Application Note
Contents
1. Although the CLT 10 can be used for testing of all types of passive components the main application of the CLT 10 is testing of resistors The CLT 10 features computerized control of all functions which opens for a broad range of system integration and statistical analysis Please refer to the Operator Manual for the CLT 10 Control Unit for detailed programming information This application note contains a variety of technical and application specific information for the convenience of the user The key features of the CLT 10 are Impedance range from less than 100 Q to more than 3 MQ 10 kHz voltage up to 1 kV Third harmonic below 160 dB Power up to 4 VA More than 30 components per second IEEE 488 interface RS 232 C interface and a versatile Measuring Unit interface The measurement voltage can be controlled externally Insensitive to external magnetic fields Easy IEC 440 set up Programmable rejection limits The system s application is very broad and includes e Production testing e Component development e Acceptance testing e Investigation of non linearity in materials e Screening of audio grade components 2 CLT 10 App Note Section 2 Principle of Operation 2 Principle of Operation 2 1 Measurement Principle In the CLT 10 the non linearity of the component under test is determined by a measurement of the third harmonic distortion generated by the component when a purely sinusoidal signal is applied to it2. Reliability Testing of Nominally Linear Components by Measuring Third Harmonic Distortion CLT 10 Component Linearity Test Equipment Application Note Danbridge A S Copyright 2002 Danbridge a s All rights reserved No part of this publication may be reproduced or distributed in any form or by any means without prior consent in writing from Danbridge a s 5 Hirsemarken DK 3520 Farum Denmark Phone no 45 4495 5522 Fax no 45 4495 4504 Email sales danbridge com Web www danbridge com CLT 10 Contents Table of Contents Section Page 1 s Introduction wei acct reticence heceteetee eeeneneees 1 1 1 The Contents of this Application Note cccceeeeeeeeeeeeeteeeeeeeees 1 1 2 Overview and Features vicsciccencicaccdtiir cc teestuortecatuisCecedscalivade in tesdae 1 2 Principle Of Operation cccccccceeeesseeeeeeeeeeeeeeeeeeeenenees 3 2 1 Measurement Principle cccccceceeeesseeeeeceeeeeeeeeeeeeenneeeeeeeeeeeeees 3 2 2 Detection of Unreliable Component eeeeeeeeeeeeeeeeeeeeeeeeeeee 5 2 3 Description of the CLT 10 00 eee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 6 2 4 Operation at a Glance cceeeeeesseessssssssssessssssssssssssssessseseees 8 2 5 General ON Impedances cccccccseceececeecteesssssessssssssssssesssssseeseees 8 3 Hints about Operation cccceccssesssesssseeeeeeeeeeeeeeeeeeeeee 11 3 1 Manual Operation 6 xscices ate s
3. 5 2 Page Principle Gl Operation sissi meiiies teas batted aiiai 3 Typical Distribution of Distortion in a Batch of Components 4 Distortion in a Batch of Components Plotted on Probability Papel cccctoer crete aa 5 Outline of the CLT 10 system 0 cece ee ceeeeeeeeeeeeeeeeeeeeeeees 6 Third Harmonic Distortion as a Function of the Temperature Coefficient in a Metal film ReSistor ceceeeeeeeeeeeeeeeees 18 A Spiralled Resistor with a Constriction in the Resistance Track wentendentanscestscs ten seat eeusisa loa terulect teres 20 Schematic Diagram of a Capacitor with an AC Current 26 Timing DiaQha Wars sen teeih beth a cece ie ke ate 32 CLT 10 App Note Danbridge A S iii CLT 10 Danbridge a s This page is intentionally left blank iv CLT 10 App Note Section 1 Introduction 1 Introduction 1 1 The Contents of this Application Note This application note contains application specific information on the CLT 10 Component Linearity Test Equipment consisting of the CLT 10 Control Unit 391 080 and the CLT 10 Measuring Unit 891 081 Please refer to the Operator Manual for each of these two units for general instructions on installation The contents of this application note are as follows Section 1 General introduction this section Section 2 A primer to the measurement principle and an overview of the operation of the CLT 10 Section 3 A guide to the operation of the CLT 10 dealing with
4. Other Types of Components ceeseeeee 29 6 1 VINGUCIONS iiei Ah ated Machen cae ae aaa E neh adie 29 6 2 PTC Resistors with Hidden Cracks ccccceeeeeeeeeeeeteeeeeeeeeeetee 29 6 3 Bad Solderings in Loudspeakers ccccceeeeeeeeeeeeeeeteeeeeeeeeeeeeee 30 CLT 10 App Note Danbridge A S i CLT 10 Contents 7 Production Line Integration ssseeseeeeeeeeeee 31 Fok nggening the CEE TOi aa ees ied at eee ices ee 31 Po2 MMM secede Sie ccet siete E a A 31 T M asu rement JIGS sci t cen ssc eaten shes Seether peter tae 33 7 4 Resistors and Resistor Ne tworksS c cccccecceeececceceeeececceeeeeeeeees 34 7 5 Data Retri Val ccc ccccccccccccecceecceccecceececcaeeceecaeeceecueeaeeceeeteeaeeeaees 35 7 6 Noise Considerations c ccccccccecceecceccececeececceeececeuceaeeceeeeeeeees 35 8 Literature ReEfCreNnCes ccccsceccsceseecescecnscecescuceeceeeees 37 9 a gt gt Geen are neces TEETE SO ee eR ar oan E arte een SORA SORE Oe 39 10 MiscellaneoUS aaannnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 43 10 1 Document Status Record 20 00 00 ccc ceececcceccecceccceceeceeeaeececeeeeaeeseeens 43 10 2 Terms and Abbreviations ccccccceececcececeececceeececceecaeeceeeneceeeass 44 CLT 10 App Note CLT 10 List of Figures List of Figures Figure Fig Fig Fig Fig Fig Fig Fig Fig 2 1 2 2 2 3 2 4 4 1 4 2 5 1
5. be verified by life tests 6 3 Bad Solderings in Loudspeakers The investigation of solderings in medium and high impedance dynamic loudspeakers is another field of application of the CLT 10 In some cases it can be difficult to check the quality of the soldered connection between the aluminium wire of the voice coil and the flexible copper wire feeding the coil If a tweeter is subjected to its maximum power and the connection is not perfect the current will heat the junction and eventually melt the solder A perfect soldering shows a very low distortion whereas imperfect solderings normally show increased distortion due to the constriction of the conductive area Defective solderings can be found on unmounted membranes and a subsequent visual inspection of the rejected ones can contribute substantially to the improvement of the soldering technique CLT 10 App Note Danbridge A S 33 Section 7 Production Line Integration 7 Production Line Integration 7 1 Triggering the CLT 10 The CLT 10 can be triggered in three ways e By pressing the Trig button on the front panel of the Measuring Unit e By connecting the trigger signal to trig input on the interface connector of the Measuring Unit e Via the interface on the Control Unit IEEE 488 or RS 232 C The manual front panel trigger Trig is used for entering a manual triggering mode Before pressing the Trig button it is advisable that the proper measuring parameters are
6. both manual and IEC 440 operation including two examples Section 4 General information on measurements of distortion in resistors Section 5 General information on measurements of distortion in different types of capacitors Section 6 Other types of components including inductors are discussed in this section Section 7 Information on system integration on production Lines Section 8 Bibliography Section 9 The Index of this application note Section 10 Miscellaneous information including a document status report and abbreviations 1 2 Overview and Features The CLT 10 Component Linearity Test Equipment is used for reliability testing of passive electronic components The CLT 10 performs a measurement of the third harmonic distortion of the component under test and it can subsequently determine whether to reject the component or not on basis of this measurement The system consists of the CLT 10 Measuring Unit and CLT 10 Control Unit which are interconnected through a fiber optic link In this application note it is assumed that the installation instructions of these two units are followed Please refer to the instructions in each of the Operator Manuals for the two units CLT 10 App Note Danbridge A S 1 Section 1 Introduction The measuring method of the CLT 10 offers a number of advantages compared to other methods of reliability testing One important feature is the measurement speed which facilitates 100 production test
