1976 , Volume , Issue Sept-1976
Contents
1. overlapping variable per e of intermitte ape de The glitch that oc casionally lows the third pulse in this pulse trai pe dis play play come a thes As shown by the timing diagram of Fig 6 in the AUTO ERASE mode a sweep trigger unblanks the CRT beam and starts the horizontal sweep circuit writing a trace At the end of the sweep the CRT beam is blanked and control is handed to the storage circuits which inhibit further sweep triggering while display ing the stored trac The trace remains on view for a time tz between Fig 2 Slow moving waveform 10 msidiv shows up as a moving dot on a conventional oscillo scope left but the waveform is een on a variable per rage CAT persistenc adjusted so the retained just ur written 1 and 10 seconds selectable by the VIEW control At the end of the view time the instrument switches to the ERASE mode wiping out the trace After 300 ms control is handed back to the sweep circuits which then await another trigger The AUTO ERASE circuit allows two sweeps between erasures when the in Fig 3 Fast waveform transit occurring at a low repi barely visible on a osc brightly se left Copr 3 1949 1998 Hewlett Packard Co repetitions are variable persis pe right Sweep time here is strument is in the alternate sweep mode2. An Easier to Use Variable Persistence Storage Oscilloscope with Brighter Sharper Traces Revising the control arrangement and operating modes of a variable persistence oscilloscope results in a more friendly instrument that also has improved display characteristics by Van Harrison Dp aAnns PERSISTENCE STORAGE oscillo scopes enable a user to view and measure oc casional signal transients that escape detection with conventional oscilloscopes Now with improved writing rates variable persistence storage scopes have become fast enough to permit their general use in the high speed transient analysis that often accom panies digital design and troubleshooting especially for finding glitches that occur randomly Fig 1 The variable persistence storage scope also retains waveforms traced at very slow sweep speeds allow ing the user to see the entire waveform rather than a moving dot Fig 2 With persistence adjusted to overlap traces these instruments can integrate fast signals that occur at too low a repetition rate for nor mal viewing making the signals brightly visible for examination Fig 3 In fact this integrating technique makes it possible to view signal transitions that are much faster than the basic writing rate of the oscilloscope In view of all these advantages in addition to the ability to do everything that conventional scopes can do the question arises why aren t variable persist
3. tegrated by the integrator At the end of this period the integrator output E is proportional to the dc in put current After the first period E is transferred to C by momentarily closing switch Sp Thus the output E is a step function whose steady state value is exactly proportional to Ipc Fig 6 shows typical waveforms Auto Phase Adjust A phase error compensation technique was first employed in the 4271A 1 MHz Digital LCR Meter That method used two phase detectors and two inte grators To produce a quality low cost unit an auto phase adjustment technique was adopted for the 4261A The auto phase adjustment block diagram is Low Pass Phase A Wo a Vv 13 m Ep 2 qe f Esinutot Roi Jo Fee 26 oof Epi dt rer Fon Ept Enn gar fy Eoin sist WOR T Ep Epe Ep Eu Bim e n S Fo Jo 1 Eunet y Ta Fig 6 Sectional average integrator converts the phase detected signal to a dc voltage within one test signal period as shown by the typical waveforms shown in Fig 7 Amplifiers A and A in Fig 7 are the same as those in Fig 3 Since the amplifiers are not ideal they shift the phase of the e and ez signals The difference between the two phase shifts er will cause a large error especially when measuring the dissipation factor of low loss capacitors For accuracy tander must be less than 0 001 Automatic phase adjustment is done in step 2 of the measurement sequence S4 is clos
4. A and Aj e and e are transferred to the measurement section where their vector ratio is detected by a phase detector and a dual slope analog to digital converter When a device is measured with the 4261A eithera series equivalent circuit mode or a parallel equivalent circuit mode is automatically selected When the DUT impedance is relatively low the series mode is selected and when it is relatively high the parallel 1 120 Hz 1 kHz Oscillator V 10 mode is selected In the series mode the 4261A se lects a source resistance at least ten times the value of the DUT impedance to achieve a constant current drive When the parallel equivalent circuit mode is chosen a source resistance less than one tenth that of the DUT impedance is selected to drive the DUT at a constant voltage The source resistor R helps to limit current flow into the current detecting amplifier when its ter minals are shorted and to suppress differential or integral noise when a capacitor or inductor is con nected For a C D measurement in the parallel equivalent circuit mode Gp joC Re 8 8 a r a 1 Gp joC Ry 1 a 1 Gp joC Ry where w 27f and f test frequency When e is the reference signal the ratio of e and ez is elez Gp jwC Rg which is proportional to the unknown admittance L D is determined in the same manner eye VR 1 joL Re For a measurement in the L D series c
