1. Sensors
ME Automation

2. Objectives Identify commonly used sensor types
Where, how and why they are used
Latest and greatest capabilities
Bottom Line (cost)
Where to go to find out more

3. Proximity Sensors
Inductive
Capacitive
Ultrasonic
Photoelectric

4. Inductive Sensors How they work
Creates a radio frequency field using an oscillator and a coil. The presence of a metal object changes the field and the sensor is able to detect this.
*Picture compliments of Baumer Electric Ltd.

5. Inductive Sensors Applications Conveyor on/off switches
Begin machine cycle
Quality control (sense lids, proper alignment, etc.)
Count, determine direction of motion/rotation, positioning
Anytime you want to sense metal

6. Inductive Sensors Advantages
Can detect metal target even through non-metallic barriers
Eliminates need for contact
Operate in harsh conditions
Rapid response time
Long life, virtually unlimited operating cycles.

7. Inductive Sensors Limitations Can only detect conductive metal
Relatively short range. Usually used for less than 1” sensing distance.
May be affected by metal chips collecting on sensor face.

8. Inductive Sensors Things to be Aware Of
Specified range is for axial approach. If object approaches from the side, range is decreased.
Range depends of metal type!!!!
St37 ( Fe ) 1
Aluminium foil ( Al ) 1
Nickel chromium ( V2A ) 0.9
Mercury ( Hg ) 0.6
Lead, brass ( Pb, Ms ) 0.5
Aluminium ( solid )
Copper ( Cu )

9. Inductive Sensors Current Specifications Range: up to 40 mm
Switching Frequency: 25 Hz to 3 kHz.
Time delay: < 2ms
Repeatability error: < 1% of range
Cost: $25 to $250 (typically just under $100)

10. Capacitive Sensors

11. Capacitive Sensors How they work
Uses two plates to form a linear capacitor (hence the name). The amount of energy that can be stored between the plates depends on the material between them. When a material other than air is present, the sensor can detect it.

12. Capacitive Sensors Applications leak detection conveyors
avoid or jam control
semiconductor manufacturing
food processing
missing component detection
bottle filling
bottle detection
thickness monitoring
gaming table chip monitoring
missing unit in shipping carton detection
bin level in silo detection
low paper roll monitoring
Applications
conveyors
robotics
jam protection
positioning
parts detection or control
indexing
bottle cap or can lid detection
counting
broken or damaged tool detection
liquid level control
volume level control

13. Capacitive Sensors Advantages Can detect aabout anything
Can detect liquid targets through non-metallic barriers (glass, plastic, etc.)
Operate in harsh conditions
Quick response time
Can detect difference of object, not just presence
Long operational life, with virtually unlimited cycles.

14. Capacitive Sensors Limitations Typically short range (less than 15mm)
Affected by varying temperature, humidity and moisture conditions
Not as accurate as inductive proximity sensors

15. Capacitive Sensors Things to be Aware Of
Again, range depends upon direction of approach
Range also depends on material
Be sure to check for ambient temperature limits

16. Capacitive Sensors Current Specifications
Range: typically up to 25 mm (can be as high as 150mm!)
Switching Frequency: up to 200 Hz
Time delay: <=25 ms
Repeatability: < 2% of range
Cost: $25 - $250 (typically $80-100)

17. Ultrasonic Sensors

18. Ultrasonic Sensors How they work
Sends out sound waves above audible frequencies (ultrasonic), and listens for the return. Uses the time delay, and the speed of sound in air to determine distance to object. Also can be used just to see if object is there.

19. Ultrasonic Sensors Different Types
Ultrasonic proximity sensor with analog output stage
Both current and voltage outputs from the sensor are proportional to the distance of the sensor from the target. This allows simple non-contact measurement

20. Ultrasonic Sensors Different Types Ultrasonic retro-reflective sensor
A fixed machine part is used here as a reflector. The time difference between the emission and the reception of an ultrasonic signal (known as propagation time) is therefore fixed and known. When an object comes within this sensing distance the output is activated

21. Ultrasonic Sensors Different Types Ultrasonic through beam sensor
These sensors are ideal for applications in which objects follow each other in quick succession. They are also recommended when high switching frequencies are required, up to 200 Hz

22. Ultrasonic Sensors Advantages
Can detect more types of objects than other three types of sensors (pretty much anything)
Very good for telling distances
Longer range than capacitive and inductive sensors
Can operate in harsh conditions
Quick response time
Long operational life, with virtually unlimited cycles.

