Understanding isolator standards and certification to meet

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Understanding isolator standards and certification to meet safety requirements David Lohbeck National Instruments Electrical products use numerous components some of which are important for protection of the product user Isolator components are commonly used to protect separate product users from dangerous voltages but knowing how to select the correct isolator for safety protection can be

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ISOLATOR TECHNOLOGIES, There are three isolator technologies in use today. Optical Uses light LED transfer across a transparent nonconductive insulation barrier Advantage is high. electrical isolation values Uses a silicone polymer insulation. Magnetic Inductive coupling transfer using transformer coil design and provides high isolation at high. frequencies Uses polyimide or silicone dioxide insulation. Capacitive Uses a changing electric field to transmit energy by means of capacitance Capable of high speeds. and relatively small package Uses silicon dioxide insulation. Optical isolators also referred to as optocouplers or optos employ an opaque silicone polymer material as the. internal insulation Optos have larger footprints and provide high levels of isolation when a film barrier is used The. newer generation of digital isolators magnetic and capacitive offer advantages in performance size and power. efficiency Digital isolators utilize polyimide silicone dioxide for their insulation Optical isolators rely mostly on. thickness for internal spacing whereas digital isolators have insulation of less than one thousandth of an inch and. rely on safety testing Figure 1,Optical Isolators Digital Isolators. Dielectric and or Silicone Insulation Polyimide Insulation Silicon Dioxide Insulation. 100 400 m Thickness Typical 20 32 m Thickness Typical 7 15 m Thickness Typical. Optical Magnetic Capacitive,Standards Standards,IEC 60747 5 5 and UL 1577 VDE 0884 10 and UL 1577. FIGURE 1 Isolators,PRODUCT vs COMPONENT STANDARDS, It is very important to understand the difference between product and component standards and that product and. component safety standards have different scopes tests and requirements. Products are ready for use equipment Examples of safety standards for products equipment are IEC 60950 1 for. Information Technology Equipment IEC 61010 1 for Measurement Equipment and IEC 60601 1 for Medical. Equipment Products undergo a one minute isolation test voltage also called dielectric withstand high potential or. hipot test Isolators cannot operate continuously at the isolation test voltage Product standards also allow partial. discharges that can degrade the insulation barrier due to small bubbles or impurities in the insulation Product. standards do not contain the tests that fully stress test the insulation of isolator components. NOTE Product standards focus on a dielectric withstand test voltage for isolation This. is a one minute transient test typically at 2 500 5 000Vac Products cannot operate. continuously at the test voltage Do not assume that an isolator rated for 2 500Vac. isolation can operate at this voltage, Components are electrical electronic parts that are assembled into built in products The associated isolator.
component safety standards are IEC 60747 5 5 for Optical Isolators VDE 0884 10 for Digital Isolators and UL. 1577 for Optical Digital Isolators Component standards have different oftentimes stricter safety requirements and. tests than product standards Isolator component standards require partial discharge testing which is performed to. check whether the isolator s internal insulation can break down Partial discharge is an IEC VDE isolator component. test which can detect small imperfections that could grow over time Partial discharge testing is a better measure of. the internal insulation of the isolator than the isolation test voltage. N E T W O R K www edn com January 26 2016 Page 2, NOTE Working voltage VIORM is specified by IEC 60747 5 5 optos and VDE 0884. 10 digital standards Working voltage is the voltage that can be continuously applied. to the isolator during its operation Working voltage ratings average between 150 and. 600Vac The isolator s working voltage must be as high as the product s operation. supply voltage, Components and products must fall within a safety standard s scope before the standard can be applied As shown. in Table 1 isolators are components which are not within a product standard s scope Therefore product standards. are not applicable for isolators,Component Standards Scope. Optical and Digital Isolators,IEC 60747 5 5 Optoisolators. This component standard gives the terminology essential ratings characteristics safety. tests as well as the measuring methods for photocouplers optocouplers Photocoupler. is an Optoelectronic device designed for the transfer of the electrical signals by utilizing. optical radiation to provide the coupling with electrical isolation between the input and. the output Reinforced insulation 1,VDE 0884 10 Non Opto Digital Isolators.
