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Encoder and Applications Overview

Encoder and Applications Overview

An encoder is an electromechanical device that can measure motion or position. Most encoders
use optical sensors to provide electrical signals in the form of pulse trains, which can, in turn, be 
translated into motion, direction, or position.

Rotary encoders are used to measure the rotational motion of a shaft. the figure below shows the fundamental components of a rotary encoder, which consists of a light-emitting diode (LED), a disk, and a light detector on the opposite side of the disk. The disk, which is mounted on the rotating shaft, has patterns of opaque and transparent sectors coded into the disk. As the disk rotates, the opaque segments block the light and, where the glass is clear, light is allowed to pass. This generates square-wave pulses, which can then be interpreted into position or motion.  

Encoders usually have from 100 to 6,000 segments per revolution. This means that these encoders can provide 3.6 deg of resolution for the encoder with 100 segments and 0.06 deg of resolution for the encoder with 6,000segments.  

 Linear encoders work under the same principle as rotary encoders except that instead of a rotating disk, there is a stationary opaque strip with transparent slits along its surface, and the LED-detector assembly is attached to the moving body.  

An encoder with one set of pulses would not be useful because it could not indicate the direction of rotation. Using two code tracks with sectors positioned 90 deg out of phase, the two output channels of the quadrature encoder indicate both position and direction of rotation. If A leads B, for example, the disk is rotating in a clockwise direction. If B leads A, then the disk is rotating in a counter-clockwise direction. Therefore, by monitoring both the number of pulses and the relative phase of signals A and B, you can track both the position and direction of rotation.

In addition, some quadrature encoders include a third output channel – called a zero or reference signal – which supplies a single pulse per revolution. You can use this single pulse for precise determination of a reference position. In the majority of encoders, this signal is called the Z-Terminal or the index.

So far, this document has addressed only what are called single-ended incremental quadrature encoders. These are called single-ended because the A and B signals are both referenced to ground, so there is one wire (or end) per signal. Another commonly used type of encoder is a differential encoder, where there are two lines per each A and B signal. The two lines for the A signal are A’ and A, and the two lines for the B signal are B’ and B. This type of configuration is also called push-pull because all four lines are always supplying a known voltage (either 0 V of Vcc). When A is Vcc, A’ is 0 V , and when A is 0 V, A’ is Vcc. In the case of a single-ended encoder, A is either Vcc or it floats. Differential encoders are often used in electrically noisy environments because taking differential measurements protects the integrity of the signal.

With incremental encoders, you can measure only changes in position (from which you can determine velocity and acceleration), but it is not possible to determine the absolute position of an object. A third type of encoder, called an absolute encoder, is capable of determining the absolute position of an object. This type of encoder has alternating opaque and transparent segments like the incremental encoder, but the absolute encoder uses multiple groups of segments that form concentric circles on the encoder wheel like a bull’s-eye on a target or dartboard. The concentric circles start in the middle of the encoder wheel and, as the rings go out toward the outside of the ring, they each have double the number of segments than the previous inner ring. The first ring, which is the innermost ring, has one transparent and one opaque segment. The second ring out from the middle has two transparent and two opaque segments, and the third ring has four of each segment. If the encoder has 10 rings, its outermost ring has 512 segments, and if it has 16 rings, the outermost ring has 32,767 segments.

Because each ring of the absolute encoder has double the number of segments of the prior ring, the values form numbers for a binary counting system. In this type of encoder, there is a light source and receiver for every ring on the encoder wheel. This means that the encoder with 10 rings has 10 sets of light sources and receivers, and the encoder with 16 rings has 16 light sources and receivers.  

The advantage of the absolute encoder is that you can gear it down so that the encoder wheel makes one revolution during the full length of machine travel. If the length of machine travel is 10 in. and its encoder has 16-bit resolution, the resolution of the machine is 10/65,536, which is 0.00015 in. If the travel for the machine is longer, such as 6 ft, a coarse resolver can keep track of each foot of travel, and a second resolver called the fine resolver can keep track of the position within 1 ft. This means you can gear the coarse encoder so that it makes one revolution over the entire 6 ft distance and gear the fine encoder so that its entire resolution is spread across 1 ft (12 in.)  

