Rotary encoders convert the angular position of a shaft into a digital code. There are two main types: incremental encoders provide position feedback through a series of pulses, while absolute encoders provide a unique code for each position. Encoders are classified based on features like type, size, resolution, speed, and output. Proper selection depends on factors like required precision, load, frequency response, and environmental protection. Omron offers a range of rotary encoders to meet different application needs.

1. Version 1
Jan 07
Rotary Encoder Technical Information
CONFIDENTIAL
OMRON

2. Topics
1.
2.
3.
4.
5.
6.
7.
What is Rotary Encoder
Types of Rotary Encoder
Classifications of Rotary Encoder
Rotary Encoder Terminologies
Application examples of rotary encoder
Omron’s Range of Rotary Encoder
Guidelines for selection of Rotary Encoder

3. 1. What is Rotary Encoder?
 An encoder is a sensing device that provides feedback from the physical
world. It converts motion to an electrical signal which can be read by some
type of control device. This signal can be used to control a conditional
event.
 Many encoder technologies are utilized to create the signal, such as
mechanical, magnetic, resistive and optical. Currently, the most common
technology employed by encoders is optical. Encoders may produce either
incremental or absolute signals.
 A rotary encoder is an electro-mechanical device used to convert the
angular position of a shaft or axle to a digital code commonly used in
robotics, rotating radar platforms & etc.

4. 1. What is Rotary Encoder?
A rotary encoder uses a slotted wheel with a single LED/ photo-detector pair
to generate pulses as the wheel turns.

5. 2. Types of Rotary Encoder
2.1 Incremental Type
2.2 Absolute Type

6. 2. Types of Rotary Encoder - Incremental
2.1 Incremental Type
 Incremental signals provide a series of high and low waves which indicate
movement from one position to the next; there is no special indication
provided by the encoder to show the specific position, only an indication that
the position has changed. They are devices that provide a series of periodic
signals in the form of pulses due to mechanical motion of shaft revolution.
 Speed of an object can be measured by counting the pulses for a period of
time. To calculate angle or the distance covered, pulses are counted starting
from a reference point.

7. 2. Types of Rotary Encoder - Incremental
Construction of Incremental Rotary Encoder
Components inside Incremental Rotary Encoder
Opaque lines

8. 2. Types of Rotary Encoder - Incremental
How Incremental Rotary Encoder works?
 The LED emits light beam which passes through a transparent disk
patterned with opaque lines.
 When the photo sensor receives the light beam, it produces a sinusoidal
wave form, which is transformed into a square wave or pulse train.
 This pulse signal is then sent to the counter or controller which will then
send the signal to produce the desired function.

9. 2. Types of Rotary Encoder - Absolute
2.2 Absolute Rotary Encoder
 Absolute encoders use a unique "word" for each position, meaning that an
absolute encoder provides both the indication that the position has changed
and an indication of the absolute position of the encoder.
 Provides information in the form of unique output for every movement of
the shaft rotation (in Binary, BCD or Gray Code).
 Uses gray code to represent each position.
 Advantage over incremental encoder => Position is maintained after a
power-down. The absolute position is recovered upon power-up without
requiring a home cycle or any shaft rotation.

10. 2. Types of Rotary Encoder - Absolute
3
2
Binary Coding
1
4
2
1
5
8
Black sectors are ‘ON’
Sector
Contact 1
Contact 2
Contact 3
Angle
1
off
off
off
off
off
on
45° to 90°
3
off
on
off
90° to 135°
4
off
on
on
135° to 180°
5
on
off
off
180° to 225°
6
on
off
on
225° to 270°
7
on
on
off
270° to 315°
8
on
on
on
315° to 360
6
0° to 45°
2
3
2 bits change
7

11. 2. Types of Rotary Encoder - Absolute
Binary Coding
From sector 4 to sector 5, it shows that contact 2 and contact 3 changes from
ON to OFF. However in a practical device, the contacts are never perfectly
aligned. They will not switch at the same time but at different time, i.e. only 1
bit changes at a time
For example: If contact 1 switches first, followed by contact 3 and then
contact 2, for example, the actual sequence of codes will be:
Sector 4:
Sector 5:
off-on-on (starting position)
on-on-on (first, contact 1 switches on)
on-on-off (next, contact 3 switches off)
on-off-off (finally, contact 2 switches off)
This behavior is undesirable and could cause the system to fail.
Sector 8
Sector 7

12. 2
2. Types of Rotary Encoder - Absolute
3
Gray Coding
4
1
3-bit Binary-Reflected
Gray code (BRGC)
5
2
3
1
8
Black sectors are ‘ON’
Sector
Contact 1
Contact 2
Contact 3
Angle
1
off
off
off
0° to 45°
2
off
off
on
45° to 90°
3
off
on
on
90° to 135°
4
off
on
off
135° to 180°
5
on
on
off
180° to 225°
6
on
on
on
225° to 270°
7
on
off
on
270° to 315°
8
on
off
off
315° to 360°
6
7
1 bit change from 1 sector to
another

13. 2. Types of Rotary Encoder - Absolute
Gray Coding
 A system of binary counting, in which two adjacent codes differ in only
one position even from sector 4 to sector 5.
 The sequence of incorrect codes shown in the previous illustration cannot
happen here.