7. chosen When pressing the Trig button a measurement is made and the CLT 10 enters a wait state Subsequent triggering can be made after entering this wait state By pressing the MV button the CLT10 returns to the Idle mode in which continuous measurements can be made by pressing MV subsequently The Rear Panel Trigger is used for entering the external triggering mode normally found in automatic test operations The correct measuring parameters have to be chosen in advance by the user When triggering the CLT 10 by the Rear Panel Trigger a measurement is made and a wait state is entered Subsequent triggering can only be made by the Rear Panel Trigger The Rear Panel Trigger pin on the interface connector on the Measuring Unit is pulled up by an internal resistor approx 5 kQ The trigger is activated by connecting this pin to digital ground on the interface connector for at least 10 us It is recommended to use an isolating switch like a relay or an optocoupler placed as close as possible to the Measuring Unit to activate this trigger The trigger must be off open circuit for at least 100 us before triggering When using the bus command MS an even more flexible shift between measurement modes continuous measurements manual triggering and external triggering is offered For further information on triggering please refer to the description of measuring modes found in the CLT 10 Control Unit Operator
8. is primarily used in the most sensitive ranges of the CLT 10 An CLT 10 App Note Danbridge A S 15 Section 3 Hints example of application is the measurement on low distortion resistors as described in subsection 4 4 The bandwidth is chosen either manually or by programming the CLT 10 When pressing the BW button the user can toggle between normal and narrow bandwidth When the narrow bandwidth is selected the annunciator NARROW is lit On the interface bus the command BW ON selects the narrow bandwidth while the command BW OFF selects the normal bandwidth The narrow measuring bandwidth increases the settling time of the 30 kHz Voltmeter so the bandwidth reduction should not be used in applications where speed is a vital parameter Please refer to subsection 7 2 for timing information 16 CLT 10 App Note Section 3 Hints This page is intentionally left blank CLT 10 App Note Danbridge A S 17 Section 4 Testing Resistors 4 Testing Resistors Production testing of resistors especially metal film resistors is by far the most frequent application of the CLT 10 In the following the types of failures causing distortion in resistors are discussed 4 1 Metal film Resistors In summary the causes of distortion in resistors are Non linearity of the resistive material Defects in the resistance track Poor connections between leads and resistor body Temperature coefficient of the resistor Traces of film left in g
9. same impedance value the third harmonic value is found to be distributed around a mean value see Fig 2 2 The distribution is Gaussian A few of the components may however exhibit a higher distortion than that of the rest of the batch due to small defects or deviations in the material composition When exposing the batch to an accelerated life test the components having a high degree of distortion will also be prone to exhibit inferior reliability 4 Number of Components Abnormal High Distortion Median Value lt t t T T 38 28 18 0 18 28 38 Fig 2 2 Typical Distribution of Distortion in a Batch of Components Some components contain materials which inherently have a high distortion Magnetic materials composition resistors high dielectric capacitors etc In these components the excessive distortion from a small defect is hidden in the high inherent distortion and cannot readily be detected At the other end of the scale we have metal film resistors where the inherent distortion is very low typically 130 dB or lower and the wire wound types which normally exhibit even lower distortion With these components defects give rise to a distortion which normally exceeds that of the rest of the batch When an electric current flows through a conductive element it can be shown that the generated harmonic voltage follows the equation I n V39 k B 4 CLT 10 App Note Section 2 Principle o
10. so reliability testing can be carried out with success In this subsection some vital relations are found regarding distortion voltage and foil thickness A schematic diagram of a capacitor with the area A the thickness t and the AC current is shown in Fig 5 1 re Fig 5 1 Schematic Diagram of a Capacitor with an AC Current I From the general formula from subsection 2 1 I n V39 k 4 we get just by changing the letters I n Vso Ke aa Ca t since the capacitance where e is the dielectric constant and the current CLT 10 App Note Danbridge A S 29 Section 5 Testing Capacitors V I ja C V Ze where 2zf and f is the fundamental frequency we get Vo ke ko G where k ke which is a constant This means 1 That the third harmonic distortion is dependent on V by the third order n 3 as is the case with resistors 2 That the distortion is dependent on the second order of the foil thickness The dependence of the foil thickness is a good tool to find capacitors with weak spots Testing on foil capacitors has been carried out with success especially where the utmost stability is required for example in case of polystyrene capacitors 5 3 Ceramic Capacitors The nominal impedance range of the CLT 10 makes it useful for measurements on ceramic capacitors The highest capacitance value is set by the lowest nominal load impedance which is 100
11. the CLT 10 Please refer to the Operator Manual for the CLT 10 Measuring Unit CLT 10 App Note Danbridge A S 31 Section 6 Testing other types of Components 6 Testing Other Types of Components In the following some other applications of the CLT 10 will be discussed In subsection 6 1 testing of inductors in general is discussed while the two following subsections describe examples of applications in which non linearity tests have been used 6 1 Inductors The nominal impedance range of the CLT 10 and the frequencies used are targeted at applications with resistors and capacitors However when attention is paid to the nature of real world inductors the CLT 10 can prove useful for measurements on some inductors The lowest inductance value is set by the lowest nominal load impedance which is 100 Q equivalent to 1 6 mH at 10 kHz The useful range is below 30 Q equivalent to less than 0 48 mH At the other end the highest inductance value is set by the highest nominal component impedance at 30 kHz which is 3 MQ equivalent to 16 H The impedance of this size of inductor is rarely purely inductive at 10 kHz or 30 kHz as the inductor most likely is a mix of inductive resistive and capacitive elements The impedance of the inductors therefore has to be measured by an impedance meter at 10 kHz and 30 kHz The inherently high distortion in ferrite based inductors is normally dominant compared to the sources of distortion related to the re
12. Manual and to the timing information found in the following subsection 7 2 Timing Fig 7 1 shows the timing of the CLT 10 when used in a triggered mode 34 CLT 10 App Note Section 7 Production Line Integration Rear Panel Tri i ig gt 10 us ENE Next Trigger Pulse ty t7 l 10 kHz Voltage Amplitude t 30 kHz Voltage Amplitude t t3 H i i ME i Measurement End i i lt 25 us lt 500 us DRDY Data Ready i t4 X ms 2 6 ms U1 On 4 l ms 0 5 10 15 20 Fig 7 1 Timing Diagram The Rear Panel Trigger signal must remain high off for at least 100 us before the trigger sequence commences When starting a trigger sequence the trigger signal must be low for at least t 10 us to ensure triggering After approx 100 us the 10 kHz level starts to rise The settling time t is approx 6 ms for a settling of 98 of final value The 10 to 90 rise time is approx 3 ms At the same time the 30 kHz distortion voltage starts to rise in the component under test The rise time t depends on the chosen bandwidth of the 30 kHz Voltmeter and the physical characteristics of the component under test When using the broad bandwidth which is the most common procedure on production lines the 30 kHz signal has normally settled to 98 of its final mean value within 9 ms At the shortest measurement time which is 6 ms the distortion is approx 70 of the final level CLT 10 App Note Danbridge A S 35 Se
