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Scholars' Mine Masters Theses Student Research & Creative Works 1949 Design and construction of an electronic gainphase meter Gabriel G. Skitek Follow this and additional works at: http://scholarsmine.mst.edu/masters_theses Part of the Electrical and Computer Engineering Commons Department: Recommended Citation Skitek, Gabriel G., "Design and construction of an electronic gain-phase meter" (1949). Masters Theses. 4878. http://scholarsmine.mst.edu/masters_theses/4878 This Thesis - Open Access is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in Masters Theses by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. DESIGN AND CONSTRUCTION OF AN ELECTRONIC GAIN-PHASE METER BY GABRIEL GEORGE SKITEK A THESIS submitted to the faculty of the SCHOOL OF MINES AND 'Mb"'TAIJJURGY OF THE UUIVERSITY OF MISSOURI in partial fulfillment of the work required for the Degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING Rolla, Missouri 1949 Approved by ~~~.-~~/_""J Professor of Electrical Engineering _ ii TABLE OF CONTENTS Page List of Illustrations • ... ·.. ·. Introduction. • ·.....·...... • • • •• · . . . . . . Review of Literature. Description of Gain-Phase Meter • • · . . . . . . List of Tables. ii iii 1 3 6 Circuit Analysis a. Circular Sweep Generator •• b. Pulse Generator • • • • • • c. Cathode-ray Tube Indicator. 10 ..... ·.... 16 21 Design Considerations a. Pulse Generator ·.. ...·...... b. Circular Sweep Generator. • c. Cathode-ray Tube Indicator. ·.. ·...... ...·.... .. . .. ..· .... ·. . ......... Summary and Conclusions • Bibliography• ... Vita• • • • • • • • • • • • • • 25 25 26 Calibration of Gain-Phase Meter • Discussion of Sources of Errors • 23 -. • • • • • • • • • 36 42 43 44 iii LIST OF ILLUSTRATIONS Figure 1 2a 2b 3 4a 4b Sa Page Block Diagram of Gain-Phase Meter. ·. ·.. · .. . . . .... . • • • Gain Scale. . . . . · . . . . . . . . . · . . . Circular Sweep Generator Circuit. . . . · . . . · . . . . Phase Angle Scale • ·.·.... Vector Plot of Voltages in Phase Shifter. • .. Phase Angle Measurement • . . . . . .. ... . . Gain Iieasurement. • • • • ..... .. Bridge Phase Shifting Network • • • 7 8 8 11 II 1.4 15 15 7a ·. Sinusoidal Voltage Input to Pulse Generator • . . . . . . 7b Voltage at the output of the First Clipper Stage. • • • • 20 7c Voltage at the Output of the Third Clipper stage. • 20 6 7d 7e 8 9 10 12 Pulse Generator Circuit. 11 20 . . ...... .... ..... output Pulse. • • • · . . . . . . . . ..... Variable Phase Voltage Generator•• • • ·...... Block Diagram of Phase Angle Test Circuit. • • · . . . . 28 Block Diagram of Cireuit Used to Measure Gain and. Phase Angle of an Audio Frequency Amplifier • • • • • • • • •• 38 Plot of Gain and Phase Angle Versus Frequency for a Transformer Coupled Audio Amplifier • • • • • • • • 39 Differentiated Wave • • Polar Plot of Gain and Phase Angle of a Transformer Coupled Audio Amplifier • • • • • • • • • • • • • • ... 20 20 21 40 iv LIST OF TABLES Table I II Page Accuracy Check of hase Angle Reading About the Circular Sweep • • • • • • • 30 Minimum Width of Blanked-out Portion of 32 Circular Sweep • • • • • • • • • • • III IV v Phase Angle Changes Due to Deviation of Pulse Generator Input Voltage From 0.5 Volt • • • • • • Gain Calibration • • • • • • ... .. Gain and Phase Angle Data of a 6c5 Transformer Coupled Audio Frequency AInplifi er. . . . . . . . . . . . . . .. 33 35 1 INTRODUCTION There are InallY' communication and electronic circuits, such as £11ters, phase-shifting networks, matching networks, voltage amplifiers with and without feedback, whose proper usage with associated equipment depends upon the knowledge of the variation with frequency of the voltage ratio and phase angle between the output and input sinusoidal voltages or currents. A connnon laboratory technique for obtaining the phase angle between two voltages is to appq the voltages to a cathode-ray oscilioscope and from the dimensions of the elliptical pattern formed, calculate the phase angle. (1) This technique gives poor accuracy, (1) F. E. Terman, Measurements in Radio Engineering, page 324, McGraw-Hill Book Company, 1935. because unequal phase shift may be introduced through the vertical and horizontal voltage amplifiers in the oscilloscope. The ratio of the output to input voltage is commonly obtained from the reading of a voltmeter, such as a vacuum tube voltmeter. Neither of the above measuring teclmiques are well suited for class roam demonstration or student laboratory work covering phase angle and gain measurements, because a good mental picture of phase angle and gain cannot be established through elliptical patterns and voltmeter readings. It is the purpose of this thesis to design and build an electronic instrument that 'Vtill measure the voltage gain and phase angle between two sinusoidal voltages or currents of collllIIWlication cir- cuits, in such a manner as to aid the student in visualizing how these 2 quantities vary with frequency, and to increase the accuracy of the phase angle measurements. This instrwnent, the gain-phase meter, will be designed to give a phase angle accuracy of ±1.0 degree or better, and gain accuracy of :!:5% or better, for input voltages from .5 to 62.5 volts over a frequency range from 40 to 10,000 cycles per second. Though several high accuracy electronic phase meters have been constructed, the author of this thesis feels that none are of the type that fulfill the above objectives.