mission and should be sustained overig pee e emetering System periods of many months.9. The system should be independent of

Vitk A utomatic C ibration power supply variations.Basic Concepts

W. E. PHILLIPS The primary objective in this develop-MEMBER AIEE

ment was to provide a high-speed tele-metering system in which the initial

Synopsis: This paper describes a high- not well suited to carrier current. The movement of the receiving recorder oc-speed telemetering system which uses fre- recent requirement of higher telemetering curs within 0.5 second or less after thefor two different frequency bands a 20 to speeds has resulted-in new developments change in primary load. It should be25 cycles and 80 to 100 cycles has been in this field and this paper describes a noted that it is not the purpose of thisdeveloped. The system is electronic and the high-speed telemetering system de- paper to prove the need for a high-speedlag between a change in the primary veloped to fulfill the present day require- telemetering system. It will sufficequantity to a change in the receiver is less ments of electrical power systems. merely to state at this point that it hasthan 0.4 second. The system is independent been found, that for those applicationsof the wave shape and amplitude of thesignal over extremely wide limits. Means Idealized Telemetering System which require fast changes in generationare provided for automatic calibration at for the automatic control of load andfrequent intervals which compensate for Before discussing the telemetering frequency, this high-speed telemeteringchanges in vacuum tubes and other circuit system which is the subject of this paper, will make possible improved control with

it would be well to outline some of the a reduction in the maneuvering of gen-characteristics of a more or less idealized erator loads.

HE USE of a variable frequency as a frequency telemetering system. The Frequency was selected as a translat-I translating means for a telemetering characteristics of such a system would ing means for a high-speed telemeteringsystem was proposed as early as 1917.1 be: system for the following reasons:This early system, which was installed on 1. The frequency band should be as nar- 1. Frequency can be transmitted longthe Chicago, Milwaukee and St. Paul row as possible in order that it takes the distances without losing any of its intel-Railway, used motor generator sets to minimum possible space in the carrier fre- ligence due to high attenuation.generate the variable frequency for tele- quency spectrum, also certain types of 2. Frequency may be transmitted con-metering. The advent of the vacuum power line carrier equipment require that tinuously and thus it constitutes a mediummetering. The the frequency change be very small. The for a continuous telemetering system.tube makes such a system cumtbersome same requirement must be met on the sub-when judged by present-day standards, multiplexing of microwave transmission. 3. Frequency lends itself ideally to beinghowever, at the time of its installation it 2. The frequency used should be low. It varied instantly to a value proportional to a

was a real achievement. should be noted that the use of a very low varying measured quantity.Since the date of the above installation frequency will be disadvantageous from the In the development of this telemetering

numerous commercial telemetering sys- standpoint of telemetering speed and modu- system particular attention was given totems using frequency as a means of trans- lation on certain carrier channels. insure that it was suitable for applicationlation have been developed. The ap- 3. The telemetering receiver should be to carrier frequency and microwave chan-

plicaion othes sysems hs notbeen independent of harmonics and extraneous nels.plication of these systetms has not been frequencies which may be present in thegeneral because the need for high-speed received signal.carrier current telemetering was not so 4. The telemetering receiver should be Telemetering Transmitteracute as at present and also the charac- independent of the amplitude of the re-teristics of the telemetering systems were ceived signal over extremely wide limits. The equipment at the transmitting end

5. There should be no error due to tempera- consists of a primary element, thermal__________________________ ture variations, converter,2'3 a Speedomax recorder,4 and

Paper 5i-228, recommended by the AIEE Joint 6. There should be no error due to aging of a phase shift type of oscillator.Subcommittee on Telemetering and approved by components. The thermal converter is connected toettoattheAIEEThnIlPSummer General Meeting, 7. The system should be instantaneous in the current and potential transformersToronto, Ont., Canada, June 25-29, 1951. Manu- response. and produces a d-c potential, propor-script submitted March 26, 1951; made avilable**for printing May 11, 1951. ,m aaa 8. The accuracy should be within the tional to a-c power, which iS recordedW. E. PHILL1PS is with Leeds and Northrup generally accepted limits for telemetering potentiometrically by the Speedomax re-Company, Philadelphia, Pa. systems applicable to carrier current trans- corder. The recorder, which is cali-

