Rockwell Automation 20-750-DNET PowerFlex DeviceNet Option Module - Manual (Page 55)

Rockwell Automation Publication 750COM-UM002B-EN-P - October 2012 55
Using the I/O Chapter 5
Using Reference/Feedback The Reference is a 32-bit REAL (floating point) piece of control data produced
by the controller and consumed by the option module. The Feedback is a 32-bit
REAL (floating point) piece of status data produced by the option module and
consumed by the controller.
When using a ControlLogix controller, the 32-bit REAL Reference word is
always DINT 1 in the output image (see
Table 2 ) and the 32-bit REAL Feedback
word is always DINT 1 in the input image. Because the I/O image is integer-
based and the Reference and Feedback are floating point, a COP (Copy)
instruction or User Defined Data Types (UDDT) is required to correctly write
values to the Reference and read values from the Feedback. See the ladder logic
program examples in
Figure 9 and Figure 10 .
The Reference and Feedback 32-bit REAL values represent drive speed. The
scaling for the speed Reference and Feedback is dependent on drive Parameter
300 - [Speed Units]. For example, if Parameter 300 is set to Hz, a 32-bit REAL
Reference value of ‘30.0’ would equal a Reference of 30.0 Hz. If Parameter 300 is
set to RPM, a 32-bit REAL Reference value of ‘1020.5’ would equal a Reference
of 1020.5 RPM. Note that the commanded maximum speed can never exceed the
value of drive Parameter 520 - [Max Fwd Speed].
Table 3 shows example
References and their results for a PowerFlex 750-Series drive that has its:
• Parameter 300 - [Speed Units] set to Hz.
• Parameter 37 - [Maximum Freq] set to 130 Hz.
• Parameter 520 - [Max Fwd Speed] set to 60 Hz.
When Parameter 300 - [Speed Units] is set to RPM, the other parameters are also
in RPM.
Table 3 - PowerFlex 750-Series Drive Example Speed Reference/Feedback Scaling
Network Reference Value Speed Command Value
(2)
(2) For this example, drive parameter 300 - [Speed Units] is set to Hz.
Output Speed Network Feedback Value
130.0 130 Hz 60 Hz
(3)
(3) The drive runs at 60 Hz instead of 130 Hz or 65 Hz because drive Parameter 520 - [Max Fwd Speed] sets 60 Hz as the maximum
speed.
60.0
65.0 65 Hz 60 Hz
(3)
60.0
32.5 32.5 Hz 32.5 Hz 32.5
0.0 0 Hz 0 Hz 0.0
-32.5 (1)
(1) The effects of values less than 0.0 depend on whether the PowerFlex 750-Series drive uses a bipolar or unipolar direction mode. See
the drive documentation for details.
32.5 Hz 32.5 Hz 32.5