(2)(3) (2) Edwin F. Florman and A. Tait, An Electronic Phasemeter, Proceedings of the IRE, Volume 37, Page 207, 1949. (3) Alan Viatton, Modulated-Beam Cathode-Ray Phasemeter, Proceedings of the IRE, Volume 32, Page 268, 1944. 3 REVIE'I[ OF LITERATURE Search into literature does not reveal any electronic instrument such as the proposed gain-phase meter for measuring voltage gain and phase angle over a wide range of audio frequencies. Although several electronic instrwnents have been designed and built to measure phaseangle, none have combined gain and phase angle measurements, and none have indicated such measurements in a manner that would be suitable for classroom demonstration and student laboratory work. In 1942 an electronic phase angle meter, 'whose phase angle read- . ings were indicated by a vacuum tube voltmeter, was designed and built by Edward L. Ginzton. (4) This instrument, the author claims, can meas- (4) Edward L. Ginzton, An Electronic Phase-Angle Meter, Electronics, Volume 15, Page 60, 1942. ure phase angles from 0 to 180° directly. Vlth the use of a trans- former, whose phase shift is 180°, the range can be extended to 3600 • The author claims that the test voltages, applied to the instrument, must be betvreen 0.5 and 5.0 volts for proper operation. The aceurac,y of angle measurement and frequency range were not discussed in this article. In this instrument, the two voltages whose phase angle is to be measured, are applied to two identical amplifier-clipper channels that convert the sinusoidal voltages to square wave voltages of sarne phase displacement. The two square wave voltages are fed into a voltage adding circuit, whose voltage output is indicated by a vacuum tube voltmeter. Theoretically, it can be shown that the sum of the two square wave voltages is a linear function of the phase angle betw-een 4 the two sinusoidal voltages under test. In 1944 a phase angle meter, whose angle readings were indicated by a cathode-ray tube, was built by JUan Watton. (5) (5) Watton, 2£. This instrument, Cit. as claimed by the author, will read angles from 0 to 360 0 with an accuracy of ~. ~ • TIle two voltages, whose phase angle is to be meas- ured, are applied separately to a circuit that converts the sinusoidal input voltage to a square wave voltage. This square wave voltage is then allorred to modulate the electron beam of a cathode-ray tube whose deflection plates are excited by quadrature voltages. The modulation of the grid blanks out one-half of the circular pattern on the screen of the tube and leaves a semi-circular trace. Another semi-circular trace is produced by the second voltage under test. The phase angle is obtained from the angular displacement of the two semi-circular patterns on the screen of the cathode-ray tube. In 1948 E. (6) E. o. o. Vandaven designed a polyphase meter(6) for use in Vandaven, Phase Meter, Electronics, Volume 21, Page 142, 1948. measuring the phase angles of voltages applied to a type 2H21 phasitron tube. Phase angle indications are produced on a cathode-ray tube screen, ..lhose deflecting plates are excited by quadrature voltages, and its grid is modulated by pulses derived from the volta es under test. In 1949 Florman and Tait(7) designed apha.se-meter having a voltage (7) Florman and Tait, Q£. Cit. 5 range of 1 to 30 volts over a frequency range of 100 to 5,000 cycles per second with an accuracy of ~o.~. This instrument operates on a principle similar to the principle of the instrument constructed by Ginzton in 1942. meter. The phase angle is indicated by a vacuum tube volt- 6 DESCRIPTION OF GAIN-PHASE METER The gain-phase meter discussed in this thesis incorporates the use of a cathode-ray tube for indicating the gain and phase angle of two sinusoidal voltages or currents. A cathode-r~ tube was chosen for the intlicating device, because it lends itself well to classroom demonstration, and leaves a mental picture with the student of gain and phase angle variations with frequency as found in communication and electronic circuits. A complete block diagram of the gain-phase meter is shown in Fig. 1. The phase angle between two voltages, ~ and E2, is indicated by the angular displacement of two blanked-out port,ions of a circle on the cathode-ray tube as shown in Fig. 2a. The circular sweep is ob- tained by applying to the cathode-ray tube equal quadrature deflecting voltages that are derived through a phase shifting network from one of the sinusoidal input voltages as shovm in Fig. 1. The blanked-out portions of the circle are produced by applying to the control grid of the cathode-ray tube negative pulses of very short time duration and steep front. These negative pulses are generated by electronic cir- cuits that amplify, clip, and differentiate the two sinusoidal. voltages El and E2 as shovm in Fig. 1. The time separation of the pulses, derived from El and E2, depends upon the phase angle between the two sinusoidal voltages El and E2. Angles from 0 0 to 360°, lead or lag, can be read directly' by this type of indicator without ambiguity. Lead or lag of angle,s i,s deduced from the direction of travel of the spot on the screen in its circular path. _.