[1]Patented Oct. 20, 1953 21656,523 UNITED STATES PATENT OFFICE 21656i523. TELEMETERING SYSTEM Waldo G. Hodson, Burbank, and Walter E. Peterson, Los Angeles, CaUf., assignors to Northrop Aircraft, Inc., Hawthorne, Calif, a corporation of California AppReation January ILL, 1951, Serial No. 205,512 18 CIaims. (Cl. 340-183) 2 T his invention relates to telemeters, and more e ral demodulator channels, each of which is p articuiarly to a new and novel telemetering systu ned to accept one of the subearrier frequencies te m. The invention is particularly adapted to a nd to reject aU other frequencies. The demodm eter and record short period, high gravityunit ul ator channels thus sei5arate the frequency a ccelerations, such as encountered in the com5 m odulated subearriers anft convert them into pl ete run of a rocket-propered sled along a D . C. currents of sufficient magnitudes to drive st raight stretch of rail track, for example. th e galvanometers of a recording osciuograph. If a vehicle is propelled by rockets along a T he subearrier oscillators which produce the r elatively short track at high speed and then af orementioned subearriers are fully shown, deq uickly brought to a halt near the end of the 1 0 s cribed and claimed in a companion application, r un for test purposes, different parts of the veS erial No. 187,981, filed October 2, 1950. Simihi cle and equipment carried on board, either rigla rly, a suitable demodulator for use as a comid ly or shock-mounted, such as personnel, are p onent of the present system is also fuuy shown, s ubjected to various severe stresses. It is ded escribed and claimed in another companion apsi rable to know what stresses the different part,, 1 5 pl ication, Serial No. 207,037, filed January 20, a re subjected to and the magnitude of the decel1 951. eration,' particularly during the short interval of time of maximum deceleration in stopping. The magnitude of deceleration may be of the order of 100 gravity-units acting within a time- 20 period of less than 0.2 second, for example, in the above inentioned vehicle runs. The associated violent 8hock and accompanying large amplitude, vibrations together with the prevailing high acoustic noise level has contributed detrimental .25 effects to the action of present telemeters. T hus, it is an object of this invention to pro' vi de means capable of producing intelligible and a ccurate measurements of short period and large s cale accelerations for transmittal and record3 0 in g from a high speed vehicle to a fixed station. It is another object of the invention to provi de means and method for the calibration and id entification of various data transmitted from a stationary or moving vehicle to remote re- - 5 c ording equipment. I A nother object of the invention is to include m eans and method for detection of intrinsic syste matic variation or malfunction, and of other e xtraneous eff ects on a telemetering system 4, ) w hich may appear in the output. A further object of the invention, requisite to th e successful operation of a telemetering syste m, is a provision of adequately shock cushione d mobile equipment. . . 45 The foregoing objects are accomplished, brie fly, by employing a multi-channel FM-AM mdi o link between sled and ground which consists of a carrier that is aniplitude modulated by several subearriers. The subcarriers in turn 50 are frequently modulated by information transdtic ers. In addition, an identifier-calibrator unit periodically shunts in sequence different valu ed resistors across the transducers, preferably just prior to the telemetering period, and 55 pro duces a series of known square waves, which app ear in the output traces. The transmitted carr ier-signal is received and detected to produce the several frequency modulated subearriers. The receiver output is fed to the inputs of sev- 60 Dummy transducers, 1. e., non-variable transducers, placed in some of the subearrier channels will provide a check on the output traces, giving evidence of any spurious signals. However, the large accelerations being measured still demand effective shock absorption. The mobile equipment is all carefuuy shock mouxited and the subearrier oscirator units and modulator are floated in an outer case by a layer of rubberize-d bri.stle and foam rubber pads. The inner sides of the outer case are further coated with a heavy, sound absorbing compound. The invention possesses numerous other objects and features, some of which, together with the foregoing, will be set forth in the following description of a preferred embodiment of the invention, and the inve:@tion will be more fully understood by reference to the following attached drawings, in which: Figure 1 is a perspective view of a high speed sled telemetering data to a remote fixed static)n, showing in block diagram form a preferred fourchannel telemetering