August 17, 1998 Design News
Encoder encompasses Hall sensor function
Geoff Nairn, Spain
A compact encoder series from Eltra s.r.l. simplifies
control of brushless dc motors by combining incremental
encoder and motor phase control in a single device.
The EF encoder series optically generates the motor
phase signals that in a traditional brushless DC motor
are produced by Hall effect sensors mounted in the motor
In addition to the standard output signals of a conventional
incremental encoder--resolutions from 200 to 2,048 lines
per revolution are offered with or without zero index--the
encoder disk of the EF series has three extra tracks
to optically simulate signals traditionally generated
by Hall-effect sensors. According to the phase angle
between these tracks, the encoder can control DC motors
with 4, 6 or 8 poles.
Eltra believes its new encoder offers several advantages
over relatively expensive Hall-effect sensors located
inside the motor case. The new encoder, for example,
is typically located in a cooler, less hostile environment
at the end of the motor shaft.
By eliminating Hall-effect sensors from the casing,
design engineers can produce cheaper, more compact motors
with simpler wiring. This, in turn, helps reduce electromagnetic
Compatible with leading commercial digital drives,
the encoder can be mounted on motors with shaft-hole
diameters of 8, 10, 14 or 15mm. Hall Effect phase outputs
can be configured as NPN open collector or line driver
outputs. Power supply options are 5V or 8-24V.
Additional information, contact: Andrea Pedron, Eltra
s.r.l., Via Monticello di Fara 32 bis, 36040 Sarego
(VI), Italy. Tel: +39 0444 436489; Fax +39 0444 835335.