23. Ultrasonic Sensors Limitations
Have a “dead zone” close to the face of the sensor – can’t detect very close objects
Can’t detect very small objects (detectable size depends on wavelength) (except for really high tech ones – 0.076mm!)
Speed depends on material (cotton, sponge, etc. require slower frequencies)
Smooth surfaced objects must be aligned correctly or echo won’t return to sensor

24. Ultrasonic Sensors Current Specifications Range: 50mm to 11.3m
Sampling Frequency: up to 2 kHz (usually about 120 Hz or less, depending on distance and material)
Maximum Target Speed: up to 400 in/sec
Time delay: 0.5 ms
Repeatability: 0.1% of range
Cost: $75 – several hundred (typically just over $100)

25. Photoelectric Sensors

26. Photoelectric Sensors
How they work
A photoelectric proximity switch is one in which the light source and light sensor are housed in the same unit. The sensor picks up the pulse of the LED (light emitting diode), which is usually in either the infrared or visible light range, as it reflects off of the object being sensed.

27. Photoelectric Sensors
Thru-Beam A source unit in one location sends a light beam to a detector unit in another location. An object is detected when it passes between the source unit and the detector unit, interrupting the light beam.
Reflex The source and detector are housed in one package and (Retro- placed on the same side of the target object’s path. Reflective) When the object passes by, the source signal is reflected back to the detector by a retro-reflector.
Diffuse The source and detector are housed in one package and Reflective placed on the same side of the target object’s path. When the object passes by, the source signal is reflected back to the detector off the target object itself.
Background This is a special type of diffuse reflective sensor that Rejection includes two detectors. This arrangement allows the sensor to detect targets reliably within a defined range, and to ignore objects just outside of this range. Unlike a standard diffuse reflective sensor, color or reflectivity has minimal effect on the sensing range.

28. Photoelectric Sensors
Applications (just a few)
Material Handling A sensor can ensure that products move along a conveyor line in an orderly manner. The sensor will stop the operation if a jam occurs. And items can be counted as they move down the line.
Packaging Sensors can verify that containers are filled properly, labeled properly and have tamper-proof seals in place.
Machine operation Sensors can watch to verify that a machine is operating properly, materials are present and tooling is not broken.
Paper Industry Sensors can detect web flaws, web splice, clear web and paper presence, while maintaining high web speeds.
In this cookie kitchen, fiber optic photoelectric sensors are placed in a hot oven. As long as the sensors detect motion as the trays of cookies move by, the oven stays on. If the conveyor stops, the sensors will detect light or dark for too long, and the output device will shut down the oven.

29. Photoelectric Sensors
Advantages
Much greater sensing range
Can tell how far away the object is
Fast response time
Typically very accurate (considering sensing range)

30. Photoelectric Sensors
Limitations
Don’t function well in contaminant environments
Sometimes too powerful (Excess Gain)
Reliability depends on object being sensed (can be too dark, too transparent, etc.)
More expensive
Require more power to operate

31. Photoelectric Sensors
Current Specifications
Range: up to 130m (typically between 0.5 and 10m)
Switching Frequency: up to 1 kHz (typically 20 – 60 Hz)
Time delay: as low as 0.5 ms (typically 8-50 ms)
Accuracy: as good as 0.5mm or less
Cost: very low end - $50, typical - $ , very sophisticated = very expensive

32. Sensors Summary Who Sells Them? (Thomas Register lists 120+ vendors)
Rockwell Automation Cutler-Hammer, Sensor Div.
TURCK, Inc. Electro Corp.
SICK, Inc. Stedham Electronics Corp.
Baumer Electric Ltd. Advance Controls, Inc.
Balluff, Inc.
Altech Corp.
Southern Controls, Inc.
Fargo Controls, Inc.

