User guide

Configuring an Application www.controltechniques.com 43
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ote
Be sure not to configure a supply voltage greater
than that supported by the encoder. The Unidrive
SP and SM-Universal Encoder Plus cannot protect
against possible damage to the encoder if the
supply voltage is set too high.
Enable Auto Encoder Configuration
When a SC.Hiper, SC.EnDat, or EnDat encoder is being
used, the Unidrive SP and/or SM-Universal Encoder Plus
module can interrogate the encoder on power-up, and
acquire many of the encoder setup parameters
automatically. To enable this feature, the Enable Auto
Encoder Configuration check box must be selected. When
the check box is selected (active) the Encoder Turns,
Encoder Comms Resolution, and Equivalent Lines Per
Revolution parameters will appear dimmed, implying that
the user no longer needs to configure those parameters. If
the check box is clear, then the user must specify the
correct values for these three parameters (Encoder Turns,
Encoder Comms Resolution, and Equivalent Lines Per
Revolution).
The aforementioned encoder parameter values are stored
in non-volatile memory embedded in the encoder. The
values stored in NVM cannot be changed by the user.
Encoder Turns
This parameter determines the maximum number of
revolutions before the Rev Counter register (3.28 or x.04)
rolls over. If using an absolute encoder, this should be set
at the maximum number of turns of the absolute encoder
or lower. The maximum number of turns is defined as
follows:
Maximum Turns = 2
N
, where N is the Encoder Turns
parameter
If the Enable Auto Encoder Configuration checkbox is
selected, then the user does not need to enter this
parameter, and the Encoder Turns box will appear dim.
Encoder Comms Resolution
Where encoder communications is used to initially read the
absolute encoder position (SC.Hiper or SC.EnDat), the
comms resolution must be set to the maximum resolution
of the absolute position data.
If the Enable Auto Encoder Configuration checkbox is
selected, then the user does not need to enter this
parameter, and the Encoder Comms Resolution box will
appear dim.
Equivalent Lines Per Revolution
When sin/cos signals are used, the equivalent number of
encoder lines per revolution must be set up correctly to
give the correct speed and position feedback. The
Equivalent Lines Per Revolution (ELPR) is defined as
follows:
For SC.Hiper, SC.EnDat and SC.SSI encoders, the sine
wave signal frequency can be up to 166 kHz, but the
resolution is reduced at higher frequencies. The table
below shows the number of bits of interpolated information
at different frequencies and with different voltage levels at
the drive encoder port. The total resolution in bits per
revolution is the ELPR plus the number of bits of
interpolated information.
If the Enable Auto Encoder Configuration checkbox is
selected, then the user does not need to enter this
parameter, and the Equivalent Lines Per Rev box will
appear dim.
Lines Per Rev Divider
The Equivalent Lines Per Revolution parameter is divided
by this value. This can be used when an encoder is used
with a linear motor where the number of counts or sine
waves per pole is not an integer.
Example:
The true number of encoder lines per rev (or electrical
cycle) is 128.123. Since The Equivalent Lines Per Rev
parameter must be a whole number, ELPR should be set
to 128123, and then the Lines Per Rev Divider would be set
to 1000 resulting in the following equation:
Encoder Comms Baud Rate
This parameter defines the baud rate for the encoder
communications. The list box allows the user to select from
various baud rates between 100kbaud and 2Mbaud.
Simulated Encoder Output Parameters
Encoder Simulation Source
The SM-Universal Encoder Plus module has a feature that
allows the user to send out a simulated encoder signal for
use by an external device. The Encoder Simulation Source
is used to define the source of the encoder signal. By
default, the Source will be configured as the SM-Universal
Encoder Plus position (x.05). Any drive parameter in the
form of a 0-65535 rollover counter can be used as the
Position Feedback Device ELPR
Ab
Number of lines
per revolution
Fd, Fr
Number of lines
per revolution / 2
SC.Hiper, SC.EnDat, SC.SSI Number of sine waves per revolution
Volt / Freq 1,000 5,000 50,000 100,000 150,000
1.2 1111111010
1.0 11 11 10 10 9
0.8 10101010 9
0.6 101010 9 9
0.499998
Actual Encoder Lines Per Rev = ELPR/Lines Per Rev Divider
= 128123 / 1000 = 128.123