordingly, the claimed additional device for a particle analyzer is new (Article 52 EPC).

3.2 According to the second paragraph on page 6 of the description, the subject-matter of the application is intended to resolve the problem of creating a simple auxiliary device for a particle analyzer which would eliminate the element of inexactitude in setting the count threshold attributable to operator tolerance differences, so that the accuracy of the analysis is maintained even when the equipment is operated by staff without much training. The problems involved in setting the threshold are sufficiently known (cf. e.g. US-A-3 638 227, column 1, lines 10-37). Experts in this field are constantly endeavouring to attain high analysis accuracy; the problem set cannot therefore be regarded as in any way exceptional. This problem is resolved by the characterising features (a), (b), (c), (f) and (g) of the claim, while features (d) and (e) permit in addition the immediate input into the analyzer after the count threshold has been fixed of the upper limit of the particle class range to be registered. The basic idea is the setting of a narrow particle size range, its adjustment along the particle size co-ordinates and the registering of the count rate as the range is adjusted, the co-ordinate value when the minimum pulse rate occurs fixing the location for setting the count threshold. There is nothing whatever in the state of the art to suggest such an approach. Even the state of the art in the embodiment coming closest to the subject- matter of the application (threshold positioning corresponding to an oscilloscopic display of the particle signals) merely discloses very simple kinds of adjustable count threshold. Still less is there anything in the remaining state of the art that might suggest to a skilled person the special circuitry claimed for putting this basic idea into effect. The claimed auxiliary device for a particle analyzer thus involves an inventibe step (Article 56 EPC).

3.3 The claim according to the main request accordingly meets the requirements of Article 52(1) EPC and is therefore allowable.

4. The present description complies with the provisions of Rule 27 EPC.

5. In these circumstances, it is not necessary to deal with the alternative request.