33. Sensors Summary Where to Find out More?
(good source for info about how they work and lists of vendors)
(excellent website for more technical information about various types of sensor and their applications)
(great source for finding vendors of a specific type of sensor)

34. Encoders

35. Objectives Present background and function of encoders
Discuss where, when, and why encoders are used
Introduce types, models, and current technology of encoders
Delineate benefits and limitations
Cite references and locations of further information

36. Background
A vast number of sensor products exist to detect all types of events. There are sensors to detect the presence of objects, the speed, the size, the structure, the color, the exact dimensions, the location, etc. Once the detection occurs, there is also a wide variety of ways a sensor can communicate, or convert, this information.
Analog-to-digital conversion begins with sampling, or measuring the amplitude of the analog waveform at equally spaced discrete instants of time.

37. As the signal is sampled the amplitude at each interval is quantized, and the values are mapped into a series of binary digits, or bits. The information is then transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted.

38. In order for a sampled signal to be stored or transmitted in digital form, each sampled amplitude must be converted to one of a finite number of possible values, or levels. For ease in conversion to binary form, the number of levels is usually a power of 2--that is, 8, 16, 32, 64, 128, 256, and so on, depending on the degree of precision required. In the figure, an analog waveform is shown being quantized on an 8-level scale (0 through 7).
28=256

39. Encoder example – An absolute optical encoder has 8 rings, 8 LED sensors, and 8 bit resolution. If the output pattern is , what is the shaft’s angular position?
Ring Angle (deg) Pattern Value (deg)
Angular Position =
Total =

40. Absolute Encoders
The term absolute defines the type of information that is relayed to the processor. There are only two options available here, either absolute or incremental.
The absolute encoder differs from the incremental encoder in that each angular location is represented by a different digital word.

41. Absolute Encoders
In the case of the incremental encoder, it is only possible to know your location relative to another location. The absolute encoder solves this problem by making each angular position unique. (An image of an absolute encoder disk is shown to the right.) Each separate location can be represented by a binary number, determined by the sequence of light transmission or blockage as you progress inward to the center.

42. Absolute Encoders
Contrary to incremental encoders, absolute encoders supply a clear code (information) in each angular position. This process offers the advantage that even in case of a power failure the actual position will be transmitted to the evaluation electronics. Furthermore, errors of measurement due to missing pulses and cumulative errors are excluded.
The primary advantage of the absolute encoder is that the position is not lost in the case of power loss or noise bursts. The largest disadvantage is added complexity and price.

43. Top of the Line – AstroCODER 150
Absolute Encoders
Top of the Line – AstroCODER 150
The only programmable absolute encoder that allows the user to
change programs on the fly.
Industry leading 680 µsecond scan time virtually eliminates error,
allowing for faster machine speeds while maximizing
productivity.
Built-in scalable resolution displays user defined units between
16 and 4096.
Includes resolver based transducers enhancing ruggedness while
maintaining absolute position even after loss of power.
Accepts inputs from one or two transducers providing independent
dual axis control.
Position data available in three user selected forms: Serial Digital, Parallel Digital and Analog Voltages.
Factory installed Astro data latch reacts to signal from PLC thereby accommodating any predetermined scan rate.
Available with Windows® or DOS® based start-up software

44. Incremental Encoders
Like any other position feedback device, the incremental encoder is used to determine rotary or linear position. The term “incremental” describes the type of information that the encoder sends out, being either incremental or absolute.
The encoder provides relative position information. As rotation or linear translation occurs, the incremental encoder sends out one pulse for each set incremental distance of travel. These pulses can be counted to determine the linear or rotary position relative to another position. Motion is quantified by a certain number of pulses.

45. Incremental Encoders
Usually, the incremental encoder will come with three channels, referred to as A, B, and Z. A and B are placed 90' out of phase. With these two channels, the
processor determines the distance
traveled by the number of steps, and
the direction traveled by the leading
wave form. The third channel is the
reference. Usually the Z channel will have only one pulse per revolution or per length of the encoder, so it can be used to determine an actual location, rather than just an incremental number. These encoders can be either magnetic, optical, contacting, or capacitive.