system in accordance witi-i this invention. Figure 2 is a combination schematic wiring diagram and partial perspective view of the identifier-calibrator unit. A Portion of the damping and isolation system is included in the perspective view. Mgure 3 is a diagram of a set of waveforms iilustiating the trace characteristics of the ldentifier-calibrator. TYPical braking waves are also shown. Reference is first made to Figure 1. A high speed r ocket-Propelled sled;l runs on slippers la along the rails of a track @ approximately 2000 feet in length. At point PI on the track, an arm 3 beside the track engages a lever 4 on the nioving sled which starts the identifleation and calibration process. After at least a full cycle of trace is transmitted and recorded for each channel, as will be described in fuH later, the sled will arrive at P2 where another track arm 5 engages another lever 6 ori the sled io stop identi:ftcation
[2]3 and calibration, and leave the telemeterin.equipment in condition for transmission of desired information. The time interval from Pi to P2 for this stage does not exceed 1 second, for example. Identification and calibration is concluded just b-@fore the sled enters the braking stretch of maximum deceleration between P3 and P4 of the track. Braking action is performed by a series of clamps 7, which grip brake rails (not shown) on the sled to stop it. The transmitting system, or mobile equipment, includes four transducers 8 (resistance type accelerometers), which sense the accelerations that are to be telemetered and convert them into resistance variations, which will cause corresponding variations in the frequencies of four corresponding subearrier oscillators 9. An identifiercalibrator unit I 0 periodicary shifts the frequencies of the subearrier oscillators by predetermined amounts to provide standards for calibration, dtiring the time interval from PI to P2. The outputs of the subearrier oscillators (nominally 10, 17, 23.5 and 37 ke. in the preferred example) Pre mixed in a common network and fed to a modulator I I which is comprised of a splitphase driver stage, resistance-capacit-y coupled to a push-pull amplifier. This unit amplitude modulates, with signal voltages from the subearrier oscillators, a 219.45 me. carrier which is generated by a flve-stage R.-F. transmitter 12. The resulting signal is radiated by an antenna 13 to the recording station. The antenna 13 consists of a single, base-fed, qtiarter wave element mounted on top of the rocket driven vehicle, and the structure of the vehicle serves as a ground plane. A battery power supply (not shown) for the transmitter and subcarrier oscillator units is also carried on board. A receiving antenna 14 which receives the radiated signal is a directional, rotatable, Yagi antenna with one driven element, two directors and one reflector. It is connected to an R.-P. superheterodyne receiver 15 which utilizes a degenerative output circuit to match the impedance Of the receiver detector stage with the input impedance of four demodulator channels 16. The receiver output is fed to the inputs of alI the demodulator channels. Each demodulator channel 16 consists of a selector which is tuned to accept only one of the subcarrier frequencies, limiter which converts the selector output into square wave voltage of constant amplitude, a converter stage which differentiates the limiter output using the resulting wave to control the peak amplitude of a saw-tooth voltage generated in this stage, a clamper-detector which produces a D. C. voltage proportional to the peak amplitude of the saw-tooth, and a paraphase D. C. amplifier to suliply a dual D. C. output to the grids of a push-pull driver which drives the galvanometers in a recording oscillograph 17. The demodulator power supply (not shown) provides regulated voltages for the demodulator channels. The high quality oscillograph 17 utilizes galvanometers having an impedance in the order of 8 ohms with the preferred equipment. A separate galvanometer and attached mirror is driven by the output of each demodulator channel, thus deflecting a light beam which falls on phOtOsensitive paper or fllzn driven at a constant speed. The transducers are the end organs which pick up the intelligence to be telemetered and convert it into electrical variations. Generally, they are placed at strategic locations in order to measijre 2,e56,523 4 various accelerations, for example, of vertical and horizontal displacements. For the four-channel telemeter under discussion, three transducers can be placed to measure the vertical, fore-andaft, and lateral components of ae-celeration of a main structure of the sled. The other remaining transducer is replaced by a duinmy or inactive transducer which consists of four fixed, precision resistors arranged in a Wheatstone bridae, and lo provides a check on the effects of vibra@i'O'n and other disturbances on the operation of the system. The identifier-calibrator unit 10, which is essentially a motor-driven switching device for shunting an appropriate resistor across one arm 1,3 of a transducer bridge so as to produce a desired magnitude of trace deflection, is shown in further detail in Figure 2. The ident-ifier-calibrator unit is shown mounted to one end of a container 18 which h(uses an 20 inner case 19 carryin-. the subcarrier osciuators 9 and modulator I 1. It is noted at this tizne the elaborate damping system applied to cushion the subearrier oscillators and the modulator. Isolation from externaldisturbances is achieved by -?