  

Things to Know About the Application  

Specifying an encoder starts with the needs of the application. Key factors to consider include:

● Environmental conditions, including temperatures, moisture, shock and vibration,
contamination

● Type of motion: unidirectional or bidirectional, etc.

● Magnitude of the motion and sensitivity to rehoming

● Mechanical design, including compliance in the system

● Electrical requirements of drives and controllers

● Physical configuration, including form factor, physical distance between encoder and
controllers

● Budget  

Collect as much information as possible before reviewing models or calling your vendor – you

want to make an informed decision.

What are the Environmental Characteristics?

The environmental conditions of the application drive the most fundamental encoder choice: type of sensor engine. The most common sensor engines are optical, magnetic, and inductive. Capacitive encoders do exist but they will not  covered in this tutorial.  

Optical Encoders  

How They Work: In an optical encoder, a patterned disc attached to the object being monitored (typically the motor shaft or the load) passes between a source (typically an LED) and a photodetector fixed to the body of the encoder. The patterning of the disc either chops the beam to generate a train of square wave pulses or generates a binary digital word. In either case, the control/readout uses this data to determine position, and possibly speed. In a linear optical encoder, both source and detector move with the load while the linear scale that generates the output is fixed to the machine frame

Pros: Optical encoders offer the highest resolution of this class of feedback devices. As
such, they can be very good for scientific and demanding industrial applications that require
tracking angular position to the order of fractions of degrees.

Cons: On the downside, optical encoders are sensitive to contamination and should not be
used for applications exposing them to dust, moisture, or corrosive chemicals. Optical
encoders with glass code discs are vulnerable to shock and vibration. These days, mylar code
discs are more commonly used and more robust to a shock and vibration.

Best Used For: Scientific applications and industrial applications with very demanding output
performance.  

Magnetic EncodersHow They Work: 

Magnetic encoders operate analogously to optical encoders. Instead of
optical code discs, magnetic rotary encoders use a different structure to perturb the magnetic
field, such as a toothed ferrous metal gear, or drums or discs patterned with alternating
magnetic domains; linear versions use linear scales. The alternating domains create a varying
magnetic field that can be detected using any of several technologies, including simple
magnetic pickups, or magneto restrictive detectors that offer better high-speed performance.
Alternatively, the Hall-Effect sensor leverages a solid-state detector array that provides an
economical, robust solution that combines high sensitivity and resolution with better
tolerance of high shock loads.

Pros: Magnetic encoders can withstand extremely harsh conditions, making them good fits
for industrial applications. They can operate under water, covered with dust, and exposed to
very high vibration. They are quite economical, making them suitable for budget
applications.

Cons: Sensitive to high magnetic fields and may require shielding. Very high shock loads
can demagnetize the magnetic domains, as can very high temperatures; as mentioned,
Hall-effect sensors are less vulnerable to shock loads. According to traditional thinking,
magnetic encoders only provide moderate resolution. Once again, Hall-effect sensors provide
improved performance. For demanding applications in extremely dirty environments, a
Hall-effect sensor may be the ideal choice.

Best Used For: Industrial applications with harsh environments.  

Inductive Encoders

How They Work: Inductive encoders are closely related to resolvers, which are differential
transformers that determine absolute angular position of a rotating load by tracking the
voltages induced in a pair of “readout” coils. The primary coil is attached to the rotor and
energized, while the secondary sine and secondary cosine coils are attached to the stator.
Rotation of the primary coil induces current in the secondary coils. As this derivation shows,taking the arctangent of the ratio of the sine coil voltage and the cosine coil voltage yields the
angle. Resolvers are extremely rugged but can be difficult to install. Inductive encoders were
designed to address this drawback.

An inductive encoder is a solid-state implementation of a resolver. Instead of conventional
coils, the coils are flat elements lithographically patterned onto a PCB. All three coils are on
the same PCB and mounted to the stator. A conductive disk mounted to the rotor or shaft
excites the coils.

Pros: Very high resolution. Robust to contamination, liquid ingress, extreme temperatures,and shock and vibration. Easier to use than resolvers and more compact, particularly eddy-current designs which use ironless thin films just 100 µm thick for the conductive disk.

