Encoders are sensors that generate digital signals in response to movement. Both
shaft encoders, which respond to rotation, and linear encoders, which respond to
motion in a line, are available. When used in conjunction with mechanical conversion devices, such as rack-and-pinions, measuring wheels, or spindles, shaft
encoders can also be used to measure linear movement, speed, and position.
Encoders are available with a choice of outputs. Incremental encoders generate a
series of pulses as they move. These pulses can be used to measure speed, or be fed
to a counter to keep track of position. Absolute encoders generate multi-bit digital
words that indicate actual position directly.
Encoders can be used in a wide variety of applications. They act as feedback transducers for motor-speed control, as sensors for measuring, cutting and positioning,

and as input for speed and rate controls. Some examples are listed below

• Door control devices • Assembly machines
• Robotics • Labeling machines
• Lens grinding machines • x/y indication
• Plotters • Analysis devices
• Testing machines • Drilling machines
• Ultrasonic welding • Mixing machines
• Converting machinery • Medical equipment
SENSING TECHNOLOGY
Encoders can use either optical or magnetic sensing technology. Optical sensing
provides high resolutions, high operating speeds, and reliable, long life operation in
most industrial environments. Magnetic sensing, often used in such rugged applications as steel and paper mills, provides good resolution, high operating speeds, and
maximum resistance to dust, moisture, and thermal and mechanical shock.
Optical Encoders
Optical encoders use a glass disk with a pattern of lines deposited on it, a metal 
or plastic disk with slots (in a rotary encoder), or a glass or metal strip (in a linear
encoder). Light from an LED shines through the disk or strip onto one or more 
photodetectors, which produce the encoder’s output. An incremental encoder has
one or more of these tracks, while an absolute encoder has as many tracks as it has
output bits.
Incremental Disk Absolute Disk Linear Scale
2 Danaher Industrial ControlsMagnetic Encoders
Magnetic sensing technology 
is very resistant to dust, grease,
moisture, and other contaminants common in industrial
environments, and to shock 
and vibration. There are several
types of magnetic sensors.
Variable reluctance sensors
detect changes in the magnetic
field caused by the presence or
movement of a ferromagnetic
object. The simplest variable-reluctance rotary sensor, often called a magnetic pickup, consists of a coil wound around a permanent magnet. This generates a voltage
pulse when a gear tooth moves past it. Rugged, reliable, and inexpensive, this
sensor is used mostly to measure speed, as it does not work unless the target is
moving past the sensor face at about 180 inches per second or faster. 
Another type of sensor uses a permanent magnet and a Hall effect or magnetoresistive device to produce a change in either voltage or electrical resistance in the presence of ferromagnetic material, which can be in the form of a gear tooth (in a rotary
encoder) or a metal band with slots (in a linear encoder). This type of sensor will
work down to zero speed, and is available in both rotary and linear forms.
Another type of magnetic sensor uses a magnetoresistive device to detect the presence or absence of magnetized “stripes,” either on the rim of a drum or on a nonmagnetic strip.
ABSOLUTE VS. INCREMENTAL CODING
Incremental Coding
Incremental encoders provide
a specific number of equally
spaced pulses per revolution
(PPR) or per inch or millimeter of linear motion. A
single channel output is used
for applications where sensing the direction of movement is not important. Where
direction sensing is required, quadrature output is used, with two channels 90 electrical degrees out of phase; circuitry determines direction of movement based on the
phase relationship between them. This is useful for processes that can reverse, or
must maintain net position when standing still or mechanically oscillating. For
example, machine vibration while stopped could cause a unidirectional encoder to
produce a stream of pulses that would be erroneously counted as motion. The controller would not be fooled when quadrature counting is used.
When more resolution is needed, it’s possible for the counter to count the leading
and trailing edges of the pulse train from one channel, which doubles (×2) the number of pulses counted for one rotation or inch of motion. Counting both leading and
trailing edges of both channels will give 4× resolution. 
