1208 
unit includes a selector switch activated by a pressure- 
sensitive aneroid capsule (Fig. 4). In the present de- 
sign the selector switch has 150 silver conducting- 
2 PHASE 
GENERATOR |MOTOR 
AND 
1680 MCS 
RECEIVER 
AZ ERROR SIGNAL 
AZIMUTH 
SERVO 
AMPLIFIER 
AZIMUTH 
DRIVE MOTOR 
SELSYN 
METEOROLOGICAL INSTRUMENTS 
reference signals for pressure measurements, and all 
other conducting strips up to the 104th are associated 
with humidity measurements. Humidity is not meas- 
PULSE 
SHAPER 
ERROR 
VOLTAGE 
AMPLIFIER 
30 CPS 
ELECTRONIC 
COMMUTATOR 
EL ERROR SIGNAL 
10-190 
METEORO- 
LOGICAL 
REGORDER 
ANGLE 
RECORDER 
ELEVATION 
SERVO 
AMPLIFIER 
ELEVATION 
DRIVE MOTOR 
AND 
SELSYN 
Fie. 1.—Block diagram of the latest automatic balloon-tracking direction finder. 
strips, each separated by an insulating segment. Every 
fifth conducting strip is 0.0065 in. wide; all other con- 
ducting strips are 0.004 in. wide; while the insulating 
Bue sy reas : : 
Fig. 2.—An automatic balloon-tracking direction finder set up 
for operation. Rawin Set AN/GMD-1. 
segments are about 0.008 in. in width. Each imsulating 
segment ts associated with a temperature measurement, 
each 5th and 15th conducting strip is associated with 
ured after the 104th contact, the remaining conducting 
strips being used for reference signals. The 150 con- 
ducting strips are printed on a polystyrene block to 
reduce fabrication costs, to avoid complicated wire 
connections, and to increase the uniformity of the 
segment alignment. 
Pressure Capsule. The pressure capsule employed in 
this new design is temperature compensated and con- 
structed so as to give approximately logarithmic re- 
sponse over the operating range—the deflection per 
millibar at 50 mb being approximately five times the 
deflection at 1000 mb. Without affecting the useful 
sensitivity and accuracy at high pressure, these cap- 
sules provide an appreciable increase in accuracy and 
sensitivity at low pressures. 
The precision of pressure measurements depends 
upon such factors as repeatability of the mechanical 
motion of the aneroid and its lever system, the tem- 
perature compensation, the precision with which the 
surface pressure can be set on the commutator, and 
the reliability of the switching operation. It is esti- 
mated that the over-all probable error in pressure 
measurement of the present modulator units is: 
mb at 1000 mb 
mb at 500 mb 
mb at 100 mb 
mbat 10 mb 
1 
=b3 
=£1.5 
1.5 
However, it should be emphasized that the in- 
cremental accuracy between contacts is very much 
