Encoder Glossary

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Encoder Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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A Quad B

refers to the set of output quadrature signals from an incremental encoder to indicate speed and direction, including complements: A, A NOT, B, B NOT (

). Most Avtron encoders offer A Quad B output at no extra cost.

Analog Tachogenerators

also known as DC tachogenerators, are small DC generators that output a voltage in proportion to speed. They cannot indicate position, only speed and direction of rotation. A common mounting style of analog tachogenerator was the General Electric BC42 and BC46 Series with NEMA 56C Foot or Face Mount, and the smaller 5PY flange mount unit. Analog tachogenerators can be replaced with modern digital encoders. This typically requires use of the existing flange adapter and coupling already on the motor and a Frequency to Voltage Converter like the Avtron K661, which resides in the drive cabinet.

Anti-Rotation Arm

is a device used to prevent hollow shaft encoders from spinning with the shaft rotation. It is also called a tether or a torque arm. To prevent encoder bearing damage, anti-rotation arms are very flexible and permit all movements, including axial shaft movement but not rotation.

Axial Shaft Movement

is motor shaft movement in or out, relative to the ends of the motor. Often motors that use roller or sleeve bearing construction have more axial shaft movement. Most Avtron modular encoders tolerate +/- 0.050" of axial movement maximum. Use hollow shaft encoders for high axial movement motor styles, such as MD motors. Most competitors� modular encoders tolerate much less axial movement than Avtron products.

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BC42

is an analog tachogenerator manufactured by General Electric, NEMA 56C face or foot mount, coupled. It may be replaced by an Avtron encoder combined with a K661 converter to eliminate brush maintenance issues.

BC46

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C-Face

is a machined flange or elevated/recessed face provided on motors for mounting accessories. Typically provided on the drive end for gearbox/load mounting, C-faces may also be provided on the non-drive end for mounting encoders, brakes, and other accessories.

Cam Screw Rotor�

eliminates the problems associated with slipping rotors of other types; it uses two cam (eccentric) head screws. The screws are preloaded into the rotor; simply rotate them (approximately 90-180�) to fully engage the shaft (4-6 ft-lbs) using a standard hex (Allen) wrench. Cam screw rotors are available on AV850, M56, M67, M85, and M115 THIN-LINE encoders. Cam Screw Rotor Patent Pending.

Cam Screw Rotor� is a trademark of Avtron.

Complements

are also known as complementary outputs. To ensure that signal noise does not cause errors between the encoder and the controller, many encoders output signals that are driven in exactly opposite directions: When A goes high, A NOT goes low (

). When A goes low, A NOT goes high. Controllers which see a transition in A, but not in the A NOT signal, would report a quadrature error.

Contamination

also known as contaminants, such as water, dirt, dust, oil, and other compounds which enter an encoder through seal failure, can cause optical errors. If the contamination is abrasive, it can also cause bearing failures in the encoder. Modular encoders are very resistant to contamination as they use magnetoresistive sensors and have no bearings.

Coupling/Coupled

refers to a flexible device that is used to link a solid shaft encoder to the shaft to be monitored. Avtron strongly recommends isolated, flexible disk style couplings wherever possible to maximize encoder bearing life. For large axial shaft movements, spider couplings may be used as an alternative.

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DC Tachogenerators

See analog tachogenerators.

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Encoder

is a device which indicates position and speed via a set of digital outputs. Incremental encoders output quadrature (A Quad B) signals, and may add a marker pulse once per revolution.

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Face or Flange Mount

A machined surface (NEMA 56C, NEMA FC) on the non-drive end of the motor is used to mount bearingless or pancake encoders such as Avtron M56 THIN-LINE encoders. Solid shaft, coupled tachometers also flange mount using flange adapters.

False Pulses

are pulses output by the encoder when no pulses should be output. They are often caused by contamination on optical disks that is misread as a line on the optical disk.