Encoder Application Handbook 3
Inductive PrincipleAn incremental encoder’s output indicates motion. To determine position, its pulses
must be accumulated by a counter. The count is subject to loss during a power
interruption or corruption by electrical transients. When starting up, the equipment
must be driven to a reference or home position to initialize the position counters.
Some incremental encoders also produce another signal known as the “marker,”
“index,” or “Z channel.” This signal, produced once per revolution of a shaft
encoder or at precisely-known points on a linear scale, is often used to locate a specific position, especially during a homing sequence.
Absolute Coding
An absolute encoder generates digital words that represent the encoder’s actual
position, as well as its speed and direction of motion. If power is lost, its output will
be correct whenever power is restored. It is not necessary to move to a reference
position as with incremental type encoders. Electrical transients can only produce
transient data errors, usually too brief to effect the dynamics of a control system.
An absolute encoder’s resolution is defined as the number of bits in its output word.
This output can be in straight binary or in gray code, which produces only a singlebit change at each step to reduce errors.
The difference between incremental and absolute encoders is analogous to the
difference between a stop watch and a clock.
A stop watch measures the incremental time that elapses between its start and
stop, much as an incremental encoder will provide a known number of pulses
relative to an amount of movement. If you knew the actual time when you started the watch, you can tell what time it is later by adding the elapsed time value
from the stop watch. For position control, adding incremental pulses to a known
starting position will measure the current position.
When an absolute encoder is used, the actual position will constantly be transmitted, just as a clock will tell you the current time.
Single vs. Multi-Turn
In a single-turn encoder, the output codes are repeated for every revolution of the
encoder’s shaft. There is no data provided to indicate if the encoder had made one
revolution—or 1000 revolutions. With multi-turn absolute encoders, the output is
unique for each shaft position, through every rotation, up to 4096 revolutions.
RESOLUTION AND ACCURACY
Resolution is the number of measuring segments or units in one revolution of an
encoder shaft or one inch or mm of a linear scale. Shaft encoders are available with
resolutions up to 10,000 pulses per revolution (PPR) directly, and 40,000 PPR by
edge-detection of the A and B channels, while linear encoders are available with
resolutions measured in microns. The bottom line is, the selected encoder must have
resolution equal to or better than that required by the application. But resolution is
not the whole story.
Accuracy and resolution are different, and it is possible to have one without the
other. This figure shows a distance X divided into 24 increments or “bits.” If X represents 360° of shaft rotation, then one revolution has been resolved into 24 parts.
4 Danaher Industrial ControlsWhile there are 24 bits of
resolution, the 24 parts are
not uniform. This transducer
could not be used to measure
position, velocity or acceleration with any accuracy. 
On the other hand, in this
figure the distance X is
divided into 24 equal parts.
Each increment represents
exactly 1/24 of a revolution.
This transducer operates with accuracy as well as resolution. Accuracy, however,
can be independent of resolution. A transducer may have a resolution of only two
parts per revolution, yet its accuracy could be ±6 arc seconds.
System Effects on Accuracy and Repeatability
System Accuracy: An encoder’s performance is typically stated as resolution,
rather than accuracy of measurement. The encoder may be able to resolve movement into precise bits very accurately, but the accuracy of each bit is limited by the
quality of the machine motion being monitored. For example, if there are deflections of machine elements under load, or if there is a drive screw with 0.1 inch of
play, using a 1000 count-per-turn encoder with an output reading to 0.001 inch will
not improve the 0.1 inch tolerance on the measurement. The encoder only reports
position; it cannot improve on the basic accuracy of the shaft motion from which
the position is sensed.
Note: Given a particular machine design, some errors in measuring motion such 
as mechanical backlash and errors in leadscrews or gearing systems, can be
electronically compensated by some of the more advanced motion controllers.
System Repeatability: Repeatability is the tolerance to which the controlled
machine element can be repeatedly positioned to the same point in its travel.
Repeatability is generally less than system resolution, but somewhat better than
system accuracy. 10,000 pulses per turn can be generated from a 2500 cycle, twochannel encoder. Typically with a Dynapar encoder, this 4× signal will be accurate
to better than ±1 count.
