BECKHOFF KL2521-0000 - Manual (Page 7)

Functional description
KL2521 5
Resolution
The base frequencies are specified with their resolution of 1 Hz per bit
(GF1: registers 36, 37 or GF2: registers 38, 39). The terminal operates
internally at 16 MHz with a resolution of 32 bits. This corresponds to a
theoretical minimum step size of 0.0037 Hz/step over the entire frequency
range. The output stage allows a maximum frequency of 500 kHz to be
output.
Ramp function
The terminal offers a facility for soft starting and stopping. The ramp
gradient for starting can be set in register 40 with a precision of 10 or 1000
Hz/s (Feature.6). Register 41 performs the same function for stopping. The
process data can be modified during transit of the ramp (Status.2), and the
terminal then takes the new value as its target frequency.
Travel distance control
If the "travel distance control" function is active (Feature.9), then a rising
edge at Control.2 will result in drive to a fixed counter value. This value
must previously be entered in register 0 (low word) and in register 1 (high
word) at runtime. Time t
1
is specified by the ramp time constant in register
40. t
2
is reached at the maximum frequency f
1
(register 2). Time t
3
is
determined by the ramp time constant in register 41 with which the slowing
down frequency f
2
(register 43) is achieved. When the given counter
contents have been reached, the terminal switches the frequency to zero.
In order to travel to a destination with precision, it is necessary that the
time constant for the falling ramp is greater than that of the rising ramp by a
certain factor. This is necessary so that the slowing down frequency is
reached before the final counter state, so that the terminal does not drive
up to the end point at full speed.
To explain in more detail: the KL2521 calculates the number of steps that
are still to be taken in time t
2
from time t
1
and from the number of steps that
have been taken. The calculation for stopping assumes the same number
of steps as that found for starting up. The downward ramp must be a little
steeper, approx. 10%, so that it is possible to reach the destination exactly
in the remaining time t
3
+ t
4
+ t
5
. This relationship changes with the
maximum frequency.