13. Median Cumulative Distribution 10 V3 7 80 7 90 gt 95 98 99 Rejection Limit 2 O from Idealized Distribution Rejection Limit At V3 99 8 99 9 li 20 50 100 200 500 pV N fo aH V3 Median 3rd Harmonic Voltage V3 Fig 2 3 Distortion in a Batch of Components Plotted on Probability Paper A straight line in Fig 2 3 corresponds to a Gaussian distribution If part of a batch deviates from the straight line it should be rejected and subjected to a further study The study could consist of an accelerated life test in which some of the accepted components take part as well for comparison With respect to resistors and ceramic capacitors the failure can often be seen under microscope after the coating has been removed chemically 2 3 Description of the CLT 10 The CLT 10 Component Linearity Test Equipment consists of two units The CLT 10 Control Unit and the CLT 10 Measuring Unit Each of these two units are described briefly in this section The Control Unit is divided into the CPU board and the display part which also holds the keyboard The CLT 10 Measuring Unit can be divided into a generator part which takes care of the generation of the 10 kHz signal and a voltmeter part which selectively measures the third harmonic level around 30 kHz As a third part 6 CLT 10 App Note Section 2 Principle of Operation we find the interface system and the power supplies w
14. Note Danbridge A S Index 43 Section 9 Operation at a Glance 8 Overloading 22 25 37 Overview and Features 1 Polarizing voltage 28 Power Amplifier 7 Principle of Operation 3 Production Lines 34 PTFE 37 38 Rejection limit 5 Residual Non Linearity 10 25 28 37 Resistance tracks 20 Resistors 19 37 Low distortion 25 Metal film 19 21 25 Network 22 37 PTC 32 Thick film 25 Thin film 25 Wire wound 4 19 RNL 10 25 28 37 RS 232 C 38 Selecting the Correct Range 15 Settling time 16 Solderings 33 Sorting 38 Spiralling 20 Steps of Operation 8 Temperature Coefficient 20 25 37 Testing other types of Components 32 Testing Resistors 19 The IEC 440 Set up 14 THI 19 24 Timing 4 34 Triggering the CLT 10 34 Trimming resistor networks 22 Wire wound resistors 4 44 Index CLT 10 App Note Section 9 Index This page is intentionally left blank CLT 10 App Note Danbridge A S 45 Section 10 Miscellaneous 10 Miscellaneous 10 1 Document Status Record CLT 10 Application Note DATE UPDATES CONCERNING AUTHORIZED New 93 03 01 CLT 10 ew This Application Note Ole Stender Appl reflects the CLT 10 Nielsen Note 1 0 Measuring Unit and Control Unit 93 09 09 CLT 10 i This Application Note Ole Stender Appl reflects the CLT 10 Nielsen Note 1 1 Measuring Unit and Control Unit 46 CLT 10 App Note Serial No No 17 3012 Rev A Section 10 M
15. The CLT 10 Measuring Unit is able to supply the component under test with a 10 kHz signal with very low harmonic contents and it is able to measure the level selectively of the 30 kHz signal generated by the component LP filter HP filter f 10 kHz f 3 kHz U Z3 kHz ZyeKHz U3 Fig 2 1 Principle of Operation If the impedance of the component is not absolutely independent of the applied voltage the sinewave current will be distorted In other words the current consists of a pure fundamental sinewave component 10 kHz and higher harmonics As the third harmonic component 30 kHz is the dominant one this is chosen as a measure of the distortion or as it is also called the non linearity of the impedance of the component Electrically the third harmonic current is equivalent to a no load voltage V3 in series with the component under test which has an impedance Z As the 10 kHz low pass filter blocks for the 30 kHz signal the third harmonic voltage V is measured over the load impedance R Knowing the values of Z and R the no load voltage can easily be found as 3 Z Vig vif R CLT 10 App Note Danbridge A S 3 Section 2 Principle of Operation The Measuring Unit contains the circuitry for making the measurement but the choice of parameters and the timing of the measurement are controlled by the CLT 10 Control Unit When measuring on a batch of components with nominally the
16. am oie wseeeceice cece ed ase ieee de ene een 11 32 MGC SetU pienien case tds os eds a baid Vol dtaad A Sevens 13 3 3 Selecting the Correct RANge ceeeeeeeeececeeeeeeeeeeeeeeeseeeeeeeeeeeeees 14 3 4 Choice of measurement bandwidth ccceeeeeeeeeeteeeeeeeeeeeeee 14 A Testing Resistors iiss cscccrtccecece ete etsk ceed ne een encase 17 4 1 Metal film RGSISIONS lt isi52 c2tsctsiesossiest cosadesideaddutaicaidessdansdesadints heaanen 17 4 1 1 Non linearity in Resistive Materials e 17 4 1 2 Defects in Resistance Tracks and Connections 18 4 1 3 Temperature Coefficient ccceeeeeeeeeeeeeeeeeees 18 4 2 Resistor NEIWWORKS yas ai kcisoitonssuntelsiincniaaacaia ei hesede hada cs 19 4 3 Calculating DIStOMiON erst awit ni aver eu eee 20 4 3 1 KSOMSUICUIO Mees wsdatnes ecdiinres ots Ores enciteed enddtciunditeed mmedivelanes 20 4 3 2 Length of Resistance Track ccceeeeeeeeeeeeeeeees 21 4 3 3 Third Harmonic Index THI ceecee 22 4 4 LOw distortion Resistors cccccccccccecceeceeeeeeeeeeceeeeeeeeeeeeeeeeeeeeeeeess 22 5 Testing Capacitors ssssssssnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 25 5 1 Electrolytic Capacitors ccccccccceeeeeeeeceeeeceeeeeeeeeeeeeeaeeeeeeeeeeeeeeees 25 K2 e FOl GApaCtOl S ann onea nenike duenik aa aaa Tan daea Feah Caka Faai baa PEAN Aa aa DANAE ER 26 53 Ceramic Capacitors siiani od serate an EAE Eea KEMARA KERKERAK EARRAK EARR nue 27 6 Testing
17. anddorf Measurement of Non Linearity on Electronic Components Ingeni ren 1966 No 3 pp 150 153 In Danish Vilhelm Peterson and Per Olof Harris Harmonic Testing Pinpoints Passive Component Flaws Electronics 1966 July 11 Arne Salomon and Tony Troianello Component Linearity Test Improves Reliability Screening through Measurement of Third Harmonic Index Reliability of Physics 1973 pp 69 73 Hans Peter Lorenz und Hans Werner P tzlberger Klirrdampfung von Widerstanden Nachrictentechnic 1974 Heft 5 pp 190 195 D O Melroy Linearity Testing of Thin Film Hybrid Integrated Circuits as a Production Screen for Defects IEEE Electronic Components 1975 pp 205 209 Susamu Kasukabe and Minoru Tanaka Reliability Evaluation of Thick Film Resistors through Measurement of Third Harmonic Index Electrocomponent Science and Technology 1981 Vol 8 pp 167 174 Method of Measurement of Non Linearity in Resistors IEC Publication 1973 No 440 Method of Measurement of Non Linearity in Fixed Resistors Technical File of EIAJ RCF 2003 1988 CLT 10 App Note Section 8 Literature References This side is intentionally left blank CLT 10 App Note Danbridge A S 41 Section 9 9 Index 30 kHz Voltmeter 7 Accelerated life test 6 AGC loop 8 AGC Generator 7 Arching 38 Bandwidth 25 Bandwidth reduction 15 26 39 Batch of components 4 5 20 Biasing 28 Cable Unit 12 30 36 37 Cables 36 Capaci
18. ce Track We start again with the fundamental formula I n V39 k a AS I i and R 8 where R is the resistance value and 6 is a material constant we get by substitution n If we keep R and V constant and set n 3 we get CLT 10 App Note Danbridge A S 23 Section 4 Testing Resistors This equation shows that a long resistance track all other factors equal decreases the distortion by the second order of the length 4 3 3 Third Harmonic Index THI If we go back to the fundamental formula and insert I ah we get LA vY ve eke B eke If we assume both I A and R to be constant we get V3 k V If we set n 3 and call the constant THI we get V THI v This constant which is called the third harmonic index can be used to express the quality of a resistor with respect to distortion without reference to the measured values If we as an example have V 100 V and V 80 uV with 6 dB correction factor we get V3 o 160 uV and thus 6 THI ls 1 6 10 100 4 4 Low distortion Resistors When measuring on an ideally linear component the calculated distortion is that of the CLT 10 itself the so called residual distortion or residual non linearity RNL This value depends on the range of impedance chosen but in the 300 Q 3 kQ range at W load power it is below 160 dB typically 170 dB Some _ metal film resistors with low temperature coefficient sometimes show a di