~-----.Ltr : : I I I .... 1 1• ITTII amp. ~6~ - (1) 6SJ7 ' ( I 1_ _- 6SS7 6SJ? -\f\--- I 1:' ~ --'1!7-- <) , . L .. 605 (3) Parar:-·hase ar.::n. Dumont 241 1.""",;~-JiI'---~ Oscillof,r8Dh Brict.~e Ph~8C Snlltter - < -- '-\)- ----~ ----- ~- ------CQ--- I I --:\} I I I I I t I I I I I I I I - E1 : I (, --lb- -----lb------%----9:J---y.U I ' I , I I • I I t I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I I I , I I • I ' , 6H6 1st anD. To Z Axis - Circular Sween 2nd 2nd Cl i!YDer Pulse Generator ar::rp. 3rd amp. 3rd C11puer t-~ 6HB I-- f Voltage ~elector BLOCK DIAGRAl-1 OF GAIN-PHASE HETER Figure 1. ..... 8 '\ \ "- - " - PBASE ANGLE SCALE FIGUHE 2a. GAIN SCALE FIGURE 2b. ~-~ Circle . - - - E1 ~lrcle 9 The voltage ratio or gain between the sinusoidal voltages, E2 and El is indicated by the radius of the circular pattern on the screen of the cathode-ray tube as shol'm in Fig. 2b. Voltage gain may be read directly on a radial scale attached to the screen of the ca.thode ray tube. Three gain ranges are obtained through the use of the attenuator at the input of the circular sweep generator. ments are not taken simultaneously. Gilln and phase measure- 10 CIRCUIT ANALYSIS The gain-phase meter can be considered as having three main elements; circular S1veep generator, pulse generator, and cathode-ray tube indicator. Circular SweeR Generator The circular sweep is generated by an electronic phase shifting circuit shown in Fie. 3. To the input of this circuit is applied either of the two sinusoidal voltages, El or E2, depending upon which is to be taken as the reference. This voltage is amplified to the de- sired level by the 6SJ7 resistance coupled amplifier(8) of conventional (8) F. E. Terman, Radio Engineers Handbook, Pages 354-366, McGraw-Hill Book Co., 1943. design and fed into a 6c5 paraphase amplifier. (9) Two equal voltages (9) L. B. Arguimbau, Vacuwn Tube Circuits, Page Book Co., 1948. 355, JaM Wiley that are 180 degrees out of phase are obtained from this tube stage, one voltage from cathode to ground and the other from a tap on the plate resistor to ground. A phase splitting arrangement of this type was chosen because it supplies equal voltages whose phase angle does not deviate appreciably from 1800 over a frequency range from 40 to 10,000 cycles per second. The balanced output of the paraphase ampli- fier is applied to a bridge type of hase shifting network(lO) as (10) staff Membe s of .I.T. adar School, Principles of Radar, Chapter 3, Page 31, McGraw-Hill Book Company, 1946. C 20 6 SJ7 +300 yolt. Yolto Q) Re 6S J 7 :.:..:: ~ E, ----0 f EZ ~ 6SJ7 Fro. 1 R I4 o.tI. ~ ttIMI e' ® PI.t D__•• 141 4 ...1•• ........ or O. c '" -=- -:- -:- -=- -::- 6SJ7 @ C CIRCULAR SWEEP GENE'RATOR Fiqure 3 CIRCUIT zT iI." .... 12 PARTS LIST FDR CIRCULAR S'NEBP GENERATOR Resistors R = 0.1 Meg. Ohnl potentiometer - 1 watt R2 = 0.2 ohm potentiometer - 1 watt M:eg. ohms - 1/2 watt = hOK ohms R4 =10K ohms R3 R, =1.0 Meg. R14' Rl" R16, Rl , R13 , - 1/2 watt - 1/2 watt = 20K ohms - 1/2 watt R6, R21' R22' R3l, R32 = 0.1 Meg. ohms - 1/2 watt R7, ~7' RIB , R27 , R28 = 600 ohms 1/2 watt = 0.1~7 Meg. ohms - 1/2 watt R34 = 0., Meg. ohms - 1/2 watt RS, R19' R20, 11.29' R30 ~, R 23' R 24, R33' R10, R12 Rll != = 2.5K R2.5, R26 6.50 ohms 1/2 watt ohms 1/2 watt = 1.0 Meg. ohm potentiometer - 1 watt Condensers Cl' C.5, C6, C7' C20, C21' C26, C27 = 0.1 ~f. (paper) condenser C2, C3' C4, C16, C17' C18, C19' C22' C23' C24' C25 (electrolytic) C8' ~5 • .00015 ~f. (mica) C9 , C14· .00025 ~f. (mica) C10, C13 = .002 !-Lf. (mica) Cll, C12 = .01!-Lf. (mica) =8.0~f. 13 shown in Fig. 3. A nore detailed illustration of this bridge phase shifting network and a vector plot of the voltage relationships is shown in Figs. 4a and l.~b. From this figm e it can be seen that four equal sinusoidal volt- ages, that are 90 degrees displaced from each other, are produced if Xc is made equal to R. These four voltages EoA' EoB' ~OD' and EoE are in- jected into conventional resistance coupled amplifiers using type vacuum tubes as shoyVIl in Fig. 3. 6SJ7 The voltage appearing between the plate of tube No. 1 fed by EoA' and the plate of tube No.2, fed by t.oB, is 90 degrees out of phase with the voltage between the plates of tubes 3 and 4 that are fed by EOD and EOE respectively. This phase relationship between the voltages appearing from plate to plate for the two pairs of amplifier stages, can be obtained in the same manner as shown in Fig. 4b for the voltages from grid to grid, EnE and EBA., of the same pair of tubes. The quadrature output voltage is then applied to the two pairs of deflecting plates to produce a circular sweep on the screen of the tube as shown in Fig. Sa. The amount of signal fed to each of the four voltage amplifiers can be controlled separately in order to correct for unequal amplification of each stage, and anY phase shift from 180 degrees that may develop in the paraphase amplifier stage. Four values of Capacitance (C) found in the bridge phase shifter were required to cover the range from 40 to 10,000 cycles per second in conjunction with two variable resistors (R) of 100,000 ohms each. Gain measurements are also made through the use of the circular sweep. To measure the gain or ratio of E2 to Er, first be calibrated by the smallest voltage .c.l. the instrwnent must This voltage is 11 A A Tube ,...