deployment, fired a squib-cutting mechanism which detached the b-ft ribbon parachute and released the 28-{t-square parachute.
The second system consisted of three parachutes, a2 6-ft fist ribbon parachute and two 28ft-square parachutes. The operation of the 6-ft ribbon and the first 28-ft parachute was identical to the previously described dual system. If the first 28-ft parachute happened to ke destroyed by radiation, resulti~’ in a free fall of the canister, a second 28-ft parachute would be
reieased by a second sqt
atting mechanism. A pressure differential between a reference
chamber in the canister a... the an.bient pressure occurs during the canister free fall because
of the pressure time lag of the reference chamber. The value of this pressure differential,
after approximately 10 sec of canister free fall, is sufficient to activate a pressure swit:h.
When this pressure switch closes, it activates the second squib-cutting mechanism, thereby
releasing the second 28-it parachute. The 10-sec delay was very desirable to prevent thermal
damage to the latter 28-ft parachute, assuming that damaging thermal effects would exist for
only 10 sec after detonation. In each test six of the canisters were supplied with the tripleparachute system since they were expected to be within the range of possible thermal damage.
The remaining six canisters, iocated at longer slant ranges, contained the dual-parachute
system. The parachute-borne canister was 86 ir.. {n over-all length, 14 in. in diameter, and
weighed 300 lb.
2.2
CALIBRATION PROCEDURE
Reference is made to Operatior Jangle Report, Project 1.3c,! for a detatled description of
blast-pressure calibration procedure.
2.2.1
Calibration of Transducers
The thermocouples were calibrated through the courtesy of the Material Laboratory of the
Brooklyn Naval Shipyard. The following description of the calibration method is quoted from
their report (Laboratory Project 5046-2, Part 6; dated 24 March 1953),
The three type K-2 thermocouple radiometers have been calibrated by tne Laboratory, This investigation was conducted at the request of the Air Force Cambridge Research Center and as part of the Thermal Radiation Program sponsored by the Armed Forces Special Weapons Project.
The radiometers were calibrated by means of a high-intensity carbon-are source whic produces 4
per cent of its energy in the ultraviolet regian, 36 per cent in the visible, and 60 per cent in the infrared.
This source provides an irradiance of 18 cal/cm* sec”! over approximately a 0.5-cmdiameter area. In
order to obtain lower irradiances, perforated metal attenuating screens with transmittances of 0.087, 0.17,
6.21, 0.41, and 0,50 were used. The response of the radiometers was measured with a calibrated recording
potentiometer. An open-ended tox with 8-inch-square cross section was used to protect the radiometers
from air draughts. Ecch radiometer at each irradiance was given a series of three 3-second exposures.
The response remained constant during the 3-second period, except for some variation due to fluctuation of
the carbon-are and cooling of the radiometer thermojunction by air currents. There was seldom as much
as 10 per cent difference between the three response readings in one series.
In the table (Table 1—-Response of K-2 Rr diometers) is the average response for each irradiance. It
is to be noted that the uncoated (No. 2563) and the aluminized (No, 2567) radicmeters have a linear response,
whereas a smooth curve drawn through the experimental points of the blackened (No. 2.65) radiometer
shows some saturition effect. This is explained by the fact that the blackened thermojunction at the temperature of interest losen a large part of {ts absorbed heat to reradiation according to the fourth-power
law, while the other thermojunctions have much too low an emissivity for this effect to be important.
The time constants (0.63 of the maximum deflection for continuous illumination) of the radiometers
were determined with a galvanometer oscillograph with a frequency response, measured under the conditions of use, flat up to 80 eps. An irradiance of 9 cal/em? sec”! was used on the blackened radiometer, and
18 cal/cm? sec! on the others. All of the ris? or fall time constants measured were within 15 per cent
of 0.21 sec,
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