- 5 surrounding the inner case 19 by an inch thick layer of rubberized bristle 20, which is sufficiently resilient to filter out most of the high frequency mechanical vibrations. Foam rubber pads 21 are placed in each end of the outer container 18 30 to prevent bottoming of the inner case 19. A thick coating of sound absorbing adhesive compound 22 is applied to th,- inside of the container 18. To the adhesive compound 22 is attached a layer of felt 23. Flexible leads (not shown) ,,,5 connect the inner case with outside circuits. The transducer bridges 8a, 8b, 8c and 8d corresponding to the 10, 17, 23.5 and 37 ke. channels of the telemeter, are show-n in the -sc@ematic of the identifier-calibrator circuit in order to clear40 ly describe the action of the switching unit. Thesetransducers may be active or inactive. It has been mentioned in the description of the telemetered run of the high speed rocketpropelled sled 1, that the arm 3 beside the track 2 45 engages the lever 4 on the sled to start the -Idelltification and calibration process. Actuation of the lever 4 on the sled closes a switch SI (M-ure 2) connecting a 22.5 volt battery 24 to start D. C. drive moto-r 26. The motor 26 drives the ,, 0 rotors of a five wafer switch 25 through a drive coupling 30. These rotors make wiping contact with twelve terminals on each wafer. rour resistors, RI, R2, R3 and R4 of differing resist-ances 250K, 75K, 125K and 50K, respectively, are 5i5 grounded together on one end and connected each to the rotors of wafers 25a, 25b, 25c and 25d on the other. The wiring is connected from the switch terminals across the four transducer bridges $a, 8b, 8c and 8d such that the resistors Co are shunted across an arm Of each transducer in cyclic sequence as the rotors are rotlated. The result is to unbalance the bridges in sequence, and a multi-valued set of square waves, includin@ both positive and negative pulses, is generated' in a 65 dfferent positive and negati-,,e Pulse sequence for each channel. The switch 25 can be connected in various other ways to produce a variety of suitable pulse waves. Just before the sled I enters the brakes, the 70 other arm 5 along the track engages the second lever 6 on the sled performing the following function. Switch S2 (Flgure 2) is opened and switch S3 is closed at the same time. The last wafer 25C of switch 25 is wired such that the 75 drive motor 26 is dynamically braked to stop only
[3]2,650,523 on an "off" (zero-deflectio@) position of the identifier-calibrator unit 10 when switches S2 and S3 are thus operated. This leaves the transducers 8 ready for detection of data during the braking distance P3-P4 immediately following. 5 A series combination of resistor R5 and condenser C I is placed across the armature of drive niotor 26 to reduce interference on the system due to sparking at the brushes on the commutator. lo The identifier-calibrator unit 10 can be operated manually by pulling an index knob 27 outwardly and moving a slide clip 28 toward the switch shaft. This disengages the D. C. motor drive 30, and holds it disengaged by means of a i5 groove 40 in the shaft with which a leg (not shown) on tl-le clip 28 makes contact. Manual rotation of the knob 21 will produce identifying and calibration waves as desired. A dial 29 indicates the percent of full scale deflection in 20 each channel for various positions of the index knob 27, the 10 kc. channel being read on the outer circle of the dial, the 17 kc. channel on the next inner circle and so on. Thus, calibration and identification of the various channels either 2;3 prior to a run or during one is easily provided by the equipment. By comparing the static and dynamic calibration, the fidelity of the system in motion can be confirmed. As the rotary switch 25 above described is used 30 to shunt the 250K, 125K, 75K and SOK resistors respectively across each transducer, the choice of resistances give 20%, 40%, 67% and 100% of full scale deflection in each channel. The typical trace characteristics are shown In PI,-Ure 3 in 35 the section from time Ti to T2 (identification and calibration period), representing time during travel between 'PI and P2 along the track on which the rocket-propelled sled runs. The sequence of positive and negative pulse deflection 4( identifies the several channels, and an adequate spread of percent of full scale deflection is provided for accurate calibration of measured data. Full scale deflection is equivalent to an acceleration 100 times that of gravity, for example. 