What is an Encoder?
An encoder is a device that senses mechanical motion. It translates mechanical motion such as position, speed, distance, and direction into electrical signals.
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Table of Contents
Table of Contents
PRODUCT SPOTLIGHT:
CAPACITIVE INCREMENTAL ENCODERS
Introduction
Welcome to the CUI Devices product spotlight on capacitive incremental encoders. This presentation will provide an overview of encoder technology and their function, including an introduction to the features and benefits of CUI Devices' AMT capacitive incremental encoder series.
Objectives
- Describe the functional theory of encoders
- Understand the benefits of AMT capacitive encoders
- Explain the different components that make up the AMT series
- Describe AMT encoder installation and assembly
- Illustrate the flexible options available with each AMT incremental encoder series
How An Encoder Functions
Inside a rotary encoder there is a disc fixed to a shaft that is free to rotate. On one side of the disc is a signal source, on the other side a receiver. As the disc turns, the signal source is alternately allowed to pass and be blocked. When the signal is passed through the disc, an output pulse is generated.
In the illustration, signal A passes through the disc generating an output pulse. At the same time signal B is blocked and no output pulse is generated. The dotted line represents the position of the disc relative to the output pulses.
Encoders Provide Directional Information
Detection of shaft direction is very useful and even critical to some applications. In a radio, the rotational direction of the volume knob tells the receiving circuit whether to increase or decrease the volume with each square wave. In automation equipment, the rotational direction is detected and other operations are initiated when a pre-set number of pulses for that direction has been achieved. An elaborate and sophisticated set of movements can be executed automatically to perform tasks like placing components on a pc board, welding seams in an automobile body, moving the flaps of a jumbo jet or just about anything that involves a set of precise motions.
- In this example, Channel A leads B, i.e., Channel A outputs a signal before Channel B. This indicates the shaft is rotating counter-clockwise.
- In this example, Channel B leads A. This indicates the shaft is rotating clockwise.
Encoders Provide Position Information
Each pulse from Channel A or B increases the counter in a user's system by one when the encoder is turning counter-clockwise and reduces it by one for each pulse when it is turning clockwise. The pulse count can be converted into distance based on the relationship between the shaft the encoder is coupled to and the mechanics that convert rotary encoder motion to linear travel.
The index channel pulse occurs only once per revolution. Often the index channel is used to initialize the position of the shaft the encoder is attached to. A motor turns the encoder until the index channel is detected as a zero or starting point and an automated process can begin. Then the number of complete revolutions the encoder shaft has moved can be read and recorded. The counter adds one revolution when the index occurs during counter-clockwise rotation and subtracts one turn when it occurs during clockwise rotation. By adding the turns count to the pulse count, complete and accurate rotation information can be maintained as long as the encoder is powered.
Encoders Provide Speed Information
Encoders can detect speed when output pulses are counted in a specified time span. The number of pulses in one revolution must also be known. In the equation below, S represents speed in revolutions per minute (RPM), C represents the number of pulses counted, PPR represents the encoder's number of pulses per revolution, and T represents the time interval in seconds during which the pulses were counted. The second equation shows that if 60 pulses are counted in a time interval of 10 seconds using a 250 PPR encoder, the shaft speed is 1.44 RPM.
The equation for calculating speed is:
S = (C/PPR) / (T/60)Therefore if 60 pulses were counted in 10 seconds from a 250 PPR encoder, the speed can be calculated as:
S = (60/250) / (10/60) = (0.24) / (0.1667) = 1.44 RPMAll of the counting, timing and calculations can be done electronically in real time and used to monitor or control speed.
Encoders Provide Distance Information
Encoders can detect distance traveled based on the number of pulses counted. In most applications, rotary motion is converted to linear travel by mechanical components like pulleys, drive gears and friction wheels. In this illustration of a cutting table, if the diameter of the friction wheel and the PPR of the encoder are known, linear travel can be calculated. Pulse count to achieve desired linear travel can be calculated in a similar fashion to the diagram above for devices that use ball screws, gears or pulleys to convert rotary motion to linear travel.
In the equation, C is the number of encoder pulses counted, L is the desired cut length in inches, D is the friction wheel diameter in inches, and PPR is the total pulses per revolution of the encoder. The second equation is based on a desired cut length of 12". Assuming the friction wheel diameter is 8" and encoder PPR is 2000 we can calculate that 955 pulses must be counted to achieve a cut length of 12".
Quadrature Decoding
Quadrature decoding is a means of increasing the accuracy of the encoder by counting every state change from both channels in one cycle. Both channel A and channel B produce two state changes per square wave cycle. The quadrature decoder circuit detects both state changes in each cycle for both channels. You can see that two quad A pulses and two quad B pulses, i.e., 4 pulses are obtained from the encoder for every 1 square wave cycle.