Cons: Although the inductors are robust, the conductive disk can still create issues. Proper
choice of the conductive disk is essential. Applications with thermal extremes should not use
soft iron code discs. Ferrous or ferrite code discs may still be used in high magnetic fields but
might require shielding.Best Used For: applications with harsh conditions and high resolution/accuracy demands. 

How to choose a rotary encoder?

When choosing a rotary encoder, you should first determine whether you should use an incremental encoder or an absolute one.
• An incremental rotary encoder provides pulses according to the rotation of the axis. A pulse
or increment is a square digital signal. The encoder resolution corresponds to its number of
increments per revolution It must be reset each time the power supply is interrupted.
• An absolute rotary encoder integrates its own counter, in the sense that it saves the last valurecorded if the power supply is interrupted.

An incremental rotary encoder is more affordable, but you should choose an absolute rotary
encoder if:


• Resetting the rotary encoder is detrimental to your application;
• Your signal processing system may be disturbed by noise that could generate false pulses;
• There is a high risk of not counting pulses (for example at high frequencies);
• The rotary motion is oscillating and does not correspond to a complete rotation;
• It is important to know the real position of the axis at all times;
• It is necessary to count the number of revolutions completed. In this case, you should select a
multiturn absolute rotary encoder.

When choosing a rotary encoder, you should also determine the size according to the system it
will be integrated into. You will need to determine its space requirement, that is the housing
diameter and length as well as the diameter of the output shaft (whether solid or hollow).

Finally, it will be necessary to identify the environmental and mechanical constraints that the encoder will have to face in order to choose the appropriate level of protection. 

What is an Incremental Encoder? 

An incremental encoder is a type of encoder device that converts angular motion or position of a
shaft into an analog or digital code to identify position or motion. Incremental encoders are one
of the most commonly used rotary encoders.


An incremental encoder can be used in positioning and motor speed feedback applications which
includes servo/light, industrial or heavy-duty applications.

An incremental encoder provides excellent speed and distance feedback and, since there are few sensors involved, the systems are both simple and inexpensive. An incremental encoder is limited by only providing change information, so the encoder requires a reference device to calculate motion.

How does an incremental rotary encoder work?

The incremental rotary encoder measures an angular displacement with respect to a reference
position. After a power failure, the data processing system must wait for the encoder to send the
information corresponding to the reference position in order to correctly exploit the angular
displacement information.


Incremental rotary encoders are designed using different technologies, each with its own
advantages and disadvantages. The most common technologies used are:


• Optical incremental rotary encoders: these encoders use light-emitting diodes (LEDs) to
“read” the angular displacement. These rotary encoders are affordable and offer high resolution
(high precision). This technology is widely used in industry, but the optical scanning system can
be disrupted if the environment presents a risk of corruption (dust, oil, etc.).
• Magnetic incremental rotary encoders: the pulses are emitted by magnets. This technology is
also commonly used in industry because magnetic encoders are less subject to the risk of fouling.
Regardless of the operating principle of the rotary encoder, the output signal is a series of pulses
that make up a binary code, i. e. a succession of 1 and 0 corresponding to the angular
displacement, depending on the encoder’s resolution. This signal can be used to determine the
direction of travel, the value of travel in relation to the reference position, the speed or the
acceleration.

With an incremental encoder, you can connect the encoder wires to the inputs of a PLC. Which
inputs you should use are determined by the encoder’s operating frequency. This frequency is
proportional to the rotational speed of the axis and the resolution of the encoder. In the case of a
high frequency, the signal corresponding to the reference position is used to correct counting
errors for certain pulses that aren’t taken into account.

Generally, a rotary encoder has 5 to 12 outputs (wires or connector terminals), which must be
connected to a counter. In the case of an encoder with 5 outputs, two wires are used for the
power supply and the other three to send the signals corresponding to the angular displacement.  

Incremental Rotary Encoder Alternatives

While incremental encoders are commonly used in many feedback applications, resolvers and
absolute encoders provide alternatives depending on the application requirements and
environment.  

Incremental Encoders vs Resolvers

Resolvers are electro-mechanical precursors to encoders, based on technology going back to
World War II. An electrical current creates a magnetic field along a central winding. There are
two windings that are perpendicular to each other. One winding is fixed in place, and the other
moves as the object moves. The changes in the strength and location of the two interacting
magnetic fields allow the resolver to determine the motion of the object.


