Encoders - Signal Conditioning

Encoders SIGNAL CONDITIONING
TECHNICAL NOTE
Most applications where rotary contacting encoders are used require the use of filters to condition the
digital output signal. Commercially available Integrated Circuits (IC) or Programmable Logic Chips
(PLCs) provide the proper debounce and noise filtration.
Although it may seem insignificant, some digital circuits may be extremely sensitive to wiper bounce.
The use of debounce filters is highly recommended with all contacting encoder models to avoid
miscounts that may be caused by wiper bounce.
Debounce filters such as the MC14490 Hex Contact Bounce Eliminator manufactured by ON
Semiconductor are often used to address encoder contact bounce. The diagram in figure 1 shows
a typical circuit configuration for encoder debounce filtering. For additional information and
(CUSTOMER LOGIC CIRCUITRY)
specification sheet on this device, visit ON Semiconductor’s
7 website
9 at http://onsemi.com.
Note: This device was formerly manufactured by Motorola.
DIRECTION
5 ms DELAY
DEBOUNCE
(CUSTOMER LOGIC CIRCUITRY)
(MC 14490)
0.0015 µf
7
9
DECODE
LOGIC
UP/DOWN
COUNTER
MAGNITUDE
DIRECTION
5 ms DELAY
DEBOUNCE
(MC 14490)
DECODE
LOGIC
UP/DOWN
COUNTER
BINARY
OUTPUT
Figure 1: Typical Debounce Circuit Configuration
MAGNITUDE
Figure 1: Typical Debounce Circuit Configuration
A second alternative for signal conditioning is
a noise filter circuit consisting of a few 10 kΩ
resistors and 0.01 μF capacitors. The circuit
should be configured as shown in figure 2.
5 VDC
10 K OHMS
10 K OHMS
10 K OHMS
10 K OHMS
TERMINAL A
TERMINAL B
0.01 µF
0.01 µF
A third alternative method for signal conditioning
is software programming. This method involves
the use of software filters generated through
program code to eliminate any miscounts that
may be caused by wiper bounce.
ENCODER
TERMINAL C
Figure 2: Noise Filter Circuit
Bourns® optical and magnetic encoders do not require signal conditioning. The custom designed
ASICs in these encoders provide sufficient signal noise filtration and produce a clean output
signal. However, if the encoders are being used in an application where vibration is present, it is
recommended that Schmitt-Trigger gates (components or software) be incorporated into the design
to prevent false triggers.
For further technical support and for complete encoder solutions, please visit
www.bourns.com
“Bourns” is a registered trademark of Bourns, Inc. in the U.S. and other countries.
COPYRIGHT© 2010 • BOURNS, INC. • 08/10 • e/SC1026
Americas: Tel +1-951 781-5500
Fax +1-951 781-5700
EMEA:
Tel +41-(0)41 768 55 55
Fax +41-(0)41 768 55 10
Asia-Pacific: Tel +886-2 256 241 17
Fax +886-2 256 241 16
BIN
OU
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