Types of Rotary Encoders
Optical
Optical encoders currently dominate the market, most often used in precision applications and built in to electronic devices to control motion.
- Generates output code using infrared light and phototransistor
- The most common type of encoder available
- Most often used in precision applications and built in to electronic devices to control motion
Magnetic
Magnetic encoders are often used in applications where there are extreme temperatures, high humidity or exposure to particulates or liquids.
- Generates output code by detecting changes in magnetic flux fields
- Most often used in adverse environments
- Resistant to most airborne contaminants
Fiber Optic
Fiber optic encoders are sometimes called 'explosion proof' and are used in applications where methane, propane, or other highly combustible gases are present.
- Generates output code by using a laser and phototransistor
- Most often used in explosion-proof applications where extremely flammable gasses are present
Capacitive
The AMT10, AMT11, and AMT13 series are not recommended for explosion-proof applications but can withstand similar environmental factors as magnetic encoders and generally outperform optical encoders thanks to their proprietary capacitive technology.
- Generates output code through detecting changes in capacitance using a high frequency reference signal
- Relatively new compared to the other types listed
- Technology has been used for years in digital calipers and has proven to be highly reliable and accurate
How A Capacitive Encoder Works
The AMT modular encoder consists of three basic parts as shown in the image. The ac field transmitter emits a signal that is modulated by the metal pattern on the rotor as it turns. The sinusoidal metal pattern on the rotor creates a signal modulation that is repetitive and predictable. This occurs as a result of varying capacitive reactance between the signal generated by the transmitter and the metal on the rotor. The field receiver uses a proprietary ASIC to convert the modulated signal into output pulses that can be read by the same circuits used to receive optical encoder output.
If you have ever used digital calipers, then you are already familiar with capacitive encoding. The code generation used in digital calipers for decades is the same technology built into the AMT.
Applications
Encoders are used is a range of industries and applications where motion feedback is required.
- Industrial
- Medical
- Security
- Test & Measurement
- Consumer
- Robotics
- Renewable Energy
- Automation
Product Benefits
The AMT series is unique among modular encoders because it is able to combine durability, accuracy and efficiency in one solution. Thanks to its capacitive design, the AMT is not susceptible to environmental contaminants such as dirt, dust and oil that would disable a typical optical encoder. Additional advantages include the lack of an LED which can eventually fail, a wider temperature range, higher vibration tolerances, and very low current consumption. The digital nature of the design also allows for increased flexibility through programmability of various features, ultimately reducing assembly time and cost. And, compared to magnetic encoders typically valued for their ability to perform in adverse conditions, the AMT Series offers higher accuracy and stable performance in the same conditions over a wider temperature range.
Rugged
- Not susceptible to airborne contaminants
- Higher operating temperature range
- No LEDs to fail
- Far less susceptible to vibration
Low Cost
- Greatly reduced assembly time & cost
- Lower price than most competitive offerings
Efficient & Accurate
- Lower current consumption
- Higher accuracy
Ideal For Direct Motor Mounting
With 9 shaft diameter options per encoder, the AMT10, AMT11, and AMT13 series can easily mount to almost any motor. Their low mass disc means virtually no additional backlash or increased moment of inertia, making them a more reliable component for measuring and controlling the motor. Their compact packages also allow for mounting in space-constrained applications.
- 9 shaft diameter options per encoder
- Extremely low mass reduces potential backlash
- Small size fits in tight spaces
- Quick and easy mounting process
- Line driver options available for challenging applications
- Up to +125° operating temperature
Simple Assembly
With the encoder's disk built-in to the assembly, mounting an AMT encoder is very quick and easy. Take a moment to watch the videos below for detailed instructions on mounting an AMT encoder. With just a few durable pieces, the encoder mounts on a motor in seconds without the risk of damaging components like with optical encoders.
AMT10 Mounting Instruction Video
AMT11 Mounting Instruction Video
AMT13 Mounting Instruction Video
Versatile Shaft and Mounting Options
The AMT10, AMT11, and AMT13 series kits each support 9 different motor shaft diameters for added design flexibility. Typical incremental encoders on the market today fit only one motor size per SKU. For example, if a manufacturer is utilizing motors with 2 mm, 5 mm and 8 mm shafts in their system, they must purchase three separate encoders. Offering several popular mounting patterns and nine shaft size options, the AMT series kits can fit all three applications under one SKU. With the ability to adapt to almost any application, the AMT10, AMT11, and AMT13 are the most flexible incremental encoders on the market today.