1256 Phillips-HSigh-Speed Telemetering System With Automatic Calibration AIEE TRANSACTIONS

E S D =UT

v -- ~~~~~~~~~POWER_ V2X40 T P Ot^ss ZL FIER [ |SAG DIFFERENTSATOR

Figure 1. Schematic diagram of oscillator frequency Figure 2. Block diagram of frequency converter showingdetermining network wave shapes at several stages

brated in primary power, has a retrans- ture coefficient of the oscillator frequency The filter for the 80-100 cycle convertermitting slidewire, the resistance of which output is 0.003 per cent per degree consists of 2'/2 Constant K band passis varied in accordance with the recorder Fahrenheit. The frequency of the oscil- sections. The loss at operating frequen-reading. This slidewire is connected in a lator is not dependent on normal changes cies is less than 6 decibels and the attenua-phase-shift oscillator circuit in such a in tube characteristics since if the tube is tion at 60 cycles and below and at 150manner that a variation in slidewire re- operating the phase shift between the cycles and above is greater than 60 dec-sistance causes a change in the oscillator grid and plate circuit voltages is 180 de- ibels.frequency. grees. The wave forms shown in Figure 2 in-

All of these things have been amply Tests conducted over a period of dicate graphically the elimination of har-described previously, however, since we several months show the oscillator drift monics by the filter.are particularly interested in the variable to be 0.05 per cent.frequency oscillator circuit and the In the case of the telemetering system, Frequency Doubler Sectionmethod of varying it, a review of this cir- resistors R and Ri, Figure 1, are mounted As indicated previously, the frequencycuit will be helpful. This oscillator and on the shaft of the recorder and their doubler section is used only on the 20-to-its control circuit are shown schematically value changes with the recorder reading 25 cycle range. The reason for thisin Figure 1. as noted previously. For each recorder doubling is that with frequencies of lowThe frequency determining network position there is a definite value of fre- values, a high-speed recorder needs ad-

consists of R, R1, C, and C1. This network quency. Thus for each value of primary ditional filtering in order that it does nothas the property that the voltage El load there is established a definite fre- tend to follow the cyclic variations in the(Figure 1) will be in phase with the volt- quency. Oscillators having ranges of 20 final output current. Any additionalage E at only one frequency. This fre- to 25 cycles or 80 to 100 cycles are used. filtering added because of the use of a lowquency is determined from the following As will be explained later both of these frequency will increase the time lag of therelation frequencies may be used simultaneously telemetering system.

1 as two tones on a multitone carrier chan- The frequency doubler section consistsRRC- (1) nel. of a phase inverter stage the output of

which is fed in push-pull to the grids of awhere Telemetering Receiver twin triode. The twin triode is connected

W=2-rf. as a cathode follower so that the resultantThe receiving end of the telemetering cathode current is of double frequency.

As shown in Figure 1, there are two system consists of an electronic converterstages of amplification, VI and V2, be- which produces a d-c voltage proportional Limiter Sectiontween the grid of Vi and its feedback tofrequency, and a Speedomax potentiom- The limiter section consists of threecircuit from the output of V2. Thus there eter recorder which is connected to the pentode stages; the first two stages serveis 360 degree phase shift, 180 degrees in output of the electronic converter. to give identical limiting to both theeach tube, in the feedback circuit exclu- The electronic converter, shown sche- positive and negative half waves of thesive of any phase shift in the frequency matically in Figure 2, consists of a filter, signal voltage. Sharp cutoff tubes aredetermining network. Since to maintain an amplifier section, a frequency doubler used which give a square wave when theoscillation, the feedback must be in section-this is used only for the 20-25 grids go negative, however, there is somephase with the original signal this means cycle range,a limiter section,a differen- rounding of the wave shape when thethere must be zero phase shift in the net- tiating section, a rectifier section and a grids draw grid current on the positivework consisting of R, R1, C, and CI. d-c power supply. half wave. Mter passing through theFor oscillation, the frequency will be .first two limiters, the wave shape is re-automatically maintained at a value Filter shaped to a form roughly resembling awhich keeps this phase shift at zero. The filter for the 20-25 cycle converter sine wave and this modified wave form isIf R and R1 are changed, the frequenlcy is of the low-loss type and consists of 2 applied to the grid of the third limiterinstantly varies to a new value which will Constant K low pass sections and one stage. The reshaping circuit in combina-satisfy the relation in equation 1. shunt M derived section. The loss at tion with the third limiter stage produceThe capacitors and resistors in the operating frequencies is less than 6 deci- essentially a square wave shown in F?igure