46. Incremental Encoders
The disadvantage of the incremental encoder is that it is unable to determine its location upon start-up, but this problem can be overcome by taking the time to do a homing or reference pulse sequence, and then moving the desired amount of steps from there. The added expense and setup time of an absolute encoder should be avoided unless completely necessary.
Another benefit of the incremental encoder is the large range of possible sizes and the high degree of compatibility.

47. Incremental Functions: Quadrature
Incremental optical encoders generate two data signals that are electrically 90° out of phase with each other, as shown below. The term quadrature refers to this 90° phase relationship. Since each full cycle contains four transitions, or edges, an encoder that generates 2500 cycles/rev, for example, provides 10,000 edges per revolution.

48. Quadrature
20+ years ago, the prevalent electronic circuitry of the day was based on "edge detection". The transitions coming from the encoder would act as the "trigger" to cause a count. At each transition, the electronics not only generates a count, but also determines direction of travel so that it knows whether to count up or down. This is done by establishing whether the transition is going high or going low, and what the state of the other signal is.
High
Low

49. Quadrature
However, modern electronics looks not at transitions, but at changes of state. Basically, the user's electronics contains a high-speed clock and constantly samples the states of A and B. When it sees a change, it counts up or down based on the following table, where 0,1 represents the states of A and B, respectively. Instead of waiting for a triggering event from the encoder, the electronics generates its own triggering based on its detection of a state change
from the encoder. A subtle difference, but critical to
the operation of modern digital circuitry.
FROM TO
0,1
1,1
0,0
1,0
Forward
Reverse

50. (For the interested reader)
Quadrature – Pulses
(For the interested reader)
Back when people were counting edges, it was often convenient to have the encoder vendor provide an output that not only identified a specific number of edges per cycle (1, 2 or 4), but also gave direction information directly. Pulse output was introduced for this purpose. Pulses differ from square waves in 2 important ways:
•       Pulse widths are of fixed time duration, whereas the width of a square wave ON state is a function of speed. (The distance between pulses is, of course, a function of position.)
•       "Quadrature" has no meaning with pulse output; you get FWD pulses on one line, and REV pulses on another. (Or pulses on one line and direction information on the other.)
       Pulse output options were fairly popular at one time, but it's been dwindling for quite a while. With quad decode chips that are available, the requirement has pretty much become obsolete.

51. A 3rd Method!?
Although many companies have attempted to develop a new method of encoding, time and again they have returned to the absolute and incremental methods. Until now….
A new type of encoder is currently being researched by Gurley Precision Instruments. A Gurley Virtual AbsoluteTM encoder is absolute in essence or effect without being formally recognized as such. (That's what virtual means.) In reality, it is neither an incremental encoder, nor an absolute encoder. It is a whole new kind of encoder based on pseudorandom encoding technology, which has certain details of construction similar to an incremental encoder, and certain kinds of behavior similar to an absolute encoder. Pseudorandom output codes directly from the disc or scale are not especially useful, so they've invented means for decoding those signals into a natural binary format you can use like any other encoder. This decoder (patent pending) stands in place of the quadrature decoder and up/down counter used with an incremental, so total cost need not be much more than an incremental encoder of comparable resolution. Yet it's effectively absolute!

52. A Virtual Absolute Encoder
A 3rd Method!?
A Virtual Absolute™ encoder uses just cyclic and index tracks, like an incremental encoder. However, the index track is a serial code similar to a bar code instead of just a single line. You do not know position immediately upon start-up, as you do in a conventional absolute, but after a very short travel, in either direction and starting from anywhere, you know exactly where you are. In a rotary VA™ encoder, this initialization angle is typically about one degree, depending on the encoder's line count; in a linear VA™ encoder, about 1/2 mm motion is needed. In a sense, from then on the encoder is truly absolute.
A Virtual Absolute Encoder

53. A 3rd Method!? Advantages of the Virtual Absolute™ technology are:
The initialization distance or angle is a fixed and very small motion, regardless of the starting position or direction of travel. Just "bump" it to find out where you are.
The encoder contains inherent built-in-test functions not found in any conventional encoder. It reports not only various encoder malfunctions, but can also help detect system problems such as too high a temperature or excessive speed.
The encoder generates the same whole-word information as a conventional absolute, so it is very easy to interface to computers, PLC's, servo controls, etc.
With its simpler optics, a rotary VA™ encoder can be smaller than a conventional absolute of equal resolution. And you can use a linear VA™ encoder for applications where a suitable conventional absolute linear would be very hard to find.
Because of its simpler electronics, reduced parts count, and less critical internal alignments, a VA™ encoder is inherently more reliable than a conventional absolute.
A VA™ encoder is usually dramatically less expensive than a conventional absolute.