ENCODER COMMUNICATIONS
The output of an incremental encoder is a stream of pulses on one or two channels,
while the output of an absolute encoder is a multi-bit word. This can be transmitted
in either parallel or serial form.
Parallel Output
Parallel output makes all output bits available simultaneously. It may be provided as
straight binary or transformed into gray code. Gray code produces only a single-bit
change at each step, which can reduce errors. The table on page 6 shows an example of conversion between straight binary and gray code. 
Some parallel-output encoders also can accept inputs from the outside—output
latching commands, for example, and direction sense setting.
Encoder Application Handbook 5The advantage of parallel output is that it’s fast: 
all the data is available in real time, all the time.
Disadvantages include bulky (and expensive) cables
and limited cable length. Most encoders come with
cables a meter or two long, but a parallel output
using differential output and shielded cabling can
be extended to 100 m using a thicker cable, at a
reduction in speed. Open-collector (sinking or
sourcing) outputs can go roughly a third that far.
Serial Output
The alternative to parallel output is to encode it and
send it in serial form. There are several dedicated
serial buses available, as well as standard industrial
buses. Tradeoffs among these include bandwidth,
update rate, hardware requirements, wire count,
proprietary vs nonproprietary nature, and availability. The table below summarizes the major
differences.
SSI® (Synchronous Serial Interface)
Synchronous Serial Interface is an all-digital point-to-point interface popular in
Europe. It provides unidirectional communication at speeds up to 1.5 MHz and uses
a four-wire cable (plus two wires for power). 
Dedicated Serial Interfaces
HIPERFACE® SSI + Sine/ Cos EnDat® BiSS
Open Protocol No No (License
available) No Yes
Connection
RS-485: Bus or
Point-to-Point
Analog: Pointto-Point
Point-to-Point Point-to-Point Bus or
Point-to-Point
Analog Signals
Required Yes Yes No No
Transmission Mode
(Digital)
Bidirectional,
asynchronous
Unidirectional,
synchronous
Bidirectional,
synchronous
Bidirectional,
synchronous
Digital Data
Transmission Rate 38.4 kBaud 1.5 MHz 4 MHz 10 MHz
Cable Length
Compensation No No Yes Yes
Protocol Length
Adjustable No No Yes Yes
No. of Wires 8 6–8 6 to 12 6
Hardware
Compatible
Alarm/Warning Bit No Definable Yes Definable
6 Danaher Industrial Controls
Decimal Gray Code Binary
0 0000 0000
1 0001 0001
2 0011 0010
3 0010 0011
4 0110 0100
5 0111 0101
6 0101 0110
7 0100 0111
8 1100 1000
9 1101 1001
10 1111 1010
11 1110 1011
12 1010 1100
13 1011 1101
14 1001 1110
15 1000 1111Some encoders also provide a 1 V p-p sin/cos output
for real-time control, since the on-demand absolute
encoder data can come in too slowly for many control
loops.
Data rate depends on both resolution and cable length,
as shown.
EnDat®
EnDat (Encoder Data) is a proprietary protocol developed by Heidenhain. Like SSI,
it is synchronous, with clock signals fed to the encoder by the controller. EnDat can
carry more information than SSI, because it provides for internal memory in the
encoder that can be read and written to by the controller. This data can include
encoder diagnostics, identification, and alarm status. In addition, the controller can
set the encoder’s zero reference point, which aids in equipment setup. As with SSI,
EnDat encoders transmit absolute position data on demand. Depending on version
EnDat can include an analog 1 V p-p sin/cos output that electronics in the controller
interpolate to derive incremental data for real-time control. EnDat uses a six- to
twelve-conductor cable up to 150 m long, 
HIPERFACE®
HIPERFACE is a proprietary protocol developed by Max Stegmann GmbH. It uses
an eight-wire cable (two for data, two for power and four for 1Vp-p sin/cos) and
has two channels: One carries 1 V p-p sin/cos incremental data, while the other is a
bidirectional RS-485 link. Absolute position data is transmitted via the RS-485 link
at power-up, and the system is incremental after that.