19. ch is equivalent to 1 6 uF In this range we find small electrolytic capacitors some which do not necessarily have to be used and tested with polarizing voltage An example is audio grade capacitors that could be even non polarized types The CLT 10 has an RNL better than 140dB down to 10Q load impedance which makes it useful for finding failures in small high quality electrolytic capacitors Please note however that the settling time of the 10 kHz signal increases at load impedances lower than 100 Q and the measurement time has to be increased accordingly With these restrictions in mind the non linearity test of small capacitors can in many cases be carried out with success An unstable internal connection will readily be seen as increased distortion Any instability will be even more clearly detected if the capacitors are mechanically vibrated during the measurement Some Al electrolytes may not have had time to develop an oxide film creating the internal bad connection 28 CLT 10 App Note Section 5 Testing Capacitors Such capacitors must be exposed to some climatic test prior to testing the third harmonic This may be done as a type testing 5 2 Foil Capacitors With a nominal load impedance from 100 Q and up equivalent to 160 nF and lower and a 10 kHz test voltage up to 1 kV rms the CLT 10 is suitable for non linearity measurements of foil capacitors At the same time this type of capacitor normally exhibits low distortion
20. ction 7 Production Line Integration When the narrow bandwidth is used the settling time is increased to approx 17 ms and at 6 ms measuring time the distortion is about 17 of the final mean value After the preset time t the Control Unit samples the 30 kHz Voltmeter and shuts down the 10 kHz voltage This time which is chosen on the Control Unit can be selected between 6 and 9990 ms The decay time t of the 10 kHz signal depends on the load At open terminals the decay time is normally 2 ms but loading the terminals reduces the decay time to approx 1 ms Handling of the component can normally be done after 2 ms without causing sparks The logic output signal ME Measurement End goes low when the 10 kHz signal starts to rise and it goes high when the measurement has ended and the 10 kHz signal starts to fall The DRDY signal Data ReaDY indicates that the signals on the interface connector of the Measuring Unit are present and ready to be read At the same time the state of the limit annunciators on the front panel of the Measuring Unit is updated The duration t of the DRDY pulse is approximately 100 us After ME has gone high a period t 4 ms must elapse before the next trigger pulse occurs It may be possible to speed up the measurement if the settling characteristics are taken into consideration By setting the measurement time to 6 ms the distortion in the component under test is approx 3 dB higher than indicated when
21. d Calculate the distortion The dB setting of the 30 kHz Voltmeter could be used If needed the corrected distortion level can be found If the IEC 440 set up has been used this is done automatically Automatic operation on a production line differs from manual operation only by the introduction of triggering and the involved timing In addition several programming features are implemented in the CLT 10 Please refer to the Operator Manual for the CLT 10 Control Unit for detailed programming information 2 5 General on Impedances The impedance of a resistor is the same at 10 kHz and at 30 kHz Non resistive components have different impedances at different frequencies The impedance of a capacitor decreases with increasing frequency where f is the frequency and C is the capacitance The impedance of an inductor increases with increasing frequency Z 2n f L where L is the inductance In general the impedance of an unknown component should be measured by an impedance meter at 10 kHz and 30 kHz Measurements on components near resonance for instance can give misleading results if the impedance at one frequency merely is calculated from the impedance at another frequency It is the impedance at 10 kHz of the component which determines the load of the CLT 10 and the power delivered to the component under test but it is the impedance at 30 kHz of the component which sets the correction factor CLT 10 App Note Danbridg
22. e A S 9 Section 2 Principle of Operation where Zx is the impedance of the component under test at 30 kHz and R is the input impedance of the CLT 10 at 30 kHz In case of resistive components the correction factor is simplified to R R 14 R The no load third harmonic voltage is reduced by the factor Fo and thus the corrected non linearity in dB is expressed as De D 20 logk where D is the measured distortion in dB The Corrected Residual Non Linearity CRNL is calculated from the Residual Non Linearity RNL in the same manner CRNL RNL 20 logE 10 CLT 10 App Note Section 2 Principle of Operation This page is intentionally left blank CLT 10 App Note Danbridge A S 11 Section 3 Hints 3 Hints about Operation A detailed description of the operation of the CLT 10 is found in the Operator Manuals for the CLT 10 Measuring Unit and the CLT 10 Control Unit The user is advised to get acquainted with these two manuals before operating the CLT 10 This section covers additional information related to the operation and cannot substitute the Operator Manuals Component specific information is found in sections 4 5 and 6 while information about integration on production lines is found in section 7 3 1 Manual Operation Basically the steps in subsection 2 4 are followed when operating the CLT 10 manually Additional application information about manual operation is given in this subsection F
23. ecretiveness Regardless of the type of jig it is important that the insulating material on which the contacts are mounted is of a very good quality preferably PTFE If the jig absorbs moisture a degraded RNL could be the consequence Parasitic shunt impedances in the jig have to be as high as possible and parasitic series impedances have to be as low as possible Consequently insulators and contacts have to be kept clean The final set up is first checked without load The uppermost impedance range is chosen and the output voltage is set to 500 V The measured distortion should read better than 140 dB When this figure is improved by more than 1 to 2dB when measuring solely on the Cable Unit the jig introduces distortion The user must determine whether to make improvements or not if distortion is introduced Similarly the final set up is checked at low value loads A 1002 low distortion wire wound power resistor is inserted in the jig The lowest impedance range is chosen the output voltage is set to 10 V and the distortion is measured If this distortion improves when measuring on the resistor connected directly on the Cable Unit the connections in the jig most likely have to be improved Generally it can be said that the lower the average distortion is in the components the more important it is that the measuring set up does not introduce additional distortion The total capacitance of any switching and contact arrangement s
24. ectively the level at 30 kHz on the output of the High Pass Filter The impedances of the High Pass and Low Pass Filters ensure that the energy at 30 kHz generated in the component under test is led to the voltmeter and not to the Power Amplifier CLT 10 App Note Danbridge A S 7 Section 2 Principle of Operation By means of the Matching Transformer it is ensured that the available power can be supplied to the Device Under Test throughout a wide impedance range At the same time the Matching Transformer ensures matching of the third harmonic voltage to the High Pass Filter Based on patented circuitry the transformer is made transparent at 10 kHz and at 30 kHz and consequently both low noise in the 30 kHz Voltmeter and optimal working conditions for the Power Amplifier are ensured The input impedance of the 30 kHz Voltmeter can be changed in order to get 1 KQ or 100 Q impedance at 30 kHz seen on the input terminals of the High Pass Filter When the Matching Transformer is inserted these impedances are increased 100 times which in total gives 4 different impedances at 30 kHz as seen on the measurement terminals 100 Q 1 KQ 10 kQ and 100 kQ The AGC Generator the Power Amplifier and the Low Pass Filter form an AGC loop The AGC Generator capacitively senses the level of the 10 kHz signal on the output terminals and adjusts the level as set by a control signal from the Interface Board At the same time the Interface Board sets the parame