5. Packard Co Van Harrison Van Harrison spent two years with the U S Navy in Ethiopia before altending the University of Florida where he obtained BSEE and MSEE degrees Upon graduation 1972 he joined HP contribut ing to the Model 1740A 100 MHz Oscilloscope before assuming project leadership of the Model 1741A A native of Ormond Beach Florida Van is married and has two children He also designs hi fi equipment does some wood working skis and golfs Switching to either the AUTO ERASE or AUTO STORE mode automatically sets the instrument for maximum persistence Switching to the AUTO ERASE mode also switches the trigger mode to NORM so the trigger cir cuit is not left in the AUTO mode which could trigger the scope randomly A hold off circuit is wired into the STORE function so that when the STORE button is pressed during a sweep the instrument does not go into the STORE mode until the current sweep completes This ar rangement is particularly desirable for slow sweeps when operating in the AUTO ERASE mode as it permits the operator to push the STORE button whenever he sees something he wishes to retain without losing part of the complete sweep Conventional Operation The manner of operating the CRT has been changed for conventional non storage display Formerly dur ing normal oscilloscope operation the voltage on the storage mesh was made negative 30 V to repel flood gun electrons and prevent them from
6. Yokogawa Hewlett Packard as a development engineer since that time He was a principal contribu tor to the design of the 4271A 1 MHz Digital LCR Meter and the 4261A Digital LCR Meter he developed the analog section cir cuitry for the 4261A He s mi In his spare time Toshio likes play tennis Copr 1949 1998 Hewlett Packard Co SPECIFICATIONS HP Model 4261A LCR Meter Common Specifications PARAMETERS MEASURED C D L D R DISPLAY 312 digit max display 1900 CIRCUIT MODES auto parallel and series MEASUREMENT CIRCUIT five terminal method RANGE MODE auto or range hold MEASUREMENT FREQUENCIES 120 Hz 3 and 1 KHz 3 TRIGGER internal manual or external 20 Me 1000 9F 10 0006 Peron Vive 1000 Yom oF ORN G 2006 cour Tee Sore p O nacn ftes sors Manoy Sees 298 2 Cusa cow inte ise ae apo mae oT 1 Typen daia Vain win vas of O and mamoe of coves 2 AIN a racing ponte a Ce capactaren raadou m coven 2S 2 counen at Vane Ace ncy appin over e ame ratu range Of ZTE C Enor onas fr OSC LD Measurement Farge 388 T O00 wi raon mi rao m vano mn 100 w T romam T vooo w Siete vono m 1000 GH 1800 mat 100 met 1908 mmt 0 04 L 10S M Ton Pwah v mel smm oma oma ima 190uk aopa CON Sarre mn nenen mose Sere es pete ce i fpe ssim sszmm Accutncy Soren DIN zona 02H J Nwa aao Same as venoe mode Same a paratei mace D Pwate aa 0 tasom 19 som secsn
7. of the Hp Hc cable or the Lp Le cable If the mutual inductance of each cable is M 2 henries then C measured a Se 1 wMC To minimize this error it is necessary to use short test leads or to twist the Hp and Lp cables together Similarly in high impedance measurements it is possible to minimize the stray capacitance between the high and low terminals by shielding with the GUARD terminal Compensation for high impedance measurement errors can also be made by using an off set voltage equal to the voltage across the DUT but opposite in polarity this is done with the 4261A in the connection configuration shown in Fig 8 The variable capacitor is adjusted for a zero display Accessories Several accessories are available for the 4261A The 16061A Test Fixture is a direct connection type for Fig 9 Mode 16061A Test Fixture for general purpose use Copr 1949 1998 Hewlett Packard Co Fig 10 Mode 16062A Test Leads for low impedance devices general purpose use The 16061A Test Fixture Fig 9 has inserts for both parallel and axial lead components The 16062A Test Leads Fig 10 are for comparatively low impedance DUTs four terminal connections The 16063A Test Leads Fig 11 are for comparatively high impedance DUTs three terminal connections Acknowledgments The authors wish to express appreciation to the many people who participated in the development of the Model 4261A The team members include
8. s ruggedness an accelerometer responds to the resulting G forces and a variable persistence storage oscilloscope cap tures the single accel erometer pulse so its magni tude can be measured This is one of the applica tions for which this type of oscilloscope is uniquely suited The HP Model 1741A variable persistence storage scope shown here is de scribed in the article beginning on this page In this Issue An Easier to Use Variable Persis tence Storage Oscilloscope with Brighter Sharper Traces by Van Harrison An Automatic Wide Range Digital LCR Meter by Satoru Hashimoto and Toshio Tamamura page 2 page 9 o Copr 1949 1998 Hewlett Packard Co minimum deflection factor 1 mV div with magnifier on selectable input impedance 502 or 1 MQ 20 pF and a third trace for viewing the triggering waveform To these basic performance characteristics the Model 1741A adds variable persistence and storage with a writing rate of gt 100 cm us in both variable persis tence and storage modes of operation fast enough to capture a single transient pulse less than 20 ns wide and taller than 1 graticule div ision Auto Erase The new oscilloscope has an AUTOE by automating the er the setting of the CR ne mode that write view cycle facilitates controls for optimum bright and focus This mode permits the operator to quickly evaluate the effect of any changes made to