Flange Adapter

"A"

"B"

provides the NEMA 56C motor mounting face and properly locates the encoder shaft. The encoder shaft and motor shaft are then connected using a flexible coupling. (Drawing "A")

Often flange adapters can be eliminated by directly mounting a modular encoder such as an Avtron AV850 or M56, M67, M85, M115 THIN-LINE unit on the motor flange. (Drawing "B")

Flowerpot

is a term for the flange adapter used to mount a solid shaft encoder to a motor face.

Foot Mount

encoders are bolted to a motor foot, shelf, or other nearby location. The solid shaft encoder is coupled to the shaft to be monitored. Modern Avtron encoders (M3-2, M4-2, M485) require a separate foot mounting bracket. To eliminate coupling and alignment maintenance issues, foot mounting installations can be upgraded to a hollow shaft encoder.

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Heavy Mill Duty

encoders are designed to withstand temperature cycling, extreme temperatures, contaminants, bearing loads, and physical force.

Hollow Shaft

encoders mount by passing the shaft of the motor into or through the encoder. Hollow shaft encoders are easy to mount and replace but are vulnerable to damage. Also, the weight of the encoder must be considered for small motor shafts < 0.75" diameter.

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Incremental Encoder

is an encoder that produces pulses in proportion to distance moved or rotated. Incremental encoders can also have a marker pulse Z, Z NOT (

) once per revolution to provide a position reference. Avtron produces a full range of incremental rotary encoders.

Industrial EPIC

is the preferred encoder connector of most users in North America. It contains a full size terminal strip and, unlike the MS connector, requires no soldering for quick field connections. Avtron offers pin-for-pin exact replacements for competitors� models using industrial EPIC� style connectors.

EPIC� is a registered trademark of the Lapp Group.

IR LED

(Infra-Red Light Emitting Diode) is the light source for an optical encoder.

Isolated Outputs

provide two or more completely separate output signals from the encoder. These separate signals can be wired to two or more devices, or used for redundant control systems for more uptime. Avtron isolated encoder outputs are always created using fully redundant electronics and sensors, isolated from each other and from the housing for maximum reliability.

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Light Mill Duty

encoders are designed for industrial applications but must be protected from contamination, temperature cycling, and physical force, including shock, vibration, and bearing loads. Examples include AV20, AV25, HS25A, and HS35A models.

Light Source

is typically an IR LED or laser which shines through or on the optical disk of an encoder. The light source is received by the optical sensor.

Lines

Encoders produce pulses that create transitions up and down in a DC voltage. Each transition is called a line. Quadrature encoders with their two channels produce four times as many lines as pulses. Some drive products can be set to count lines in one direction (up/down) or all directions, creating more counts in the drive than the rated PPR (pulses per revolution) of the encoder.

Line Driver

is the chip or output circuit that forms the electrical pulses output from the encoder. Avtron has extremely advanced line driver technology to prevent damage from overvoltage and short circuits. Avtron offers optional high-power line drivers to permit Avtron encoder signals to travel farther down long wires to remote controller/drive locations without the need for repeaters or amplifiers.

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Magnetic Encoder

Magnetic and magnetoresistive encoders typically use a magnetized rotor with north and south poles lined up around the perimeter of the disk. A magnetoresistive sensor detects the transitions, and these are the counts or pulses generated by the encoder. Magnetic encoders withstand dirt, dust, water, and temperature changes far better than optical encoders.

Magnetic Rotor

is a magnetized disk with multiple north and south poles lined up around the perimeter of the disk. A magnetoresistive sensor detects the transitions and generates the pulses generated by the magnetic encoder.

Magnetoresistive Sensor

detects the magnetic poles on an encoder's magnetic rotor and transforms them into pulses. Avtron magnetoresistive (MR) sensors use advanced technology to reject external magnetic signals such as brake solenoids and motor magnetic fields. MR sensors enable Avtron magnetic encoders to ignore dirt, oil, water, and other contaminants.

Marker Pulse

occurs once per revolution. The purpose of the marker pulse is to provide a repeatable home position location for positioning applications. The marker pulse is often abbreviated as "�Z" in the USA and "C" or "N" in Europe.

Mill Duty

encoders are sturdier than light mill duty and can withstand more shock, vibration, and bearing loads. Mill duty encoders must be protected from temperature cycling and contaminants.

