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Rockwell Automation 1336E IMPACT Adjustable Frequency AC Drive User Manual V 1-4.XX User Manual

Page 149

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Applications

9-9

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
parameter 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 An In 2 Scale (parameter 101), 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). An In 2 Offset (parameter 100) 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 9.2.

In this example, the filter parameter, An In2 Filter BW
(parameter 183), is not used. The filter parameter is a low pass filter
that helps to reduce the affects of noise on the system.

Figure 9.2
Potentiometer with +10V Range to Control 0 to +100% Base Speed

For a second example, a 0 to 10 volt potentiometer adjusts the torque
reference from -100% to +100%. To do this, you need to adjust both
the scale and offset parameters. By linking An In 1 Value
(parameter 96) to Torque Ref 1 (parameter 69), the potentiometer
connected to analog input 1 becomes the torque reference signal. This
signal must be scaled and offset to get the entire

±100% in the 0 to 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.

As shown in Figure 9.3 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 is +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.

10V Pot

0

–10V

Multiplexer

A

D

An In 2 Scale

Par 99

+2048

0

–2048

+2048

0

–2048

+4096

0

±4096

Range of 20V

0

0
0
0

–10V

–2048

X 2

–4096

+10V

+2048

X 2

+4096

Par 101

X 2

+

+10V

Par 36

+ 2048

(=

± 10V)

An In 2 Offset

Par 100 = 0

Potentiometer
Digital Value
Scale
Final Value in Par 99

An In 2 Value

Speed
Ref 7

An In2 Filter BW

Par 183

0