AI-Tek Instruments (formerly Airpax Instruments) is the leading supplier of industrial speed sensors and tachometers.
Tachometers can be blind (with analog and/or relay outputs), or they can have an integral digital display as well.
Speed sensors can be two-wire (passive) or three-wire (powered).
Guide to obsolete tachometers:
Tachpak 1 (T77130-xx) has been replaced by the Tachpak 10 (T77510-xx)
Tachpak 3 (T77430-xx) has been replaced by the Tachpak 30 (T77530-xx)
Tachtrol 3 (T77310-xx) has been replaced by the Tachtrol 30 (T77630-xx)