25. emotely controlled switching arrangement or by a number of separate CLT 10s connected individually to the resistor network If pressure contacts are used to make contact to the substrate the contacts should be gold plated and individually spring loaded The wires connected to the contacts must be welded or soldered The insulating material used as socket for the contacts should be PTFE or a similar material in order not to introduce distortion A remotely controlled switch must also have very good contacts and preferably PTFE insulation If relays are used coaxial relays intended for high frequency applications are recommended Beware of short circuits in the measuring jig or premature disconnections of the component under test when the 10 kHz voltage is applied as this may cause arching that could ruin the contacts of the jig 7 5 Data Retrieval The sorting data HIGH LOW GO for the last measurement are available on the interface connector of the Measuring Unit These three open collector outputs may be used for activating a sorting mechanism directly or the result could be read into a shift register for retaining the data until the defective component reaches the rejection mechanism down the production line On the RS 232 C interface the distortion reading is sent together with the sorting result as soon as the data are ready For high speed automatic test applications it is recommended to use the IEEE 488 interface The IEEE 488 inte
26. en on the basis of the impedance at 30 kHz In case of inductors on the other hand or in case of unknown components the load of the CLT 10 at 10 kHz has to be checked Coils exhibit decreasing impedance at lower frequencies which dictates that the impedance range of the CLT 10 is chosen on the basis of the impedance at 10 kHz rather than on the basis of the impedance at 30 kHz In case of resistors the impedance range is chosen directly on the basis of the impedance of the component under test It would often be advisable however to change between the 300 Q 3 kQ range and the 3 kQ 30 kQ range at a resistance of approximately 5 6 kQ rather than 3 kQ in order to get the lowest CRNL and the highest power capacity 3 4 Choice of measurement bandwidth The reduction of measurement bandwidth is used for measurement range enhancement By reducing the bandwidth of the 30 kHz Voltmeter from approx 400 Hz to approx 75 Hz the contribution to the Residual Non Linearity RNL from broadband noise is reduced Depending on the relationship between the RNL contributions from broadband noise power white noise and narrowband noise power 30 kHz residuals the reduction of bandwidth gives an improvement of the RNL between 0 and 7 dB The contributions from broadband and narrowband noise depend on the impedance of the component under test the chosen impedance range and the type of man made noise around 30 kHz outside the CLT 10 The narrow bandwidth
27. equivalent to 160 nF at 10 kHz At the other end the lowest capacitance value is set by the highest nominal component impedance at 30 kHz which is 3 MQ equivalent to 1 8 pF The useful impedance range of the CLT 10 however goes from below 30 Q to above 100 MQ which is equivalent to a capacitance span from practically nothing below 0 05 pF to above 530 nF At low capacitances the correction factor is high however due to the load at 30 kHz which in the upper impedance range is 100 kQ At the same time it is important to use the Cable Unit or a shunt capacitance of 50 pF in order not to get erroneous readings when measuring capacitors in the upper impedance range On the other hand the use of cable in the upper impedance ranges in this application makes the CLT 10 ideal for production line testing of ceramic capacitors 30 CLT 10 App Note Section 5 Testing Capacitors As the third harmonic is dependent on the material the CLT 10 can test the variations in the material used in a given capacitor This may be of importance with type 1 capacitors used for temperature compensation When the voltage is increased towards the permitted break down voltage for the capacitor any start of flash over will be indicated as an increase in the distortion The maximum voltage which is limited to 1 kV rms is sufficiently high to test even high voltage type ceramic capacitors The maximum voltage however is limited in each of the 4 impedance ranges of
28. f Operation is the 10 kHz current A is the area of the conductor is the length of the conductor and k is a material constant For resistive elements the exponent n is close to 3 If a conductor has a constriction for example due to a flaw in the track the area A will decrease locally and consequently the third harmonic voltage for the defective part of the conductor increases by the third order of magnitude Even if the length of the constriction is short the increase in the third harmonic is often high enough to reveal itself as an increase in the total distortion of the component A constriction may also occur in contacts if the conduction only takes place over a fraction of the conductive surface bad soldering for instance 2 2 Detection of Unreliable Components The actual value of the distortion in a good component must be found experimentally The distortion of the components which may be unreliable is found by selecting the components which have a higher distortion than the rest of the batch Sometimes the defective components have a distortion much higher than that of the rest of the batch At other times it may be more difficult to determine the rejection limit In such cases it is useful to plot the third harmonic values on probability paper as shown in Fig 2 3 CLT 10 App Note Danbridge A S 5 Section 2 Principle of Operation 0 2 Ideal Distribution a i 4 05 20 40 50 60
29. hich serve both the generator and voltmeter parts The division between the generator part and the voltmeter part is very distinctive in the CLT 10 Measuring Unit in order to get a proper grounding and a low self induced signal deterioration Furthermore the communication between the CLT 10 Measuring Unit and Control Unit is based on optical fibers which makes the system reliable in noisy environments The following diagram of the structure of the CLT 10 Measuring Unit and Control Unit shows the division between the generator and voltmeter parts pen SSN Control Unit Optical Interface Power Amplifier Generator Measurement 10 al w kHz D Sense ime Low Pass High Pass Voltmeter D U T Fig 2 4 Outline of the CLT 10 System The AGC Generator generates a 10 kHz sinewave signal with a level determined by the Interface Board which communicates with the CLT 10 Control Unit The 10 kHz Power Amplifier amplifies the signal from the AGC Generator in order to get sufficient level and in order to achieve the desired current capability The Low Pass Filter attenuates the contents around 30 kHz in the signal from the Power Amplifier in order to get a sufficiently low 30 kHz residual level The output impedance of the Low Pass Filter is high at 30 kHz The High Pass Filter has a high impedance at 10 kHz and it is constructed so that the distortion is very low at that frequency The 30 kHz Voltmeter measures sel
30. hould be kept as low as possible If the capacitance exceeds 20 pF it is recommended that the length of the cable of the Cable Unit is reduced so the total capacitance of the cable and the jig including switching and contact arrangements equals 50 pF 20 pF In this way the additional measuring error due to deviation from the nominal capacitance is kept below 1 dB 7 4 Resistors and Resistor Networks A constriction in the resistance track lowers the current capability of a resistor and the constriction may also result in lower reliability Such a failure may show up as increased distortion as explained in section 2 but if the temperature coefficient of the resistor is very low the distortion caused by the failure is reduced and the failure will consequently be more difficult to detect CLT 10 App Note Danbridge A S 37 Section 7 Production Line Integration For this reason it would often be recommendable to include an overload test prior to the distortion measurement The overload should only last a few ms but should stress the resistance path to the maximum capacity Any constriction will in this way make the resistor act like a fuse Since the final test on the production line is of the resistance value such open circuited resistors are easily sorted out In case of resistor networks it is necessary to have access to each of the resistors either through wires or through pressure contacts This is done either by some means of a r