HIPERFACE can access the encoder’s memory area for manufacturer’s data, status,
alarm information, and so on. In addition, the controller can write to certain memory areas, and can set the absolute zero position. 
BiSS 
BiSS (Bidirectional Synchronous Serial interface), is an open protocol and is the
newest of the encoder interfaces. It takes a somewhat different path: BiSS sends full
absolute position data whenever the controller polls the encoder, rather than just at
startup. It allows easy recovery from momentary data dropouts during operation.
Since it is an all-digital system, it eliminates the cost of A/D converters needed in
drive systems that connect to encoders using some proprietary protocols. It is hardware-compatible with SSI, requiring only software changes. 
BiSS uses four data lines, one pair carrying data from the encoder and one carrying
clock data to it, plus two power conductors. 
BiSS can address internal registers in the encoder that can be read by and written to
by the master with data about the encoder itself (identification, device data, resolution, etc.). It can also carry other digital data (temperature, acceleration, etc.) and
transmit it to the master on demand, without interfering with real-time operation.
BiSS, like HIPERFACE, can be connected either point-to-point or via a bus.
Cable Length Data Rate
50 m 400 kHz
100 m 300 kHz
200 m 200 kHz
400 m 100 kHz
Encoder Application Handbook 7Industrial Bus Interfaces
Three general-purpose industrial buses are commonly used with encoders.
DeviceNetâ„¢
Based on the Controller Area Network (CAN), this system’s basic trunklinedropline topology provides separate twisted-pair wires for both signal and power
distribution, enabling 24 VDC devices to be powered directly from the bus. End-toend network distance varies with data rate and cable size. 
Profibus
This open communication standard developed by the European Community
(European Common Standard EC50170), comes in two variations: FMS, which 
is used for upper level cell-to-cell communication, and Profibus DP, which is
optimized for data transfer with local field devices like valves, drives and encoders.
There are specific device profiles defined, including one for encoders. DP is good
for applications that require high speed transmission of fairly large amounts of
information (512 bits of input data and 512 bits of output data over 32 nodes 
in 1 ms).
Interbus®
Designed by Phoenix Contact in the mid ‘80s, Interbus is the longest-standing open
industrial network. A true token ring topology, Interbus is actually divided into two
buses. The remote bus is an RS-485 transmission medium with length capabilities
up to 13 km. The local or peripheral bus enables connection of up to eight devices
within a 10 m range. 
Bus Network Comparison
DeviceNet Profibus Interbus
Topology Linear
(trunkline/dropline)
Linear
(trunkline/dropline) Closed Loop
Communication
System Master/Slave Multimaster
(Producer/Consumer) Master/Slave
Data Exchange Polled, Change of State,
Cyclic Polled Polled
Max. Length 500 m 1200 m (w/repeaters) 13 km
Max. Nodes 64 126 512
Data Packet 0–8 bytes 244 bytes Flexible
Transmission
Speed
125 Kbps @ 500 m
250 Kbps @ 250 m
500 Kbps @ 100 m
9.6 Kbps to 12 Mbps 500 Kbps
Transmission
Media
2-wire twisted pair with
2-wire bus power cable
w/drain wire
2-wire twisted pair
w/shield
Local: 3-pair twisted
w/drain
Remote: 5-pair twisted
w/drain
8 Danaher Industrial ControlsAPPLICATIONS
Linear/Straight-Line Measuring with Shaft Encoders
Through mechanical means, usually racks and pinions or leadscrews, rotary
encoders can measure straight-line or linear motion. Calibrating the number of pulses per unit of measure involves selecting the proper transducer and may include a
separate calibration step. 
Measuring Length with Leadscrews
The relationship between resolution, lead screw pitch, and PPR is shown below.
Lead 1 Resolution = ______ =
______________
PPR PPR× Pitch
Lead 1
PPR = ___________ =
_____________________
Resolution Resolution × Pitch
The table below shows some examples. Note that the PPR of an encoder can be
doubled or quadrupled by counting the rising and falling edges of one or both output channels, so a 1000 PPR encoder with a 4× multiplication will act like a 4000
PPR encoder.