------------,!L----------------O No.1 r -_ _ ~Tube No.2 E: Tube '-----t""I No.3 D TUbe r---<l No.4 BRIDGE PHASE SHIFTING NETWORK FIGURE 4a. DE ~ -OD " ..... , \ \ \ \ \ , \81) or B I ... B T-------~ \ A I \ \ . \ \ I ,, .._ r: / / / ..... / .... ", ('I - _~/... -- VECTO . PL.)T OF VOLTAG7S IN FI'} R_: 4b. P~.A E SHIFTER 15 e n ure e 5 n 16 selected at the input of the pulse generator, amplified, and fed to the circular sweep generator by sw:i tch position Eo at its input. The mag- nitude of this voltage is adjusted by Rl' and/or Rk' to give a circular pattern of 1/2 inch in diameter on the cathode-ray tube. when the range selector at the input to the sweep generator is set to position 1-5. With the instrument calibrated, the larger voltage (E 2 ) is applied at the input of the pulse generator and the gain can be read directly from a radial gain scale. This scale is l~ inches long and is divided into 25 equal divisions of 1/20 of an inch in width. set to 1-5, a maximum gain of 5 can be read. With the range switch The gain scale can be in- creased to 25 on the 1-2.5 scale setting and to 125 on the 1-125 scale setting. meter. Gains from -12.5 to +12.5 can be measured 'with the gain-phase Fig. 5b shows the circles for gain measurements produced by E:t and E2 simultaneously through double exposure. Pulse Generator The blanked-out portions of the circular sweep used for phase angle indication are produced by the pulse generator shown in Figs. 1 and 6. Since only one pulse generator is used, one blanked-out por- tion of the circular sweep appears for each voltage selection made by the switch at the input of the pulse generator. one pulse generator instead of two, one for E:t The reason for using and the other for E2, will be discussed under "Design Considerations". The voltage at the input of the pulse generator is passed through the 6SN7 cathode follower stage ,vhose output voltage appears across the low cathode impedance Rk and ground. The amount of voltage fed to the first 6AC7 amplifier stage of the pulse generator must be .. 300 volta t300 nih R To R 7 Rig I3 ot Ci 3 I 6H6 6SN7 2 E, 2 Rg ~C, RI !! 6H6 RZI 6H6 DulllOll' 241 fiH6 +j 0----<> O.cillo~w. . . J Co E2 To Z Aai. of ~, Cg A CII5 A R 27 -:::::::- 300 yolta PULSE GENERATOR Fiqure 6 CIRCUIT A VR-IOI To Laboratory R.I.lo t. d Po .. ., Suppl Y 18 PARTS LIST FOR PULSE GENERATOR Resistors: R1 =1.0 Meg. Rk = 20K R3 = 0.5 Meg. ohms - 1/2 watts ohms - 1/2 watt ohms - 10 watt potentiometer R4' R10' R16 • 190 ohms - 1 watt R5, R6, R11, R12' R17' R1 8 =10K ohms - 2 R7, R13' R19 = 60K RS, R1.4' R20 = 0.5 Meg. ohms - 1/2 watt ~, R15' R21 =.22 Meg. R23 =0.2 Meg. R24 =6K ohms o~~ - y~tts 1 watt ohms - 1 watt ohms - 1 watt - 10 watts R26 = 200 ohms - 1 "watt R27 =3.25 K ohms - 10 watts Condensers: Gl, C2 C3' =0.1 G4' C5' ~. C6' C7' C8' C11 , C1 5 =8.0 j.1f. (electrolytic) C , C12 , G , C c 1.0~. (paper) 13 14 9 GIO = 28 - 60 - 120 - 300 - 675 ~. (mica condensors) 19 adjusted to approximately selector switch. 0.5 volt for both settings of the voltage This adjustment of input voltages is made through the use of the circular sweep generator with the cathode ray tube as an indicator. With potentiometer Rl of the circular sweep generator set to tile pre-calibrated position that will give a 2" circular pattern for an input voltage of 0.5 volt, the potentiometer Rk in the cathode follower circuit of the signal generator is adjusted to produce a 2" circular pattern for the two voltages under test. The reason for using a cathode follower stage and making the input voltage to the first 6AC1 volt will be discussed under IIDesign Considerations ll • The output voltage of the first 6AC7 amplifier is fed into a full wave 6H6 diode clipper that clips off the top and bottom portions of the sinusoidal input voltage as shO\m in Figs. 7a and ?b. This clipped wave is amplified by the second 6AC7 amplifier and clipped again by the second full wave clipper. This process of amplifying and clipping is repeated in the third amplifier and third clipper stages respectively. The output of the third clipper stage is a square wave that has a steep rise and fall as shown in Fig. 7c. This square wave voltage is applied to an R-C differentiating circuit that produces narrow, steep-fronted positive and negative pulses as shown in Fig. 1d. This differentiated voltage is applied to a voltage selector(ll) that clips off the nega(ll) B. Chance, V. Hughes, E. F. Ma.cNichol, D. Sayre, andF. C. VTilliams, Waveforms, pp. 44-55, McGraw-Hill Book Company, 1949. tive pulse and selects only the top portion of the positive pulse as shown in Fig. 1e. These positive pulses are applied to the g axis 21 amplifier of a type 241 Dumont Oscillograph (12) where the polarity of (12) Manufactured by Allen B. Dumont Laboratories, Inc., Passaic, N. J. the pulse is reversed through amplification. These negative pulses are then applied to the control grid of a SJPI cathode-ray tube cutting off the electron beam for the duration of the pUlse; thereby, producing a blanked-out portion of the circular sweep. Since the circular sweep is of the same frequency as the repetition rate of the pulse, the blankedout portion will remain stationary on the circular sweep. Due to un- equal changes in phase shift in the circular sweep and pulse generator with frequency, the zero reference will change