31. ind the impedance at 10 kHz and at 30 kHz of the component to be tested Select the impedance range of the CLT 10 based on the impedance at 30 kHz The comments on impedances in subsections 2 5 and 3 4 and in sections 5 and 6 should be observed Set up the 10 kHz Generator so the desired power is delivered into the impedance at 10 kHz If the impedance is complex the numeric value at 10 kHz should be used The CLT 10 can deliver 0 25 W throughout the nominal 100 Q 3 MQ impedance range but more than 4 W in certain ranges Observe the limits of the CLT 10 as indicated in the Operator Manual for the CLT 10 Measuring Unit In the upper impedance range the Cable Unit must be used in order to get impedance matching and thus correct measurements In case of resistors the IEC 440 set up can be used This set up sets the 10 kHz Generator and impedance range based on the chosen impedance and power level At the same time the corrected distortion is calculated on the basis of the chosen impedance If the component is non ohmic the calculated distortion may be erroneous Connect the component to be tested to the measuring terminals and switch the 10 kHz voltage on It is important that the terminals are tightened properly in order to achieve low residual distortion In case the Cable Unit is used all four terminals have to be tightened properly Please observe that the 10 kHz signal could be hazardous For safety reasons the measuring terminal
32. iscellaneous 10 2 Terms and Abbreviations CRNL_ Corrected Residual Non Linearity DUT Device Under Test RNL Residual Non Linearity TC Temperature Coefficient THI Third Harmonic Index CLT 10 App Note Danbridge A S 47
33. istor within the specified limits Since the CLT 10 can give accurate results within 10 ms after triggering a considerable overload can usually be applied without damaging the resistor Details on timing are given in subsection 7 2 The power capacity of the CLT 10 is sufficiently high to accommodate the method to resistors within a broad range of power rating Especially in case of many thin and thick film resistors with a rating of 100 mW or lower the overloading during a short time interval is a strong tool for expanding the measuring range The reduction of bandwidth is another method of measuring range expansion and it can be used independently of the overload method The two methods can be combined by evaluating the mix of demands to power level dynamic range and measuring speed The decrement of the measuring bandwidth from about 400 Hz to about 75 Hz increases the settling time of the 30 kHz Voltmeter Please refer to subsection 7 2 for timing information Normally the improvement of the distortion figures is around 5 or 6 dB at 1 4 W load power or lower when measuring on low distortion resistors using reduced bandwidth but the improvement is normally reduced at higher power levels CLT 10 App Note Danbridge A S 25 Section 4 Testing Resistors due to a higher relative contribution from 30 kHz residuals In this way the bandwidth reduction method is especially valuable in case the overload power is not too high and the method
34. liability of the inductor Air core inductors are thus the only type of inductor for which the non linearity method can be used for reliability testing In some cases however the distortion in itself is an interesting parameter An example is filter inductors for audio applications which often use ferrite cores In case the distortion of low value ferrite core inductors has to be measured a resistor can be inserted in series with the inductor A 100 Q wire wound type is recommended Though the generated distortion is attenuated in the series resistor the distortion of the ferrite core inductor is usually adequately high to facilitate the measurement When using this method both the attenuation of the 30 kHz distortion and the attenuation of the 10 kHz test signal should be taken into consideration 6 2 PTC Resistors with Hidden Cracks A PTC resistor has a high positive temperature coefficient One of the most common applications of this resistor is the use in combination with the start winding of single phase motors A problem in this application can be sudden interruption due to internal invisible cracks in the resistor 32 CLT 10 App Note Section 6 Testing other types of Components By examining the third harmonic distortion in a batch the resistors with hidden cracks can be found The increased distortion is caused by the increased current density in the resistors with cracks As part of the investigations the presence of cracks can
35. n this subsection a variety of formulas is shown for the user s convenience 4 3 1 Constriction As previously mentioned a flaw in the resistance track will reduce the conductive area and thus increase the total distortion A simplified calculation is shown below Let us assume that we have a Spiralled resistor with the diameter D and the length L see Fig 4 2 Wi L D t L CO Co lo W Wo gt N turns a b C Fig 4 2 A Spiralled Resistor with a Constriction in the Resistance Track Let the track have a width w and a thickness t From the general formula we have where If we assume the length of the constriction to be and the width w the distortion of the constriction alone equals ce Ess k 2 2 22 CLT 10 App Note Section 4 Testing Resistors and the total distortion is nls E50 yay E40 E39 E30 aes 3 0 Here the small reduction of is not taken into account due to the constriction By dividing E s with Ez we get Eso b 2 L sb 1 E 4 A I w t I w As an example we assume that L 10 mm N 10 turns and D 3 mm For simplification we set w N L or w 1 mm Then h N z D 100 mm Let us set the length of the constriction 2 mm and the width w 0 2 w 0 2 mm Then we get 5 aH eS a s Ezo 100 and Y Eg Eg9 1 2 5 B59 3 5 corresponding to an increase in the total distortion of 20log3 5 11 dB 4 3 2 Length of Resistan
36. pedance and power level according to IEC 440 At the same time the corrected distortion is calculated on the basis of the chosen impedance If the component is non ohmic the calculated distortion will be erroneous The resistance can be entered as either three or four digit values with the last digit being the multiplier in both cases The numeric keys of the keyboard are marked with colour bars for convenient entering of resistor values according to IEC 62 The corresponding entry via the interface is a single string command Both entry types are shown in the example below Example The distortion of a 10 kQ resistor at 0 25 W is measured manually by using the IEC 440 set up The basic steps listed in subsection 2 4 are followed The impedance at 10 kHz is 10 kQ and The impedance at 30 kHz is 10 kQ as well It is not necessary to select the impedance range The 0 25 W mode is chosen by pressing the 1 4W button once Enter a brown black orange ENTER 1 0 3 10 kQ in E 24 or brown black black red ENTER 1 0 0 2 10 kQ in E 192 sequence and the correct 10 kHz voltage is set automatically At the same time the 3 kQ 30 kQ impedance range of the CLT 10 is selected automatically as the resistance is 10 kQ The corresponding command for the IEC set up at 10 kQ and 0 25 W is SX 10K 250mW Please refer to the Operator Manual for the CLT 10 Control Unit for detailed information on operation The resistor is connected
37. rface can be set up to send a service request SRQ to the bus controller after each measurement After a serial poll the controller can retrieve the measurement result 7 6 Noise Considerations The CLT 10 is inherently insensitive to magnetic fields but the measuring terminals are very sentitive so the CLT 10 should be kept away from any strong noisy signals 38 CLT 10 App Note Section 7 Production Line Integration Power installations with rectifiers SCRs or similar power semiconductors can emit harmonics of the mains frequency The harmonics around 30 kHz could deteriorate the RNL if such installation couples to the measuring terminals or to the measuring jig Some computer installations especially CRTs can also inject unwanted noise around 30 kHz In most cases the noise level has to be found experimentally on the measuring site and the noise sources if any must be localized by turning off surrounding equipment one after another If the coupling from noise sources to the measuring terminals or the measuring jig causes problems some shielding of the measurement site may prove useful Depending on the type of noise the use of reduced measuring bandwidth may also prove useful Please refer to subsection 3 4 for information on bandwidth reduction CLT 10 App Note Danbridge A S 39 8 1 2 3 4 5 6 7 8 40 Section 8 Literature References Literature References S P Str
