2
Block Diagram
The HEDS-9040 and 9140 have
two channel quadrature outputs
plus a third channel index output.
This index output is a 90
electrical degree high true index
pulse which is generated once for
each full rotation of the
codewheel.
The HEDS-9040 is designed for
use with a HEDX-614X codewheel
which has an optical radius of
23.36 mm (0.920 inch). The
HEDS-9140 is designed for use
with a HEDS-5140 codewheel
which has an optical radius of
11.00 mm (0.433 inch).
The quadrature signals and the
index pulse are accessed through
five 0.025 inch square pins
located on 0.1 inch centers.
Theory of Operation
wheel. These detectors are also
spaced such that a light period on
one pair of detectors corresponds
to a dark period on the adjacent
pair of detectors. The photodiode
outputs are then fed through the
signal processing circuitry
resulting in A, A, B, B, I and I.
Comparators receive these signals
and produce the final outputs for
channels A and B. Due to this
integrated phasing technique, the
digital output of channel A is in
quadrature with that of channel B
(90 degrees out of phase).
The HEDS-9040 and 9140 are
emitter/detector modules.
Coupled with a codewheel, these
modules translate the rotary
motion of a shaft into a three-
channel digital output.
Standard resolutions between 256
and 2000 counts per revolution
are available. Consult local
Agilent sales representatives for
other resolutions.
As seen in the block diagram, the
modules contain a single Light
Emitting Diode (LED) as its light
source. The light is collimated
into a parallel beam by means of a
single polycarbonate lens located
directly over the LED. Opposite
the emitter is the integrated
detector circuit. This IC consists
of multiple sets of photodetectors
and the signal processing
circuitry necessary to produce the
digital waveforms.
Applications
The HEDS-9040 and 9140
provide sophisticated motion
control detection at a low cost,
making them ideal for high
volume applications. Typical
applications include printers,
plotters, tape drives, and
industrial and factory automation
equipment.
The output of the comparator for
I and I is sent to the index
processing circuitry along with
the outputs of channels A and B.
The final output of channel I is an
index pulse PO which is generated
once for each full rotation of the
codewheel. This output PO is a
one state width (nominally 90
electrical degrees), high true
index pulse which is coincident
with the low states of channels A
and B.
Note: Agilent Technologies
encoders are not recommended
for use in safety critical
applications. Eg. ABS braking
systems, power steering, life
support systems and critical
care medical equipment. Please
contact sales representative if
more clarification is needed.
The codewheel rotates between
the emitter and detector, causing
the light beam to be interrupted
by the pattern of spaces and bars
on the codewheel. The photo-
diodes which detect these
interruptions are arranged in a
pattern that corresponds to the
radius and design of the code-
HP [ HEWLETT-PACKARD ]