The simplicity of the resolver design makes it reliable in even extreme conditions, from cold and
hot temperature ranges to radiation exposure, and even mechanical interference from vibration
and shock. However, the forgiving nature of resolvers for both origin and application assembly
comes at the expense of their ability to work in complex application designs because it cannot
produce data with enough accuracy. Unlike incremental encoders, resolvers only output analog
data, which can require specialized electronics to connect with.  

Incremental Encoders vs Absolute Encoders

Absolute Encoders work in situations where accuracy for both speed and position, fail tolerance,
and interoperability matters more than system simplicity. The absolute encoder has the ability to
"know where it is" in reference to its position in case of system power-down and restart if the
encoder were to move during a power-down.

The absolute encoder itself understands the positioning information – it doesn’t need to rely on
outside electronics to provide a baseline index for the encoder position. Especially when
compared to resolvers and incremental encoders, the obvious strength of absolute encoders is
how their positioning accuracy affects the overall application performance, so it is typically the
encoder of choice for higher precision applications such as CNC, medical and robotics.  

Incremental Encoder Uses & Applications


An Incremental Encoder is designed to be versatile and customizable to fit a wide variety of
applications. The three broad categories of applications based on environment are:

● Heavy Duty: demanding environment with a high probability of contaminants and
moisture, higher temperature, shock, and vibration requirements as seen in pulp, paper,
steel, and wood mills.

● Industrial Duty: general factory operating environment which requires standard IP
ratings, moderate shock, vibration, and temperature specs as seen in food and beverage,
textile, generally factory automation plants.

● Light Duty/Servo: controlled environment with high accuracy and temperature
requirements such as robotics, electronics, and semiconductors.  

What is an Absolute Encoder ?

Absolute encoders are feedback devices that provide speed, position information by outputting a
digital word or bit in relation to motion. Unlike incremental encoders that output a continuous
stream of ubiquitous pulses, absolute encoders output unique words or bits for each position. 

By outputting a digital word or bit instead of a stream of pulses, absolute rotary encoders offer
several advantages:

● Higher overall resolution vs incremental encoders

● Better start up performance because of low homing (or initial position) time

● Accurate motion detection along multiple axes

● Multiple output protocols for better electronics integration

● Better recovery from system or power failures


Types of Absolute Encoders

Absolute encoders can be categorized based on their sensing technology type (optical or magnetic) or their output over multiple turns of the motor shaft (single-turn or multi-turn) Optical absolute encoders use a code disc with markings and an LED that shines light through the code disc. As the disc turns with the motor shaft, changes in positions can be detected. For magnetic absolute encoders, the optical markers are replaced by magnetic poles and the LED is replaced by a magnetic sensing array.

While all absolute rotary encoders provide feedback based on the rotation of shaft (position of the encoder within 360 degrees or single turn), applications differ based on the requirement to know how many times the encoder has made a complete rotation or multiple turns. Multi-turn absolute encoders offer additional feedback for the number of 360 degree turns.  

How does an absolute rotary encoder work?

An absolute rotary encoder indicates an angular position as soon as it is switched on. It
continuously delivers a signal that corresponds to the real position of the axis to which it is
connected. There are two types of absolute encoders:

1. A single turn rotary encoder indicates the position of the axis. The value sent by the
encoder is the same for each revolution. A simple single-turn rotary encoder makes it
possible to know the position of the axis at any time (even when stationary), in addition
to information related to angular displacement.

2. A multi-turn rotary encoder integrates secondary rotary encoders to indicate the
number of revolutions performed in addition to the position of the axis.
As with incremental rotary encoders, the technology mainly used for absolute rotary encoders is
optical which offers a high level of accuracy, but may be sensitive to a risk of corruption from
dust, oil, etc., and magnetic.


With an absolute rotary encoder, the axis position is defined by a unique code that is sent as soon
as the encoder is powered on. It can be operated as is or transformed to be transmitted as a digital
signal through a fieldbus system such as SSI, CANopen or Profinet.  

Advantages of Absolute Encoders

Absolute encoders offer unique advantages over incremental encoders. They have a unique code
for each shaft position, meaning that they can provide very unique position information as no
two positions on a track are identical. They measure actual position by generating a stream of
unique digital codes that represent the encoder’s actual position and therefore do not require an
index or reference point. This also provides absolute encoders an advantage in applications
returning to a home position may present issues in the event of a power loss.