Missed Pulses

are errors made by an encoder when a pulse should have been generated due to movement but was not. They are often caused by contamination on optical disks that cause a line to be missed.

Modular Encoders

mount to a machined C-face or flange adapter on the motor (drive or non-drive end). Modular encoders consist of a rotor that mounts on the shaft, and a stator that bolts to the motor frame. Modular encoders are very rugged, and Avtron encoders feature Wide-Gap sensors to avoid complex shimming or fitting to the motor. Modular C-face encoders are typically used on DC motors; but some AC motors, such as Rockwell�s RPM III AC and Marathon�s Blue and Black Max motors, have C-faces standard on the non-drive end for mounting an encoder.

(Magnetoresistive) Magnetoresistive sensors are used in Avtron encoders to provide high accuracy and superior reliability.

MS Connector

is the most used encoder connector style in North America. Available in 6, 7, and 10 pin versions, with 10 pins being the most common. Avtron offers pin-for-pin exact replacements for competitors� models using MS connectors. MS connectors are extremely reliable but require soldering. Many users prefer industrial EPIC � style connectors instead.

EPIC� is a registered trademark of the Lapp Group.

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NEMA 56C

face or flange mount, also known as bearingless or pancake encoder, is a 4.5" flange with (4) bolts located in a 5.88" circle. Originally designed as the standard for mounting solid shaft, coupled tachometers on flange adapters, the NEMA 56C is also a standard for mounting modular encoders. Avtron M56 THIN-LINE encoders mount on NEMA 56C faces. Marathon Blue Max and Black Max AC motors feature a NEMA 56C face on the non-drive end.

NEMA FC

"A"

"B"

face mount is a 8.5" flange with (4) bolts located in a 7.25" circle. Originally used for mounting solid shaft, coupled tachometers using flange adapters, the NEMA FC 8.5" face is a standard for mounting modular encoders. (Drawing "A")

Avtron M85 and AV850 encoders mount directly on NEMA FC 8.5" faces. (Drawing "B")

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Optical Disk

is typically a glass, metal, or plastic disk with fine lines or slots etched around the perimeter that interrupt the beam of light from the light source to an optical sensor. Optical disks can be quite fragile. Avtron uses only shatterproof optical disks with Wide-Gap technology.

Optical Encoder

typically uses a light source shining through, or reflecting off, an optical disk with lines or slots that interrupt the beam of light to an optical sensor. Electronics count the interruptions of the beam and generate the encoder�s output pulses.

Optical Errors

include false pulses, missed pulses, and quadrature errors that are generated when there is any type of contamination (dirt, oil, water, condensation) on the optical disk.

Optical Sensors

are typically phototransistors or other light sensors which sense the light emitted by the light source, as interrupted by, or passed through, the optical disk.

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PPR

(pulses per revolution) Most Avtron encoders output quadrature pulses, with four times as many lines as pulses. Often lines can be counted in the drive/speed controller for higher resolution applications.

Pulses

are also known as counts and are the low voltage output transitions which indicate movement of the encoder. Encoders are rated by resolution or PPR (pulses per revolution). Pulses are not the same as lines.

PY Face

is a 2.0" flange with (4) bolts located in a 3.978" circle. It is used for mounting solid shaft, coupled 5PY style DC tachogenerators using flange adapters. Avtron M925 digital encoders fit PY face mount. An adapter is available to fit M3 and M4 to PY faces as well.

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Quadrature

To determine which direction an encoder is revolving, encoders output quadrature signals: two streams of pulses, A & B, generated at 90� timing angles. (Also called A Quad B) A leading B indicates rotation in one direction; B leading A indicates the encoder is rotating in the opposite direction. Example: �A leads B with clockwise rotation as viewed from the encoder face on an M4 encoder.� Many encoders with quadrature outputs also have complementary outputs: A NOT and B NOT signals (

Quadrature Errors

are failures of the encoder to generate properly formatted quadrature signals. Most typically, these are failures to create the proper 90� signal separation between the A and B channel outputs, with a less than perfect stream of square waves. Most controllers, when presented with a quadrature error, will report a drive fault or encoder fault and then shut down.

