Remote Sensing and Indication

It is often impractical or impossible to utilize direct reading gauges for information needed to be conveyed in the cockpit. Placing sensors at the most suitable location on the airframe or engine and transmitting the collected data electrically through wires to the displays in the cockpit is a widely used method of remote-sensing and indicating on aircraft. Many remote sensing instrument systems consist simply of the sensing and transmitter unit and the cockpit indicator unit connected to each other by wires. For pressure flight instruments, the ADC and pickup devices (pitot tubes, static vents, etc.) comprise the sensing and transmitter unit. Many aircraft collect sensed data in dedicated engine and airframe computers. There, the information can be processed. An output section of the computer then transmits it electrically or digitally to the cockpit for display. Remote-sensing instrument systems operate with high reliability and accuracy. They are powered by the aircraft’s electrical system.

Small electric motors inside the instrument housings are used to position the pointers, instead of direct-operating mechanical linkages. They receive electric current from the output section of the ADC or other computers. They also receive input from sensing transmitters or transducers that are remotely located on the aircraft. By varying the electric signal, the motors are turned to the precise location needed to reflect the correct indication. Direct electric transmission of information from different types of sensors is accomplished with a few reliable and relatively simple techniques. Note that digital cockpit displays receive all of their input from a DADC and other computers, via a digital data bus and do not use electric motors. The data packages transmitted via the bus contain the instructions on how to illuminate the display screen.