Absolute encoders also offer higher resolution options compared to incremental encoders. While
incremental encoders must add more increments to a single track on a code disc and are thereby
limited to the physical size of the disc and the number of pulses that can be decoded vs the
rotating speed of the encoder (frequency response), absolute encoders add additional tracks to
achieve higher resolutions and do not continuously output a stream of pulses. Instead they are
limited by the number times the encoders is interrogated within a given sample period of baud
rate.  

Absolute Situations: When You Need Absolute Encoders  

The absolute rotary encoder itself understands the positioning information – it doesn’t need to
rely on outside electronics to provide a baseline index for the encoder position. Absolute
encoders enable applications which rely on non-linear positioning to work without additional
external components.


In real life, absolute encoders allow more precision work from applications:

● Determining multi-axis orientation for CNC machines used in parts manufacturing

● Automatically determining the height of scissor beds used in hospitals

● Accurately positioning multiple stabilizers for large vehicles like cranes or aerial lifts

● Moving automatic doors or bays without a limiting switch

● Continuing robotic movement cleanly even after a power failure

Especially when compared to resolvers and incremental encoders, the obvious strength of absolute encoders is how their positioning accuracy affects the overall application performance.

What is the resolution of a rotary encoder?

The resolution of a rotary encoder corresponds to the maximum number of points it can measure
over a revolution. For an incremental rotary encoder, the resolution is directly linked to the
number of pulses it delivers per revolution. For an absolute rotary encoder, it is linked to the
number of bits coding is performed on. For example, a 16-bit encoder will have a resolution of
65,536 dots per revolution.

You should choose an encoder resolution that will meet the requirements of your application and
the accuracy of the mechanical components that form the measuring chain. The encoder is
connected to an electronic device, controller or counter, which has a maximum input frequency
that must be respected. A high-resolution incremental encoder provides a greater number of
pulses over a revolution than a low-resolution incremental encoder. Depending on the rotational
speed imposed by the application, the encoder output signal may have a higher frequency than
the device connected to the encoder is able to handle. In this case, you will need to use a rotary
encoder with a lower resolution  

 

How Much Resolution Do You Need?

Choice of resolution is probably the biggest pitfall in specifying an encoder. There’s a
widespread assumption that a higher resolution encoder will automatically increase positioning
accuracy. That’s not necessarily the case. The accuracy of any positioning system is limited by
the mechanics. Even the highest resolution encoder will be ineffective if there is so much
compliance in the system that it can’t reliably position to the accuracy required.

To determine resolution, start by determining the smallest detection distance required by the
application. Choosing a resolution that is about four times that minimum increment is a good rule
of thumb. It could be boosted up to a factor of 10 for sensitive applications. Much higher than
that will most likely be useful only in a handful of cases. Rotary incremental encoders are
specified in terms of pulses per revolution (PPR). This refers to the number of lines patterned on
the code disc.linear incremental encoders are specified in terms of lines per unit length.  

There is a wide difference between the resolution required for the application and the resolution
that can actually be achieved in the real system. For a rotary incremental encoder, the angular
speed of the application (RPM) and the electronics bandwidth, or operating frequency (hertz),
control the number of pulses that can be transmitted by the hardware. We can calculate the
resolution that is physically possible for a given an encoder using the following formula for
maximum line count:

Operating frequency is internal to the encoder electronics. It is provided by the manufacturer,
and is typically on the order of kilohertz or megahertz. If you need high resolution output for a
high-speed system, look for an encoder with a faster operating frequency.

To simplify encoder selection, manufacturers provide data plots of resolution as a function of
speed. Again, these data plots are specific to a given encoder and make it possible to balance
between speed and performance.  

Adding lines is not the only way to increase resolution. Resolution is a function of both PPR and
how the signal from the photodetector is read out. The latter is referred to as decoding and
depends upon what parts of the signal the system uses to trigger readout.


There are three formats typically used. Triggering off of the rising edge of channel A (1X
decoding) provides a resolution equal to the PPR of the code disc. Triggering off of the rising
and falling edges of channel A (2X decoding) provides the actual resolution of twice the PPR.
Triggering off the rising and falling edges of both channel A and channel B (4X decoding) gives
a resolution quadruple that of the PPR. Depending on the application, it may be a good way to
boost resolution with minimum additional cost.  

