Definition
An electrical reference signal whose three defining characteristics — voltage level, frequency in cycles per second, and waveform shape (such as sine, square, or sawtooth) — are precisely specified so that equipment receiving or producing it behaves in a known, repeatable way. In avionics, such signals are used as test inputs, calibration references, or operating signals for instruments and systems that depend on a known electrical input to function correctly.
Plain English
An electrical signal where exactly three things are spelled out: how strong it is, how fast it cycles, and what shape it traces out over time. Because all three are defined, the signal is predictable and can be used as a reliable reference.
Context Anchor
Seen in aircraft electrical and avionics maintenance when a test set or signal generator sends a known electrical signal into a piece of equipment.
Derivation
Signal comes from the Latin signum, meaning a sign or mark. In electrical use, a signal is a changing electrical condition that carries information or provides a known reference.
Why Pilots Care
Many cockpit instruments and avionics rely on precisely defined electrical signals to operate or to be tested accurately. If any one of the three properties drifts, the equipment may give wrong readings or fail to function as designed.
Analogy
It is like checking a scale with a known weight. If the input is known, any wrong response points to a problem in the equipment being tested.
Intuition Check
Do not read signal here as a hand sign, light signal, or radio message in general. Here it means a controlled electrical pattern with known voltage, frequency, and shape.
Example Sentence 1
The test bench supplies a signal having a specified voltage, frequency, and waveform to verify that the instrument responds correctly.
Example Sentence 2
Before reinstalling the unit, the technician confirmed the output was a signal having a specified voltage, frequency, and waveform matching the maintenance manual.