Automatic "Zero-Time" Mark For Microbarograph Record

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Do Not Take From This Room AUTOMATIC "ZERO-TIME" MARK FOR companying a nuclear detonation is maployed to place automatically a zero-time signal (time of detonation of a nuclear weapon) on microbarograph records. Feasibility of this system was proven during Operation TEAPOT at stations up to 134 miles distant from the Nevada

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The microbarograph program performs two important functions during the r;evada Test Opel— ions. The first of these is to record, at a number of distant populated points, blast pressures from HE charges detonated before shot time near the bomb tower. This information is then used to predict where and with what intensity blast will strike, thereby making possible a last minute "shoot" or "don!t shoot" recommendation. The second function is to operate during the nuclear shot and record the acteal pressures that struck these localities (useful for scientific reasons as well as being a valuable aid in adjusting claims for window breakage and popped plaster): In add tion to the microbarograph pressure record, it would be desirable to obtain accurately the 'travel time' of the shock wave. Shock wave travel time can sometimes be used to obtain an indication of the yield of the weapon and is also valuable for subsequent metaorological studies. This travel time could be very conveniently obtained if an accurate zerotime mark were placed on the microbarograph trace. With the present (old) recording system, the operator places a zero-time mark on the record manuaaly by pushing a button when, according to scheduled shot time, he counts down to zero on his pocket watch which has been set as accurately as possibleft=WV. Or, he may more accurately mark the record if ;le sees the flash from the bomb. However, since many of the microbarograph stations are windowless, plus the fact that some shots are detonated during daylight hours, the operator freeuently can not see the flash. Either way, pocket watch or bomb flash, the human element involved in placing the zero-time mark often results in an error of possibly a second or more. Thus, some automatic method of marking the record at the instant of detonation would be highly desirIdeally, this zero-time 'Tanker" signal should be generated by the actual detonation, that is, not simply by the count down time zero signal. Besides being more accurate from standpoints of true zero time and automatic marking, a system such as this would provide the additional a6vantage of indicating to the microbarograph operator whether or not the shot was detonated, a fact which now often must be relayed to him. The Proposed method fulfills these requirements. Proposed Zero-Time Signal Source The detonation of an atomic device (above ground) is always accompanied by an extremely powerful electromagnetic transient. This transient, the object of much scientific scratiny and measurement, is a composite pulse

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resulting in a damped wave of several cycles in the Very Low Frequency During past operations, the transient has been naught but a nuisance, o',:structing instrumentation records and often burning out gauges. During Operation TEAPOT (February to May 1955), an attempt was made to employ this transient for a practical purpose: to place automatically a. zero-time signal on the microbarograph record. i7,nal Pickup and Record Marl:i g Method The experimental automatic zero-time indicator consisted of a loop antenna feeding into a final stage of the regular microbarograph amplifier through a 11134A crystal and filter. This is shown in the block diagramInc antenna e - nsisted of seventy turns of No. 18 hookup wire wound on a qcuare plywood form, ? feet on a side. The result was a low 0, loop, broadly resonant between 10 and 70 ke. In general, zero-time transients consist of several cycles, of say 20 usec/cycle (50 he). These damped wave trains were rectif5ed by the crystal and then. filtered, resulting in a single Positive TA1J.se of long enough duration for the recorder to At the beginning of the TEAPOT series, two stations were equipped with the automatic zero-time indicator. One was at the CP, approximately 10 to 15 miles from the various shot towers. The other was at Lund, Nevada, 134 miles from the shot site. Both stations operated successfully throughout the series, receiving and recording the zero-time transient on all but the underground shot. (The Lund station aid not receive the signal from the Zucchini shot, but there is a question of whether the antenna was connected.) Figures 2 and 3 are examples of microbarograph records at the CP and at Lund, These were most accurate manually placed zero-time signals of dicator, where a comparison could thus be made). As is customary, each record is composed of two traces. Beth are produced by the some pressure CASTLE Recorded in Albutwercue, Sandia Corporation report SC-3592(TR),

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RECTIFIED AMPLIFIED AND PI TIME MARK 1 GRAPH TIME BRUSH Fig, 1 Block Diagram of Exl.erimental Automatic Zero-Time Indicator

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I Inaccurate zero-time ACCURATE ZERO-TIMEas marked by operator according to clock. Fig. 2 Microbarograph Record from MET Shot, Recorded at CF Station, 12 Miles from the Shot Tower, with Zero-Time Transient Pickup Loop Installed USH DEVELOPMENT CO. PRINTED IN 118.A. Pulse from RF LINMENN

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Fig, :3 Microbarograth Record from BEE Shot, Recorded at Lund, Nevada, 134 Miles from the Shot Tower, with Zero-Time Transient Pickup Loop Installed as marked by operator according to WWV time VELOPMENT CO. PRINTED IN U.S.A.

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transducer, but one trace is given greater amplification than the other to rdinimize error in estimating expected signal strength. At the station in Fig. 2, the received RF transient signal was injected into both traces. In Fig. 3, it was connected to deflect only the lower trace. record by the transient versus the manual zero-time signal superimposed by the operator pressing a button (microswitch) according to a clock set with WW. The pressure pulse is not shown on this early portion of the Conclusions and Recommendations It is obvious that the tremendously powerful zero-time transient that ?eeompanies an atonic detonation is an ideal signal source with which to mark microbarograph records (and other instrumentation records). The following recousiendations are made for the design and construction of automatic zero-time indicators for permanent installation in each 1. low Q. antenna should be employed, broadly resonant around 30 kc and not over 2 feet in d4_ameter (or on a side). 2. Rather than utilize the amplifier stages of the regular microbarograph unit to amplify and shape the signal from the antenna, as was done during this experiment, a separate amplifier should be constructed having its output coupled to the recorder without going through the microbarograph amplifier. This is recommended because the microbarograph amplifier employs a phase-sensitive system, whereas all that is required with the loon is a simple AC amplifier with sufficient output to drive a Brush recorder. The amplifier should be fixed-tuned to pass from 10 to 100 kc. The output of the zero-time signal amplifier should be fed into the Brush recorder through an appropriate mixer stage so as not to shunt the normal signal from the microbarograph unit. For convenience, especially with portable stations, a telescoping "whip" antenna might be substituted for the more cumbersome loop. This would, of course, necessitate higher gain in the 'zero-time amplifier' stages.