Contents Purpose To familiarize you with rotary encoders and to show the benefits of the AMT102 & 103 Objectives Understand what makes the AMT102 & 103 revolutionary Explain the different components that make up the AMT102 & 103
and how they are assembled Illustrate why the 16 programmable resolutions offer incredible flexibility Content: 28 pages Learning time: 15 minutes
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Welcome to the CUI Inc training module for the AMT102 & 103. This module will discuss how encoders function, what makes the AMT102 & 103 unique, and the various parts that make up these revolutionary modular encoders.
An encoder is a device that senses mechanical motion. It translates motion such as speed, direction, and shaft angle into electrical signals.
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An encoder is a device that senses mechanical motion. It translates motion such as speed, direction, and shaft angle into electrical signals. There are many different shapes and kinds of encoders. Most encoders generate square waves making them ideal for use in digital circuits. For this training module we will consider only rotary encoders although encoders are also available in linear configurations.
Generates output code by making and breaking a circuit. Most often used as panel controls such as the volume on a car radio.
Optical low to high cost, low to high resolution
Generates output code using infrared light and phototransistor. The most common type of encoder available. Most often used as panel controls in precision applications and
built in to electronic devices to control motion.
Magnetic medium to high cost, medium resolution
Generates output code by detecting changes in magnetic flux fields. Most often used in adverse environments. Resistant to most airborne contaminants.
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There are many types of technology used with the rotary encoder style. Mechanical rotary encoders generate output code by making and breaking a mechanical circuit. These are typically very low cost, low resolution encoders used most often in panel controls. Optical encoders are high resolution and low cost, generating output code using infrared light and phototransistors. Magnetic encoders generate code by detecting changes in magnetic flux fields. These are usually medium to high cost devices and are used in environments that encounter adverse conditions.
Generates output code by using a laser and phototransistor. Most often used in explosion-proof applications where extremely
flammable gasses are present.
Capacitive low cost, low-high resolution
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.
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Fiber optic encoders generate code using a laser and phototransistor and are high cost, high resolution devices. Finally, capacitive encoders generate output code through detecting changes in capacitance using a high frequency, reference signal. The capacitive style are low cost, high resolution encoders and are perfectly suited for high precision applications.
Inside an optical encoder there is a slotted disc fixed to a shaft that is free to rotate. On one side of the disc is an IR LED (infrared LED), on the other side a PTR (phototransistor). In high resolution encoders there is a lens between the IR LED and the disc to focus the light for better accuracy. As the disc turns, light from the IR LED alternately passes through a slot in the disc and is prohibited from passing in between slots. When the infrared light reaches the PTR, it generates a signal. In the illustration, the light from the IR LED in Channel A passes through a slot in the disc, exciting the PTR and causing it to generate an output signal. At the same time the light from the IR LED in Channel B is blocked and no signal is generated. The dotted line represents the position of the disc relative to the disc position. Notice there is only one slot for the index, Channel I. It occurs only once per revolution and is used as a reference or starting point.
Each pulse from Channel A or B increases the counter by one in when the encoder is turning counter-clockwise and reduced by one for each pulse from the encoder 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. Through a method known as quadrature decoding as seen in slide seven, 2,000 pulses are detected from 500CPR encoder in one revolution. One pulse from Channel A or B represents 1/2000 of a revolution or 0.18° of rotation. 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. 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 obtained.
Quadrature decoding circuit for obtaining count up/down signals.
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In each square wave cycle of a two-channel encoder there are four discrete states. The four dotted lines in Figure 1 above represent one square wave cycle. The term 'quadrature' derives its name from the Latin word 'quarter' which means 'four times.’ When an encoder specification reads 500 CPR, it means each encoder channel produces 500 square wave cycles in one complete revolution. Since each cycle represents four discrete states or pulses, the encoder resolution can be increased times four through quadrature decoding. Thus, 2000 PPR (Pulses Per Revolution) can be obtained from a 500 CPR (Cycles Per Revolution) encoder. This is important for high-precision applications. The maximum resolution for a 500 CPR encoder without quadrature decoding would be 360° ÷ 500 = 0.72°. With quadrature decoding, the same encoder attains a resolution four times finer, 360° ÷ 2000 = 0.18°.
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.
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Detection of shaft direction is very useful and critical to some applications. In a radio, the rotational direction of the volume knob tell the receiving circuit whether to increase or decrease the volume. In industrial equipment, the rotational direction is detected and stopped when a preset number of pulses for that direction has been received.
Where "S" is speed in rpm, "C" is the number of pulses counted in a "t" time interval. If 60 pulses were counted in 10 seconds from a 360PPR encoder, the speed can be calculated:
S = = 0.1666 ÷ 0.1666 = 1 rpm 60 360
10 60
÷
All of the counting, timing and calculations can be done electronically in real time and used to monitor or control speed.
Encoders can detect speed when the number of output pulses is counted in a specified time span. The time element is typically provided by an internal oscillator or clock. The number of pulses in one revolution must also be known.