frequency determining network are ex- bels and the attenuation at frequencies 2, which is constant in amplitude andtremely stable and have low temperature of 60 cycles or above is 60 decibels or wave shape for a wide range of inputcoefficients so that the over-all tempera- greater. signals.

1951, VOLUME 70 Phillips-High-Speed Telemetering System With Automatic Calibration 1257

OUTPUT SPEEDOMAXRECORDER SPEEDOMAX

ELECTRONIC / SPEEDOMAX SPEEDOMAX TELEMETERING AMPLIFIER BALANCINGSIGNAL CONVERTER RECORERBALANCING SIGNAL DIFFERENTIATOR MOTOR

io-REC.SLIDEWIREL -AMECHANiCAL

MECHANICAL RECORDER NECTIONIVO" 8O%u CONNECTION 60% SLIDEWIRE ,,

D.C+ FREIZING D.C.+( FROM D.C.FPOWER SUPPLY /STANDARDI

RHEOSTAT

Figure 3. Schematic diagram of recorder measuring circuit Figure 4. Schematic diagram of method employed to standardizereceiving recorder

Differentiator Section through a parallel combination of resist- d-c voltage changes it affects both the

This section, as the name indicates, ance and capacity. The voltage across output of the converter and the slidewire

differentiates the square waves derived this resistance-capacitance network is voltage in the same direction. By the use

from the limiter section. The differen- proportional to the average number of of proper constants in these circuits the

tiator circuit is conventional in design and impulses and it is this voltage which is effects of changing d-c voltage are mini-

consists of a capacitor of small capacitance recorded by the potentiometer recorder. mized.

in series with a comparatively low re- The negative pulses are short circuited by As described previously, the electronic

sistance. Thus the impedance is deter- the other half of the 6116 so that they do converter contains vacuum tubes; varia-

mined primarily by the capacitor. not appear in the output. tions in some of these tubes will have an

Due to the low time constant of the effect on the output. This variation in

circuit and the fact that the reactance of D-C Power Supply tube characteristics is a relatively slow

the capacitor is small for the very high The d-c power supply is electronically process and if some automatic means can

rates of change experienced with square regulated using a VR-150 tube as a ref- be provided for checking and compensat-

waves, current will flow, through the erence. The d-c voltage is held within ing for these variations at intervals of

capacitor only at a time when the square 1/4 per cent for a change of 95 to 130 once a week we will have no significant

wave is changing sharply. volts in the a-c input. changes in the telemetering calibration.

A true derivative of the square waves, As a practical matter it is convenient to

which are shown in Figure 2 at the input Recorder and Calibrating Circuit perform this automatic calibration at 45

to this section, would have a vertical am- minute intervals.

plitude but zero width. This would not The recorder measuring circuit is shown Figure 4 is a schematic diagram of the

be satisfactory for the end use which, as schematically in Figure 3. method used to automatically calibrate

will be described later, is to integrate the The output of the electronic converter or standardize the telemetering con-

positive pulses. After the derivative is is opposed to the electromotive force verter. Switches A and B are normallyobtained, the wave is amplified and re- set-up by the recorder slidewire circuit so closed as shown and the recorder balanc-

shaped so as to have some width as shown that any unbalance will cause the balanc- ing motor is mechanically connected only

in Figure 2. ing motor, by means of its amplifier, to to the recorder slidewire. Thus the circuitmove the slidewire until the two poten- functions exactly as described previously