Examples:
1. An incremental encoder is required on a milling machine to provide a digital
readout display. The display must read directly in ten thousandths of an inch. The
travel is regulated by a 10-pitch precision leadscrew, which moves the bed 1/10th
inch for every revolution of the leadscrew. Using the formulas, 
1 1
PPR = ___________________ =
______________
Resolution × Pitch 0.0001 × 10
Alternatively, 
Lead 0.1
PPR = ___________ =
________ = 1000 Resolution 0.0001
Encoder PPRs and Servo Resolutions for Typical Leadscrew Applications
Servo Resolution
Encoder PPR and Logic Multiplier
0.5-in. Lead (2 pitch) 0.25-in. Lead (4 pitch) 0.2-in. Lead (5 pitch)
0.0001 in. 1250 × 4 625 × 4 500 × 4
0.00005 in. 2500 × 4 1250 × 4 1000 × 4
0.0005 in. 250 × 4 250 × 2 200 × 2
0.00025 in. 500 × 4 250 × 4 200 × 4
0.0002 in. 625 × 4 625 × 2 500 × 2
0.001 mm 3175 × 4 (special) 3175 × 2 1270 × 4
0.002 mm 3175 × 2 3175 × 1 635 × 4
0.01 mm 635 × 2 635 × 1 508 × 1
0.005 mm 635 × 4 635 × 2 508 × 2
Encoder Application Handbook 9So the encoder must have 1000 PPR, whichever way we calculate it. If we like,
we could also use a 500 PPR encoder with a 2× logic multiplier.
2. To measure 10 inches of travel to 0.01 inch resolution: Total count = 1000;
Resolution = 0.01 inch. If the encoder makes one full turn over the total travel, a
1000 PPR encoder can satisfy this requirement. At full travel, the encoder and
counter will read 9.99, which is within the stated tolerance of 0.01 inch.
Measuring Length with Wheels and Rolls
An encoder can also measure linear distance using a measuring wheel or roll. The
table below gives the calibration constant, K, that must be set on the counter or tach
readout in order to give the display resolution desired.
Examples:
Length Application
Display Resolution Type 1 Measuring Wheel Type 2 Measuring Roll
1 Foot C
K = ____
12N
0.2618D K = _________
GN
1 Inch C
K = ___
N
3.1416D K = _________
GN
0.1 Inch 10C K = ____
N
31.416D K = _________
GN
0.01 Inch 100C K = _____
N
314.6D K = _______
GN
1 Meter M K = ___
N
0.079796D K = ___________
GN
1 Decimeter 10M K = _____
N
0.797966D K = ___________
GN
1 Centimeter 100M K = ______
N
7.97966D K = __________
GN
1 Millimeter 1000M K = _______
N
79.796D K = _________
GN
0.1 Millimeter 10,000M K = _________
N
797.966D K = __________
GN
10 Danaher Industrial ControlsExample: In a Type 2 application we wish to display feet to the nearest 1 foot.
From the table above:
0.2618D
K = _________
GN
If G = 2.6, N = 1, D = 9.15,
0.2618 × 9.15
K = ______________ = 0.92133 2.6 × 1
Ratio Calibration
In some cases, the desired display
is the ratio of two inputs, A and B.
This table shows how to calculate
the calibration factor, K, for the A
and B inputs to the counter to give
the desired display resolution.
WHERE: 
G = Gear Ratio (increases rpm of encoder in relation to rpm of roll)
N = Encoder pulses per revolution
D = Roll diameter in inches
C = Measuring wheel circumference in inches
Example: Assume that both inputs are Type 2 and you want a 0.001-in. display
resolution.
Input A Input B
15.708D 15.708D
K = _________ K = _________
GN GN
D = 17.0 in. D = 19.2 in.
