Table of Contents
Advertisement
6. Appendices
008-0738-00
Example
The following is an example of typical filter settings as applicable to a standard production
TMS 9250 torque measuring system.
•
Consider a sensor with a 1000 Nm full scale torque measuring range.
•
Consider a test running at steady state torque of 550 Nm.
•
Consider FiltLevel set at 1000. The unit of measure for FiltLevel approximates to
0.01%FS (where FS is the full scale of the sensor), therefore a FiltLevel of 1000 sets
a threshold of change of 10% of FS which in this example is 100 Nm, above which the
filter is reset and the output value becomes equal to the input value again. Note that
the threshold is with respect to the current value, and not with respect to zero torque.
Therefore, if the torque is fluctuating within a band of less than 100 Nm, the filter
performance will be determined by FiltSteps alone.
•
In the case where torsional vibrations and spikes may be present in the input signal,
then the threshold set by FiltLevel should be raised so that the filter is not being reset
by events which are not of interest. A safe value to use when setting up is 5000, which
corresponds to 50% of FS, then reduce the threshold later if required.
•
Now consider an input change of 0.1 Nm, which is below the threshold and therefore
subjected to filtering. The difference between the input and the output is 0.1 Nm so
this is the change that will be used by the filter comparator.
•
If the FiltSteps parameter is set to 10, then the output of the TMS 9250 will be
incremented towards the input in 10 steps, as follows:
1 / 2(0.1 Nm), 1 / 3(0.1 Nm), 1 / 4(0.1 Nm), 1 / 5(0.1 Nm), . . 1 / 9(0.1 Nm), 1 / 10(0.1 Nm)
•
The filter update rate being 1104 Hz gives an update period of 1/1104=0.000906
seconds, therefore the filter will settle to 63% of its final value in 0.00906 seconds
(being 0.000906 * FiltSteps).
Using the formula described in Table 1, it can be seen that the filter will settle to within
•
99.9% of its final value in 0.063 seconds (being 0.000906 * FiltSteps * 7)
Desired Settling Time to 99.9%
of Final Value (seconds)
6.3 s
3.2 s
1.3 s
0.63 s
0.32 s
0.13 s
0.063 s
0.032 s
0.013 s
0.006 s
42
© 2012 – Honeywell International Inc. All rights reserved
Table 2: Quick look up table
Equivalent to Cut-Off
Frequency of (Hz)
0.18 Hz
0.35 Hz
0.88 Hz
1.75 Hz
3.50 Hz
8.76 Hz
17.5 Hz
35.0 Hz
87.6 Hz
175 Hz
TMS 9250 Product User Manual
FiltSteps setting
required
1000
500
200
100
50
20
10
5
2
1
Rev B
April 2012
Advertisement
Table of Contents
