Siemens SINUMERIK 840C - Manual (Page 633)

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Siemens AG 2001 All Rights Reserved 6FC5197– j AA50 9–12
SINUMERIK 840C (IA)
e.g. for 125 m s sampling time (cycle)
Owing to the short measuring times, traversing paths of a few revolutions are
sufficient for the frequency response measurement. The measurement time is
calculated as follows:
Meas. time [s] +
512 x No. of averaging ops
Bandwidth [Hz]
) Setting time
The frequency response measurement on a drive with a sampling time of 125
m
s
and 20 averaging operations therefore takes approximately 2.5 s; given an offset of 5
rev/min, a traversing path of less than 0.3 revolutions is required for the mea-
surement.
Always begin measurements with the lowest possible values for offset and am-
plitude. Do not increase the number of averaging operations or the amplitude
unless you obtain extremely noisy results. Excessively high amplitude values
lead to incorrect results and may cause mechanical damage.
The offset should always be higher than the amplitude. The measuring results
at very low values may differ from those obtained at higher traversing speeds
owing to backlash or static friction.
By decreasing the bandwidth, you can increase the frequency resolution,
particularly at low frequencies.
After evaluating the measurement series – which takes between 5 and 20 s
depending on the MMC-CPU, you can call up the result as a Bode diagram under
the “Display” softkey.
X marker
Y marker
Expand
Picture 1
Picture 2
x
lin/log
Programm. Services Diagnosis Parameter Machine
Ampl. response
axis: X
Phase resp
axis: X
Measure-
ment Meas.
parameters Contr.para
MSD Display File
functions
dB
Deg
Contr.para
FDD
Fig. 9.5 New softkey bar as from SW 5: See Fig. 9.3
You can identify the position and intensity of any critical mechanical resonant
points in the frequency response diagram – in the above diagram, you can see
resonant points at 450 Hz, 600 Hz and 1200 Hz. Increasing the P gain of the
speed controller would cause instability if filters were not used.
611D offers low-pass or bandstop filters as standard; the parameters of these
filters – stop frequency, bandwidth or limit frequency – can be estimated using
the Bode diagram.
9 Drive Servo Start-Up Application (as from SW 3)
9.2 Measuring the drive servo loops (current, speed, position)
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