N = 12 N = 12
G = 3.5 G = 2.8
Then:
15.708 × 17.0 15.708 × 19.2
KA
=
_____________ KB
=
______________
12 × 3.5 12 × 2.8
= 6.3580 = 8.9760
Establishing Reference Position
Reference Pulse
An incremental encoder’s reference pulse (sometimes called a Marker or Index
Pulse) occurs at a precisely-known point in a 360° revolution of a shaft encoder or
along a linear scale. A unique position can be identified by using the referenceRatio Application
Display
Resolution Type 1 Type 2
.001 5C K = ___
N
15.708D K = _________
GN
.0001 50C K = ____
N
157.08D K = _________
GN
Encoder Application Handbook 11pulse output only, or by logically relating the reference pulse to the A and B data
channels. Thus it is most frequently used in positioning and motion control applications as an electronic starting point of known position from which counting or position tracking begins.
In long travel or multiple turns of the encoder, the reference pulse is sometimes
used by the control to initiate an electronic check on the total count received from
the encoder. For example, each time a reference pulse is received by the control, the
total count received from channels A and B should be an even multiple of the
encoder’s pulses per revolution.
Ballscrew Position Table Example
In motion control encoder applications, a PLC, CNC, or motion
controller will usually command a
sequence of moves with each axis
of a positioning system to bring
the table to the same starting position before beginning a task. The
following is a typical automatic
referencing and backlash compensation sequence for establishing a
home position through the use of an encoder marker pulse.
1. If the Home Switch is open (indicating a position on the positive side of home)
when the command is received, the axis is accelerated in the negative direction at
the JOG ACCELERATION rate and moved at the FAST JOG VELOCITY until
the Home Switch closes. 
Note that a mechanical home-position limit switch is usually not repeatably
accurate enough for this application. The encoder reference or marker pulse has
much greater repeat accuracy and is therefore a better reference point to establish a starting point for subsequent measurements. The home limit switch is used
to signal the control that the next marker pulse signal received is “Home” in
multi-turn encoder applications.
2. The axis is stopped at the JOG ACCELERATION rate.
3. The axis is accelerated in the positive direction at the JOG ACCELERATION
rate and moved at the FAST JOG VELOCITY until the Home Switch opens.
4. The axis is accelerated in the negative direction at the JOG ACCELERATION
rate and moved at the SLOW JOG VELOCITY until the Home Switch closes
and an encoder marker pulse is sensed by the control (in that order).
5. The axis is stopped at the JOG ACCELERATION rate.
Transducer Operating Speed
All transducers have inherent mechanical and electronic speed limitations, and
exceeding them may result in incorrect data or premature failure. The maximum
operating speed for a given application will be the maximum electronic operating
speed of the encoder and the electronics to which it is connected, or the encoder’s
maximum mechanical RPM specification, whichever is less.
12 Danaher Industrial ControlsGENERAL WIRING AND INSTALLATION GUIDELINES
The most frequent problems encountered in transmitting an encoder’s signal(s) to
the receiving electronics are signal distortion and electrical noise. Either can result
in gain or loss of encoder counts. Many problems can be avoided with good wiring
and installation practices. The following descriptions and recommendations are presented as general guidelines and practices for field-installed equipment.
Protecting Signals from Radiated and Conducted Noise
Take reasonable care when connecting and routing power and signal wiring on a
machine or system. Radiated noise from nearby relays (relay coils should have
surge suppressors), transformers, other electronic drives, etc. may be induced into
the signal lines causing undesired signal pulses. Likewise, the encoder may induce
noise into sensitive equipment lines adjacent to it.
Route machine power and signal lines separately. Signal lines should be shielded,
twisted and routed in separate conduits or harnesses spaced at least 12 inches from
power leads. Power leads are defined here as transformer primary and secondary
leads, motor armature leads and any 120 VAC or above control wiring for relays,
fans, thermal protectors, etc.
Maintain continuity of wires and shields from the encoder through to the controller,
avoiding the use of terminals in a junction box. This helps to minimize radiated and
induced noise problems and ground loops.
In addition, operation may be influenced by transients in the encoder power supply.
Typically, encoder power should be regulated to within ±5%, and it should be free
of induced transients.