54. Principal Types of Encoders
Rotary (77 Companies)
Linear (42 Companies)
Optical (69 Companies)
Magnetic (17 Companies)
List obtained from

55. Rotary Encoders

56. Rotary Encoders How they work
Most actuator systems contain some form of rotary motion. Often times, it is necessary to accurately locate the rotary position of that motion. One way of accomplishing this is with a rotary encoder. This device is used to convert a pattern on a rotary disc into an electrical signal which can be processed to determine angular position.

57. Rotary Encoders
Rotary encoders can be classified by two different characteristics:
1) technology used to convert rotary position to an electrical signal
type of electrical output
Several technologies are now used to convert rotary
information into an electric signal. The original method was
through physical contacts. This created obvious limitations in
speed, resolution, and life expectancy. This led to the evolution of
optical, magnetic, and capacitive techniques. The two most
commonly used encoders today are the optical encoders and the
magnetic encoders.

58. Rotary Encoders Applications
The rotary encoders are most often mounted to the back of a motor to determine the shaft position, but they are definitely not limited to this. They can be mounted to rotary positioning tables, screw drives, gearheads, machining tools, or any other application where a rotary actuator exists. Many drives and motion controllers can process common rotary encoder signals. Since the range of rotary encoders is so broad, there is one for almost every application requiring position feedback.

59. Rotary Encoders Current Specifications Measurement range of up to 360°
Contactless : no wear, no friction, high reliability
Magnetic : high mechanical ruggedness
Temperature range from -40°C to +85°C
Provides absolute position
Accuracy range of 1° to 0.05°
Digital or analog output
Low cost
Built-in self-test

60. Top of the Line – MicroE Systems G1400
Rotary Encoders
Top of the Line – MicroE Systems G1400
FEATURES
Miniature Sensor Package
Line Counts from 82K to 2.68B CPR
Safe Transmissive Design
Broad Alignment Tolerances
APPLICATIONS
Servo Track Writers
Head/Media Testers
Precision Stage Feedback
Grating Period: 5 µm
Resolution from 76.6 µrad to 2.37 nanoradians
Signal Period: 2.5 µm
Power Supply: VDC +/- mA, 12 VDC +/- mA
Speed: 1714 rpm

61. Linear Encoders

62. Linear Encoders How they work This device is used to convert
linear position information into an
electrical output signal. The linear
encoder consists of a linear tape scale
made up of glass or steel, a light source
(e.g. LED, laser), and a photoreceptor.
The light source, photoreceptor, and
additional scale are usually housed together. This housing either surrounds the tape scale in through beam encoders or resides on one side of the tape scale in reflective linear encoders.

63. Linear Encoders
Light is projected through or off the tape scale and is detected by the photoreceptor. The fixed scale modulates the light as the receptor and light source progress. The receptor detects these modulations and converts the input into an electrical output usually in the form of a quadrature signal (shown here). The two channels are always ' out of phase. The direction of the motion can be determined by the leading channel. The output is the same as that of the incremental encoder.

