Rockwell Automation 1336T ControlNet Frn1.02 Rev 1.5 User Manual
Page 33
2–7
Starting Up
Publication 1336 FORCE–5.18 ––March, 1999
As shown in Figure 2.2, the offset voltage adds the corresponding
digital value to the range. In this case, an offset of –5 volts adds a
digital value of –1024 to the range. This causes 0 volts on the
potentiometer to register as –1024 digital internal to the drive and 10
volts on the potentiometer will be +1024 to the drive. This can then
be scaled by a factor of 4 (8192 drive units) so that 0 volts sends a
digital value of –4096 for –100% torque, and 10 volts sends a digital
value of +4096 for +100% torque.
Figure 2.2
Potentiometer 0–10V Range to Control +100% Torque Reference
0–10V Pot
0
10v
Multiplexer
A
D
Scale
0
to
2048
–1024
+1024
+4096
+4096
Offset
Par 394 = –5V (–1024)
Range of 20V
0
0
0
–10V
–2048
+10V
+2048
Par 395
X 4
+0v
Potentiometer
digital value
offset by –5V.
10V
–10V
5V
1024
0
0
–1024
–4096
+1024
+4096
Adding –1024
Scale by 4
Par 340
Par 162
Analog In 2
Ext Torque
Reference 1
+ 2048
(= + 10V)
Understanding the Scale and Offset Parameters for Output
Analog outputs are similar to analog inputs. Each output has a scale
and offset parameter, along with a specific variable parameter used
for linking. Differences occur because of the direction of
information flow. The drive sends a digital value in drive units,
which must be matched to the voltage of the monitoring device.
Similar to analog inputs, the analog output converts a
±
2048 value to
±
10V
DC. Thus, when the drive sends
±
100% base speed (equal to
±
4096), it must be scaled by 0.5 to be in the proper range (
±
4096
×
0.5 =
±
2048). The offset can be
±
20V DC, even though the physical
limit is
±
10V
dc. This allows you to offset the signal anywhere
within the entire range.
In Figure 2.3
,
Analog Output 1 is used as an example to show the
scale and offset parameters. At Analog Output 1, a meter with a
range of 0 through 10V DC has been connected. Analog Output 1
has been linked to Velocity Feedback (parameter 269).