38. rial constant which is independent of the applied voltage The THI is explained in more detail in subsection 4 3 4 1 2 Defects in Resistance Tracks and Connections As mentioned in subsection 2 1 the generated third harmonic voltage V3 is related to the current density of the fundamental current l I n V39 k a where A is the area of the conductor is the length of the conductor and k is a material constant For resistive elements the exponent n is close to 3 A failure in the resistor track due to a failure during the spiralling process or in the ceramic body usually causes a considerable reduction of the conducting area Even if the length of the defective track is short the increase in the distortion with the exponent of 3 is usually sufficient to reveal the failure If the failure is localized in the contact connection the contact area is usually considerably reduced Also the material in a poor contact may not be purely metallic and this in itself causes a higher distortion Finally an even slightly unstable contact produces a distorted current which is also detected as an increase in the third harmonic voltage 4 1 3 Temperature Coefficient If the distortion is measured on a batch of resistors having the same ohmic value but a different temperature coefficient a curve can be drawn as shown in Fig 4 1 Fig 4 1 Third Harmonic Distortion as a Function of the Temperature Coefficient in a Metal film Resi
39. rooves In homogeneous spots in the materials 4 1 1 Non linearity in Resistive Materials A wire wound resistor of a good quality has a third harmonic distortion so low that it normally is very difficult to detect The metal film resistors of today are approaching the same low distortion as that of the wire wound types The improvements are widely based on the investigations on resistive materials carried out on the basis of non linearity measurements Both accelerated life tests and theoretical studies have shown that a low distortion and a good long term stability are closely related A measurement of the distortion can therefore be used to optimize the choice of the metal film composition the ceramic material and the metallization process Experience has shown that failures during the evaporation of the metal film are clearly revealed as an increase in the distortion This fact can be used during production to check a small lot of unspiralled resistors for non linearity In this way capping and spiralling of poor resistors can be avoided In order to compare resistors of different construction the Third Harmonic Index THI can be calculated n 1 V THI V where V3 is the third harmonic no load voltage V is the applied voltage and n is an exponent equal or close to 3 The formula shows that for a resistor it CLT 10 App Note Danbridge A S 19 Section 4 Testing Resistors is possible to calculate an index or mate
40. s must not be touched when the MV ON indicator is lit Even at low 10 kHz voltages the terminals must not be 12 CLT 10 App Note Section 3 Hints touched during the measurements as palpation of the terminals mostly leads to excessively high measured distortion Do not use long laboratory wires or similar to connect the component under test to the CLT 10 as this mostly causes high residual distortion regardless of the wires being twisted or not Keep metal objects that are not grounded at least 10 cm away from the measurement terminals In general non linear materials should be kept at least 10 cm away from the measurement terminals Even an ordinary pencil can cause distortion when pointed at the hot terminal due to the coupling to the highly non linear pencil lead Select a suitable range of the 30 kHz Voltmeter For best accuracy select the most sensitive range possible The autoranging could be used Calculate the distortion When the dB setting of the 30 kHz Voltmeter is used the ratio between the 10 kHz level and the measured 30 kHz level is calculated in dB The corrected distortion level can be calculated by the formulas in subsection 2 5 If the IEC 440 set up has been used this calculation is done automatically Example Manual measurement of the distortion of a 10 kQ resistor The basic steps listed in subsection 2 4 are followed The impedance at 10 kHz is 10 kQ and The impedance at 30 kHz is 10 kQ a
41. s thereby complement each other nicely 26 CLT 10 App Note Section 4 Testing Resistors This page is intentionally left blank CLT 10 App Note Danbridge A S 27 Section 5 Testing Capacitors 5 Testing Capacitors The wide impedance range of the CLT 10 makes it useful for testing capacitors even though its primary application is testing of resistors Some of the failures where the non linearity test method has proven useful are e Imperfect connection from leads to plates e Failures in the dielectric material e Flash over or insufficient insulation strength The frequencies in the CLT 10 the 10 kHz generator frequency and the 30 kHz measuring frequency together with the impedance range set the range of capacitance which can be tested Consequently the ability to find failures in capacitors depends on the type of capacitor Three different types of capacitor will be dealt with in the following 5 1 Electrolytic Capacitors The CLT 10 is not provided with DC biasing of capacitors so the measurements have to be made without polarizing voltage At the same time the CLT 10 is not intended for low impedance measurements which greatly limits the applications for high value electrolytic capacitors There are however certain types of electrolytic capacitors which the CLT 10 is suited for The lowest nominal load impedance of the CLT 10 is 100 Q equivalent to 160 nF at 10 kHz but the lowest useful load impedance is around 10 Q whi
42. s well The 3 kQ 30 kQ impedance range of the CLT 10 is chosen as the impedance at 30 kHz is 10 kQ If the test power has to be 0 25 W the 10 kHz voltage is set to 50 V This power is within limits of the CLT 10 as the available power is more than 1 W at 10 kQ load impedance The resistor is connected to the measuring terminals It is not necessary to use the Cable Unit as the additional measuring error without the Cable Unit in this range and at 10 kQ component impedance is below 0 1 dB Switch the 10 kHz voltage on by pressing the MV ON button Select a the most sensitive range of the 30 kHz Voltmeter without causing overload The autoranging could be used Let us assume that the measured 30 kHz voltage is 2 8 uV Calculate the ratio between the 50V measuring voltage and the measured 30 kHz voltage The dB setting of the 30 kHz Voltmeter could be used In both cases the result is 145 dB CLT 10 App Note Danbridge A S 13 Section 3 Hints In the 3 KQ 30 kQ range the input impedance at 30 kHz is 10 kQ and the correction factor is thus 6 dB according to the formulas in subsection 2 5 The corrected distortion is consequently 139 dB After the test the measuring voltage is set off 3 2 The IEC Set up The IEC 440 standard literature reference 7 defines measuring voltages for given resistor values The CLT 10 can automatically set up the 10 kHz Generator and the impedance range on the basis of the chosen im
43. stor 20 CLT 10 App Note Section 4 Testing Resistors The reason for the relation between distortion and temperature coefficient is the varying temperature of the thin metal film as a function of time and the involved resistance variations the resistance is modulated with the applied voltage and the higher the temperature coefficient the higher the resistance variations and distortion The temperature variation in the film is in the order of 0 01 to 0 2 C If the metal film resistor for instance has a high positive temperature coefficient its ohmic value will increase slightly when the applied sinewave is at its maximum voltage value This will decrease the current compared to that of an ideal resistor of the same value and the current is therefore distorted This interesting fact was described in 1974 in literature reference 4 The curve in Fig 4 1 can even be drawn based on calculations of the heat transfer from the metal film This finding is very important It means that it is possible to check if the temperature coefficient is within a certain limit both positive and negative even on the production line Especially when producing metal film resistors with a very low temperature coefficient the measurement of the distortion provides the manufacturer with a unique tool to verify at high component rates that both the temperature coefficient and the overall quality are within the specified limits Metal film resistors of today s s
