Rockwell Automation 1336T PLC Comm. Adapter, Series B, FRN 2.xx-3.xx - Manual (Page 39)

2–11
Publication 1336 FORCE–5.13 –– September, 1998
Understanding the Scale and Offset Parameters for Input
Analog Input 1 and Analog Input 2 are used in explaining the scale
and offset parameters. At Analog Input 1, between TB21 terminals 9
and 10, a potentiometer with a range of
±
10V dc has been connected.
Analog Input 1 has been linked to Velocity Reference (parameter
101) in the drive, which gives the potentiometer control of the
external velocity reference.
To calibrate the pot to control 100% base speed in both directions,
you need to adjust the scale parameter. The default value of the scale
parameters allows a total range of 4096, –2048 to +2048. This
allows only 50% base speed in each direction. By setting a scale
factor of 2 in Analog Input 1 Scale, the digital input is multiplied by
2. This provides a range of
±
4096, or 100% base speed in both
directions.
If you want a range of
±
2 times base speed, the scale factor would
be 4 (base speed is 4096, 2 times base speed is 8192, 2048 times 4 is
8192). Analog Input 1 Offset remains at the default value of zero,
allowing the input range to be
±
10V. The range of the offset
parameter is
±
20V dc as shown in Figure 2–1.
Figure 2.1
Potentiometer with +10V Range to Control 0 to +100% Base Speed
10V Pot
0
–10V
Multiplexer
A
D
Scale
Par 339
+2048
0
–2048
+2048
0
–2048
+4096
0
–4096
Offset
Par 392 = 0
Range of 20V
0
0
0
0
–10V
–2048
X 2
–4096
+10V
+2048
X 2
+4096
Par 393
X 4
+
+10V
Potentiometer
Digital Value
Scale
Final Value Par 401
Par 104
Analog In 1
Velocity
Reference 2
Hi
+ 2048
(= + 10V)
For Analog Input 2, a 0 to 10 volt potentiometer is used to adjust the
Torque Reference from –100% to +100%. To do this, you need to
adjust both the scale and offset parameters. By linking Analog Input
2 to Torque Reference (parameter 162), the potentiometer connected
to Analog Input 2 becomes the Torque Reference Signal. This signal
must be scaled and offset to get the entire
±
100% in the 0 through 10
volt range. A digital range of 8192 (
±
4096) must now be scaled for
an analog range of 10 volts, and must be offset so 5 volts on the
potentiometer indicates 0% Torque.