Retifier Section tials are equal. This is the conventional when measuring the telemetering fre-

potentiometer method of measuring a quency.The rectifier section consists of a twin potential. The slidewire circuit voltage is As noted in Figure 4 the potential at the

diode (6H6) so connected that the positive obtained from the d-c power supply which one end of the recorder slidewire cor-

current pulses are permitted to flow supplies the electronic converter. If the responds to the converter output at 80

d~iarm oi tee iE g

Figure 5. Pictorial

metering channeleequipment

1258 Phillipsm-High-Speed Telemetering System With Automatic Calibration AIEE TRANSACTIONS

THERMALCONVERTER

BALANCINGMOTOR AMPLIFIER MECHANCAL VARIABLE

SPEEDOMAX L CONNECTIONS | FREQUENCYI I~~~~~~~~~~~~SPEEDOMAX WRECORDER OSCILLATOR

MEASURING Figure 6. Block diagram of equipment attransmitting end of telemetering channel

cycles and the other end of the slidewire Figure 4, switches A and B are connected amplifier will, through the medium of theto the output at 100 cycles. If 60 cycles to the calibrating or standardizing posi- balancing motor, cause the standardizingwere the converter input, its output would tion which is the position opposite to that rheostat to decrease its resistance. Thisbe a potential which is designated as 60 shown in figure. Switch B connects a decrease in resistance shunts more of thecycles at resistor R1. known 60-cycle frequency to the con- current out of the slidewire circuit whichFor purposes of explanation, it is as- verter input just after the filter and lowers the potential of the 60-cycle point

sumed that with an 80-cycle input the switch A connects one side of the Speedo- and also the recorder slidewire potential.recorder will balance at the 80-cycle point max recorder amplifier to the 60-cycle When the recorder is returned to itson the slidewire and with a 60 cycle input point on R1. The same recorder mech- normal measuring state, the recorderthe converter output will equal the poten- anism which controls switches A and B slidewire will again be correctly calibratedtial at the 60 cycle point on R1. This re- also controls the mechanical connection for 80 to 100 cycles for the conditions ex-lation, once potentiometrically estab- between the recorder balancing motor and isting in the converter at this time.lished, is fixed since the slidewire and the the standardizing rheostat. This is It should be noted that any change incoils shown are made of high grade, low shown as a double dashed line on Figure 4. the d-c potential to the slidewire circuittemperature coefficient resistance wire. When switches A and B are thrown to the as well as changes in the converter will be

After a period of operation the con- standardizing position, this mechanical compensated.verter output may change due to some connection is made. This mechanism has The use of a 60-cycle standardizingchange in tube characteristics or other been used on potentiometer recorders for frequency has just been discussed. Thiselements in the converter. If for example a great many years. may be either system frequency or athe output decreases, then it will be low If, as assumed, the output of the con- standard 60-cycle frequency which is nowby the same percentage at either the 80- verter is low when connected to 60 cycles, quite commonly available in generatingor 60-cycle frequency. By connecting the then to achieve a balance with the 60- stations and dispatching centers. Whenconverter to a known 60-cycle frequency cycle point on R1, it will be necessary to a standard frequency is available, therewe can check the converter calibration in reduce the potential of the 60-cycle is no question of inaccuracy from thisthe following manner. Referring to point. The unbalance in the recorder source. When system frequency is used,

Figure 7. Block dia-gram of equipment

r ~ I DIFFERENTIATOR at receiving end oftelemetering chan-

VARIABLE rnel-~IFRETAOFREQ. FILTER ILLIMITERneINPUT L r SPEEDOMAX RECORDER

-REOEG ISTANDARDIZINGPULSE I KEY

D.C.SUPPLY RECTIFIER J'' MECHANICAL AI 2' y~ONNECTIONS

[ STANDARDIZING SLIDEWIRE -

* THIS CONN'ECTION MADE ONLY WHEN STANDARDIZING. aSYSTEM FREQUENCY CAN BE USED IN CONJUNCTION WITH

*CONTACTS CLOSED TO OPPOSITE SIDE W5HEN STANDARDIZ1NG. CONTACTS IN EXISTING SYSTEM FREQUENCY RECORDER.