That said, the approach involves trade-offs. For OEMs confident of the resolution they need, a
higher actual resolution rather than one generated through software may be less prone to error.
There are techniques that can be used to reduce noise over long cable runs.  

How to assemble a rotary encoder?

Assembling a rotary encoder depends on its form. It is therefore important to determine how the
rotary encoder will be connected to the axis to be measured.
There are three main types of assemblies:

1. A rotary encoder with a solid shaft that can come in different shapes such as a truncated
cylinder, square or hexagon. This type of encoder can be mounted at the end of a hollow
axle or, for example, in a gear pinion.
2. A rotary encoder with a hollow shaft, in which an axle can be inserted.
3. A rotary encoder in two parts. This includes a disc that is mounted at the end of the axis
and a “pick-up head” that will be fixed above the disc

 

What is A Motor Encoder?

A motor encoder is a rotary encoder mounted to an electric motor that provides closed loop
feedback signals by tracking the speed and/or position of a motor shaft. There are a wide variety
of motor encoder configurations available such as incremental or absolute, optical or magnetic,
shafted or hub/hollow shaft, among others. The type of motor encoder used is dependent upon a
number of factors, particularly motor type, the application requiring closed-loop feedback, and the mounting configuration required.

How to Specify A Motor Encoder

When selecting components for a closed loop control system, the motor encoder choice is first
determined by the type of motor chosen in the application. The most common motor types are:  

AC Motors Encoders

AC induction motors are popular choices for general automation machine control systems as
they are economical and rugged. Motor encoders are used for more precise speed control in
applications using AC motors, and often times need to have more robust IP, shock and vibration
parameters.  

Servo Motor Encoders

Servo motors encoders (permanent magnet motor encoders) offer closed loop feedback control
systems to applications that require higher precision and accuracy, and are not as robust as AC
induction motors. The motor encoder used on servo motors can be modular, incremental or
absolute depending on the level of resolution and accuracy required.  

Stepper Motor Encoders

Stepper motors are cost effective, precise, and are typically used in open-loop systems. In
systems using stepper motors where speed control is required, an incremental motor encoder is
often mounted to this motor and will allow the stepper motor system to achieve closed loop
feedback. Stepper motor encoders can also be used in some applications to allow for improved
control of stepper motors by providing precision feedback of the location of the motor shaft in
relation to the step angle. 

DC Motor Encoders

DC motor encoders are used for speed control feedback in DC motors where an armature or rotor
with wound wires rotates inside a magnetic field created by a stator. The DC motor encoder provides a mechanism to measure the speed of the rotor and provide closed loop feedback to the drive for precise speed control. 

Motor Encoder Mounting Options

The next factor impacting motor encoder selection is the mounting option, and the most common
options are:

Shafted Motor Encoders: Uses a coupling method to connect the motor encoder shaft to
the motor shaft. The coupling provides mechanical and electrical isolation from the motor
shaft but can add cost via the coupling and the longer shaft length required to mount the
motor encoder

Hub/Hollow shaft Motor Encoders: Hollow shaft encoders directly mount to the motor
shaft via a spring loaded tether. This method is easy to install and required no shaft
alignment, but proper care must be taken to provide electrical isolation.

Bearingless Motor Encoders: Also known as ring mount, this mounting option is
comprised of a sensor assembly in the form of a ring that is mounted on the motor face,
and a magnetic wheel which is mounted on the motor shaft. This type of motor encoder
mounting configuration is mostly found in heavy duty applications like paper, steel and cranes.  

What is Video Encoding?

In the most basic sense of the term, video encoding is compressing video files so that they are
not saved as individual images but as fluid videos. Here’s one definition of video encoding.

In video editing and production, video encoding is the process of preparing the video for output,
where the digital video is encoded to meet proper formats and specifications for recording and
playback through the use of video encoder software.

In the early days of digital video, video files were all RAW video. This means that video files
were a collection of still photos. For a video recorded at 30 frames per second, you had 30 photos
per second of footage. That’s 1800 images per minute of video. As a result, video file sizes were
massive. The only sensible solution was to compress these videos, but the quality was lost
through this process. Engineers developed video encoding which provided a way to compress these files without compromising the quality.