positions on the circular sweep. This requires the phase angle scale to be rotated to make the zero of the angle scale correspond with the reference voltage blanked-out portion of the circular sweep. From the above discussion on the formation of the pulse, it can be readily seen that the separation expressed in degrees between two pulses, one evolved from E1 and the other from E2, will be equal to the phase angle between the sinusoidal voltages E1 and E2• Fig. Sa shows, through double exposure, two blanked-out portions produced by voltages Cathode-rq Tube Indicator The SJP1 cathode-ray tube, g axis amplifier, and associated power supply of the type 241 Dumont Oscillograph were used in conjunction with the circular sweep and pulse generators in order to make gain and phase angle measurements. 22 The output of the circular sweep generator is ted directly to the deflecting plates of the 5JPl to produce an Wldistorted circular pattern 3-1/4 inches in diameter. The average sensitivity of the de- flecting plates was found to be equal to approximately 32 volts d-c per inch. 23 DESIGN CONSIDERATIONS In the design of this gain-phase meter, special attention had to be paid to circuits and measuring technique to reduce or prevent errors in phase angle and gain measurements. Pulse Generator A pulse generator of the clipper-differentiator type, as found in Fig. 6, was used to produce the narrow blanking pulse because of its simplicity and ability to generate voltage pulses of desired width. ide band amplifier tubes and circuits(13) were used in the square wave (13) F. E. Ter,man, Radio Engineers Handbook, Pages 413-416, McGraw-Hill Book Co., 1943. and pulse amplifier stages of the pulse generator to produce steep front square wave and pulse voltages. A steep fronted pulse voltage is required to produce a sharp cut-off of the electron beam. Two pulse generators, one for voltage E1 and the other for voltage E2, were not used, because it was found upon building two identical pulse generators, that there existed a maximum phase difference of approximately three degrees between the generators. enee varied vdth the frequency of the input voltages. This phase differAlthough this phase difference could have been corr:pensated for by the use of a phase shifting network, a much simpler instrument is had with only one pulse generator. The voltage input to the first 6AC7 amplifier must be adjusted to approximately 0.5 volt for the two input voltages El and E2. This adjustment of input voltage is required, because it has been found 24 (see Table III) that a phase shift, in the order of 0., degree, is induced in the pulse generator for an input voltage variation of ~,O% from 0., volt. This phase change is associated with changes in the amo"Wlt of distortion produced in the first 6AC7 stage. By using the technique for voltage adjustment as discussed "Wlder Circuit Analysis, the error in phase angle readings due to unequal input voltages is reduced to practically zero. A potentiometer located in the cathode circuit of the preceding cathode follol~r is used to equalize the input voltages to the first 6AC7 amplifier. A cathode follower stage was used to prevent ~ large phase change due to the adjusting device used for the voltage equalization. Another good characteristic of the cathode follower is that it offers a low sh"Wlt capacitance to the input signal. (13) A ,OO,OOO-ohm (13) Lawrence B. Arguimbau, Vacuum. Tube Circuits, page 354, John Wiley Book Co., 1948. potentiometer located at the input of a convElltional triode 6C, amplifier was found experinlentally to produce a maximum phase change of approximately four degrees. Three stages of amplification and clipping were found sufficient to produce the desired square wave over a frequency range from 10,000 cycles per second. 40 to The increase in rise and fall time of the square wave at high frequencies was compensated for by the decrease of the capacitance in the differentiating circuit. A regulated laboratory power sup!)ly was used to supply d-c voltage to the pulse and circular sweep generators. De-coupling in the plate leads of the 6AC7 tube stages in conjunction with a regulated power 25 supply prevents coupling between stages. Circular Sweep Generator A paraphase circuit using a plate loaded 6c5 tube with its cathode resistor un-bypassed was used to obtain t,vo equal voltages that are 180 degrees out of phase. This circuit was found to produce equal voltages of opposite polarity over a larger range of frequencies than a two-tube phase inverter. A balanced output voltage is used in the circular sweep to produce a large undistorted voltage for the production of an undistorted circular trace on the cathode-ray tube. The 6SJ7 balanced resistance coupled voltage amplifiers are designed to produce a large undistorted output voltage. To reduce the loading effect of the gain-phase meter during gain and phase measurements, a cathode follower stage was used at the input of the pulse generator and a pentode stage at the input of the circular sweep. Cathode-Ray Tube Indicator The 5JPl and associated g axis amplifier of the type 241 Dumont Oscillograph was used in conjunction with the pulse and circular sweep generators. A cathode-ray tube was used as the indicating device be- cause it lends itself well to classroom demonstration and student