Air core gauge

The air core gauge is a type of "air-core motor".

[1] There are four common types of rotary actuators:[2] The air core gauge consists of two independent, perpendicular coils surrounding a hollow chamber.

A typical air core gauge has four terminals, two for each coil, as shown.

Air core gauges require special electronics to properly drive the coils.

Some driver integrated circuits have a serial input data port and two pair of output lines.

The input data defines: Some typical driver ICs include:

An auto tachometer has a sweep of about 240-250 degrees and typically uses an air core gauge.
Back side of an auto instrument cluster showing four mounting terminals for an air core gauge.