BS 9720:1989

Foreword
Committees responsible
Section one. General
1.1 Scope
1.2 Related documents
1.3 Definitions
1.4 Letter symbols, signs and abbreviations
1.5 Graphical symbols
1.6 Marking of the component and package
1.7 Delayed delivery
1.8 Certified test records
1.9 Standard ratings and characteristics
1.10 Ordering information
Section two. Tests
2.1 Test and measurement conditions
2.1.1 General
2.1.2 Measurement uncertainty
2.1.3 Alternative test methods
2.2 Visual inspection
2.2.1 General
2.2.2 Isolating screen position
2.2.3 Quality of solder joints (isolating screens)
2.3 Dimensioning and gauging procedure
2.4 Electrical test procedures
2.4.1 General
2.4.2 Winding resistance
2.4.2.1 D.C. winding resistance
2.4.2.2 Continuity
2.4.3 Insulation resistance
2.4.3.1 Insulation resistance (standard atmosphere)
2.4.3.2 Insulation resistance (hot)
2.4.4 Losses
2.4.4.1 No-load current
2.4.4.2 No-load loss
2.4.5 Voltage proof (electric strength test)
2.4.6 Induced high voltage
2.4.7 Magnetic fields
2.4.7.1 Magnetic shielding
2.4.7.2 Magnetic influence (compass safe distance)
2.4.8 Inductance and a.c. resistance
2.4.9 Screens
2.4.9.1 Electrostatic screen(s)
2.4.9.2 Isolating screen
2.4.10 Q factor
2.4.11 Capacitance unbalance
2.4.12 Impedance unbalance
2.4.13 Voltage unbalance
2.4.14 Resistance unbalance
2.4.15 Leakage inductance
2.4.16 Capacitance
2.4.16.1 Self-capacitance
2.4.16.2 Interwinding capacitance
2.4.17 Voltage transformation ratio
2.4.18 Resonant frequency
2.4.18.1 Inherent self-resonance
2.4.18.2 Resonant assemblies
2.4.19 Signal transfer characteristics
2.4.19.1 Insertion loss
2.4.19.2 Return loss
2.4.20 Frequency response
2.4.21 Pulse characteristics
2.4.22 Total harmonic distortion
2.4.23 Temperature rise
2.4.24 Voltage regulation at full load
2.4.25 Magnetic radiation
2.4.26 Acoustic noise
2.4.27 Polarity (phase) test
2.4.28 Non-linearity of magnetizing current
2.4.29 Maximum surface temperature
2.5 Environmental test procedures
2.5.1 General
2.5.2 Soldering
2.5.3 Robustness of terminations
2.5.4 Shock
2.5.5 Bump
2.5.6 Vibration
2.5.7 Acceleration, steady state
2.5.8 Rapid change of temperature, thermal shock in
          air
2.5.9 Sealing
2.5.10 Climatic sequence
2.5.11 Damp heat, steady state
2.5.12 Dry heat
2.5.13 Mould growth
2.5.14 Salt mist
2.5.15 Sulphur dioxide
2.5.16 Flammability
2.5.17 Solvent resistance
2.6 Endurance test procedures
2.6.1 Short-term endurance (load run)
2.6.2 Long-term endurance (life test)
Section three. Capability approval procedures
3.1 Eligibility for capability approval
3.2 Application for capability approval
3.2.1 General
3.2.2 Scope of capability
3.2.2.1 General
3.2.2.2 Environmental characteristics
3.2.2.3 Core type
3.2.2.4 Range of mass
3.2.2.5 Type of construction
3.2.2.6 Form of statement
3.2.3 Add-on and built-in components
3.3 Description of capability
3.4 Appraisal of capability
3.4.1 Capability qualifying components (CQCs)
3.4.2 CQC test schedules
3.4.2.1 General
3.4.2.2 Sample selection and test flow chart for the
          appraisal of capability
3.4.2.3 Failure procedure
3.4.3 Schedule 1: Preconditioning
3.4.4 Schedule 2A: Assessment of climatic durability
3.4.5 Schedule 2B: Assessment of long-term endurance
3.4.6 Schedule 2C: Assessment of mechanical/
          environmental durability
3.4.7 Schedule 3: Selective assessment of
          mechanical/environmental durability
3.5 Announcement of capability approval
3.6 Maintenance of capability approval
3.6.1 General
3.6.2 Annual testing
3.6.3 Three-yearly testing
3.6.4 Additional boundaries to the approval
3.6.5 Procedure in the event of failure
3.7 Quality conformance inspection
3.8 Changes to the approved capability
Appendices
A Allocation of numbers to generic, sectional
          and blank detail specifications
B Sample format for certified test record
C Sample format for abstract of manufacturer's
          report
D List of clauses corresponding to those in
          BS 9720 : 1983
Tables
1 Preferred values of acceleration and
          displacement for vibration testing
2 Proof test voltages
3 Data for magnetic radiation test
Figures
1 Pulse waveform parameters
2 Examples of good solder joints
3 Examples of poor solder joints
4 Helmholtz structure
5 Measurement of capacitance unbalance
6 Measurement of impedance unbalance
7 Measurement of voltage transformation ratio
8 Measurement of resonant frequency: Inherent
          self-resonance
9 Measurement of resonant frequency: Resonant
          assemblies
10 Measurement of insertion loss and frequency
          response
11 Use of two identical transformers when
          transformation ratio is not unity
12 Measurement of non-linearity of magnetizing
          current
13 Maximum non-linearity of magnetizing current
14 Sample selection and test flow chart for the
          appraisal of capability
15 Sample selection and test flow chart for the
          maintenance of capability approval

Lists the test methods that are used in the test schedules for the assessment and maintenance of capability approval; and selected for inclusion in customers\' detail specifications. Also gives marking requirements and relevant terminology.

This British Standard specifies the requirements that manufacturers of custom-built transformers and inductors need to comply with in order to achieve and maintain capability approval to BS 9000, and the component test schedules to be used for the assessment of that capability. It applies to components, including polyphase types, that are primarily intended for use in electronic equipment.

This standard also specifies marking requirements and related symbols and terminology; and describes the methods of test for transformers and inductors that are required by the relevant sectional specifications (which contain the customer’s blank detail specification), and the schedules for the assessment and maintenance of capability.

NOTE 1 The transformers and inductors that are the subject of this specification may include other components essential to the operation of the device, e.g. capacitors associated with constant voltage transformers and resonated windings.

NOTE 2 This standard should be read in conjunction with BS 9000 and BS 9005; such general details and definitions given in those standards as are appropriate to this standard should be held to be part of this standard unless otherwise stated herein.

NOTE 3 The allocation of numbers to generic sectional and blank detail specifications in the 9700 series is given in Appendix A.