laboratory work. A type 5JPl cathode-ray tube 'was used because its screen size, 5 inches in diameter, is sufficient for small classroom demonstrations and its deflection sensitivity is reasonably high. 26 CALIBRATION OF GAIN-PHASE METER To check the accuracy and calibrate the gain-phase meter, several tests were performed. TIle accuracy of the phase angle reading at various points on the circular sweep )'{as checked by applying to the gain-phase meter two voltages that were separated by constant phase rr.i.th respect to each other, but of variable phase with respect to the input voltage of the circular sweep generator. With these two voltages it was possible to produce blanked-out portions of the circular sweep, of constant phase separation, on any portion of the circular pattern on the cathode-ray tube. Any inaccuracy in phase angle reading was evidenced by the dif- ference in measured phase displacement of the two blanked-out portions of the circular sweep, as the angle between the two input voltages and the circular sweep voltage was varied from 0 to approximately 360 degrees. It should be noted that the phase angle between the two test voltages is not required to be main constant. mown, but it is important that it re- The circuit used to produce the two test voltages of constant phase separation is shown in Fig. 8. A block diagram showing its conneetion to the gain-phase meter is shown in Fig. 9. The variable phase angle be~7een the t~ test voltages of constant phase separation and the circular sweep voltage was obtained through the use of t,vo phase splitting bridges (14) as shown in Fig. 8. The (14) F. A. verest, Phase Shifting up to 360 degrees, Electronics, Vol. Ih, pp. 46-49, 1941. constant phase rolgle between the two test voltages was obtained from 605 o C4 E r---,'-UII-- 0 ¢l 2 ~~--1~~06 • HewlettPackp..rd Audio Osc. 2000 +300 . T I II I I 0'5---0 E¢ C .. . 5 Meg. ohm Pot . = .1 Meg. ohms • 2.0 Meg. ohms ::I: 5 K ohms 1\ R1 lI\2, ~'3 F· 4 , 1\5 R 'P 6' °3' C 4' 0 , 0,., , 6 IT! ... = .5 Meg. ohms = 400 ~t. a .01 J,Lt. ,., 0 0 1 , O2 , +300 .01 ° = 8.0 J-Lf. 1J,t'. b :::I = Gener81 ltad10 Company TrHnsforoer b78-A VARIABI.Z PHASE VOLTAGE GEr-lERATOl\ Figure 8 ro -..:z HewlettPackard Auo.i0 Oscillator -0~ Sweep Generator ·200C o-J u-- .n C1I;cular Dumont 241 Oscillograph .E~1 I....- Variable Phase Voltage . Generator 0 - Pulse -- Generator ~ Z Axis 4- E¢ BLOCK PHASE E 1 E Z DIAGFUU~ ~GLE Z OF TEST CI1\CUIT Figure 9 !:" en 29 the R-C network. Absolute phase angle calibration from any fixed reference point was not used because the reference point of the gain- hase meter changes with frequency. The gain-phase meter was tested for angle accuracy at 100, 1000, and 5000 cycles per second. The results of the test, as shown in Table I, show a maximum deviation in angle measurement of :to.5 degree over the range covered. The minimum width of the blanked-out portion of the circular pattern varies with frequency as shown in Table II. For wide blanked- out portions of the circle, the angle measurements were made between the ends of the blanked-out portions that correspond to the steep front of the pulse applied to the grid of the cathode-ray tube. The amount of phase angle shift in the pulse generator, due to the input voltage of the first 6AC7 stage deviating from 0.5 volt, was found at 1000 and 10,000 cycles per second and is tabulated in Table III. This data was obtained for t"l"0 voltages of zero phase separat' on applied to the terminals of the pulse generator. The variations in the magnitude of the input voltage to the first 6AC7 tube were produced by the potentiometer in the cathode circuit of the preceding cathode follower stage. from 0.5 From this data it can be seen that a deviation of :t50% volt will produce an error of approximately ±D., degree.. If the method outlined under "Circuit Analysis ll is used for adjusting the two input voltages, the error can be reduced practically to zero. Gain measurement accuracy wa obtained by checking the gain read- ings on the cathode-ray tube scale against the gain calculated from the )0 TABLE I Accuracy Check of Phase Angle Readings About the Circular Sweep "l(-f = 100 cycles per sec. *f = 1000 cycles per sec. 53.5° ~ 5.SO 15.0° 18° 53.0° 15.5° 15.0° 36° 53.0° 25.0° 61° 53.5° 35.5° 15.0° 15.0° 87.5° 53.5° 45.0° 15.0° 104.5° 53.5° 55.5° 15.0° 112.0° 53.5° 65.5° 15.0° 127.0° 53.0° 15.0° 144.5° 53.0° 65.5° 75.0° 151.5° 53.0° 85.5° 15. SO 164.0° 53.0° 94.0° 15.5° 107.5° 15.5° 119.0° 15.5° 130.0° 15.5° 140.0° 15.0° 150.0° 15.0° 160.0° 15.0° 170.0° 15.0° 178.SC 15.0° 187.0° 15.0° 198.0° 15.0° 209.0° 15.0° ~ -& 0° ...e- 15.0° 31 TABLE I (Cont.) -:<f = 5000 ~ 15.0° cycles per sec. -e17.5° ¢ = The angle of displacement of with zero reference, taken at 3 o'clock on the cathoderay tube screen. ~1 35.5° 17.0° 47.5° 11.5° 62.0° 17.0° 77.0° 17.0° 91.0° 11.0° 108.0° 17.0° 123.0° 16.5° J.42.00 16.5° 159.5° 16.5° 118.0° 16. SO 19h.Oo 16.5° 216.0° 11.0° 229.5° 11.0° 284.5° 17.0° 298.0° 17.0° 310.0° 17.0° 323.5° 11.0° 343.0° 17.0° 355.0° 17.5° ..e- = Angle between E1 and E2 as read on the angle scale on the front of the cathode-r~ tube. * = Yith 0.5 volt input to first 6AC7 amplifier stage of the pulse generator. 