HBK TIM-PN Montageanleitung Seite 33

CASMA (Crank Angle Synchronous Moving Average) filter
The CASMA filter is a moving average filter with low-pass filter characteristics. The filter
does not work on a time base, in the usual way, instead it uses angular synchronism,
which allows an automatic response to changes in the rotational speed. This enables the
filter to eliminate the recurrent interference occurring synchronously to the shaft rotation
and the signal is "smoothed".
For the filter to function in the TIM-PN, an angle of rotation pulse is required, as well as
details from the user. The TIM-PN is fitted with an input for measuring rotational speed.
When a rotational speed measuring system is connected, angle of rotation pulses (Ф) are
available to trigger the filter. Parameters transmitted over the web interface are used for
filter parameterization. For filter operation, the size of the window, i.e. the number of
measured values to be used for averaging, must be calculated.
Ф
M
(t)
Fig. 10.10 Required configuration for the CASMA filter to function
Fig. 10.10 shows the CASMA filter with the required input parameter. "M
measurement and "Ф" the angular velocity. "M
angular velocity. "Ф". With each pulse, the current torque measurement is accepted into
filter and the last value is cleared from the filter. Then the sum of the measured values in
the filter is divided by the number of values to be averaged (n), and the result is output.
With the "D" input, the angle of rotation pulses can be divided down via an internal divisor.
This can be necessary when working over a wide angle range and high angle resolution.
Information
The maximum number of measured values that can be averaged is n
you must ensure that this value is not exceeded. The number of n can be reduced by using
the divisor.
You must also ensure that the angle of rotation pulses do not arrive any faster than the
torque measurements. Otherwise the calculation of the moving average will be incorrect,
as the applied torque measurement will be taken into account more than once in the aver­
age value filter. This means that the maximum permissible rotational speed must be
defined and taken into account in the active CASMA filter.
TIM-PN
SETTINGS
CASMA filter
n
" is the moving average subject to the
(Φ)
M
(Φ)
D
= 4096 values. So
max
" is the torque
(t)
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