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One of the primary benefits of using an encoder is the ability to measure rotation speed. Encoders can detect speed when the number of output pulses is counted in a specified time span. Encoders allow counting, timing, and calculations to be done in real time and used to monitor or control speed.
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:
C = L ÷ (π * D) * PPR
Where C = encoder pulse count, L = desired cut length in inches, D = friction wheel diameter in inches, and PPR = total pulses per one revolution of the encoder. For a desired cut length of 12", assuming the friction wheel diameter is 8" and encoder PPR of 2,000:
C = 12 ÷ (3.142 * 8) * 2000 = 955
Pulse count to achieve desired linear travel can be calculated in a similar fashion for devices that use ball screws, gears or pulleys to convert rotary motion to linear travel.
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.
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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.
Encoder in a mouse Inside a mouse there are three encoders – one mechanical encoder and two optical encoders Notice the sets of slotted discs, phototransistors and IR LEDs, one for horizontal motion, the other for vertical motion As the trackball moves it turns the disc shafts.
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Inside a mouse there are one mechanical and two optical encoders. Feedback from the two optical encoders causes the cursor to move up and down, back and forth on the monitor in concert with the motion of the mouse. The mechanical encoder is mounted on the thumbwheel. You will notice the sets of slotted discs, phototransistors and IR LEDs, one for horizontal motion, the other for vertical motion. Each phototransistor is an array of two so that direction along with distance traveled is detected. You can see the slots in the disc used for the X (horizontal) axis. As the trackball moves it turns the disc shafts. The trackball was removed for this illustration.
Typical Optical Encoder Configuration From the illustration you can see that optical encoder construction is fairly complex. Alignment of optical components must be precise in resolutions above 300 CPR. Alignment becomes even more critical in resolutions above 1000 CPR. For this reason ball bearings must be staked in a rigid housing to assure little or no radial shaft movement or ‘wobble.’
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The schematic flowchart in the lower right shows the stages of an optical encoder. The signal processing circuitry amplifies the rough output from the photodiodes and converts it into clean square waves for accurate processing by the receiving circuitry. The emitter stage is most susceptible to failure because of possible LED burnout or lens contamination.
The AMT102 & AMT103 are comprised of a top field receiver, middle rotor, and bottom ac field transmitter. The ac field transmitter emits a signal that is modulated by the rotor as it turns. Because of the sinusoidal metal pattern on the rotor, signal modulation is predictable. The field receiver uses a proprietary ASIC to convert the modulated signals into output pulses that can be read by the same circuits used to receive optical encoder output.
One of the main benefits of the AMT102 & 103 is the absence of a glass optical disk. This greatly simplifies assembly because the AMT disc is not fragile like a glass optical disc. The benefit of this is reduction in assembly time and cost.
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The AMT is unique among modular, incremental encoders because it is capacitive (the same technology used in digital calipers) and not optical. This eliminates handling of the sensitive optical disk and issues related to LED burnout or lens contamination. It also simplifies the assembly process.
The AMT's dip switch enables setting the AMT to any one of 16 different selectable resolutions. Starting at 48 PPR and reaching 2048 PPR, the AMT's selectable resolution settings make it ideal for use in many different applications.
48 96 100 125
196 200 250 256
384 400 500 512
800 1000 1024 2048 16 resolutions available via the dip switch
Resolutions (PPR)
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AMT102 and 103 VersaPak models come standard with an on-board dip switch to access 16 selectable resolution options ranging from 48 to 2048 PPR. It also includes an index pulse as a standard feature. The output is TTL voltage.
The top cover of the AMT102 & 103 houses the circuitry that detects the motor shaft rotation. These top covers are metal, adding durability. The boards are swaged into the casing to make assembly even easier. The dip switch can also be accessed here. top cover with
built in circuit board
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The circuit boards that are responsible for detecting rotation are swaged into the top cover casing. This allows access to the dip switch and makes assembly and resolution selection easier.
AMT is Smaller Because it has no optical disk, the AMT is smaller than competing optical encoders.
length width height
competitor 46.50 31.00 16.26
AMT102 43.39 28.77 9.00
AMT103 34.20 28.60 9.00
The AMT102 & 103 are smaller in every dimension, allowing them to fit into tighter spaces. Competitor AMT102
Dimensions (mm):
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Because the AMT102 & 103 have no optical disk they are smaller than the competitor’s models. This increases their opportunity for use because the AMT can fit into smaller spaces than competing encoders. The design is a drop-in replacement for other industry standard optical encoders, and is easier to assemble and approximately half the depth.
The AMT is Rugged Dust & Dirt The AMT, being an ASIC driven product, is not affected by dust and dirt build-up. This results in much more rugged, reliable performance.
Temperature The AMT’s ASIC technology is less sensitive than an optical disk to heat and cold, offering reliable operation between a wider temperature range.
Vibration The AMT encoder’s ASIC-based construction is far less susceptible to vibration than the glass disk of an optical encoder.
