Operating instructions

Principles of Rotary Encoders
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PEPPERL+FUCHS
Operating Instructions for Absolute
Rotary Encoders
Absolute encoders do not generate pulses, but entire data
strings. The sampling unit in an absolute encoder reads the
code disk to determine the shaft position and the data is
transmitted by parallel or serial interface.
Single-turn
In single-turn absolute rotary encoders, each revolution of the
encoder (360°) is divided into a maximum of 65,536 measuring
steps (16 bit). After each complete revolution, the count begins
again at the initial value. A single turn absolute rotary encoder
does not count the number of revolutions.
Multi-turn
In addition to the coded disk in a single-turn encoder, a multi-
turn encoder adds a gear that counts up to 16,384 revolutions
(14 bit). Overall resolution amounts to 16 bit (single-turn
resolution) plus 14 bit (multi-turn resolution) for a total of 30
bits of resolution. The resulting 1,073,741,824 measuring
steps can be used to divide very long linear distances into
small measuring steps.
Interfaces
The Pepperl+Fuchs encoder line includes the industry’s largest
range of interfaces for absolute encoders:
SSI-Interface:
The Synchronous Serial Interface (SSI) has been developed
to transfer output data to a controller. The controller sends a
bundle of timer pulses and the absolute encoder responds
with the position value.
Parallel Interface:
With a parallel interface, data is sent directly from the Gray-
coded encoder measurement. A parallel interface’s primary
advantage is data transfer speed.
AS-Interface:
AS-Interface uses a multi-slave solution to provide real-time
encoder data transfer.
DeviceNet:
Encoders are available with fully integrated DeviceNet
interfaces that support all DeviceNet functions.
PROFIBUS:
PROFIBUS operation is supported in accordance with Class 1
and Class 2, and satisfies the PROFIBUS profile for encoders.
CAN:
Pepperl+Fuchs offers encoders with a recessed hollow shaft
and solid shaft design in single- and multi-turn versions. Each
model is in accordance with the CAN standard DSP406 (Class
1 and Class 2).
Ethernet:
These encoders are available with Ethernet TCP/IP interface.
The Ethernet interface is programmable via any web browser.
Types of Code
Binary Code
Binary code is a dual number system, consisting of the
numbers 0 and 1. When using binary code, it is important to
note that several bits may change at the same time from step
to step. For example, counting from seven to eight, the bits
0, 1, 2 and 3 change. In order to ensure high transmission
integrity, P+F recommends using a code which changes only
one bit at each step. The evaluating control can then be used
to determine whether the data string is accurate.
Gray Code
Gray code is a unit-distance code; only one bit changes from
step to step. To use this code for distance calculation, it must
be converted to a binary code. Gray code is recommended
for encoders because the data can be transmitted by a serial
interface. To check the unit-distance, every code change has
to be detected by the test logic.
Gray Excess Code
The Gray excess code is extracted from the complete Gray
code. In the process, clipping takes place symmetrically,
permitting the use of even sections only. The idea is that a
different number of measuring steps other than those given by
a power of 2 can be used. Frequently it is necessary to reduce
a 9-bit value (512 measuring steps) to 360 measuring steps.
The unit distance remains unaffected.
Intrinsic Safety Devices
Ignition Protection Class "Intrinsic Safety"
(EEx i) DIN EN 50020
By using the latest technology, it is possible to incorporate
a binary switching behavior in the sensor (with simultaneous
switch condition change on the sensor and amplifier), while
retaining the standardized voltage and current values. The
characteristic values of voltage and current are kept so low
that a NAMUR sensor can be used in an explosive area
(ignition protection class "Intrinsic safety").
NAMUR sensors are mounted to external amplifiers which convert
the current changes into a binary output signal. P+F offers a large
number of amplifiers for intrinsic safety applications.
NAMUR Sensors, Two-wire
NAMUR sensors in accordance with IEC 60947-5-6 are two-
wire sensors.
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