1951, VOLUME 70 Phillips-High-Speed Telemetering System With Automatic Calibration 1259

it may possibly deviate as much as 1/3 A change from sine wave input to a Accutraciesper cent and it would cause an appreciable square wave input produces a change in The over-all accuracy of the telemeter-error if the system frequency were off the receiver reading of less than 0.5 per ing system including the primary elementthis much at the time of standardization. cent. Square wave distortion as deter- is 1.75 per cent of the full scale readingIn order to overcome this objection the mined by Mark and Space relations may and the factory checking accuracy is 0.9existing station frequency recorder, by be as great as 60 per cent without ap- per cent of the full scale reading. Thismeans of back disk contacts, suspends preciable effect on the record. accuracy will be maintained many monthsstandardizing if the frequency is not The frequency selectivity of the re- without adjustment of the calibratingwithin 0.05 per cent. This is accom- ceivers is such that the 20 to 25 cycle and dials.plished by disabling the balancing motor the 80 to 100 cycle receivers can be oper-during the standardizing period if the fre- ated in parallel over the same circuit Power Supply Variation Effectsquency is not within the limits indicated. without cross interference. The telemetering equipment is inde-

It should be noted that if system fre-quency is used without suspension -of Signal Level Variations pendent of power supply changes between105 and 125 volts and operates satisfac-standardizing when the frequency de- Changes in the steady state signal level torily over the limits of 100 to 135 volts.viates beyond certain limits, the errors in of 34 decibel (50 to 1) will cause a shift in Either instantaneous or slow changes incalibration will not be cumulative but the receiver record of approximately 0.2 this voltage supply, within these limits,will result only in temporary errors pro- per cent. Instantaneous changes in signal will have little effect on the receiver.portional to the frequency deviation. level of 50 per cent cause a momentaryThe over-all telemetering system is deviation of 0.5 per cent in the receiver Conclusion

shown in pictorial form on Figure 5. reading.Figure 6 shows the transmittinog endFigure 6 shows the transmitting end

A comparison of the performance dataequipment in schematic form and Figure 7 Temperature Effects of this to hstelemetering system with theshows the receiving end equipment also The temperature coefficient of the oscil- characteristics outlined for an idealizedin schematic form. It will be interesting lator (transmitter) output frequency is system shows that the latter has beento compare the performance and charac-0.003 per cent per degree Fahrenheit. closely approached. The ability of theteristics of this telemetering system with The temperature coefficient of the tele- telemetering system to operate with sus-those of the idealized telemetering system metering receiver is 0.016 per cent per tamned accuracy over a wide variety ofwhich were outlined earlier.

which wereout~lined earlier, degree Fahrenheit before the receiver is carrier channels has been demonstratedTelemetering Frequencies standardized at the new temperature. by installations over a period of more than

After standardization this error is reduced two years. One installation on theTheasumengthod usletedoringfrenuertin to 0.004 per cent per degree Fahrenheit. Tennessee Valley Authority system trans-measuring the telemetering frequencies ~~~~mits the telemetered load for a distance of

is extremely flexible and any desired fre- mit th.eeeee od o itneo

Effects of Tube Variations 500 miles and employs three differentquency can be used for the translation types of carrier current circuits in tray-of readings. The telemetering systems The receiver is independent of wide ersing this distance.which are now installed have made use of changes in vacuum tube characteristics. This installation has also permittedtwo different frequencies. Some of the This is due to the fact that the telemeter-present installations use a frequency of 80 ing receiver is periodically standardized. practical demonstration of the fact that

the over-all response of the telemeteringto 100 cycles and the remainder of the in- .stallations employ a frequency of 20 to 25 Response Time system is comparable to that of an indi-

cating wattmeter.cycles. Other frequencies can be used if The over-all response of the telemeter-there is a justifiable need for them. ing system including the primary element

is less than 0.4 seconds from the instant of ReferencesInterference Factors a primary load change to a movement of

