Rockwell Automation 1746-HSRV SLC Servo Control Module User Manual - Manual (Page 29)

Publication 1746-6.1.2 - July 2000
2-6 Selecting Power Supplies, Encoders, and Drives
Specification Rating
Maximum
channel
frequency Incoming quadrature frequency is limited by the following
relationship:
FQUAD (Hz) = (3334)(90°–EQ)
where:
EQ = quadrature error (degrees, electrical)
For example, for an 845H encoder with 22° quadrature error,
the maximum frequency would be:
FQUAD (Hz) = (3334)(90°-22° quadrature error) = 226,712 Hz
Important:The maximum quadrature error is a limit, and
system design should include acceptable margins.
Maximum axis
speed The SLC Servo Module decodes the incoming encoder
feedback in quadrature to extract the maximum resolution with
four counts per electrical cycle. The maximum number of
encoder counts per second can be determined by:
Maximum # of counts/second = 4 counts/cycle × F
QUAD
The maximum axis speed as limited by the encoder feedback
would be:
(maximum # of counts/second)(60)
(4E)(N)
where:
E = the number of encoder lines per revolution
N = number of revolutions of the encoder per inch or millimeter
of axis travel. (For a rotary axis, N = number of revolutions of
the encoder per revolution of the axis.) For a linear axis the
units are inches or millimeters per minute. For a rotary axis the
units are revolutions per minute.
Input signal Encoder feedback must be differential with 5V compatible
output signals, open-collector outputs are not supported (i.e.,
channels A, B, and Z must have source and sink current
capability, 8830 line driver outputs or equivalent). The encoder
input must have a 0.00 to 0.80 for off state and 4.75 to 5.25 for
on state to encoder common reference.
Input sink current 7 mA (max)
Marker channel Gated markers
Cable length Depends on the user-side power supply. Power voltage at the
encoder must be greater than or equal to the power voltage
requirement specified by the manufacturer. The minimum
power requirement for the 845H is 4.75V, and the maximum
limit is 5.25V. To meet the power requirement of the encoder
and still attain maximum cable length, you can:
•
Raise the voltage of the power supply to meet the
encoder requirement, but you cannot exceed the 5.25V
limit of the control.
•
Increase the gage of the wire from the termination
panel to the encoder (12 AWG maximum).