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A radiosonde is the simplest and most convenient
instrument for obtaining atmospheric data at various altitudes. It is a
small
hydrogen-filled balloon with a lifting force of approximately 2 kg.
Suspended
from it is a gondola containing a single-tube radio transmitter,
temperature,
pressure, and humidity sensors, and switches.
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The transmitting
antenna is a wire attached to the balloon's sling, and the
counterweight is a
freely hanging wire.
In flight, the
measuring instruments use switches to control the transmitter. Its
antenna
emits radio pulses of varying durations, with varying intervals between
them.
The switch axis is rotated during flight using a windmill.
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The aerological
laboratory receives radiosonde signals. These signals are then used to
determine the temperature, pressure, and humidity of the atmospheric
layers
through which the radiosonde passes.
A radiosonde can be
used to accurately determine temperatures from +40°C to -60°C,
pressures from
30 to 700 mmHg, and humidity up to 100%. Its use facilitates weather
forecasting, which is crucial for our national economy.
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| The block diagram
of a radiosonde is shown in Figure 1 |
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| and its schematic diagram is shown in
Figure 2. |
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The high-frequency
oscillation generator G is excited only if the anode battery circuit is
closed
through the contacts of one of the pressure (Dd), humidity (Dv) or
temperature
(Dt) sensors and the contacts of switches K1 and K2.
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TEMPERATURE
DATA TRANSMISSION
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The temperature
sensor's sensitive element is the T plate (Fig. 2), consisting of two
metal
strips with different temperature coefficients. When the temperature
changes,
the plate flexes, causing the pointer UT, connected to it by a hinged
transmission, to move along the metal teeth of combs G1, G2, G3, and
G4,
arranged so that the pointer sequentially moves from one comb to the
next (Fig.
3). The combs are insulated from each other and from the sensor
housing. Each
is connected to one of the plates PT1, PT2, PT3, and PT4 of switch K1
(Fig. 2).
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Opposite each plate
on the commutator axis are contact stars Z1, Z2, Z3, and Z4; the number
of arms
on each star equals the number of the plate next to it. As the
commutator
rotates, the stars touch the plates, connecting the negative terminal
of the
anode battery Ba through the teeth of combs G1, G2, G3, or G4, the
indicator
needle UT, the sensor plate T, and the instrument housing to the
cathode of the
high-frequency generator tube L. During one revolution of the
commutator, star
Z1 touches plate PT1 once, star Z2 touches plate PT2 twice, Z3 touches
plate
PT3 three times, and so on.
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<>The radio
transmitter emits pulses only when any of the commutator sprockets
touches the
plate connected to the corresponding comb, on whose tooth the indicator
UT is
located. Therefore, if the indicator UT touches, for example, comb
tooth G1,
the transmitter's generator power circuit is closed by sprocket Z1 once
per
commutator axis rotation, and during this time, one pulse is emitted;
if the
indicator is on comb tooth G2, two pulses are emitted per commutator
axis
rotation, and so on.
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<>When the
temperature changes, the movement of the UT pointer from one tooth of
the comb
to the other
causes a change in
the frequency of the radio transmitter's signals. By continuously
monitoring
the signals, the number of pulses per revolution of the commutator can
be used
to determine the moment the UT pointer moves from tooth to tooth. To
determine
which tooth of the comb the pointer is on, note its position when the
radiosonde is released. Since each pointer position corresponds to a
specific
temperature, the air temperature can be determined by observing the
change in
the frequency of the signals. |
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To ensure that
temperature can be determined even in the event of a break in
radiosonde signal
reception, the commutator axis is equipped with a control star (Zk)
with seven
arms spanning a 288° sector, and a contact plate (PTk) that closes with
them.
The latter is connected to the control comb (Gk) of the temperature
sensor.
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<>The teeth of the
temperature sensor combs are grouped into 19 sections (Fig. 3), each of
which
includes four teeth located on different combs, with the first tooth of
the
control comb on the right replacing the first (right) tooth of the
fourth comb
in the third section, and the following teeth of the control comb
respectively
replacing: the second (right) tooth of the fifth section, the third
tooth of
the seventh section, etc. Starting from the 12th section, the order of
substitution is repeated.
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<>This combination of
teeth allows the operator receiving the radiosonde signals to determine
the
comb and tooth number on which the UT indicator is located. For
example,
suppose, after a break in signal reception, the operator first hears
one dot,
then seven dots, and then three more dots.
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He knows that a
single short signal (a dot) is emitted by the radiosonde transmitter
per
rotation of the commutator axis when the UT indicator is positioned on
one of
the teeth of comb G1 and sprocket Z1 closes the circuit of plate PT1.
If the
circuit is closed through plate PT2 and the UT indicator is positioned
on one
of the teeth of comb G2, then two short signals will be received per
rotation
of the commutator axis. Accordingly, when the circuits are closed
through
plates PT3, PT4, and PTk and the UT indicator is positioned on the
teeth of
combs G3, G4, and Gk, the operator will hear signals consisting of
three, four,
and seven dots.