9. step 7 If the charging time is n times the period of the clock frequency the following equation is similarly es tablished ni fc n y K oC Re ey fe K Gp Rgez G Thus n is a measure of the dissipation factor C D Measurement The C D measurement employs an unusual tech nique e is the reference signal for the series equiva lent circuit mode In step 3 Sp is connected to e and phase detected by a signal in phase with e In other words e is phase detected by e The integrator is charged for a period equal to n times the reciprocal of the test frequency f The charge stored on the inte grator during this time is Qes Keyn f Step 4 is the discharge cycle Sp is connected to ez which is phase detected by a signal whose phase is shifted from e by 270 The integrator discharges until its output crosses the zero volt point If the dis charge time is n f the charge dissipated is Q K 1 ny B aGRa fk Then because Qes Qesas Ng 27f ngC Re Hence from n4 C is directly obtained This technique is the widely used dual slope method except that the slopes occur in reverse order Usually the integrator discharge slope is constant but here the slope decreases as the C count increases At full scale the discharge slope is one tenth that of the charging slope This results in a good signal to noise ratio and precise resolution and makes it possible for the new meter
10. al to Sectional Average Integrator oS of eg gt Analog Switch gt a ROM Centered i Logie Ve 11 the vector ratio of e and e A block diagram and timing chart for this section are shown in Figs 3 and 4 The instrument goes through a seven step se quence to take a measurement In step 1 an autozero is performed S connects the input of the phase de tector to ground and S is closed Thus with no input S is shorting the input to ground the integrator loop is adjusted for zero input and the adjustment vol tage is stored on C This cancels any phase detector leakage current error as well as compensating for any dc offset voltage throughout the loop During step 2 an auto phase adjustment is performed this will be described later Steps 1 and 2 are performed just be fore ratio detection Assume that a capacitor is being measured in the parallel circuit mode C ez is the reference signal as previously described and is applied to the four phase generator Step 3 is the integrator charging period T S is on and switch Sp is connected to e is then phase detected by a signal whose phase is shifted 90 from e as determined by control logic in the ROM The integrator charge Qep stored dur ing T is Qep KoC ReTye2 where K is the product of the efficiency of the phase detector and the integrating constant Step 4 is the integrator discharge cycle Sp is connected to e
11. als The averaging also provides an auto matic intensity correction when changing sweep speeds as for example when switching from main sweep to a much faster delayed sweep Auto Focus Normally a change in CRT beam current requires a readjustment of the FOCUS control AUTO FOCUS allows the intensity limit system to alter the beam current without requiring any adjustment of the FOCUS control The change in focus voltage required by a change in beam current is diagrammed in Fig 10 This curve is approximated by the circuit of Fig 11 A voltage Fig 7 Signals that do not repeat identically are difficult to analyze on a conventional scope left but can be presented in a repeti tive single shot mode right when the Model 1741A is operating in the aur E mode Copr 1949 1998 Hewlett Packard Co A Brighter More Sharply Focused Variable Persistence Storage Cathode Ray Tube Variable persistence storage CATs originally developed for radar applications retain oscilloscope traces on a storage mesh located precisely 0 08 inch behind the phosphor surface The mesh is a fine metallic screen coated with a dielectric magnesium fluoride When a trace is to be stored the storage surface is brought to 10 V Electrons in the CRT beam strike the surface with suffi cient energy to dislodge several electrons for each electron in the beam raising the potential of the storage surface where the beam strikes The dislodged electrons ar
12. and three sweeps if the TRIGGER VIEW mode is added Dual or triple channel displays are thus possible in the AUTO ERASE mode Besides permitting the operator to adjust the CRT beam controls quickly for optimum settings before making a transient measurement the AUTO ERASE mode is also useful as a repetitive single shot mode for examining the voltage levels and transition times of random binary sequences for examining high frequency signals contaminated with time jitter or low frequency noise or for examining the charac teristics of other types of signals that are obscured in normal oscilloscope operation when successive traces are not identical Fig 7 Auto Store One limitation in the application of storage scopes has been the length of time that the CRT can wait ina state prepared to capture a transient when looking for powerline transients power supply transients or any other transients or noise that occur at unpredictable times This wait time usually about 30 seconds was the time it took for the CRT screen to fade positive become illuminated all over washing out any trace that might subsequently be written The AUTO STORE mode of the Model 1741A extends this wait time to several hours As shown by the timing diagram of Fig 8 the instrument remains in the ERASE mode time t while the sweep trigger Fig 4 New Model 1741A Os cilloscope has variable persis e and storage modes of operation in addition to having all
