Definition
An engine-mounted sensor that detects the rotational speed of a turbine or shaft and sends an electrical signal to the cockpit tachometer indicator, where the speed is displayed as RPM or as a percentage of maximum rated speed.
Plain English
A small device on the engine that measures how fast a shaft is spinning and sends that reading to the gauge in the cockpit so the pilot can see the engine speed.
Context Anchor
Seen in turboprop engine systems, especially when discussing how the cockpit shows propeller speed or engine shaft speed.
Derivation
From Greek 'tachos' meaning speed, plus 'meter' (to measure). A 'transmitter' sends the measurement somewhere else — in this case, from the engine to the cockpit display. So: a device that measures speed and transmits the reading.
Why Pilots Care
Correct tachometer transmitter operation ensures the pilot receives accurate RPM readings needed to stay within engine and propeller limits.
Intuition Check
Do not read “transmitter” here as a radio transmitter. In this term, it means a device that sends engine-speed information through the aircraft’s instrument system.
Example Sentence 1
The tachometer transmitter on the free turbine sends the propeller shaft speed to the Np gauge in the cockpit.
Example Sentence 2
During the preflight, the mechanic checked the tachometer transmitter connection on the accessory gearbox for the free-turbine section.