14. 2. Types of Rotary Encoder - Absolute
BCD Coding
BCD is Binary Coded Decimal; the output is represented by decimal
numbers (integers) where each digit is signified by four bits

15. 2. Types of Rotary Encoder - Absolute
BCD Coding
Features/ model
E6C3-AB5C
Resolution
6, 8, 12
Output code
BCD
Output code
Resolution (P/R)
Code number
BCD
6
0 to 5
8
0 to 7
12
0 to 11
2
90
3
1
4 180
5
Example: Resolution (P/R): 8 steps
45
135
In this case, each code represents
0 rotation of 360/8= 45°.
0
225
315
270 6
7

16. 3. Classifications of Rotary Encoder
1. By Type
 Absolute
E6A2-C
Compact low cost model
E6B2-C
General Purpose Model
 Incremental
E6C-N
Multi-turn model
E6C3-A
Space-saving model
E6H-C
Hollow Shaft Model

17. 3. Classifications of Rotary Encoder
2. By Size
 25mm dia – E6A2-C
 40mm dia – E6B2-C
E6A2-C
 50mm dia – E6C2-C, E6C3-C, E6C-N, E6CP-A, E6C3-A
E6C-N
 55mm dia – E6D-C
 60mm dia – E6F-C, E6F-A
3. By Shaft Diameter
 4mm – E6A2-C
 6mm – E6B2-C, E6C2-C, E6D-C, E6CP-A
 8mm – E6C3-C, E6H-C, E6C-N, E6C3-A
 10mm – E6F-C, E6F-A
E6F-C

18. 3. Classifications of Rotary Encoder
4. By Resolution / Pulses per Rotation
 Incremental Type => 10, 20, 30, 40, 50, 60, 100, 200, 300, 360, 500, 600,
720, 800, 1000, 1024, 1200, 1500, 1800, 2000, 2048, 2500, 3600, 5000,
6000
 Absolute Type
i) Single-turn
ii) Multi-turn
5. By Maximum Permissible Speed
 1000 r/min , 1500r/min, 5000 r/min, 6000 r/min, 10000 r/min , 12000 r/min
6. By Power Supply Voltage
 5 VDC, 5 to 12 VDC, 5 to 24 VDC, 12 VDC, 12 to 24 VDC

19. 3. Classifications of Rotary Encoder
7. By Output
 Incremental => NPN, PNP, Complementary Outputs (NPN/PNP), Voltage
Output, Line Driver Output, Open-collector Output
 Absolute => BCD, Binary, Gray Code,

20. 4. Rotary Encoder Terminologies
Terms
Explanation
Absolute
Code
1) Binary code
A pure binary code, expressed in the format 2n. Multiple bits may
change when an address changes.
2) Gray code
A code wherein only one bit changes when an address changes.
The code plate of the rotary encoder uses gray code.
3) Remainder gray code
This code is used when expressing resolutions with gray code that are
not 2n such as 36, 360, and 720. The nature of gray code is such that
when the most significant bit of the code changes from "0" to "1" and
the same size of area is used for both the larger value and the smaller
value of objects, the signal only changes by 1bit within this range when
changing from the end to the beginning of a code. This enables any
resolution that is an even number to be set with gray code. Note that in
this case, the code does not begin from place 0, but from an
Intermediate code, and thus when actually using a code it must first be
Shifted so that it starts from "0". The example in the code table shows
36 divisions. With respect to the change from place 31 to 32 here,
(See table)

21. 4. Rotary Encoder Terminologies
Terms
Explanation
when 18 places each are taken for the objects, the code extends from
place 14 to place 49. When changing from place 49 to place 14, only
one bit changes, and we can see that the characteristic of gray code is
preserved. By shifting the code 14 places, it can be converted to a code
that starts from place 0.
4) BCD code
Binary Coded Decimal Code.
Each digit of a decimal number is expressed using a binary code.
Ambient
Temperature
The ambient temperature that meets the specifications, consisting of
the permitted values for the external air temperature and the
temperature of the parts that contact the rotary encoder.
Backup-type
Absolute
Encoder (E6CM)
A rotary encoder with an internal counter IC that can detect multiple
rotation quantity. The E6C-M uses an internal capacitor and the E63SR5C uses an internal lithium battery to back up data when the main
power is off.
CW
Clockwise rotation of rotation.
Viewed from the shaft axis, the shaft rotates to the right.
With the incremental type, the A phase normally leads the B phase in
this rotation direction.