45 T'he sled enters the brakes at time T3 (corresponding to travel P3) and is stopped at time T4. The measured decelerations are represented by the traces 35 (Figure 3) in the 10 kc., and 23.5 ke. channels, assuming three active trans- 50 ducers are em,-oloyed in these channels. The braking traces 35 presented by these channels are continuously fluctuating indicating the sensitive high frequency response of the system. The effective, main force of the deceleration is given by the curve upon which the small oscillations are superimposed. A dummy transducer placed in the 37 ke. channel presents a relatively straight, even line 36. At the end of the braking period, after time 60 T4, the dummy channel produces a strongly varying trace 37 and finally retums to normal. This also occurs in the other three channels. The function and purpose of a dummy transducer is clearly illustrated by this example, and 65 points to the necessity for tbem, as will now be further explained. The braking trace 35 may be interpreted as satisfactory functioning of the system until the sled is full3@ stopped, and at such instance, possi- 70 ble vibratory reaction of systematic overload results in the transient fluctuation $7. If such a variation occurred only in the dummy channel, it would be evidence of malfunction of that particular channel only. However, when similar 75 6 varlations 37a occur during the same interval of data measurement, that portion of disrupted trace must be disregarded, since probably the cause of such variations lies iri the modulator or transmitter. More than one chdhnel ca.-i be installed with dummy transducers. Thi,-, practice insures detection of improper indication, particularly at the interval of peak acceleration when systematic variation cannot be easily distinguished from very high accelerations. @ The preferred equipment is capable of excellent high frequency response and will record 63 percent of the maximum amplitude of a square wave input in less than 0.0025 second, for example. The overall accuracy with calibration curves is within 5 percent of error for all channels. Even without the use of calibration curves, the nonlinearity of the system produces an overall accuracy average (f less than 9 percent error for all channels with the present equipment. However, these figures are not to be construed as performance limitations since error of the various components, including simple resistors, the transducers, the recording oscillograph, and any nonlinearity due to system construction are all subject to wide variations. They are merely indicative of the high accuracy achieved with this invention in measuring very large accelerations which heretofore are not known to have been satisfactorily metered. . Thus, it may be stated that the present invention and its high frecluency response of the order of 500 C. P. S., and which is capable of metering and recording accelerations as high as 100 gtavity-units within an overall accuracy of 5 percent error, far outdistances the performance of prior art devices. In -additiori- to su@periority of performance and accuracy, there are provided the novel features of an identification and calibration method and means which may be operated manually or automatically prior to a run or during one, respectively. Duminy transducers are provided to monitor the data to give an account of intrinsic systematic variation or malfunction. Although the presexit invention is especially adapted to meter and record accelerations, it can be equally well used to telemeter any other data that is sensed by an end instrument having a variable resistance output. From the above description it will be apparent that there is thus provided a device of th,-character described possessing the particular features of advantage b&fore enumerated as desirable, but which obviously i's susceptible of lnodification in its form, pioportiorls, detail construction and arrangement of Parts without deParting from the principle involved or sacrificing any of its advantages. While In order to comply with the statute, th,-invention has been de@,icribed in language more or less specific as to structural features, it is to be understood that the invention is not limited t;O the specific features shown, but that the mems and construction herein disclosed comPrise the preferred forin of several niodes of puttin-- the invention into effect, and the invention is, therefore, claimed in anY of its fornis or modifications within the legitimate and valid scope of the appended claims. What is