This component standard gives the terminology essential ratings characteristics safety. test and the measuring methods of magnetic and capacitive couplers Magnetic and. capacitive couplers consist of a transmitter stage and a receiver stage on either side of a. galvanic insulation barrier The device transmits a signal across the insulation boundary. where a receiver stage is able to detect the transmitted signal and uses the information. to generate the electrical output signal This standard specifies magnetic and capacitive. isolation barrier mechanisms and the insulation functions for Basic and Reinforced. insulation 1,UL 1577 Optocouplers and Digital Isolators. This component standard covers optical isolators also called optical couplers or. photocouplers a intended to provide unidirectional signal transfer between dielectrically. isolated circuits and b intended for use in equipment with a supply voltage not. exceeding 600Vac rms or dc These requirements evaluate the electrical isolation. properties of single and double reinforced 1 protection insulation between the isolated. circuits of the optical isolator,Product Standards Scope. Information Technology Measurement and Medical Equipment. IEC 60950 1 Information Technology Equipment, This equipment standard is applicable to mains powered or battery powered information. technology equipment including electrical business equipment and associated. equipment with a rated voltage not exceeding 600V, IEC 61010 1 Measurement Control and Laboratory Equipment. This equipment standard specifies general safety requirements for the following types of. electrical equipment and their accessories wherever they are intended to be used. a electrical test and measurement equipment b electrical industrial process control. equipment c electrical laboratory equipment,IEC 60601 1 Medical Electrical Equipment.
This equipment standard applies to the Basic Safety and Essential Performance of. Medical Electrical ME Equipment and Medical Electrical Systems hereafter referred to. as ME Equipment and ME Systems, 1 Reinforced insulation required for safety protection. TABLE 1 Scope of Component and Product Standards,N E T W O R K www edn com January 26 2016 Page 3. Another issue with standards is that component standards are not equivalent between Europe International. IEC VDE and North America UL which means that isolators need to meet both the IEC VDE and UL component. CAUTION Always look for the correct isolator component standard for safety evaluation. and testing Isolators also need to meet both IEC VDE and UL component standards. for International IEC VDE CE and for North America UL Isolator component safety. standards are IEC 60747 5 5 VDE 0884 10 and UL 1577. SPACINGS CLEARANCE CREEPAGE BASIC REINFORCED, In addition to testing safety standards require separation of specific circuits for user protection These are the. spacing distances between hazardous voltage and nonhazardous touchable voltage circuits Basic Double and. Reinforced are safety insulation levels Basic is a single layer and Double is two layers Reinforced is a single. insulation system which is equivalent to Double Products and components must remain safe even when there is a. single fault or failure in the insulation It is assumed that a single fault can occur in one layer of insulation. Reinforced is required to protect users in case of a single fault of the first Basic layer In other words if a fault. occurs in the Basic insulation the second insulation will still protect the user Basic is not adequate for protection of. product users Reinforced solves the single fault issue. NOTE Safety standards require Reinforced insulation to protect product users from. hazardous voltages 30Vrms 42 4Vpeak 60Vdc,FIGURE 2 Clearance and Creepage. External spacings are measured from inputs to outputs in Clearance and Creepage Figure 2 Clearance is the. shortest distance between two circuits through air Creepage is the shortest distance on a surface An isolator s. external input to output AC to DC circuit spacings need to meet the distances of a product standard which is. based on the supply voltage to the product IEC 60950 1 is the primary standard describing spacing requirements. An example is 4 0 3 0 mm Clearance distance and 6 0 mm Creepage distance for an isolator used in a 250Vac. product Table 2,Overvoltage Clearance for Creepage for.
Supply Voltage Supply Voltage Test Voltage,Category II Reinforced Reinforced. V ACrms Vpeak or dc Vpeak or dc,Vpeak mm mm,150 210 1500 2 0 1 0 3 0 2500. 150 300 210 420 2500 4 0 3 0 6 0 4000,300 600 150 300 4000 6 4 6 0 12 0 6000. 1 Values are based on IEC 60950 1 product safety standard. 2 Values in brackets apply only if manufacturing is subjected to a quality control program that provides at least the same level of assurance given in annex R 2 of. IEC 60950 1,3 Reinforced insulation,4 Pollution Degree 2. 5 Overvoltage Category II,6 Material Group IIIa IIIb.