The encoder case must also be grounded to insure proper and reliable operation. Dynapar encoders usually have
provisions for a case ground connection through the connector/cable if a ground cannot be secured through the mounting bracket/machine ground. DO NOT ground the encoder case through both the
machine and the cable wiring. Use high quality shielded wire only and connect the
shield only at the instrument end, as shown.
For more protection against electrical
noise, specify an encoder with complementary output signals and connect
with twisted-pair shielded wire—
induced currents will self-cancel, as
shown.
In industrial environments, high current
fluxes are created by motors, remote
control switches and magnetic fields.
This can result in varying electrical
potentials at different ground points. 
To avoid problems, ground the shield,
together with all other parts of the system requiring grounding, from a single
point at the instrument end, as shown.
Encoder Application Handbook 13Signal distortion can be eliminated
by complementary encoder signals
(line drivers), used with differential
receivers (line receivers or comparators) at the instrument end, 
as shown here.
Grounding requirements, conventions and definitions are contained in the National Electrical Code. Local codes will
usually dictate the particular rules and regulations that are to be followed concerning system safety grounds.
Signal Distortion
The majority of signal transmission problems involve electrical noise. Severity of
the problem increases with transmission
distance. Good shielding practice, as
described previously, should be observed.
The primary cause of signal distortion is
cable length, or more specifically, cable
capacitance.
Generally, the receiving electronics will
respond to an input signal that is either logical “0” or logical “1”. The region
between logical 0 and logical 1 is undefined, and the transition through this region
must be very rapid (less than about 1 microsecond). As the leading edge of the
waveform is distorted, the transition time increases. At some point, the receiver
becomes unstable and encoder counts may be gained or lost.
To minimize distortion, low capacitance cable (typically less than 40 picofarads per
foot) should be used. The longer the cable, the greater the potential for signal distortion. Beyond some cable length, the signal must be “reshaped” before it can be
used reliably.
Squarewave distortion is not usually significant for cable lengths less than about 50
feet (capacitance up to about 1000 picofarads). Encoders supplied with differential
line drivers are recommended for applications with cable length requirements of
hundreds of feet.
Greater assurance of signal integrity is
best achieved when an encoder with
line driver outputs is used in conjunction with a line receiver.
14 Danaher Industrial ControlsMECHANICAL INSTALLATION
Encoders are available in (below, l to r) shaft, hub shaft, and hollow shaft configurations. 
The method of coupling the encoder to the machine is important because of possible errors or stresses which can be introduced. Take care not to exceed the rated
shaft loading, both radial and axial.
Common causes of difficulty are end thrust, misalignment, and belt or gear thrust.
Backlash or modulation in the coupling can cause errors in position indication. The
smallest misalignment can result in high radial loads, which lead to premature bearing failure. To prevent this, use a flexible coupling that compensates for the misalignment between the shaft of the encoder and the machine. Generally, the greater
the misalignment, the quicker the coupling will fail. When selecting the coupling
determine how long it will last under operating misalignment, and the effect of this
misalignment on shafts and bearings. This will yield better results than just choosing a coupling solely on the basis of how much misalignment it will take. A coupling will last indefinitely if there is no misalignment. 
Encoders usually require a precision instrument coupling to prevent errors caused
by backlash and to prevent damage to shaft and bearings. Specifically, do not use
fingered motor couplings with rubber spacers.
Timing Belts
Use Series XL timing belts. Reliable long-life encoder performance is achievable
provided the belt is installed in accordance with the manufacturer’s instructions.
Belt Tension: The belt’s positive grip eliminates the need for high initial tension. 
A properly tensioned belt will last longer, cause less wear on encoder bearings, and
operate more quietly.
General Guidelines
Encoders are used to provide precise measurements of motion.
• Never hammer the end of the shaft.
• Avoid hammering the encoder case when mechanical fits are tight.
• Do not subject the encoder to radial or axial shaft stress.
• Do not use a rigid coupling or makeshift mounting techniques.
Encoders provide quality measurements and longer life when common sense, care,
and accurate alignments are achieved at the time of installation.