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<>Therefore, by
successively receiving one, seven, and three points, the operator can
determine
that the UT indicator was initially located on the tooth of comb G1,
then on
comb Gk, and finally on the tooth of comb G3. Such a sequence of signal
groups
can only occur if, during the radiosonde's ascent, due to a change in
temperature, the UT indicator moved from section 2 to section 3 or from
section
11 to section 12 (Fig. 3). However, uncertainty in the temperature
determination is eliminated, since the sensitivity of the sensor is
such that
the temperature difference transmitted through the teeth of the third
and
twelfth sections is approximately 40°.
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PRESSURE
DATA TRANSMISSION
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Signals
characterizing atmospheric pressure are transmitted similarly by
Professor
Molchanov's radiosonde. The pressure receiver is a barometric tube D,
hinged to
an indicator UD. As the pressure changes, this tube flexes, and the
indicator
UD moves along a comb Gd, consisting of metal teeth of varying widths:
two
narrow teeth are followed by one wide one. This comb is connected to
the plate
Pd of the K1 commutator. The star located opposite it on the commutator
axis
has one tooth in the form of a sector of a circle approximately 72°
wide.
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<>All temperature
sprockets are positioned so that their final points (along the
commutator path)
are aligned with the point of sprocket Zk (Fig. 4). The beginning of
the sector
of pressure sprocket Zd also coincides with this line. Therefore, when
the UT
indicator is positioned on a tooth, the transmitter's power supply
circuit is
closed through sprockets Z1, Z2, Z3, Z4, Zk, as well as through
sprocket Zd.
As a result, the
final point of the signal group turns into a dash. |
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For example, if the
UT indicator is positioned on comb tooth G1, one dash will be
transmitted
instead of one dot. If it is positioned on comb tooth G3, two dots and
one dash
will be transmitted instead of three dots. Figure 5a shows the
temperature
signals when the UD indicator is positioned between comb teeth Gd,
while Figure
5b shows them when positioned on the teeth.
By noting the
appearance and disappearance of dashes in the pressure signals and
knowing the
initial pressure, one can determine the moment the UD indicator
transitions
from the insulator to the tooth and, consequently, the pressure value
corresponding to that moment.
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HUMIDITY
DATA TRANSMISSION
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The humidity meter
in Professor Molchanov's radiosonde is a bundle of defatted human hair
(PV),
connected to the pointer of the humidity indicator (UV) (Fig. 2). As
the
humidity changes, the length of this bundle also changes, causing the
UV
pointer to move along the comb (Gv), which contains ten teeth insulated
from
each other and from the housing. Each tooth is connected to one of the
contacts
P1, P2, and P10 of the 13-pin humidity switch K2. Contacts Pk1 and Pk2
of this
switch are connected to the housing of the device and serve as control
contacts, while contact Pr is connected to the pressure-transmitting
contact
(Gd), which is insulated from the other teeth of the comb.
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All humidity switch
contacts have the same angular dimension {1}. The gap between contact
Pk2 and
contact P1, connected to the first tooth of comb Gv, is equal to the
width of
each of these contacts.
<>Brush Shch slides
across the contacts of humidity switch K2, which rotates from the
windmill via
a worm gear, slowing the movement by a factor of 20.
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When the brush
touches contact Pk1, Pk2, or any contact connected to the teeth of the
humidity
comb Gv, the anode battery circuit closes beyond switch K1, and a
"humidity pulse" is emitted. During one complete revolution of switch
K1, the brush of humidity switch K2 passes one of its contacts;
therefore, the
duration of one "humidity signal" is equal to the duration of a
complete series of "temperature signals."
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As it rotates,
brush Ù first passes contacts Ïê1 and Ïê2. At this point, two long
dashes are
heard in the receiver's handsets. After this, the humidity signal
circuit is
broken, and the temperature and pressure signals are transmitted. As
soon as
brush Ù touches the contact connected to the tooth of comb Ãâ, where
the UV
indicator is located, the temperature and pressure signals stop, and
the
humidity signal is transmitted again. Thus, first two long humidity
signals are
transmitted, then several temperature and pressure signals, and then
one long
signal again (Fig. 5, c).
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The number of
temperature signals between two long humidity signals is therefore
equal to the
comb tooth number on which the UV indicator is positioned. This allows
for
immediate determination of the humidity level, as the GV comb is
pre-calibrated. For example, if the UV indicator is positioned on the
first
tooth of the GV comb (corresponding to 100% humidity), then after two
long
signals, one set of temperature and pressure signals will be heard,
followed by
another long humidity signal.
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When the UV
indicator is positioned on the second tooth, a long humidity signal
will be
heard only after two temperature signals, and so on. Temperature and
pressure
signals will then begin to be transmitted until the brush Ù returns to
the
plate Ïê1. Since the tooth of the pressure comb to which the Pr contact
is
connected is located between the 9th and 10th teeth of this comb and is
insulated from them, two long control signals for humidity will be
heard before
the signal transmitted via the 9th tooth.
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At the moment of
passing the 9th tooth, they will be preceded by one long pressure
control
signal. Starting from the 10th tooth of the GD comb, only two humidity
control
signals will be heard again. This alternation of control signals
facilitates
pressure determination.
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