44. stortion of the same order of magnitude as the CLT 10 perhaps even lower Low distortion resistors may often exhibit fluctuating distortion readings One reason is the varying phases of the 30 kHz signals of the component s distortion and the residual non linearity This variation of the readings calls in itself for an increased measurement range 24 CLT 10 App Note Section 4 Testing Resistors This subsection explains how it is possible to increase the measuring range through overloading The technique is applicable if the desired power is within the power limits of the CLT 10 Another method is reduction of the measurement bandwidth How the bandwidth is changed is explained in subsection 3 4 The method of expansion of measuring range by overloading is based on the cubic relationship between the current of the test signal and the distortion The distortion in the resistor is given by 3 I v k 4 A The increase AD in distortion can be expressed as I i Pio i AD 20log 10log Li Pi Here gt and are the 10 kHz currents at the normal and increased current respectively Accordingly P and P are the 10 kHz power at the normal and increased power respectively It is seen that a 10 times increase in test power gives 30 dB higher distortion level This is a remarkable increase in the measurement range The overloading is done within a short period of time only in order to keep the temperature of the res
45. tandard often have a temperature coefficient well below 50 ppm C This means that a standard batch of good resistors could have a distortion which on an average is below 140 dB This on the other hand makes the CLT 10 a very sensitive instrument to any inherent failure whether this is caused by constriction failure in the material or a too high temperature coefficient 4 2 Resistor Networks The principles for testing the quality of single metal film resistors can be applied directly to resistor networks One example is testing of resistors on substrates One difference between resistor networks and single resistors is the way of trimming the resistor network to the correct ohmic value Defects in this trimming process will show up as increased non linearity especially if the cut in the resistance track is too deep The connection to the resistors is usually done by metallization of the ends of the resistors Experience has shown that insufficient contact between the metallization and the resistance track will increase the distortion The individual resistors in the network can be measured as explained for normal metal film resistors CLT 10 App Note Danbridge A S 21 Section 4 Testing Resistors In order to increase the sensitivity of the measurement it could be recommended to overload the resistors as explained in subsection 4 4 Further discussion on resistor networks is found in subsection 7 3 4 3 Calculating Distortion I
46. ters of the 30 kHz Voltmeter By controlling both the settings in the 10 kHz generator system and in the voltmeter while receiving data from these boards the Interface Board serves as link between the Measuring Unit and the Control Unit and hence the user Please consult the Service Manual for the CLT 10 Measuring Unit Service Manual for a detailed description of each of the parts of the Measuring Unit 2 4 Operation at a Glance The CLT 10 can be operated both manually and automatically Various features of the CLT 10 make the operation easier and fill the gap between manual and automatic operation e Set up according to IEC 440 e Autoranging of the 30 kHz Voltmeter e Set ups can be stored e Programmable rejection limits On both the production line and in the laboratory the following basic steps are found Find the impedance at 10 kHz of the component to be tested Find the impedance at 30 kHz of the component to be tested Select the impedance range of the CLT 10 based on the impedance at 30 kHz 8 CLT 10 App Note Section 2 Principle of Operation Set up the 10 kHz Generator so the desired power is delivered into the impedance at 10 kHz The limits of the CLT 10 should be observed In case of resistors the IEC 440 set up can be used Connect the component to be tested to the measuring terminals Switch the 10 kHz voltage on Select a suitable range of the 30 kHz Voltmeter The autoranging could be use
47. to the measuring terminals It is not necessary to use the Cable Unit as the additional measuring error without the Cable Unit in this range and at 10 kQ component impedance is below 0 1 dB Switch the 10 kHz voltage on by pressing the MV ON button Select the most sensitive range of the 30 kHz Voltmeter without causing overload The autoranging could be used Let us assume that the measured 30 kHz voltage is 2 8 uV 14 CLT 10 App Note Section 3 Hints It is not necessary to calculate the ratio between the measuring voltage and the measured 30 kHz voltage when using the IEC set up as this is done automatically In this example the result is 145 dB In the 3 kQ 30 kQ range the input impedance at 30 kHz is 10 kQ and the correction factor is thus 6 dB according to the formulas in subsection 2 5 The corrected distortion which is shown on the display of the 30 kHz Voltmeter is consequently 139 dB After the test the measuring voltage is set off 3 3 Selecting the Correct Range Normally the impedance range of the CLT 10 is chosen on the basis of the impedance at 30 kHz of the component under test in order to get the best impedance matching In case of non resistive components however the impedance of the component at 10 kHz could become too low for the CLT 10 Capacitors exhibit increasing impedance at lower frequencies and the load impedance range of the CLT 10 is therefore not exceeded when the impedance range is chos
48. tors 28 Audio grade 28 Ceramic 6 30 Electrolytic 28 Foil 29 Constriction 5 22 37 Contact in resistors 20 Contents Of Application Note 1 Table of i Control Unit 4 6 Corrected Non Linearity 9 14 Corrected Residual Non Linearity 10 15 Correction factor 30 CRNL 10 15 Current density 20 Data Retrieval 38 Description of the CLT 10 6 Detection of unreliable components 5 Dielectric constant 29 Distortion 1 3 19 22 29 36 Calculations 22 Example IEC 440 measurement 14 Manual measurement 13 Figures List of iii Filter 42 Index CLT 10 App Note Section 9 High Pass 7 Low Pass 3 7 Flash over 31 Foil thickness 29 Gaussian distribution 4 6 General on Impedances 9 High Pass Filter 7 Hints about Operation 12 IEC 440 12 13 14 IEEE 488 38 Impedance Capacitor 15 Capacitors 9 Inductors 9 15 Inductors 32 Air core 32 Ferrite 32 Inherently high distortion 4 Input impedance 7 Insulation 36 38 Interface IEEE 488 38 RS 232 C 38 Interface Board 7 Introduction 1 Key features 2 Length of Resistance Track 23 Life test 4 6 19 Literature 40 Low Pass Filter 3 7 Manual Operation 12 Matching Transformer 7 Measurement jigs 36 Measurement Principle 3 Measuring Terminals 12 Measuring Unit 6 Metallization 22 Moisture 37 Narrow bandwidth 15 No load voltage 3 Noise 15 38 Man made 15 Narrowband 15 White 15 CLT 10 App
49. using the normal bandwidth Please observe that the accuracy is degraded with approx 1dB when reducing the measurement time from 10 ms to 6 ms 7 3 Measurement Jigs The CLT 10 Measuring Unit should preferably be placed just above the measuring jig The Cable Unit must be able to connect the CLT 10 to the measurement jig without strain on the cable The Control Unit does not have to be placed close to the jig but can be placed at a convenient position to the operator Metal objects that are not grounded should be kept at least 10 cm away from the measurement terminals In general non linear materials should be kept at least 10 cm away from the measurement terminals When using connection cables the quality of the cables is of great importance Do not use long laboratory wires or similar to connect the component under test to the CLT 10 as this most likely causes high residual distortion regardless of the wires being twisted or not Low distortion is generally achieved by high voltage RF cables withstanding more than 36 CLT 10 App Note Section 7 Production Line Integration 1 kV rms Make sure that all the wires of the center conductor and the screen are unbroken and soldered The measurement jig can be constructed in many ways The most common one is made with contacts which give pressure upon the leads or terminals when the component is in position A great variety of jigs have been devised and some are surrounded by a lot of s
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