Small Optical Encoder Modules
Technical Data
HEDS-973X Series
Features
• Small Size
• Low Cost
• Multiple Mounting Options
• Wide Resolution Range
• Linear and Rotary Options
Available
• No Signal Adjustment
Required
• Insensitive to Radial and
Axial Play
• - 40
°
C to +85
°
C Operating
Temperature
• High Resolution Version of
the HEDS-970X
• Two Channel Quadrature
Output
• TTL Compatible
• Single 5 V Supply
• Wave Solderable
Description
The HEDS-973X series is a high
performance, low cost, optical
incremental encoder module.
When operated in conjunction
Package Dimensions
Mounting Option #50 - Standard (Baseplane Mounting)
Contact Factory for Detailed Package Dimensions
ESD WARNING: NORMAL HANDLING PRECAUTIONS SHOULD BE TAKEN TO AVOID STATIC DISCHARGE.
2
with either a codewheel or
codestrip, this module detects
rotary or linear position. The
module consists of a lensed LED
source and a detector IC enclosed
in a small C-shaped plastic pack-
age. Due to a highly collimated
light source and a unique photo-
detector array, the module is
extremely tolerant to mounting
misalignment.
The two channel digital outputs
and 5 V supply input are accessed
through four solder-plated leads
located on 2.54 mm (0.1 inch)
centers.
The standard HEDS-973X is
designed for use with an 11 mm
optical radius codewheel, or
linear codestrip. Other options
are available. Please contact
factory for more information.
a low cost, making closed-loop
control very cost-competitive!
Typical applications include
printers, plotters, copiers, and
office automation equipment.
produce the digital waveforms.
The codewheel/codestrip moves
between the emitter and detector,
causing the light beam to be inter-
rupted by the pattern of spaces
and bars on the codewheel/code-
strip. The photodiodes which
detect these interruptions are
arranged in a pattern that corre-
sponds to the radius and count
density of the codewheel/code-
strip. 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 fed through the signal
processing circuitry. Two com-
parators 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 channel B (90
degrees out of phase).
Theory of Operation
The HEDS-973X is a C-shaped
emitter/detector module. Coupled
with a codewheel, it translates
rotary motion into a two-channel
digital output. Coupled with a
codestrip, it translates linear
motion into a digital output.
As seen in the block diagram, the
module contains a single Light
Emitting Diode (LED) as its light
source. The light is collimated
into a parallel beam by means of
a single 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
Applications
The HEDS-973X provides
sophisticated motion detection at
Block Diagram
3
Output Waveforms
Phase (φ): The number of electrical
degrees between the center of the
high state of channel A and the
center of the high state of channel
B. This value is nominally 90°e for
quadrature output.
Phase Error (∆φ): The deviation of
the phase from its ideal value of
90°e.
Direction of Rotation: When the
codewheel rotates counterclock-
wise, as viewed looking down on
the module (so the marking is
visible), channel A will lead
channel B. If the codewheel rotates
in the opposite direction, channel
B will lead channel A.
Optical Radius (Rop): The distance
from the codewheel’s center of
rotation to the optical center
(O.C.) of the encoder module.
Angular Misalignment Error (E
A
):
angular misalignment of the sensor
in relation to the tangential
direction. This applies for both
rotary and linear motion.
Mounting Position (R
M
): Distance
from Motor Shaft center of rotation
to center of Alignment Tab
receiving hole.
Definitions
Count (N) = The number of bar
and window pairs or counts per
revolution (CPR) of the
codewheel, or the number of lines
per inch of the codestrip (LPI).
1 Shaft Rotation = 360
mechanical
degrees
= N cycles
1 cycle (c) = 360 electrical
degrees (°e)
= 1 bar and
window pair
Pulse Width (P): The number of
electrical degrees that an output
is high during one cycle. This
value is nominally 180°e or 1/2
cycle.
Pulse Width Error (∆P): The
deviation, in electrical degrees, of
the pulse width from its ideal
value of 180°e.
State Width (S): The number of
electrical degrees between a
transition in the output of channel
A and the neighboring transition
in the output of channel B. There
are 4 states per cycle, each
nominally 90°e.
State Width Error (∆S): The
deviation, in electrical degrees, of
each state width from its ideal
value of 90°e.
4
Absolute Maximum Ratings
Parameter
Storage Temperature
Operating Temperature
Supply Voltage
Output Voltage
Output Current per
Channel
Soldering Temperature
Symbol
T
S
T
A
V
CC
V
O
I
O
Min. Max. Units
-40
-40
-0.5
-0.5
-1.0
85
70
85
70
7
V
CC
5
260
°C
°C
V
V
mA
°C
t
≤
5 sec.
Notes
Option A & Q
All Other Options
Option A & Q
All Other Options
Recommended Operating Conditions
Parameter
Temperature
Supply Voltage
Load Capacitance
Count Frequency
Angular Misalignment
Mounting Position
E
A
R
M
-2.0
0.0
R
OP
-0.14
(R
OP
-0.006)
Symbol
T
V
CC
C
L
Min.
-40
4.5
5.0
Typ.
Max.
85
70
5.5
100
40
+2.0
Units
°C
V
pF
kHz
deg.
mm
mm (in.)
(inch)
Shaft
c
0.13 mm (0.005”)
L
Notes
Option A & Q
All Other Options
Ripple < 100 mV
p-p
3.2 kΩ pull-up
(Velocity (rpm) x N)/60
See Mounting Considerations
Note:
The module performance is specified at 40 kHz but can operate at higher frequencies.
Electrical Characteristics
Electrical Characteristics over Recommended Operating Range, Typical at 25°C.
Parameter
Supply Current
High Level Output Voltage
Low Level Output Voltage
Rise Time
Fall Time
Symbol
I
CC
V
OH
V
OL
t
r
t
f
180
40
2.4
0.4
Min.
Typ.
17
57
Max.
40
mA
85
V
V
ns
ns
All Other Options
I
OH
= -200
µA
I
OL
= 3.86 mA
C
L
= 25 pF,
R
L
= 3.3 kΩ pull-up
Units
Notes
Option A & Q
5
Encoding Characteristics
Encoding Characteristics over Recommended Operating Condition and recommended mounting tolerances.
These characteristics do not include codewheel/codestrip contribution. The Typical Values are averages over
the full rotation of the codewheel. For operation above 40 kHz, see frequency derating curves.
Parameter
Pulse Width Error
Logic State Width Error
Phase Error
Symbol
∆P
∆S
∆φ
Typical
5
3
2
Maximum
45
45
15
Units
°e
°e
°e
Note:
3.3 kΩ pull-up resistors used on all encoder module outputs.
Frequency Derating Curves
Typical performance over extended operating range. These curves were derived using a 25 pF load with a
3.3 k pull-up resistor. Greater load capacitances will cause more error than shown in these graphs.
A
0
CHANGE IN PULSE WIDTH ERROR
(ELECTRICAL DEGREES)
CHANGE IN STATE WIDTH ERROR
(ELECTRICAL DEGREES)
B
15
-40 °C
10
+25 °C
5
+85 °C
0
+85 °C
-5
+25 °C
-40 °C
-10
-15
0
50
100
150
200
FREQUENCY (KHz)
-5
0
50
100
150
200
FREQUENCY (KHz)
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