13. as of the storage mesh up to the potential of the written area washing out the trace This limits storage time in the view mode to about 30 seconds Increasing the viewed brightness accelerates this process so there is a trade off between trace brightness and storage time in the ois PLay mode Taking a CRT One Step Further The design of the CRT for the Mode 1741A Oscilloscope is based on this same scheme the CRT used in the Model 184A Copr 1949 1998 Hewlett Packard Co 6 Oscilloscope being taken as a starting point for the design The major design goal for the new tube was to increase full area writing rate Within limits writing rate can be improved by increasing the accelerating potential in the electron gun The consequent increase in the electron beam energy results in a higher secondary emission ratio of the storage surface and hence in a faster writing rate To meet design goals within a reasonable development time it was decided to retain the successful manufacturing techniques developed for the storage elements in the Model 184A CRT and concentrate design efforts on obtaining higher electron beam energy from the electron gun Unfortunately deflection sensitivity is adversely affected by higher beam energy so the major effort was concerned with optimizing this trade off To begin with some loss in deflection sensitivity could be tolerated because the Model 1741A s deflection amplifiers are Capable of higher drive
14. components when RANGE HOLD is set to ON 1 kHz CIL 220 260 ms R 120 160 ms 120 Hz C L 900 ms A 700 ms TIME REQUIRED FOR AUTORANGING RANGE HOLD OFF 1 kHz 180 n ms 120 Hz 670 n ms where n is the number of ranges stepped by the autorange circuit READING RATE the period between the start of a measurement and the start Of the next measurement is equal to the measuring time plus 30 milliseconds typical hold time PRICE IN U S A 1740 MANUFACTURING DIVISION YOKOGAWA HEWLETT PACKARD LTD 941 Takakura cho Hachoj shi Tokyo 192 Japan Bulk Rate U S Postage Paid Hewlett Packard Company Copr 1949 1998 Hewlett Packard Co a
15. d Kohichi Maeda who directed the project Hiroshi Sakayori who designed the process amplifier sec tion Kenzo Ishiguro who designed the display and decoder section Seiji Mochizuki who did the power supply design Toshio Manabe and Yoshimasa Shi bata who contributed to the mechanical design and Fig 11 Mode 16063A Test Leads for hig devices h impedance 15 Kazu Shibata and Yoshio Satoh who handled the industrial design Hitoshi Noguchi provided many useful suggestions for the project Akira Yamaguchi designed part of the logic section in the early stages of the project References 1 T Sugiyama and K Yamaguchi Pulsewidth Modu lation DC Potentiometer IEEE Transactions Vol IM 19 No 4 November 1970 2 K Maeda An Automatic Precision 1 MHz Digital LCR Meter Hewlett Packard Journal March 1974 Satoru Hashimoto Satoru Hashimoto received his BSEE from Tokyo Metropolitan University in 1971 and soon after wards joined Yokogawa Hewlett Packard He worked on the design of the logic section of the 4271A 1 MHz Digital LCR Meter then joined the 4261A Digital LCR Meter project He developed the counter and the sequence con trol section circuitry for the 4261A In his spare time Satoru enjoys mountain climbing and photography Toshio Tamamura Toshio Tamamura received his BSEE degree in 1971 trom the University of Electro Communica tions in Tokyo He has been with
16. del 4261A Fig 1 is designed to provide the wide range and ac curacy of a universal impedance bridge without the bridg s disadvantages of manual balancing and meter reading ambiguity The new LCR meter is fully automatic displaying the value and dissipation fac tor of an unknown inductor or capacitor or the value of an unknown resistor on its 342 digit display a frac tion of a second after the unknown is connected to minals Selection of the measurement equiva t circuit is made automatically according to the value of the unknown component The new LCR meter typically can take four or more readings per second at a 1 kHz measurement fre quency and one or more at 120 Hz with basic accur acies of 0 2 for capacitance inductance resistance ents 9 wide measurement range two high reliability optional HP IB a Reritnbiatarewitke PA Ke it suitable for a wide rar and dissipation factor The unknown terminals are configured in a five terminal arrangement that is ca pable of four three suitable and two terminal connections respectively for low impedance high impedance and ordinary measurements The unit measures capacitance from 0 1 pF to 1900 uF at 1 kHz and from 1 pF to 19 00 mF at 120 Hz inductance from 0 1 H to 190 0 H at 1 kHz and from 1 wH to 1900 H at 120 Hz resistance from 1 m to 19 00 MQ at 1 kHz or 120 Hz and dissipation factor of capacitors or induc tors from 0 001 to 1 900 For measureme