Mounting Patterns
| Hole Pattern mm/in |
Number of Holes | Recommended Screw | AMT Series |
| Ø16/0.63 | 2 | M1.6 | AMT10/11 |
| Ø19.05/0.75 | 2 | #4 | AMT10/11 |
| Ø21.55/0.848 | 3 | M1.6 or M2 | AMT10/11 |
| Ø25.4/1.0 | 4 | M1.6 or M2 | AMT10/11 |
| Ø32.44/1.277 | 2 | #4 or M2.5 | AMT10/11 |
| Ø43.84/1.726 | 2 | #4 or M2.5 | AMT13 |
| Ø46.02/1.812 | 2 | #4 or M2.5 | AMT10/11 |
AMT10/11 Shaft Adapter & Sleeves
AMT13 Sleeves
Output Options
The standard output for the AMT10, AMT11, and AMT13 is CMOS voltage. Line driver output is available as an option in the AMT11 and AMT13 series, which is recommended for environments with significant electrical noise or when the distance between the AMT and the receiving circuit exceeds 30 feet.
The standard output for the AMT10, AMT11, and AMT13 is CMOS voltage (fig. 1).
Line driver output (fig. 2) is available as an option in the AMT11 and AMT13 series.
AMT Viewpoint
Thanks to the AMT encoder's innovative design, CUI Devices is able to deliver an unprecedented level of visibility and control through the AMT Viewpoint™ Graphical User Interface. Via the simple to use software, users are able to set and control resolution and zero position, reducing development time and virtually eliminating tedious steps in the assembly process. Additionally, the software allows engineers access to a range of diagnostic data for quick analysis during design or in the field.
With the AMT Viewpoint GUI you can:
- Resolution
- Zero Position
- Resolution
- View timing diagrams of output waveforms, encoder firmware, and date code
- Encoder diagnostics
Available Products
AMT10 Series
Supporting 9 different shaft sizes from 2 mm to 8 mm, the AMT10 series offers 16 resolutions ranging from 48 to 2048 PPR, selectable via an onboard DIP switch. The encoder features CMOS voltage with quadrature A and B outputs, a wide temperature range of -40 to 100°C to address adverse operating conditions, and low current consumption of 6 mA at 5 V. Depending on the required application orientation, customers can also select between radial and axial mounting versions.
- Supports 9 shaft sizes from 2 to 8 mm - AMT10-V Kit
- 16 selectable resolutions from 48 to 2048 PPR
- CMOS voltage output
- Quadrature A, B channels
- Low current consumption of 6 mA at 5 V
- -40 to +100°C operating temperature range
- Radial and axial orientations
Available Products
AMT11 Series
Supporting 9 different shaft sizes from 2 mm to 8 mm, the AMT11 series offers 22 programmable resolutions ranging from 48 to 4096 PPR, which can be programmed via CUI Devices' AMT Viewpoint software. The encoder features CMOS voltage outputs as well as differential line driver versions for environments with significant electrical noise or long cabling distances. Available in radial or axial orientations, the AMT11 series further carries an operating temperature range from -40 to 125°C and low current consumption of 16 mA at 5 V.
- Supports 9 shaft sizes from 2 to 8 mm - AMT11-V Kit
- 22 programmable resolutions from 48 to 4096 PPR
- CMOS voltage output
- Differential line driver versions
- Low current consumption of 16 mA at 5 V
- -40 to +125°C operating temperature range
- Radial and axial orientations
Available Products
AMT13 Series
Supporting 9 different shaft sizes from 9 mm to 15.875 mm (5/8 in), the AMT13 series offers 22 programmable resolutions ranging from 48 to 4096 PPR, which can be programmed via CUI Devices' AMT Viewpoint software. The encoder features CMOS voltage outputs as well as differential line driver versions for environments with significant electrical noise or long cabling distances. Available in radial or axial orientations, the AMT13 series further carries an operating temperature range from -40 to 125°C and low current consumption of 16 mA at 5 V.
- Supports 9 shaft sizes from 9 to 15.875 mm (5/8 in) - AMT13-V Kit
- 22 programmable resolutions from 48 to 4096 PPR
- CMOS voltage output
- Differential line driver versions
- Low current consumption of 16 mA at 5 V
- -40 to +125°C operating temperature range
- Radial and axial orientations
Summary
The AMT10, AMT11, and AMT13 series deliver the best of both worlds, combining levels of accuracy and durability unrivaled in other encoder technologies. The AMT's unique platform also delivers an unparalleled level of flexibility and intelligence thanks to the digital nature of the design. Not to mention, the encoders are easy to install, greatly reducing assembly time and cost. Lastly, the AMT encoder kits with a range of mounting options allows them to adapt to virtually any size motor, making them the most versatile encoder series on the market today.