LED burn-out The AMT, on the other hand, avoids this issue thanks to the use of a semiconductor instead of an LED.
Simple Assembly Assembly of the AMT102 & 103 requires minimal time and effort. With just a few durable pieces, it snaps together in seconds without risk of damaging a glass optical disk or other fragile components.
The AMT102 has a straight output connector and the AMT103 has a right angle output connector.
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With the disk built-in to the top cover, the assembly is very quick and easy. Just snap the shaft adapter over a selected sleeve on the back shaft of a dc motor, align and mount the selected base unit with one of the mounting hole options, and snap the top cover into place in seconds. The difference between the AMT102 and 103 is that the 102 has a straight output connector while the 103 has a right angle output connector.
Ideal for Direct Motor Mounting The AMT Series can be used on any rotating shaft, however, it is ideal for mounting directly to motors.
mounting patterns for hundreds of AC & DC motors
9 shaft diameter options
extremely low mass reduces potential backlash
small size fits in tight spaces
Mounting Options
hole pattern (mm/in)
# of holes hole size available
Ø16/0.63 2 M1.6 AMT102/103
Ø19.05/0.75 2 #4 AMT102/103
Ø20/0.787 2 M1.6 or M2 AMT102/103
Ø20.9/0.823 3 M1.6 or M2 AMT102/103
Ø22/0.866 3 M1.6 or M2 AMT102/103
Ø25.4/1.0 4 M1.6 or M2 AMT102/103
Ø32.43/1.277 2 #4 AMT102
Ø46.025/1.812 2 #4 AMT102
0.62" x 0.825" 2 #4 AMT102
Ø2 mm Ø3 mm Ø1/8 in.
Ø4 mm Ø3/8 in. Ø5 mm
Ø6 mm Ø1/4 in. Ø8 mm
Shaft Bushings
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With up to 16 mounting options and 9 shaft bushings the AMT encoder can easily mount to almost any motor. Its low mass disc means virtually no additional backlash or increased moment of inertia making it a more reliable component for measuring and controlling the motor. Its small size allows for mounting in tight spaces and to small motors.
Simplify Inventory with AMT102-V & 103-V The AMT102-V & 103-V were designed to be flexible enough to handle many different applications, reducing inventory to only two encoder models.
AMT102-V and AMT103-V includes: 9 shaft adaptors Standard and wide base for the AMT102 Tools for simple assembly
In addition to all of this, custom versions are available. Both models are RoHS compliant.
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To aid in assembly, all AMT102-V & AMT103-V models include 9 color coded sleeves to fit most shaft diameters from 2 mm to 8 mm and two simple mounting tools. Base plates are pre-drilled with 9 (AMT102) or 7 (AMT103) mounting hole patterns including a wide base plate for AMT102 to adapt to 1.27” or 1.81” bolt circles.
Shaft Adapter and Sleeves Using the shaft adapter and the 9 color-coded sleeves, both the AMT102-V & AMT103-V can be adapted to 9 different motor shaft sizes. This is done by snapping one of the sleeves into the shaft adapter.
2.00 3.00 3.17
4.00 4.76 5.00
6.00 6.35 8.00
Shaft Adapter Sleeves Sleeve Diameters (mm):
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The AMT102 & 103 VersaPak models come with 9 color coded sleeves that will adapt to 9 different motor shaft diameters.
AMT102-V= 9 different mounting options AMT103-V= 7 different mounting options Along with the standard base, the AMT102-V also comes with a wide base to accommodate more motor options. This accounts for the additional mounting options for the AMT102-V.
AMT102 wide base AMT102 standard base AMT103 base
The bases for the AMT102-V & 103-V offer 16 different mounting options.
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The AMT102-V has 9 discrete mounting options and comes with both a standard base and a wide base. The base for the AMT103-V has 7 discrete mounting options.
Tool A is a wrench-like tool used as a spacer between the motor and the encoder. Tool B is used to center the AMT's components on the motor shaft and ensure that the components are flush.
tool A
tool B
The AMT102-V & AMT103-V come with two tools that are necessary for correct assembly.
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Two tools are included with the AMT102-V and AMT103-V. Tool A is a wrench-like tool that is used as a spacer between the motor and the encoder. Tool B is used to center the AMT’s components on the motor shaft and ensure that the components are flush.
The standard output for both the AMT102 & AMT103 is TTL voltage (see fig. 1). Line-driver output (fig. 2) is available through the use of a line-driver cable that converts the TTL output. The line-driver output is recommended for environments with significant electrical noise or when the distance between the AMT and the receiving circuit exceeds 30 feet.
Ch A
Ch B
Ch I
Ch A Ch A
Ch B Ch B
Ch I Ch I
fig. 1
fig. 2
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AMT102 and AMT103 come standard with an on-board dip switch to access 16 selectable resolution options ranging from 48 to 2048 PPR. It also includes an index pulse as a standard feature. The output is TTL voltage.