17. e swept up by the positively charged collector mesh nearby see drawing CRT beam electrons that pass through the storage mesh strike the phosphor surface generating a trace that shows where writing occurs After completion of the sweep the stored trace is made visible by flood gun electrons The low velocity electrons from the flood guns are repelled by negatively Charged areas of the storage surface and gathered by the collector mesh but where the storage surface has been charged by the electron beam the electrons approach close enough to the mesh to be pulled through by the high accelerat ing potential of the phosphor surface 5 2 kV striking the phos phor with sufficient energy to produce a visible trace To erase the stored trace the storage mesh is raised to the same potential as the collector electrode 156 V for 50 ms The entire storage surface then becomes uniformly charged obliterating the trace The storage surface is then returned to 10 V for the next write cycle Variable persistence is obtained by shortening the erase cycle so only partial erasure occurs The erase cycle repeats at a 1 kHz rate so the trace slowly fades from view By varying the width of the erase cycles the rate of fade can be controlled q_ Electron Gun within a range of 100 ms to 1 minute During the view phase the few inevitable gas molecules in the CRT become ionized These collect on the storage mesh slowly bringing the non written are
18. ed and a first order feedback loop is created through the integrator to reduce fer When the loop has settled a dc voltage proportional to er is stored in C and maintained for the measurement period ROM Centered Design To control its various measurement modes and to manage the complex decoding necessary to provide simple operation with wide range measurements the Fig 5 Four phase generator develops precision phase shifts and eliminates the need for a Standard capacitor Copr 1949 1998 Hewlett Packard Co Asinut Phase Detector o gt WA P Acosust gt EN lt Asin at Ger eo 0 drp A G V Fig 7 Circuit diagram for auto phase adjustment Closing S4 creates a first order feedback loop that stores on capaci tor C3 a voltage proportional to the differential phase shift of amplifiers A and As 4261A uses a ROM centered design It has two 4K bit ROMs one for sequence control and the other a de coder With this design it was easy to add the self test functions The ROMs are n channel MOS ROMs manufactured by HP Full Autoranging The 4261A has two autoranging modes One is a fixed measurement circuit mode in which the opera tor selects either the series or the parallel equivalent circuit and the other is full autoranging including circuit mode changing Measurement circuit mode changes are done by switching Sc in Fig 3 In the full autoranging mode the instrument selects an appro
19. ence storage scopes used more often Part of the answer may be cost They do cost more But more than that may be the duller fuzzier trace the esoteric controls these intimidate the casual user and the tediousness of setting up the instrument for storage Then too there has been the fear of burning the storage surface of an expensive to replace CRT A new variable persistence storage scope Fig 4 has been designed to make this type of instrument more acceptable to the average user by eliminating most of these problems A new arrangement of the controls with LED indicators to show what state the instrument is in takes some of the mystery out of instrument operation Auto store and auto erase modes of operation simplify instrument use Im provements in the CRT result in a brighter trace that is 2 more sharply focused with trace quality as good as or better than that of some comparably performing con ventional oscilloscopes Fig 5 Protection circuits reduce the likelihood of burning the storage surface while simplifying beam intensity and focus adjust ments Basically the new oscilloscope Model 1741A is identical to and can be used like the Model 1740A described in the HP Journal December 1975 with the added advantages of variable persistence and storage Both scopes are dual channel delaying sweep oscil loscopes with dc to 100 MHz response 5 mV div Cover A shock test machine slams down to test an instrument
20. ey one Seren 02 a 2000 couren hoe 2 to S a sones mae 1 Typem cata Vanes win value of D and numer ot coura 2 iN o mang court 1 La a duetan raadot 1 count Accuracy apoios over s temperate range of ZC 53 C Erot doing for OSS Hewlett Packard Company 1501 Page Mill Road Palo Alto California 94304 HEWLETT PACKARD JOURNAI CHANGE OF ADDRESS siram u nener Paane sumer 10i Pope noes Pal Aia Catone S508 USA hon PO ao 9 ee a L me f T Pome Sye lmm moma ioma ima Oud vosa i Sew ma heres made ie Pon Pare na Ss C poe 5 ME n 1 Types asta vanes th mamoe ot ooun 2 eof reasrg eni Accumcy appien owe a MBNA range OI ZFC C Eno aouns or 035C DC Bias INTERNAL SOURCE 1 SV 22V 6V selectable on tront panel Accuracy 25 EXTERNAL SOURCE Provision for external dc bias voltage of 30V maximum at binding posts on rear panei General OPERATING TEMPERATURE AND HUMIDITY 0 C to 55 C to 95 RH at 40 C VOLTAGE REQUIREMENTS 100 120 220 240 10 48 66 Hz POWER CONSUMPTION 25 W with any option DIMENSIONS 213 W x 134 H x 422 D mm WEIGHT Approximately 6 kg Reference Data MEASURING TIME the period between start of a measurement and completion of the measurement is equal to measuring time when RANGE HOLD is set to ON plus time required for autoranging The following are typical times for a measurement of approximately 1000 counts on low loss