TABLE 2 Clearances Creepage and Test Voltage,N E T W O R K www edn com January 26 2016 Page 4. Internal spacing is the distance through an insulation which is typically 100 400 m thickness for an optical. isolator A digital isolator s internal spacing on the other hand is verified by testing not thickness since the. insulation thickness is very thin typically 7 32 m Figure 1. The VDE UL Certificates or specifications of the manufacturer usually give the isolator s external spacing values. Spacing distances can also be easily measured on an isolator sample for verification For more information on. spacings refer to the relevant product safety standards. SPECIFICATIONS and CERTIFICATIONS, It s important to know what to look for before selecting an isolator for a product design Isolator specifications can be. confusing and may not tell the whole story Specifications sometimes state an isolation test voltage e g 2 500. 5 000 Vac and product standards IEC 60950 1 etc when the specifications should highlight the isolator working. voltage e g 150 600 Vac and component standards IEC 60747 5 5 etc Another issue is that a specification. may state Reinforced according to product standard when the isolator is actually only Basic according to a. component standard Remember that product standards and Basic insulation are inadequate for safety protection. Always verify that an isolator has VDE and UL Certifications You can determine if an isolator has. the necessary Certifications on the VDE and UL Certification Directories However some of the. safety ratings may not be found on the Directories The best way to make sure the isolator meets the. safety rules is to obtain a copy of the VDE and UL Certificates from the isolator manufacturer. You may also need the VDE UL Reports if the Certificates do not show the information. CAUTION Focus on the isolator s safety ratings and certifications Beware if the. specifications highlight product standards or isolation voltage Specifications should. clearly show the component standard s working voltage and Reinforced insulation. Obtain VDE and UL Certifications as proof of safety compliance. CONCLUSION, It is important to verify the standards tests and ratings used to evaluate and certify the isolator before selection and. incorporation into product designs Meeting all the isolator component safety rules helps ensure that the end. product can meet International and North America safety requirements IEC VDE UL CE etc Product standards. such as IEC 60950 1 or similar do not adequately address isolator component safety Be sure to verify that the. applicable component standards IEC 60747 5 5 VDE 0884 10 and UL 1577 have been applied to protect product. users and avoid costly product redesign, The most important things to know when looking for safety isolators are in order of importance. 1 Component Standards IEC 60747 5 5 VDE 0884 10 UL 1577. 2 Reinforced Insulation tests and spacings, 3 Working Voltage VIORM supply voltage e g 150 600Vac 210 840Vpeak.
4 Isolation Voltage VIOTM test voltage e g 2 500 5 000Vac. 5 VDE and UL Certifications International and North America. Artwork by Audrey Durney National Instruments,AUTHOR S BIOGRAPHY. David Lohbeck is Principal Safety Engineer at National Instruments Lohbeck is also an ANSI Lead and Technical Assessor. Previously he has worked for Dell Motorola and TUV in the field of international product safety machine safety and. electromagnetic compatibility EMC Lohbeck has published numerous articles about product safety and EMC. N E T W O R K www edn com January 26 2016 Page 5,FURTHER READING. Lohbeck David Safety isolation protects users and electronic instruments EDN September 30 2004. www edn com design test and measurement 4329915 Safety isolation protects users and electronic instruments. Lohbeck David Hazardous voltage primer EDN May 11 2006. www edn com design test and measurement 4319799 Hazardous voltage primer. Lohbeck David Design for Dust EDN April 1 2008, http www edn com design test and measurement 4380262 Design for dust. Lohbeck David Product safety testing limits risk of shock fire and injury Part 1 EDN March 1 2013. www edn com design test and measurement 4408106 Product safety testing limits risk of shock fire and injury. Lohbeck David Product safety testing limits risk of shock fire and injury Part 2 EDN March 15 2013. www edn com design test and measurement 4410045 Product safety testing limits risk of shock fire and injury Part 2.

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