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Reluctance

is an early style of analog tachometer. It only provides output above a minimum speed. The output is a low power analog sine wave. Avtron offers the M460 reluctance tach, which is not compatible with modern encoders.

Resolution

is the number of PPR (pulses per revolution) in an encoder.

Rotor

is the disk-shaped portion of the modular encoder that is mounted on the motor shaft. Avtron modular encoder use magnetic rotors.

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Sandwich

is an older style of encoder that fits between an existing solid shaft coupled tachometer and the motor. It is commonly replaced by modular encoders such as the Avtron M56 THIN-LINE.

Seal Failure

Many encoders come sealed from the factory, but as they are temperature cycled, the air inside expands and contracts at a different rate from the air outside the encoder. This puts pressure on the seals of the encoder and eventually breaks them down, creating an unobstructed path to the inside of the encoder. Likewise, external pressure (wash-downs, submersion) creates the same path. If an encoder has seal failure, contaminants get into the encoder and cause errors in optical encoders. Avtron heavy mill duty and severe duty encoders are highly resistant to seal failure, and feature magnetic technology to ignore most contaminants.

Sensor Crash

When the rotating disk in an encoder contacts the sensor (optical or magnetic/magnetoresistive), it damages or destroys the sensor. Sensor crashes can be caused by excessive vibration, shaft runout, or alignment problems in encoder mounting. Avtron encoders feature Wide-Gap technology to eliminate sensor crashes.

Severe Duty

encoders have the best ability to withstand temperature cycling, extreme temperatures, contaminants, bearing loads and physical abuse.

Shaft Current

is the undesirable electrical current flow common to motors controlled by variable speed drives. This current attempts to circulate within the motor or discharge to ground. Avtron encoders are protected against shaft currents.

Shaft Grounding

To eliminate damage from shaft current, the encoder may be provided with a conductive brush that contacts the motor shaft and discharges the voltage before it damages the motor or encoder bearings. Many Avtron encoders offer a shaft grounding kit option.

Shaft Runout

is the wobbling motion produced by a shaft that is not perfectly true and straight. Shaft runout is often abbreviated T.I.R. (Total Indicated Runout).

Shimming

Often, to produce precise stub shaft, modular encoder, or foot mount installation, shims are placed between the two items to be aligned. Avtron encoders are designed to eliminate the need for shimming. Many competitors� modular encoders still require shimming for proper operation.

Shims

are thin pieces of metal used to precisely space two parts. They are used for shimming a stub shaft, encoder rotor, or foot mount installation.

Solid Shaft

encoders are coupled to the shaft to be measured. The solid shaft encoder body is typically C-Face mounted using a flange adapter, or some models can be foot mounted.

Stator

is the portion of a modular encoder that bolts to the motor frame.

Stub Shaft

is the portion of the shaft (often on the non-drive end of the motor) used to mount an encoder. To add an encoder to a motor or other shaft that lacks enough extra shaft length to install the encoder, an additional shaft length is added. The stub shaft is threaded into the center of the motor shaft, or the existing motor shaft is enclosed in a sleeve that grips the shaft. Avtron offers many standard and custom stub shafts.

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Tachometer

is also known as a tach, a device which indicates speed of rotation. Modern tachometers are actually rotary incremental encoders which indicate position, speed, and direction of rotation.

T.I.R.

(Total Indicated Runout) This is a measurement of how much a shaft wobbles with each revolution. (shaft runout).

Torque Arm

type of anti-rotation arm used to mount hollow shaft encoders to large frame motors. It features a threaded rod for adjustable radius.

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VSO

(Vane Switched Oscillator) This is an older type of encoder that produces a unique signal output that cannot be replaced with a modern encoder. Contact Avtron for upgrade path.

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Wide-Gap Technology

Avtron magnetic encoders use special optical sensors and magnetoresistive sensors, combined with proprietary circuit designs to allow the sensor to be located much farther from the magnetic rotor. This eliminates sensor crashes and makes mounting easy and forgiving of mechanical variation.