64. Top of the Line - GEL 221 Linear Scale IP66 - motor technology
Linear Encoders
Top of the Line - GEL 221 Linear Scale IP66 - motor technology
Features
Magnetic sensing principle
Corrosion resistant 12 mm measuring rod
Easy mounting and adjustment
0.01 mm resolution (w/ external edge-evaluation)
200kHz maximum output frequency
Temperature range °C or ºC
Supply voltage 5VDC±5% or VDC
IP66 protection

65. Optical Encoders

66. Optical Encoders How they work
This feedback device is used to detect rotary or linear position and convert it to an electrical output. A light source, usually either an LED or a laser, is projected through thin slits in a rotary disc for rotary encoders, or a thin tape scale for linear. The LED is adequate for most applications, although the laser has found niches in several high precision, high resolution applications The disk and tape can either be made of covered glass with thin etchings in the cover, or thin metal with etchings through it. Each has appropriate applications. As light is transmitted, a photo receptor on the opposite side of the disc or tape detects the light and converts it to an electrical output Different optical encoders can create a wide range of signals, (e.g. silicon cell, analog, sinusoidal).

67. Optical Encoders Advantages Optical encoders offer a higher resolution
and accuracy than all other encoders. Some
can offer in excess of 1 million counts per
Revolution (cpr). Often times the best way
to decide what feedback device you should use for your application is to determine what type of information your controller, PLC, smart drive, or other processor that you are using is capable of processing without too much trouble. Frequently many types of feedback will fit your needs, but only a couple will be simple to integrate. Due of the different signal options and versatility of the optical encoder, this is a very popular position feedback device.

68. Optical Encoders Pos. /Description 1 Circlip 2 Washer 3 Spacer
4 Ball bearing
5 Housing
6 LED support
7 LED 
8 Spacer ring
9 Codewheel 
10 Stator disk 
11 Printed circuit 
12 Cover
13 Ribbon cable
14 Connector 

69. Top of the Line - S5S single-ended optical shaft encoder
Optical Encoders
Top of the Line - S5S single-ended optical shaft encoder
Features
Small size
Low cost
Positive finger-latching connector
2-channel quadrature,
TTL squarewave outputs 3rd channel index option
Tracks from 0 to 100,000 cycles/sec
Ball bearing option tracks to 10,000 RPM
-40 to +100°C operating temperature
The S5S single-ended optical shaft encoder is a non-contacting rotary to digital converter. Useful for position feedback or manual interface, the encoder converts real-time shaft angle, speed, and direction into TTL-compatible quadrature outputs with or without index. The encoder utilizes an unbreakable mylar disk, metal shaft & bushing, LED light source, and monolithic electronics. It may operate from a single +5VDC supply.

70. Magnetic Encoders

71. Magnetic Encoders How they work
This device is used to convert position information into an electrical output that can be interpreted by a system controller. The two main components of a magnetic encoder are the read head and the magnetic disc. The read head contains a magneto resistive sensor, which is basically an inductor that detects changes in the magnetic flux. The disc is magnetically coded. The magnetic code is interpreted by the sensor as a series of on and off states One magnetic code is interpreted as a 0 bit value and the next as a 1 bit value. Through this combination the magnetic encoder is able to transmit pulses representing incremental rotary motion.

72. Magnetic Encoders Advantages Disadvantages
The magnetic encoder offers good resolution
can operate in a wide variety of conditions
requires low power for operation
Disadvantages
they cannot achieve very high speeds

73. Magnetic Encoders Pos. /Description 1 DC-Micromotor 2 Terminals
3 End cap
4 Housing
5 Magnet disk
6 Hall sensor 
7 Printed circuit 
8 Isolation
9 Cover 
10 Ribbon cable
11 Connector

74. Who Sells Them? (Thomas Register lists 100+ vendors)
>ACC >ATS >AVG Automation >Astrosystems Automation >Balluff Inc >Baumer Electric Ltd. >Computer Conversions Corp. >Dynamics Reseach Corp. >Eastern Air Devices >Globetron Electronics >Gurley Precision Instruments
>MicroE >Motor Technology UK Limited >NC Servo Technology >Omron Electronic Inc. >Ormec Systems Corp. >Parvex Inc. >Quin Systems Ltd. >Southern Power Inc >Space Age Control Inc >Stegmann Inc. >U.S. Digital Corporation

75. Where to Find out More? http://www.gpi-encoders.com/
(good source for info about how they work and lists of vendors)
(excellent website for more technical information about various types of encoders and their applications. Also source of VA encoders.)
(source of several leading encoders)
(great source for finding vendors of a specific type of sensor)

