This is the second part of avionic sensors and instruments. This post shows other instruments and sensors used in aircraft.
Click in the button below to see the first part.
Avionic sensors and instruments (Part 1)Click here
Measuring the airspeed
The airplane’s speed in relation to air is one of the most important parameters, because airplane’s stability depends on it. The air enters through a pitot tube and has a chamber that does not receive air flux, and with static pressure.
The speed is measured by difference in pressure between air chambers. When the aircraft is stopped, the chamber pressure that receives the air flux is equal to the static pressure. When the aircraft flies, the difference pressure transducer moves mechanisms that turn the pointer, as shown in this video.
This sensor stays in the front part of airplanes.
Measuring altitude
Altimeters to aircrafts use an aneroid barometer to measure the altitude from air pressure variation. Has aneroid wafers with an internal pressure. When the air is more rarefied, the wafers expand, moving mechanisms to turn the pointer. When the atmospheric pressure increases, the wafers contract.
Indicating vertical speed
The vertical speed indicator (VSI) works in a similar way to the altimeter, serving to indicate if the airplane is climbing, descending, or keeps in constant altitude. In this instrument, the wafers are linked to a static pressure tube, and the case has a hole to control the air leaking.
When the airplane climbs, the pressure inside the wafer decreases faster than in the case, which decreases the pressure by the hole. When the airplane descends, the pressure inside the wafer increases faster than in the case. When it stays at the same altitude, the pressures inside and outside the wafer are equal. For what serves the static port? Has the function to transmit air to the instruments, to stay calibrated and to measure the pressure difference.
Air data computer (ADC)
In more modern aircraft, these avionic sensors are integrated in the air data computer. Purely pneumatic instruments lose precision in high altitudes. The computer has pressure sensors which send electric signals to the computer, which has analog-digital converters and an error corrector. The ADC offers a better vision of data than the analog pointers.
The purely pneumatic instruments stay in reserve for backup, in case ADC fails. Other avionic sensors and instruments are for other posts.
