Page 743 - Sensors and Systems - North American Catalog
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Rotary Encoders
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Rotary Encoders
Introduction
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
The Gray code is a one-step 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.
Application Notes for Rotary Encoders for
Hazardous Areas
"Flameproof enclosure" type of protection
(EEx d) DIN EN 50016/VDE/0170/0171 Part 5
“Ignition protection class in which the components that might ignite in an
explosive atmosphere are enclosed in a housing capable of withstanding
the pressure of an explosion inside and prevents the explosion from
spreading to the hazardous environment outside the housing.”
The housings are not constructed gas-tight, but have a gap serving as a
pressure relief aperture. Escaping gases are cooled down sufficiently so
that they cannot ignite the explosive atmosphere outside the housing. An
ignition is prevented if the minimum ignition temperature and the minimum
ignition energy of the surrounding explosive atmosphere are not reached.
For this reason, devices in this ignition protection class are approved for
the explosion groups I, IIA, IIB, IIC with different minimum gap lengths and
maximum gap widths (see table 1 and 2 of EN 50018) depending on the
type of gap.
The most important aspect of the ignition protection type Ex d is the relief
aperture that may neither be enlarged (e.g, removal of rust) or reduced
(e.g., lubrication with resinous oils or greases).
If devices with pressurized enclosures are used, the electrical connections
must comply with the ignition protection class “Increased safety.”
Series 14 and series 78E rotary encoders are designed in accordance with
ignition proctection class “Pressurized enclosure” and have ATEX approval.
