BECKHOFF DK9222-0909-0012 - Manual (Page 3)

I/O
Bus Terminal
Application Note DK9222-0909-0012
In the Pulse Train technology, the provision of the set value and the validation of the actual position is implemented with
the aid of just one digital Bus Terminal. The actual position, which is otherwise acquired with the aid of incremental encoder
techniques, is calculated, depending on the specified set value frequency using, for instance, the TwinCAT software PLC/NC
(Figure 2). A difference between the set and actual value is indicated to the Bus Terminal using the target or following error
digital output which is present in all common servoamplifiers.
The KL2521 Pulse Train Bus Terminal supports three different frequency pulse patterns (Figure 3). These may be selected in
using the KS2000 configuration software, or by the higherlevel controller.
A
B
A
B
A
B
Frequency modulation
Pulse/direction signals
Incremental encoder simulation
Fig. 3 frequency pulse patterns
The pulse patterns are output through the two channels, A and B. They correspond to all usual input circuits::
– Frequency modulation: rotation to the right is associated with output of the frequency signal on channel A, while rotation
to the left is associated with output on channel B. The inactive channel remains at a logical „low“ state.
– Pulse/direction signals: the frequency pattern is always output on channel A, the direction of rotation being indicated by the
„high“ or „low“ level on channel B.
– Incremental encoder simulation: channels A and B output a signal with a 90° phase shift. The shift from A to B is positive
or negative, thus encoding the direction of rotation. The output signal is thus exactly the same as that of an incremental
transducer. The advantage here is the possibility of directly driving frequency converters through the „synchronous axes“
signal input (Figure 4). Ontop of the simple positioning, this arrangement permits a master/slave structure. Users can
therefore couple this system to fieldbusses through existing interfaces - i.e. without additional costs.
New Automation Technology Beckhoff 3
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