5
8902/E1 Sin/Cos Speed Feedback Option
Parameter Descriptions
ENCODER MECH
O/S
PREF: 71.06
Default: 0.0000 deg Range: 0.0000 to
360.0000 deg
(encoder mechanical offset) Use this parameter ro enter a mechanical offset of between 0
and 360 degrees to allow the output shaft position to be correctly zeroed. This value is
subtracted from the LOAD POSITION which is reported by the encoder.
To zero the shaft position: turn the shaft to the zero position; note the value of the LOAD
POSITION parameter, and enter this value into the ENCODER MECH O/S parameter.
LOAD POSITION will now read zero.
Note that “load position” refers here to the shaft position on the other side of a gearbox
which may be mounted on the motor output. It does not refer to the motor shaft position,
unless the output gearbox ratio (LOAD G'BOX RATIO) is set to 1 (i.e. no gearbox fitted).
ENCODER FBK %
PREF: 71.08
Default: —.xx %
Range: —.xx %
This parameter shows the mechanical speed of the motor shaft, calculated from the encoder
feedback, as a percentage of the user maximum speed setting (MAX SPEED in the
REFERENCE function block).
SHAFT POSITION
PREF: 71.09
Default: —.xx deg
Range: —.xx deg
This diagnostic provides the motor shaft position (before the gear box).
LOAD POSITION
PREF: 71.10
Default: —.xx deg
Range: —.xx deg
This is the position of a shaft on the other side of a gearbox attached to the motor. If a
gearbox is not fitted, set LOAD G'BOX RATIO to 1. This variable is controlled by the
position loop, i.e. the position loop will force the load position to equal the demanded
position.
Save the Application
Remember to save your new configuration in DSE 890 and install it in the drive. In DSE 890,
select "Command
Æ
Install At Selected" to install the currently opened configuration into a
drive.
Functional Description
A Sin/Cos encoder uses 2 input signals, SIN and COS
which by definition are offset by a quarter of a cycle
(90
°
). Direction is obtained by looking to see if SIN is
leading or lagging the COS signal.
A course position is obtained by incrementing or decrementing a counter when the polarity of
the SIN signal changes with the COS signal high. This gives one count per encoder line.
The SIN and COS inputs are further sampled by a 12-bit ADC (analog-digital converter) so that
encoder positon can be interpolated within one line count, eg. for a 1024 line encoder this gives:
1024 x 2
12
counts per revolution = 4,194,304 counts per revolution
High resolution speed can now be calculated from this high resolution position:
position
time
t
p
speed =
position
time
COS
SIN