32 TABLE II M:i.nimum Width of Blanked-out Portion of Circular Sweep Frequency Width (Inches) 100 1/100 1000 l/SO 5000 1/16 10,000 1/4 33 TABLE III Phase Angle Changes Due To Deviation of Pulse Generator Input Voltage from 0.5 volt. f (Voltage measured at the grid of first 6AC7 amplifier tUbe.) = 1000 cycles per second E2 El ~ ~ .50 .5 83.0 83.0 .80 .5 83.0 82.5 1.2 .5 83.0 81.5 .3 .5 83.0 83.5 f = 10,000 cis E2 El ~ ~. .5 .5 102 102 .75 .5 102 101.5 1.35 .5 102 104.0 .3 .5 102 102.5 34 ratio of the input and output voltage as read by a vacuum tube voltmeter. The gain scales were calibrated by applying 0.5 volt to the El terminals of the pulse generator and adjusting, by the controls Rl and Rb the diameter of the C"Lrcle to read 1 on the 1-5 gain scale. The maESIlitude of the voltage applied to the E2 terminals of the pulse gener tor 'i'fas varied from 0.5 to 62.5 volts to check the three gain scales, 1-5, 1-25, and 1-125, on the screen of the tube. of this test are tabulated in Table IV. seen that ~1e The results From these results it can be accuracy decreases with the larger readings on each scale, with a maximum error of -4% at the highest gain reading. From the method used for gain measurement it can be seen that the gain scale calibration obtained for El equal to 0.5 volt can be used for any other value of El that is within the linear voltage response of the circular sweep generator and the cathode follower stage of the pulse generator. 20 volts. This linearity was found to exist up to value of This means that the gain scale can be calibrated with any magnitude of voltage up to 20 volts input to the pulse generator. For El values greater than 20 volts, the error in gain measurement will increase and the circular pattern will become distorted. To prevent this error and distortion, an external attenuator could be used, common to El and E2' so as to reduce El below 20 volts. 35 TABLE IV Gain Calibration F equency a 1000 cycles per second Measured Calculated Gain %Deviation~~' El* E2* 0.5 0.5 1.0 1-5 1.0 0 0.5 1.0 2.0 1-5 2.0 0 0.5 1.5 3.0 1-5 3.0 0 0.5 2.0 3.9 1-5 4.0 2.5 0.5 2.5 4.8 1-5 5.0 4.0 0.5 2.5 5.0 1-25 5.0 0 0.5 5.0 10.0 1-25 10.0 0 0.5 7.5 15.0 1-25 15.0 0 0.5 10.0 20.0 1-25 20.0 0 0.5 12.5 24.0 1-25 25.0 4.0 0.5 12.5 25.0 1-125 25.0 0 0.5 25.0 50.0 1-125 50.0 0 0.5 37.5 75.0 1-125 75.0 0 0.5 50.0 98.0 1-125 100.0 2.0 0.5 62.5 120.0 1-125 125.0 4.0 Gain~H< Scale * = Voltages measured by Ballentine Model ** = The precision measure of the line 'Y' of full scale reading. (See Fig. 2b..) 300 vacuwn tube voltmeter • n scale is equal to :!:2% 36 DISCUSSION OF SOURCES OF ERRORS The error in angle readings due to non-orthogonality of the cathode-ray tube deflecting plates and non-quadrature deflecting voltages is reduced to zero i f a precisely circular pattern is formed on the cathode-ray tube. (15) This means that the non-orthogonal"ty of the (15) Sollar, Stan, and Valley, Cathode-Ray Tube Displays, M.l.T. RaQtation Series, page 299, McGraw-Hill Book CompaQY, 1948. deflecting plates is compensated by an equal departure from quadrature of the two voltages app1jed to the deflecting plates. Errors due to ellipticity of the circular sweep are reduced to a ver,y small value since small ellipticities are easily detected by the eye when a reference circle is provided on the screen of the tube. (16) (16) Sollar, Stan, and Valley, Ope Cit., page 301. The greatest error associated with the circular sweep is due to distortion of the circular pattern when harmonics are present in the quadrature voltage output of the circular sweep generator. This dis- tortion causes the angular velocity of the spot on the cathode-ray tube to depart from constancy; thereby, producing an error in the angle measurements. Analysis of this type of distortion is quite compli- cated, for it not only is a function of the magnitude of distortion, but also of the harmonic content of the quadrature voltages. To reduce this type of error the gain-phase meter should not be operated below or above the frequency band that will produce a highly distorted circular sweep. A frequency range from 40 to 10,000 cycles per second was found 37 to produce a circular pattern with slight distortion. The harmonic content of the quadrature voltage also produces an error in the gain measurements, for it may distort the circle at the location of the gain scale. Error in phase angle measurement, due to distortion in the first 6AC7 amplifier stage of the pulse generator, are reduced to a minimum by equalizing the input voltage to this stage as discussed in "Circuit Analysis". The poor accuracy of gain measurements is largely attributed to the inability to interpret a reading closer than 1/40 of an inch by a 1/40 of an inch wide circular sweep trace. of error are; non-linearity of cathode-r~ Other contributing sources tube deflection, increases in capacitance shunting effect of the range attenuator with frequency, and slight non-linearity of sweep generator amplifiers. To demonstrate the gain-phase measurement ability of the gainphase meter, the gain and phase shift of a transformer coupled audio frequency amplifier was obtained over a frequency range from 40 to 10,000 cycles. 10. A block diagram of the circuit used is shown in Fig. A plot of gain and phase angle shift about the middle frequency value of 1800 is shcrnn in Figs. 11 and 12. test are given in Table V. Tabulated results of this Hew1ettFa ckflrcl AUdio Oscillator 200C El '!'rpnsformer Cou.Dled AUdio Amplifier E2 ---- ~ :.:. 