76. Glossary of Encoder Nomenclature
ACCURACY is a measure of how close the output is to where it should be. It is usually expressed in units of distance, such as ±30 arc seconds or ± inch. If it's expressed as a percent, make sure to state whether it's a percent of full scale (not usually meaningful with a rotary encoder) or a percent of nominal resolution.
BIT is an abbreviation for Binary digit; it refers to the smallest element of resolution.
CPR can mean either cycles/rev or counts/rev. To avoid confusion, this term should not be used.
ERROR is the algebraic difference between the indicated value and the true value of the input.
FREQUENCY RESPONSE is the encoder's electronic speed limit, expressed in kilohertz (1 kHz = 1000 Hz = 1000 cycles/sec). For calculations, rotational speed must be in rev/sec (rps = rpm/60); linear speed must be either in/sec or mm/sec, depending on the scale line count.

77. Glossary of Encoder Nomenclature
INDEX SIGNAL is a once-per-rev output used to establish a reference or return to a known starting position; also called reference, marker, home, or Z
INTERPOLATION involves an electronic technique for increasing the resolution from the number of optical cycles on the disc or scale to a higher number of quadrature square waves per revolution or per unit length. These square waves can then be quadrature decoded. MEASURING STEP is the smallest resolution element; it assumes quadrature decode. (see also QUANTUM) PPR (pulses per revolution) Commonly (but mistakenly) used instead of cycles/rev when referring to quadrature square wave output.
QUADRATURE refers to the 90-electrical-degree phase relationship between the A and B channels of incremental encoder output.

78. Glossary of Encoder Nomenclature
QUADRATURE DECODE (or 4X Decode) refers to the common practice of counting all 4 quadrature states (or square wave transitions) per cycle of quadrature square waves. Thus, an encoder with 1000 cycles/rev, for example, has a resolution of 4000 counts/rev.
QUANTIZATION ERROR is inherent in all digital systems; it reflects the fact that you have no knowledge of how close you are to a transition. It is commonly accepted as being equal to ±1/2 bit.
QUANTUM (plural is “quanta”) = BIT. It is the smallest resolution element. (quanta and bit are more commonly used with absolute encoders; counts/rev or measuring steps are more common with incremental encoders.) REPEATABILITY is a measure of how close the output is this time to where it was last time, for input motion in the same direction. It's not usually specified explicitly, but it is included in the accuracy figure. (As a rule of thumb, the repeatability is generally around 1/10 the accuracy.)

79. Glossary of Encoder Nomenclature
RESOLUTION is the smallest movement detectable by the encoder. It can be expressed in either electrical terms per distance (e.g., 3600 counts/rev or 100 pulses/mm) or in units of distance (e.g., 0.1° or 0.01 mm). SLEW SPEED is the maximum allowable speed from mechanical considerations. It is independent of the maximum speed dictated by frequency response.

80. Conversion Factors
ANGULAR MEASURE 1 revolution = 360° = 21,600 minutes = 1,296,000 seconds » 2pi radians (rad) 1° = 60 minutes (min) = 3600 seconds (s) » rad 1 min = 60 s = ° » mrad 1 s = min = ° » 4.85 µrad 1 rad » 57.3°; 1 mrad » 3.48 min; 1 µrad » s Sometimes the terms "arcminutes" and "arcseconds" are used to differentiate the units of angle
from the units of time. If the context makes the meaning clear, the "arc" prefix need not be used. Occasionally, the symbols ' and " are used to indicate arcminutes and arcseconds, respectively.
Because they can be confused with feet and inches, they should not be used.

81. Conversion Factors
LINEAR MEASURE 1 foot (ft) = 12 inches (in) = millimeters (mm) 1 in = 25.4 mm in = 25.4 micrometer (µm) 1 meter (m) » ft » in 1 mm » in 1 µm » µin The terms "mil" (= in; short for milli-inch) and "micron" (= 1 µm) should not be used.

82. Conversion Factors
SPEED 1 rev/min (rpm) = 1/60 rev/s (rps) 1 rad/s » 57.3 deg/s » rev/s 1 in/min » mm/s 1 mm/min » in/s