Scaling of the Position
Position values generally are 32-bit values and therefore must be transmitted in two process data
words. It is up to the user to decide in which process data word he wishes to transmit the more
significant part of the position (high word) and the less significant part of the position (low). The
position is therefore transmitted as signed 32-bit integer. The following table shows the scaling for
Position process data.
Data type:
Integer32
Resolution:
360°
1 motor revolution = 4096 increments, i.e. 1digit =
4096
Range [°]:
-188,743,680° ....0..... +188,743,679°
[Motor revolutions]:
-524 288 ....0.... +524287
[Increments]:
8000
0000
hex
......0...... 7FFF
FFFF
hex
High
Low
High
Low
Applies to:
Position actual value
Position setpoint
If the motor is connected correctly position values are incremented for CLOCKWISE direction of
rotation and decremented for COUNTERCLOCKWISE direction of rotation! After power-up the inverter
is in position 0.
IMPORTANT
When handling the position setpoints in the application program of the higher-level automation unit
make sure that both process output data words containing the position data, are dealt with
consistently, i.e. that the position setpoint high is always transmitted together with a position setpoint
low! Otherwise the inverter might approach undefined positions, as, e.g. an old position setpoint low
and a new position setpoint high might be active together!
Example: Entry of a position setpoint via the process data channel
This example shows how position setpoints must be set specified by the higher-level control using
the process data channel. In our example positions 1 and 2 shown in Fig. 10 shall be specified via
the fieldbus system. For this example to work the motor must be in position 0 after power-up.
Position 1 is 35 motor revolutions CCW away from starting position 0, position 2 is 19 motor
revolutions CW. The two positions then have the following process data codings:
Position
Conversion of the scaling
Transferred process data
Position 1:
35 revs CCW
-35 · 4096 = -143360
dec
=
FFFD D 000
hex
FFFD D000
hex
Position LO
Position HI
Position 2:
19 revs CW
19 · 4096 = 77824
dec
= 0001 3000
hex
0001 3000
hex
Position LO
Position HI
Position 1
Position 0
Position 2
Direction of rotation CW
00320AEN
Fig. 10: Positioning example with starting position (0) and two target positions (1 and 2)
Inverter Control
with Process Data
3
24
MOVITRAC
®
31.. Fieldbus Unit Profile
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: [email protected]
