variocoupler in a sentence

1. A widely used design was the variometer ( variocoupler ).
2. This is an older type of regulator used in the 1920s that uses the principle of a fixed-position field coil and a second field coil that can be rotated on an axis in parallel with the fixed coil, similar to a variocoupler.
3. It's difficult to find variocoupler in a sentence.