21. illuminat ing anything written on the storage surface This also happened to reduce the intensity of the electron beam In the new oscilloscope the flood gun grids turn off the electron flow in the conventional mode At the same time the storage mesh is raised to the potential of the collector mesh 156 V so no secondary emission occurs and traces are not stored Acknowledgments I would like to thank Stan Lang and Johan Sverdup for constant support encouragement and many useful ideas during the project Al Best for his leadership and support during the latter stages of the project Joe Millard and Eldon Cornish for flexible vertical and horizontal designs that allowed for new control ideas Jim Carner for the mechanical design Dick Stone and Herman Hinton for their customer oriented in puts and Chuck Gustafson for his many hours of help in understanding the subtleties of storage CRTs ABRIDGED SPECIFICATIONS HP Model 1741A Oscilloscope HME mase ACCURACY Seven Tine Oh omit bmn chante 04 wh Baar Bu sro senon CHOP Oumar A pou chan B aber anon re Pe ae Vertical Amplifiers 2 ton actors Wom OC Yo BB vee sur SON ara MA rout modes fat 15s 88 mae 7 s arg AC COUPLED agoror 10 Ke 0 100 Mie 3 Pir wih 131 de proban SE Ts 28 rani om TOX Se BON ponte ot a h aw mp i DEFLECTION FACTOR RANGES 5 Vid 1e 20 Vi in 1 2 5 sequence VERNIEN cortruciay vanao Deawoen Bt sargat elas menmun artec fon moo at ea 0 Vi POLANY chan
22. ircuit mode the equations for e and e are Fig 2 Current to voltage conver ter section applies the test signal to the unknown and develops two voltages e and e gt whose ratio is proportional to the unknown im pedance or admittance Selection of series or parallel equivalent cir cuit for the unknown is made automatically Copr 1949 1998 Hewlett Packard Co Rg aa R R joL R joL a Ro R jo When e is the reference signal the ratio of e e is ee Ro joLV Re The equation for a CyD measurement becomes ele R 1 joC Rp In all cases the vector ratio multiplied or divided by Rp produces the DUT impedance or admittance The 4261A has five range resistors from 109 to 100 kQ having tolerances of 0 05 It is possible to ignore the residual resistance of the range switch which adds to Rg and might contribute to the error since the current and potential terminals of the range resistors are separated Detecting the voltage differentially minimizes the error contributed by the residual resistance of the lead connections to the DUT and similarly the residual voltage of the cur rent detecting amplifier Measurement Section This section consists of a four phase generator for phase detection a sectional average integrator SAI that smooths the signal from the phase detector a dual slope analog to digital converter and logic cir cuitry The output is a digital quantity proportion
23. llowing a large drive voltage with high beam current in the single shot mode the intensity limit circuit holds the drive to lower levels in repetitive operation Acknowledgments Many people contributed to the design of the new CRT Johan Sverdup and Chuck Gustafson provided continuing encour agement and guidance Special thanks are due Roy Wheeler Dave Granteer and Jim Haley for valuable technical advice and programming assistance Much help was also provided by John Hawton Paul Carnahan Frank Balint and Hank Ragsdale Robert G Wickiliff Jr Reference 1 H Moss Narrow Angle Electron Guns Academic Press New York and London 1988 Fig 9 Intensity limit circuit responds to the average current in the electron gun anode and limits the excursions of the CRT unblanking pulse accordingly proportional to intensity is taken from the INTENSITY control R2 of Fig 9 and buffered by Q4 Fig 11 The turn on threshold of transistor Q5 is set by poten tiometer R6 and this threshold becomes the break point for the curve of Fig 10 Above the break point the slope of the focus voltage vs intensity setting curve is determined by the ratio of R7 toR4 R5 The focus voltage vs intensity setting curve is thus ap proximated closely enough that manual adjustment gains only marginal improvement if any at all Model 1741A has a BRIGHTNESS control in addition to the INTENSITY control The INTENSITY control ad justs CRT bea
24. m current whereas the BRIGHTNESS con trol by determining the steady state voltage of the i Fig 10 Graph of the optimum focus voltage as a function of CAT intensity solid line The dotted line is the curve gen erated by the auto focus circuit Fig 11 storage mesh affects display intensity when viewing a stored trace With the BRIGHTNESS control at its most negative position the storage surface repels most flood gun electrons allowing only a few to be at tracted by the phosphor voltage through the mesh where the trace is written At its most positive level many electrons pass through where the trace is writ ten giving a bright trace but the display also fades positive more quickly The BRIGHTNESS control per mits the operator to find the best balance between trace brightness and viewing time It replaces the MAX WRITE switch of earlier HP variable persistence storage scopes which gave only two levels of control for this function Added Conveniences Other features contribute to ease of operation For instance when the instrument is in the SINGLE SWEEP mode pushing the manual ERASE button not only erases the trace but it also resets the sweep eliminat ing the bother of pushing two different buttons to reset the instrument for a single shot measurement Fig 11 The auto focus circuit modifies the voltage applied to the Focus control in response to the INTENSITY Control setting Copr 1949 1998 Hewlett