22. 4. Rotary Encoder Terminologies
Terms
Explanation
With the absolute type, this is the direction of code increase.
The reverse of CW rotation is counterclockwise (CCW) rotation.
Hollow Shaft
Type
The rotating shaft is hollow, and the drive shaft can be directly
connected to the hollow hole to reduce length along the direction of the
shaft. A leaf spring is used as a buffer to absorb vibration from the drive
shaft.
Maximum
Response
Frequency
The maximum frequency at which the signal can respond.
Metal Disk
The rotating slit desk in the encoder is made of metal for higher shock
tolerance than glass. Due to slit machining limitations, the metal disk
cannot be used for high-resolution functions.
Moment of
Inertia
The inertia of a rotating body. This expresses the magnitude of inertia
when starting and stopping.
Output Circuit
1)
Open Collector Output
An output circuit where the emitter of the output circuit transistor
is common and the collector is open.

23. 4. Rotary Encoder Terminologies
Terms
Explanation
2)
3)
Voltage Output
An output circuit where the emitter of the output circuit transistor
is common and a resistor is inserted between the collector and
the power supply to convert the output from the collector to a
voltage.
Line Driver Output
An output method that uses a special IC for high-speed, longdistance data transmission, which complies with the RS-422-A
standard. The signal is output as a differential second signal, and
thus is strong with respect to noise. A special IC called a line
receiver is used to receive the signal output from a line driver
Output Duty
Ratio
The ratio of the duration of H level during one period to the average
period of pulse output when the shaft is rotated at constant speed.
Output Phase
The output signal count in the case of the incremental type.
Types include a 1-phase type (A phase), 2-phase type (A phase, B
phase) and a 3-phase type (A phase, B phase & Z phase). The Z
phase is a zero position signal that is output once a revolution.

24. 4. Rotary Encoder Terminologies
Terms
Explanation
Output Phase
Difference
The time difference between the rise and fall of A phase & B phase
signals when the shaft is rotated. Expressed as a proportion of the
period of one signal, or as an electrical angle where one signal period
equals 360°. The difference between A phase & B phase as an
electrical angle is normally 90°.
Resolution
The pulse count of an incremental signal output when the shaft
revolves once, or the absolute address count.
Rise Time/
Fall Time
The elapsed time from 10% to 90% of the output pulse.
Serial
Transmission
In contrast to parallel transmission where multiple bits of data are
simultaneously output, this output method outputs data serially
from a single transmission line, enabling the use of less wires.
The receiving device converts the signals into parallel signals.
Servo Mount
This is a method of mounting the encoder whereby the servo mount
fittings are used to clamp down the flange of the encoder. The
position of the encoder in the direction of rotation can be
adjusted, and thus this method is used to temporarily mount the
encoder for adjustment to the zero position.

25. 4. Rotary Encoder Terminologies
Terms
Explanation
Shaft Capacity This is the load that can be applied to the shaft. The radial load is the
load that is perpendicular to the shaft, and the thrust is the load in the
direction of the shaft. Both are permitted on the shaft during rotation,
and the size of the load affects the life of the bearings.
Startup
Torque
The torque needed to rotate the shaft of the rotary encoder at startup.
The torque during normal rotation is normally lower than the startup
torque. A shaft that has a waterproof seal has a higher startup torque.

26. Absolute Code Table

27. 5. Application example of Rotary Encoder

28. 6. Omron’s Range of Rotary Encoder

29. 7. Guidelines for Selection of Rotary Encoder
1. Incremental Type / Absolute Type
Select a type that is suitable in terms of cost vs capacity, return (or not) to home
position at startup, speed limit & noise tolerance.
2. Resolution Required
Select the optimal model in view of required precision and cost of machine
equipment. It recommends selecting the resolution from ½ to ¼ in integrated
precision of a machine.
3. External Dimensions
4. Permitted Shaft Load
Take into consideration how the mounting method affects the load on the shaft and
mechanical life.
5. Maximum Permitted Number of Revolutions

30. 7. Guidelines for Selection of Rotary Encoder
6. Maximum Response Frequency
Maximum Response Frequency =
Number of rotations
60
x Resolutions
7. Degree of Protection
IP50 – Dust proof only
IP52 – Existence of oil & water
IP64 – Oil & water resistance
8. Startup Rotational Torque of Shaft
9. Output Circuit Type
For long distance transmission, line driver output is recommended.