Decoding gray code, Plc output, Models ddn & ddp – Electro Cam PS-4456 Absolute Gray Code Encoder User Manual

Page 3: Model ddh, O:2.0 ( ) 0

Use a limit test function to program a pulse in the PLC. The limit test uses a test reference (in this case the integer
register that the Gray Code is going into), and compares it to see if it is between a lower limit and an upper limit. If the
integer value is between the lower limit (ON setpoint), and the upper limit (OFF setpoint), the rung is true and an output
is turned on. If the integer value does not fall between the upper and lower limits, the rung is false, and nothing happens.

For every output pulse to occur, a different limit test must be programmed with the appropriate limits. Reminder: The
limit values are position values, not degrees.

Decoding Gray Code?

The Ladder Programming examples shown below apply
for all Gray Code Encoder models. The examples show
how to convert the 8 Bit Gray Code output signal (G0-G7)
of the encoder to a binary number (B0-B7) during each
scan of the PLC. The value of the Binary result will al-
ways be in the range of 0 - 255 because the 8 bit encoder
divides each revolution into 256 uniform increments. Lad-
der rungs which follow the conversion can compare the
rotary position value to known positions for control of
machine devices that must operate at specific positions
within the overall machine cycle. The rotary position of

the machine cycle can also be used to gate input sensors
and shift register functions.

Converting Gray Code to Binary involves a sequence of
"Exclusive OR" operations. It is simple to program this
same conversion logic in other programming languages
besides ladder logic. In addition to decoding the rotary
position of the encoder, controls with arithmetic capability
can be programmed to perform direction reversal, posi-
tion offset and re-zero functions, as well as convert the
position value to degrees for ease of monitoring and setup.

Limit Test
Low Lim

107
107 <

Test

N7:0

0 <

High Lim

128
128 <

PLC

Output

O:2.0

( )

LIM

Models DDN & DDP

CLOCKWISE ROTATION

DRAWING L-1

COUNTER-CLOCKWISE ROTATION

DRAWING L-2

COUNTER-CLOCKWISE ROTATION

DRAWING L-3

CLOCKWISE ROTATION

DRAWING L-4

Model DDH

This manual is related to the following products:

PS-4256 Absolute Gray Code Encoder