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Mast Ozonesondes...
Lightweight, Reliable, and Rugged
Technical Discussion

Figure 1
Internal view of Mast Model # 730 Ozone Sensing Device

Mast Ozonesondes employ a bubbler sensor (U.S patent No. 3,329,599), conceived and patented by Dr A. W. Brewer of the University of Toronto and licenced to Mast Development Company for development and sale. The senor works on a simple principle in which an electrochemical reaction takes place when air containing ozone is bubbled into a potassium-iodide sensing solution. The resulting exchange of electrons within the reagent is measurable in microamperes so that the quantity of ozone introduced through continuous air sampling is directly proportional to the resulting reading in microamperes. Two milliliters of potassium-iodide sensing solution added just prior to launch is sufficient for the entire flight. The air sample is supplied to the sensor by constant volume reciprocating piston pump at a rate of 200 cc/min. (calibrated at factory). Power is supplied by self contained batteries. Current balloon-borne radiosonde packages that relay back information on humidity, temperature, and pressure are completely compatible with the Mast Ozonesonde. To prevent ozone information from ineterfering with meteorological data, a transistorized electronic switching circuit was deigned by Mast for models 730-5 and 730-6.

This switching circuit is part of a printed circuit board also containing a transistorized amplifier. The electronic switch alternately opens and closes a small relay to provide 3.5 seconds of ozone concentration signal while the relay contacts are closed, and 3.5 seconds of no ozone signal while the contacts are open. During the 3.5 seconds when he contacts are open, other meteorological data can be transmitted by the radiosonde in its normal manner.

Other ozone meteorological data cycles besides 3.5/3.5 seconds are available upon request, making Mast ozonesondes highly compatible with radoisondes and study programs used throughout the world. The mast electronic switch is powered by the same self-contained water-activated battery which powers the ozone sensor air pump motor.

The Mast model 730-7T Ozonesonde was developed for use by the United States Air Force. It does not use the electronic switch and thus differs from the Models 730-5 and 730-6. It uses a rotary printed circuit switch driven at about 0.2 rpm by the other end of the air air pump motor via suitable speed-reducing gears. It also includes a tiny termistor mounted in the air pump cylinder for monitoring temperature of the air sample.sample.

Figure 2
Model #730 flight case… made of expandable polystyrene beads
The motor-driven switch allows for more test or calibration signals than does the electronic switch. The Mast Model 730-7 is the same as the Model 730-7T but does not have a termistor.

A balloon is used to carry the ozonesonde/radiosonde to approximately 100,000 feet at a speed of 1,000 feet per minute. After the balloon ruptures, the sonde decendes at a rate of between 2,000 and 4,000 feet per minute by parachute. To allow for variations in time aloft, the model 730 is built to operate for four hours.

The Mast model 730 Ozonesonde is designed to withstand extreme environmental conditions encountered during flight. The blubber solution is self-degassing so that internal pressure is always equal to that of the surrounding atmosphere (figure 4, below). Temperature control for this unit is more difficult to control as the reagent in the Ozone sensor has approximately the same freezing and boiling point as water. Consequently, an internal temperature must be maintained just above freezing while the unit is exposed to temperatures as low as -95ēC at 36,000 feet. Because the Model 730 spends 80% of its flight time in sub-zero temperatures, a specially moulded flight case of expanding polystrene beads is used to maintain an internal operating temperature of +2ēC to +7ēC (figure 3, below).

Mast Ozonesondes are light (approximately 1 lb.), durable, and made of high quality components to assure constant reliability . . . Another reason why more and more people working with ozone - Look up to Mast.

Mast Ozonesonde Diagramed parts and Technical data

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