What is Video Compression?

Video compression is using encoding to reduce the size of a digital video file.
It analyzes the content of a video to reduce the overall file size by determining which frames are
essential and which can go. If two frames are basically identical, you can get rid of the data for
one frame and replace it with a reference to the previous frame. In this simple example, you can
reduce your video file size by about 50 percent. All types of video compression use variations of
this process to reduce file sizes. When we talk about video encoding, however, we’re referring to a specific type of video compression

Video Encoding vs. Transcoding: What’s the Difference?  

It’s fairly common to hear the terms video encoding and transcoding used interchangeably. However, encoding and transcoding are not one and the same.

● Transcoding is the process of creating copies of video files in different sizes.

● Encoding refers to either the initial process of compressing RAW video or to the
process of re-encoding a video into a different format.

Transcoding is always encoding, but encoding is not always transcoding. There are a variety of
reasons why you might want to transcode or encode a video:

● Reduce file size

● Reduce buffering for streaming video

● Change video resolution or aspect ratio

● Change audio format or quality

● Convert obsolete files to modern formats

● Meet a certain target bit rate

● Make a video compatible with a certain device (computer, tablet, smartphone,

smartTV, legacy devices)

● Make a video compatible with certain streaming software or service

What is printer encoder strip?

The Linear Encoder Strip is a plastic film in your printer that is etched with several vertical
lines that are read by an encoder sensor located on the print head carriage, which distributes ink to the page

How does printer encoder work?  

A linear encoder is a sensor, transducer or readhead paired with a scale that encodes position. The sensor reads the scale in order to convert the encoded position into an analog or digital signal, which can then be decoded into position by a digital readout (DRO) or motion controller.

Questions to Ask When You Need a Rotary Encoder

Choosing the correct industrial encoder is easy when you know the answers!  

There are many reasons why you may need a rotary encoder, but what questions should you ask
to determine which one is the most appropriate? Here are seven questions that can help you make
the best decision:

1. Do I need an incremental encoder or an absolute encoder?
2. What output do I need?
3. What resolution does the application call for?
4. How will I mount this encoder?
5. How will I connect the encoder to my controls?
6. What environmental and mechanical stresses does the encoder need to withstand?
7. Does this encoder need safety or hazardous location approvals?

This is a good starting point to determine the right encoder characteristics for your application. Let's go through each question and explore the many options you have when selecting an industrial rotary encoder.  

1. Do I need an incremental encoder or an absolute encoder?

Incremental and absolute encoders can be used for speed, direction, and position. The absolute
encoder
will retain your position after power loss and an incremental encoder will not. The incremental encoder usually needs to perform a “homing” sequence after a power loss.

Absolute encoders have an option of 16 bits (65536) per turn which provide higher resolution
than incremental encoders. Incremental encoders are generally less expensive and the output
needed is a square wave or sine/cosine for counting, speed, and direction. Absolute encoders are
normally used for continuous position and possess other attributes such as speed, scaling, preset,
and fieldbus functions.  

2. What output do I need?

For incremental encoder output, there are open collector (OC), push-pull, line driver, and
sine/cosine. The open collector (OC) has lower leakage current and less voltage drop than
push-pull, but push-pull output has better immunity and slew rate. Push-pull can be NPN
(sinking) or PNP (sourcing), and therefore has better flexibility in matching an input of your
controller or counter. The line driver has a high level of immunity (higher than open collector
and push-pull) so this should be used for longer cable runs. The sine/cosine is used for speed and
position computation. Some motor drive and safety systems have sine/cosine inputs.

For absolute encoder output, selecting a specific fieldbus is necessary. There are many to choose
from such as Ethernet (EtherNet/IP, TCP/IP, PROFINET, Powerlink), CANopen, PROFIBUS,
DeviceNet, SSI, AS-Interface, and Parallel. The fieldbus is usually chosen as a preference, to match existing hardware, or is mandated by the company (that the equipment is for).