25. ne B may be ewer Hot pare arbi INPUT RE aici AC ORA DC U MI 2 shut by aban 20 pF Aan Time Base sening 100 radu 620 mec a maion 1 Bu Aad Vhs lor tomoerones om C io ISPC ane 498 C 8 80 Triggering eo nggere Dy marrat or extra monat tren atte 1 opt janes VERTICAL MAGNIFICATION os A vs B Operation IYAN sar an shanna a ae CHANEL B KARD oo 5 Mie ae ENON FACTOR if 20 V s 12 ctr pe n E Temo nange PHASE OPFERENCE BETWEEN CHANNELS 9 00 Tube and Controls IFFUMENTIAL TE MEABUREMENT ACCURACY Acovaty tewe sae HIN OY OM wa CONVENTIONAL natura preatnce of Pt shower agoros 40 us STORAGE WAITWA SPEED 100 cyan 138 Bus over core 7 gt 9 oy saving ho STORAGE Tie DISPLAY MODE i an 10 12 C STORE MODE alias 30 1 i ZC BRIOHTWESS aggro 170 co 50 ERASE TIME sopros 300 me ARIS PUT DETENSITY WOOUATION 4 V S08 win ou tesa eny ereny ant MME noma manay nat Y General AMPLITUDE CALIBRATOR 0c is SEC OUTPUT VOLTAGE Vee ANSE TIME lt 0 pa FREQUENCY apo POWER 10 120 270 240 Vac 10 aiis 4a r 100 VA mae VIBRATION verna free arms or 5 meen wem 0 254 me 0010 r1 cw 100 8 He Copr 1949 1998 Hewlett Packard Co An Automatic Wide Range Digital LCR Meter Easy operation a measurement frequencies t compatibility andlowco compationity and iow cost m a of component and impedance measurem by Satoru Hashimoto and Toshio Tamamura A NEW DIGITAL LCR meter Mo
26. nts in semi conductors two test voltages 50 mV and 1V rms are available for making capacitance measurements in the parallel equivalent circuit mode An internal dc bias source provides switch selectable 1 5V 2 2V and 6V External bias from OV to 30V can be supplied Copr 1949 1998 Hewlett Packard Co to a rear panel connector An offset adjustment for canceling stray capacitance between the unknown terminals is provided a capacitance offset signal available at a rear panel BNC connector provides an offset range of 0 to 100 pF when fed into the low current terminal through a variable capacitor A low power design keeps total power consump tion below 25 watts helping to assure reliability For automated testing or data gathering under computer or calculator control an option provides an interface to the HP IB HP Interface Bus HP s implementation of IEEE Standard 488 1975 How It Works The 4261A measures L C R and dissipation factor by determining the impedance or admittance of the unknown device under test DUT In the current to voltage converter section Fig 2 the measuring signal is applied to the DUT and an operational amp lifier is used as a current detection amplifier The cur rent through the DUT is almost equal to that flowing in the range resistor Rg Voltages e and e are ob tained by detecting the voltages produced across the DUT and range resistor Rx respectively using differ ential amplifiers
27. priate range from the eight available ranges according to the value of the component being tested In this mode the function switch need only be set to L C or R to make the measurement Self Test The 4261A has self test functions that enable it to check most performance areas No additional equip ment or circuitry is required for making the self check Leu Loon Hpoten Hee LA a a 4261A f C Ottset Terminal a ei 6 6 Variable Stray C Capacitor Fig 8 To cancel stray capacitance between the unknown terminals a capacitance offset signal available at a rear panel connector provides a capacitance offset of O to 100 pF when fed into the low current terminal through a variable capacitor The capacitor is adjusted for a zero display with no unknown connected 14 The user need only set two slide switches Two tests are provided One tests the logic systems and the other mainly checks the analog circuits Slide switches located on the sequence control board are set to the appropriate positions to put the 4261A into its self test mode Minimizing Errors The five terminal connection configuration minimizes the measurement error caused by residual impedance of the test leads It is especially useful for the measurement of low impedances below 10 However some care is required in making the test lead connections when measuring capacitors from 100 to 1000 pF at 1 kHz Here an error is caused by the mutual inductance
28. selects the AUTO STORE mode if the SINGLE SWEEP pushbutton is also pressed Otherwise the AUTO ERASE mode is selected Releasing the button returns the scope to normal variable persistence operation Intensity Limit The storage surface of storage CRTs can be dam aged by excessive beam current The possibility of this happening is reduced in the Model 1741A even though the beam current can be set high enough to achieve a 100 cmius single shot writing rate An intensity limit circuit monitors the CRT beam current and limits the average current to a safe level A diagram of the intensity limit circuit is shown in Fig 9 Resistor R1 is in series with the cathode ray gun accelerator anode When the anode current which is approximately proportional to total beam 5 Write Mode Fig 8 n auto store mode oscilloscope waits in the ERASE mode until the sweep triggers At the conclusion of the sweep the instrument switches to the mode to retain the trace current is sufficient to cause the voltage drop across R1 to turn on transistor Q1 Q2 restrains the voltage at the wiper of the INTENSITY control from going any further negative keeping the CRT beam current at or below this level Capacitors C1 and C2 average the voltage across R1 so the very low average of fast single shot or low duly cycle signals does not restrict the beam current per mitting maximum writing rate and bright display of these sign
