Page 740 - Sensors and Systems - North American Catalog
Basic HTML Version
Rotary Encoders
4
Rotary Encoders,
Absolute Rotary Encoders,
Standard
4
.1.1
Rotary Encoders,
Absolute Rotary Encoders
for hazardous areas
4
.1.3
Rotary Encoders,
Absolute Rotary Encoders
for safety applications
4
.1.2
Rotary Encoders,
Incremental Rotary Encoders
with pulse outputs
4
.2.1
Rotary Encoders,
Incremental Rotary Encoders,
Sine/Cosine
4
.2.2
Rotary Encoders,
Incremental Rotary Encoders
for hazardous areas
4
.2.4
otary Encoders,
Incremental Rotary Encoders
for safety applications
4
.2.3
Rotary Encoders,
Safety Speed Monitor
4
.5
Rotary Encoders,
Cable pulls
4
.3
Rotary Encoders,
Accessories
4
.4
738
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Refer to General Notes Relating to Product Information
Pepperl+Fuchs Group
USA: +1 330 486 0001
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Copyright Pepperl+Fuchs
Rotary Encoders
Introduction
Application Notes for Incremental Rotary
Encoders
Incremental rotary encoders emit pulses as the shaft is rotated, and the
number of pulses is used to calculate angular position. The resolution (Z)
of an incremental encoder is the number of pulses per revolution. The
signal frequency is used to determine the angular speed (ω) and the
change in position for a given period of time is used to calculate the angular
acceleration (α).
Rotational direction monitoring with incremental
rotary encoders
In order to determine the direction of rotation of a movement, the scanning
principle is used on both channel A and channel B. The direction of rotation
can be determined by evaluating the two signals, which are phase-shifted
by 90 degrees.
In the first figure below (I cw), channel A precedes channel B.This indicates
clockwise rotation. II ccw shows counter-clockwise rotation.The direction of
rotation is determined by viewing the encoder shaft head-on.
Depending on the type of incremental rotary encoder, channel A or channel
B is the leading channel. For more information, refer to the encoder data
sheet.
A
B
A
B
90˚
I cw
II ccw
Q
P
Zero signal
Determining the frequency of the pulses is the job of the controller, PLC or
tachometer. The zero signal is a pulse that occurs once per revolution at a
fixed point and is transmitted using a third channel (often called channel 0
or Z). The zero signal is usually used as a reference signal for positioning.
The diagram below illustrates the output of a 3-channel incremental rotary
encoder.
A
B
0
Note:
catalog refers to zero channel signal as “Z” channel. This position
signal can also be referred to as “0” channel or encoder marker pulse.
Inverted channels
Inverted
signals
are
transmitted
in
addition
to
channels
A, B and Z to improve signal quality. Inverted signals are a standard feature
in RS-422 interfaces and are optional on push-pull outputs.
A
A
B
B
0
0
The advantage of normal and inverted signal transmissions is that filtering
of unwanted signals is possible. If a noise pulse occurs, it will be induced
equally on all channels.Subtracting the normal and inverted encoder signals
from each other eliminates the noise pulse. The figure below illustrates how
this is done.
5 V
A
0 V
5 V
0 V A
A
5 V
0 V
Pulse multiplication
Pulse multiplication is used to increase the number of measuring steps or to
reduce the output frequency of an incremental rotary encoder. The signals
of an incremental rotary encoder can be doubled or quadrupled by linking
channels A and B.
For example, an application may need 20,000 measuring steps for each
revolution at a speed of 3000 RPM. If the control unit (PLC, counter
or tachometer) provides the option to quadruple the signal, then an
inexpensive rotary encoder with 5000 pulses can be used. In addition, the
output frequency of the incremental rotary encoder is reduced.
•
Without quadruple multiplication: 1 MHz (this frequency is too high for
most control units)
•
With quadruple multiplication: 250 kHz
A
B
x 2
.Doubling of signals
Interference
Signal cable
Inverted signal
cable
Filtered signal
