IEC_60068-2-68-1994.pdf

2ContentsPageIntroduction 31General 31.1Scope 31.2Description of Test L 32Normative references 33Definitions 44Test La:non-abrasive fine dust 54.1Method La1:cyclic air pressure 54.2Method La2:constant air pressure 74.3Guidance for test La 105Test Lb:free settling dust 165.1Object 165.2Method Lb 165.3Guidance for test Lb 186Test Lc:blown dust and sand 236.1Method Lc1:recirculating chamber 236.2Method Lc2:free blowing dust 276.3Guidance for test Lc29Annex A(informative)Guidance 40Annex B(informative)Bibliography 47Figure 1 Structuring of test methods 34Figure 2 Pressure cycle in the test chamber Category 134Figure 3 Example of a suitable test chamber for method La1 35Figure 4 Example of a suitable test chamber for method La2 36Figure 5 Example of test apparatus for test Lb37Figure 6 Principal layout of test apparatus for method Lc1 38Figure 7 Example of dust injection system for method Lc2 39Figure A.1 Particule size distribution 45Figure A.2 Relative humidity according to temperature(example)46Table 1 Summary of test characteristics4Table 2 Typical dust and sand sedimentation rates 22Table 3 Acceleration factor 22Table A.1 Hardness scale 41Table A.2 Comparison of test methods 443IntroductionThe tests described in this part of IEC 68-2 give information on effects for which the relevant specification may specify assessment criteria.Some of such effects are:a)ingress of dust into enclosures;b)change of electrical characteristics(for example,faulty contact,change of contact resistance,change of track resistance);c)seizure,or disturbance in motion of bearings,axles,shafts and other moving parts;d)surface abrasion(erosion);e)contamination of optical surfaces;contamination of lubricants;f)clogging of ventilating openings,bushings,pipes,filters,apertures necessary for operation etc.Different tests have been specified to consider diversified aspects which may be used to verify constructional integrity of electrotechnical products or to simulate the conditions of operation in service.The tests differ by the character of the air flow carrying the particulate matter,and by the type of such matter,resulting in a special methodology for each test.1 GeneralThis survey indicates the general structure of the dust/sand tests included in this publication.The structuring and a summary of the characteristics of the different tests are given in Figure 1 and Table 1.It should be noted that the dust test of IEC 529 has its equivalent in the proposed method La2.See also Annex A.1.1 ScopeThis part of IEC 68-2 specifies test methods to determine the effects of dust and sand suspended in air,on electrotechnical products.The test methods of this standard are not intended for the testing of air filters.Only method Lc2 is suitable for the simulation of the erosion effects of high velocity(more than 100 m/s)particles.1.2 Description of Test LThe dust and sand test is structured into three groups:2 Normative referencesThe following normative documents contain provisions which,through reference in this text,constitute provisions of this part of IEC 68-2.At the time of publication,the editions indicated were valid.All normative documents are subject to revision,and parties to agreements based on this part of IEC 68-2 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below.Members of IEC and ISO maintain registers of currently valid International Standards.IEC 529:1989,Degrees of protection provided by enclosures(IP code).IEC 721-2-5:1991,Classification of environmental conditions Part 2:Environmental conditions appearing in nature Section 5:Dust,sand,salt mist.La:non-abrasive fine dust.A test which is primarily oriented towards investigation of the seals of the test specimen.The test specimen is exposed to a very fine dust in the form of talc or an equivalent.The effects of temperature cycling resulting in a pressure difference between the inside and outside of the specimen may be reproduced.Lb:free settling dust.A test which is oriented towards investigation of the effects when simulating conditions at sheltered locations.The test specimen is exposed to a low-density dust atmosphere created by the intermittent injection of a small quantity of dust which is allowed to fall by gravity onto the specimen.Lc:blown dust and sand.A test which is oriented towards investigation of the seals and the effect of erosion when simulating outdoor and vehicle conditions.The test specimen is exposed to either a turbulent or a laminar air flow to which is added a quantity of dust,sand or a dust/sand mixture.43 DefinitionsFor the purpose of this part of IEC 68-2 the following definitions apply.3.1 dustparticulate matter of unspecified origin or composition whose size ranges from 1 4m to 150 4m(see note to 3.7)Table 1 Summary of test characteristics3.2 dust concentrationtotal mass of dust particles per unit volume of air3.3 humidityrelative humidity is defined as the ratio of the actual vapour