29. the other attributes of a high quality laboratory grade 100 MHz Oscilloscope Storage controls with LED indicators to show what state the instrument is in are grouped conveniently to the left of the CRT circuit waits in the armed state As soon as a trigger occurs the instrument switches automatically to the WRITE mode and the sweep starts When the sweep terminates the instrument switches to the STORE mode and retains the written trace up to 30 minutes for examination Front panel LED indicators show what state the instrument is in clearly indicating when the scope is triggered and when it switches to and storage mo ed here while the Copr 1949 1998 Hewlett Packard Co Sweep Triggers S 4 T View Mode oe ae io ji li Erase Mode t I 1 i I ee t t ts Time Variable Variable 300 ms Trigger Inhibit and L Intensity Gate i L Gate Blanking Fig 6 In auro ERASE mode trace writing viewing and erase occur repetitively STORE Pressing the STORE DISPLAY button makes the trace visible for viewing Storage time in the DISPLAY mode however is reduced to 10 to 30 seconds de pending on the setting of the BRIGHTNESS control To keep front panel clutter at a minimum the AUTO ERASE and AUTO STORE modes are selected by the same pushbutton LED indicators showing which mode is selected see Fig 4 Depressing this button
30. to use only five range resistors for its eight range measurement capability Copr 1949 1998 Hewlett Packard Co Four Phase Generator The precision 90 phase shift needed for phase detection is normally derived from a standard ca pacitor but when the test frequency is low such as 120 Hz standard capacitors are very expensive and very large The 4261A measures L C R and D with out a standard capacitor The four phase generator technique makes this possible Fig 5 is a circuit diagram of the four phase generator The reference signal is shaped and fed toa phase detector point A whose other input is the 0 output signal thus forming a phase locked loop The filtered phase detector output tunes a voltage control led oscillator that produces a signal at four times the input frequency Two J K flip flops driven by the VCO provide 0 90 180 and 270 four phase outputs A potential problem of this method is phase noise which causes fluctuations in counting the discharge time In the 4261A phase noise is less than 70 dB Sectional Average Integrator The phase detected signal of Fig 3 has to be trans lated into a de voltage very quickly for precise opera tion of the dual slope technique The sectional average integrator or SAI Fig 6 is especially useful at the 120 Hz test frequency If CR is suitably selected the settling time is one test sig nal period During the first period T the input current is in
31. voltages than those of the Model 184A Nevertheless the tube length was increased by 34 mm with the extra length being applied to the deflection plate to phosphor surface distance to increase deflection sensitivity With the new tube dimensions the flood guns are further from the screen improving flood gun display uniformity To further improve uniformity the flood gun grid leads were brought out separately on neck pins to enable balancing of the flood gun Outputs The deflection plates themselves were redesigned using cal culator programs that clearly showed the various trade offs between operating voltages deflection plate dimensions fre quency response and the other parameters that affect perior mance From this a deflection plate shape was derived that allowed the closest possible spacing for maximum sensitivity without intercepting the beam The electron gun was reproportioned to realize greater beam Current while optimizing spot size using curves published by Hilary Moss This resulted in a shorter anode that intercepts fewer electrons leaving more beam current The shortened anode also permitted a further increase in the deflection plate to phosphor spacing All of these steps increased deflection sensitivity to the point that the cathode potential could be increased 855 volts to 2295 V The result was a substantial increase in beam current and consequently in writing rate gt 100 cm s Cut off voltage is 100 V a
32. z which is phase detected by a signal in phase with ez The integrator begins to discharge and continues discharging until its output crosses the zero volt point If the discharge time is T the charge dis sipated is D lt gt gt Fig 3 Measurement section develops and displays a digital representation of the vector ratio of e and e gt Copr 1949 1998 Hewlett Packard Co Cp D Measurement Integrator on S2 on e 7 Phase Cs D Measurement Integrator On on On Se on Sy e So o Phase Fig 4 The measurement sequence consists of seven steps including autozero and auto phase adjust steps The dual slope analog to digital conversion method is used except that in the C D measurement the slopes occur in reverse order Qep2 KT per From steps 3 and 4 Qepr Qepa Tep C RRTy T is n times the period of the test frequency f and Tep is counted as n by the clock frequency fe ny 27f Ren C The clock frequency is selected so that C is directly obtained Next step 6 immediately initiates the D measure ment Switch Sp is connected to e and the phase of the detector signal is controlled at 0 The phase detected dc voltage is integrated and discharged in steps 6 and 7 with the phase of the detector signal changed from 0 to 270 in step 7 If the discharge time is Ty 12 Qai KG ReT2e2 in step 6 and Qaz KaC ReT ye in
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