Contact tachometer:
§
Used when rotor is accessible
§
It’s used in concentric mode. It’s always applied to
shaft center. Shaft should have a centering hole, so the rotating element will
not slip out
§
It can also be applied in tangential mode if the rotor
has an external circular rim, but rpm recalculation must be conducted based on
the diameter ratio between rotor and the rotating element
§
No need for rotary encoder
§
Transfers rotational motion of rotor and converts it
internally to pulses
§
Measures instantaneous rpm (based on number of
divisions of the internal-rotary encoder)
§
It must be parallel to the rotating shaft.
Non-contact
(laser) tachometer:
§
Requires too much tuning before each measurement.
§
It’s –in most cases- supplied with a counter feature
§
It’s sensitive to distance between it and rotor.
§
It’s used for indoor use only.
§
Sensitive to reflectivity of rotor.
§
An external encoder is needed. Some models use a reflecting
tape for generating pulses.
§
It can be used also with an external emitter (sender),
so it will counts pulse receptions.