1. REGULATION OF FREQUENCY FOR MEASURE-W\hen operating with a sine wave input the receiving recorder. The time re- MENT PURPOSES, B. H. Smith. AIEE Transac-and the input signal at normal operating quired for the initial movement of the re- tions, volume 40, 1921, pages 425-38.levels, the receiver is not appreciably af- ceiving recorder is extremely important 2. A THERMAL CONVERTER FOR TELEMETERINGAND TOTALIZING, W. C. Downing, Jr. AIEEfected by distortion as great as 100 per in control applications. Early establish- Transactions, voiume 68, part II, 1949, pagescent. This holds true for frequencies of ment of the trend will produce improved 879-84.60 cycles and below and 150 cycles and control. 3.A NMw HlGElH-PEc l Engineering (AlEEabove for the 80-100 cycle converter and The over-all response time of the tele- Transactions), volume 60, January 1941, pagesfor frequencies of 60 cycles and greater metering system is less than 2 seconds to 37 40y ~~~~~~~~~~~~~~~4.ELECTRONICALLY BALANCED RECORDER FORfor the 20-25 cycle converter. Normal 90 per cent of the final reading and less FLIGHT TESTING AND SPECTROSCOPY, A. J. Wi-operating level is considered to be in the than 3 seconds to 99 per cent of the final liams, Jr, W. R. Clark, R. E. Tarpley. Electrical

Engineering (AIEE Transactions), volume 65,range of 1 to 10 volts, reading. April i946, pages 205-208.

Disusio has been further divided into impulse- would be substantially sinusoidal in form,ISCUSSIOn ~~counting, impulse-duration, and impulse- while the electrical pulses used in an impulsefrequency, types, this distinction having system, though idealized as square waves,

Perry A. Borden (The Bristol Company, been recognized in the AIEE Report on might have almost any conformation, evenWaterbury, Conn.): In its classification of Telemetering2 and in other more or less to being of alternating polarity, so long astelemetering systems, the Standard Defini- authoritative writings. At the time these they intermittently attained a zero value.tions of Electrical Terms1 includes two classifications were promulgated (1932) it Another somewhat hazy distinction lay incategories, "Frequency' telemeters and was tacitly assumed that the currents or the former system having a frequency"Impulse" telemeters. The latter group voltages utilized in a frequency system sufficiently high (say, over 16 cycles) to be

1260 Phillips-High-Speed Telemetering System With Automatic Calibration AJEE TRANSACTIONS

predominantly governed by the laws of signal, this voltage being measured in a telemetering system in which the trans-transmission in a-c circuits, while the latter, conventional manner. The conversion of mitted signals approximate a sine wave, itwhose frequency might range down to zero, the a-c signal to a measurable voltage in- may be said that there no longer exists anycould be considered as a succession of dis- volves several steps, in which the identity distinction between the two classes. Thus,crete electrical impulses. of the incoming wave form is completely it appears that such line of demarcation as

Less inhibited by tradition, the radio lost. may have existed between frequency sys-group and the exponents of mobile tele- Eventually, the rectifier section of tems and any of the subclasses of impulsemetering do not appear to have burdened the receiving network delivers a voltage systems is becoming most indefinite, andtheir terminologies with the foregoing dis- proportional to the average number of that the joint efforts of the several com-tinction; and their term "pulse-rate" impulses; and it is this voltage which is mittees now collaborating on definitions inseems generic to all measurements based on recorded by the potentiometer. telemetering should seriously consider suchthe frequency of recurrence of electric im- The idea of producing a measurable grouping as will eliminate the presentpulses, regardless of symmetry or of wave potential proportional to the number-in-a- nebulosity in classification.form. The soundness of this reasoning is selected-time, or frequency, of a successionwell exemplified in the consideration of Mr. of electrical pulses is of course not new, and REFERENCESPhillips' paper. The receiving end of the has long been recognized as standard prac- 1. AMERICAN STANDARD DEFINITION OF EMC-system which he describes includes a con- tice in the so-called "impulse-frequency" TRICAL TERMS. AIEE, 1942.verter which produces a d-c voltage pro- systems of telemetering. Now, with its 2. TELEMETERING, SUPERVISORY CONTROL, ANDportional to the frequency of the incoming definite application in a refined form to a ASSOCIATED CIRCUITS. AIEE, 1948.

1951, VOLUME 70 Dhiliips-IHigh-Speed Telemetering System With Automatic Calibration 1261