1 ~ t-+ ~~<'., E l ~ ~ E2 Cir-cular Sweep Gerlerator :o~ ~ I Pulse Gel!erator Dumont 241 OacillogrslJh ) BLOCK DIAGRAH OF CIRCUIT USED TO f-lEASURE GAIN AND PHASE AiGLB OF AN AUUIO FREQUENCY AMPLIFISR Figure 10 ~ l S .2 ': )( J ~ ." "!~ 0: u 0: :j ~] ;}... w l~-T"1-~:T--r--;-iTIT-,-~~-r;--;:-;-..,...-;--;-:-...,..,.---:------,.--- ~ -I-H-'--.-.l - ~-t- T T• i 11;-- ,I' ;::r-_ -:- - ~. 1T - . 'l \ l' L . - .- \ \ . ~ ; ~ : ... - 1 . \. , ol[,) + . n m . rl II ~ ,.;o~ :i~ .... I(/) ,r!0 r~ . . . t Q> ~ .::l • • en 11') § L-+----l I l- -- -4---- ~ 8_1'"~ii'...~~t-_!+-t----: t~Vr-?_-_"+-.~..~i:...:~...:.·~·~~J_-J'_ I- -:-I-t-~~R,,-=-)<---1/-7/Li-_-;~'*.~ ;' ;~-_2..~.t--- J~: ~ 3 2 1 9 8 7 6 5 4 II 1(');1 :::K . ~K -BK / / / , / / , \ 0 \\ . I \ \ I I I 1° I t· . I'l) lr-f I i. I. / - - --.-- / ," . TABLE V Gain and Phase Angle Data of A 6c5 Transformer Coupled Audio Frequency Amplifier Frequency ~ l'.:2 Gain El Phase Angle Ee") -&-- 1800 40 20.5 223.5 + 53.5 60 23.0 215.5 + 80 24.0 208.5 + 28.5 100 25.0 202.5 + 22.5 200 25.5 193.0 + 13.0 400 26.0 184.5 + 4.5 600 26.0 179.5 - 0.5 800 26.0 177.0 - 3.0 1000 26.0 174.0 - 6.0 2000 26.0 163.4 - 16.6 3000 25.5 155.0 - 25.0 4000 2L~.5 145.5 - 34.5 6000 22.5 128.0 - 52.0 8000 20.0 112.0 - 68.0 10000 18.0 97.0 - 83.0 held constant at .5 volt. 35.5 42 SUMMARY AND CONCLUSIONS The gain-phase meter, when properly adjusted, will give unambiguous phase angle readings from 0 to 360 degrees with a variation of degree and a gain reading of -125 to +125 with a deviation of :!.5 4% for sinusoidal input voltages of frequencies from 40 to 10,000 cycles per second. To obtain the above measurements, the two test voltages or currents must establish a minimum of 0~5 volt at El and E2 terminals. Input voltages greater than 20 volts require a common attenuator ahead of the gain-phase meter. It has been found that the time required to adjust the circular sweep and to calibrate the gain measuring scale, which has to be carried- out with each frequency change, is reduced considerably when the operator becomes farJiliar with the usage of the gain-phase meter. The gain and phase-angle measurements of two sinusoidal voltages or currents are indicated by the gain-phase meter in such a manner that one can easily correlate the results with the vector plot of the same voltages or currents. A 5-inch cathode-ray tube, used for the gain and phase-angle indication, makes it possible to use this instrument for classroom demonstration. The author of this thesis feels that this instrument, the gainphase meter, will be of great value in classroom demonstration i'fOrk and will allow rapid and accurate laboratory measurements of gain and phase-angle of voltages or currents as found in communication and electronic circuits. Although this instrument was designed primarily for communication work, it can be used to measure the gain and between any two or more voltages or currents. phase-an~le 43 BIBLIOGRAPHY Arguimbau, L.B., Vacuum Tube Circuits, N.Y., Wiley, 1948, pp. 354-356. Chance, B., Hughes, V., I!acNichol, E.F., Sayre, E., and Williams, F.E., Vvaveforms, N.Y., McGraw-Hill, 1949, pp. 4h-h5. Everest, F.A., Phase Shifting up to 360 Degrees, Electronics, Vol. 14, pp. 46-49, 1941. Florman, E.F., and Tait, A., An Zlectronic Phasemeter, Proceedings of the I.R.E. Vol. 37, Feb. 19M, pp. 207-210. Ginzton, E.L., An Electronic Phase-Angle Meter, Electronics Vol. 15, 1942, pp. 60-62. May M.I.T. Radar School Staff Members, Principles of Radar, N.Y., McGrawHill, 1946, Chapter 3, pp. 31-33. Sollar, T., starr, M.A., and Valley, G.E.,Jr., Cathode-R~ Tube N.Y., McGra~Hill, 1948, pp. 299-302. Displ~s, Terman, F.E., Measurements in Radio Engineering, H.Y., MCGraw-Hill, 1935, pp. 324-325. Terman, F.E., Radio Engineers Handbook, N.Y., McGraw-Hill, 1943, pp. 354-366. Vandaven, E.O., Phase Meter, Electronics Vol. 21, June 1948, pp. 1421!~3. Watton, A., Modulated-Beam Cathode-Ray Phasemeter, Proceedings of the I.R.E. Vol. 32, May 1944, pp. 268-272. VITA Gabriel George Sldtek was born on October 25, 1919, at st. Joseph, Missouri, the son of tIr. and 1Irs. Felix John Sldtek. His pre-college education was obtained in the public schools of St. Joseph, Missouri between the years 1926 and 1938. From 1938 to 1939 he ormed and opera~ed an electric service shop that brought about financial aid to the college work begun in 1939. On September 15, 1939, he entered the 1ussouri School of ,·nes and Metallurgy where he received a degree of Bachelor of Sdence in b~ectrical Engineering in Januar,y 1943. From January 1943 to July 1943, he VlaS employed by the Missouri School of Mines and Metallurgy as an instructor in the E.S.M.W.T. Program. On July 19, 1943, he reported for duty at the Army Air Force Officers Candidate School in Miami Beach, Florida and on November 13, 1943 he was commissioned second Lieutenant in the Air Force Reserve. He was assigned to the Air 1~teriel Command, Engineering Division at Wright Field, Dayton, Ohio, "mere he remained until discharge from the A'rrJW. He became a Captain in the Officer's Reserve Corps upon his separation from tlle Army on November 2, 1946. In November, 1946, he became an Instructor at the School of Mines and lletallurgy of the University of Missouri in which capacity he still serves.