3. What resolution does the application call for?

The incremental encoder can have 50,000 pulses per revolution (ppr) and an absolute encoder
can have 16 bits (or 65536) per revolution (turn). To determine the resolution, the circumference
of the rotating part (whether it’s a pulley, gear, measuring wheel, or cable-pull) will need to
divide by the pulses per turn of the encoder. For example, if you had a 200 mm circumference
measuring wheel and an incremental encoder with 5000 ppr, the resolution would be 0.04 mm.

The resolution also depends on the precision of the mechanical and electrical components being
used as well as the needed resolution to solve a problem or to meet the process demand. In
certain instances, some controllers cannot handle the frequency response of a high-resolution
incremental encoder, so a lower-resolution encoder would need to be chosen. The specification
of the controller/counter input response time would need to be compared with the maximum speed (RPM) of the application along with the pulse count of the encoder.

4. How will I mount this encoder?

The encoder can be selected with a solid shaft, hollow shaft, or recess-hollow shaft. The hollow
shaft and recess hollow shaft are quick and easy to mount. But if there is movement or “run-out”
in the shaft, the solid shaft with the appropriate coupling would be the better solution. A coupling
can have a radial offset of +/- 1.5 mm, an axial offset of +/- 1 mm, and can have an angular error
of 5 degrees. This may be enough flexibility to help prevent overloading the bearings of the
encoder. There are magnetic encoders that have targets that mount as a hollow shaft and the
“sensor” is mounted next to the magnetic target. These types of magnetic encoders eliminate
mechanical wear, but there are tolerances between the magnetic target and the sensor that need to
be observed.  

5. How will I connect the encoder to my controls?

The encoders can be selected with cable or connector. If you choose the connector option, you
will need a mating connector or a cordset (both connector and cable). This will give you a
connection point to the encoder but does not necessarily get you all the way to your control
cabinet. Depending on the distance, you may need a junction box, conduit, and cable tray. Care
should be taken when routing encoder cable to reduce the influence of "noise". To reduce this
influence, the cable should have a braided shield around the wires and the wires should be
twisted pair. The encoder cable should be in a conduit with only low DCV cables and keep AC
and high-power cables separated. If there are cable trays with AC and DC cables, there should be
a grounded metal divider between the DC and AC cables. If the encoder cable does need to cross
an AC cable, it should cross perpendicular (90 degrees to each other). The shield should be
connected to one earth ground location in your control cabinet (so it has a star topology). 

6. What environmental and mechanical stresses does the encoder need to withstand?

Not all encoders are created equal. The less expensive encoders do not have the same
environmental (IP) protection and mechanical resistance as the higher priced harsh-duty
designed encoders. To answer this question completely, the questions “What resolution does the
application call for?” and “How will I mount this encoder?” need to be answered. The answer to
these questions helps determine how much movement (“run-out”) there is and the speed of the
shaft. These values, shaft speed and run-out, help in determining the shaft loads and angle offset
that the encoder bearing will be exposed to. The vibration of the machine should also be
measured by using an accelerometer.


For the environmental aspects, the amount of moisture, duration of moisture, chemicals, and cleaning regimen need to be verified. The IP54 rating is good for most applications with minimum moisture exposure, but if moisture is present for a longer duration, then you should select IP65 or higher. For high-pressure washdown, the encoder should have an IP69K rating. 

7. Does this encoder need safety or hazardous location approvals?

The safety approval is related to a person’s safety and hazardous location approval is for an area
with possible explosive gas or dust. The safety incremental encoders usually have sine/cosine
output, which would be processed by a safety speed monitor or safe drive. Usually, safety
encoders have SIL3 (EN 62061) and PLe (IEC 13849) type standards.


There are many hazardous approvals, i.e., Ex (ATEX), FM, UL, CSA, NEMA, SIL2 (IEC
61508), and SIL3 (IEC 61508).


There are Zone and Division methods for the time duration of the hazardous material (explosive gas or dust) being present. The Division method is usually used by North American companies and the Zone method is usually used by European companies. Having both Zone and Division approvals is becoming more important.


Division 2 and Zone 2 is when ignitable mixture is not normally present, Zone 1 is when
ignitable mixture is present intermittently, Zone 0 is when ignitable mixture is present
continuously (for long periods), and Division 1 is when ignitable mixture is present
intermittently and continuously (for long periods). A qualified person will need to analyze the
safety and hazardous location to determine the proper classification.  

6th Sep 2021 Sadia Naseer

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