Allen-Bradley 1444-TSCX02-02RB User Manual page 127

Table 21 - Filters (continued)
Parameter Values
Fmax (Alternate) Displays the result of: (60 x 93750 / x Sample Rate Divisor) / (Samples Per
maximum Speed Revolution x 2)
Orders Displays the number of orders that are available in an FFT processed from
the synchronous data.
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Measurement Definition
Comments
Displays the maximum speed (RPM) at which the machine can operate
while measuring synchronously with the specified filter performance
(number of orders).
• If the machine speed exceeds this RPM while in Synchronous Mode,
the measurement does not stop. Rather, the performance of the Low
Pass Filter degrades until the speed increases above a "hard stop"
filter value.
• When synchronous measurements are taken while at speeds greater
than the calculated maximum, some signal attenuation occurs at
the higher frequencies. Attenuation is greatest at FMAX, with
decreasing attenuation at lower frequencies. The frequency where
attenuation begins goes lower as speed increases further above the
maximum.
• The accuracy of signals at frequencies up to the 2x order frequency
are verified at speeds up to 2x the calculated maximum.
• As machine speed decreases, there is no point at which the filter
performance degrades. But there is a hard stop limit to how low the
LPF cutoff can be set.
Low Pass Filter Hard Stop Limits
When measuring synchronously the module is limited in how high, or
low, it can set the Low Pass Filter corner. So, if the calculated filter
corner (per the previous) exceeds the hard stop limit (high or low) the
filter corner no longer increases (or decreases).
The Hard Stop Limits are based only on the Sample Rate Divide value
and are calculated as:
High Limit = 32000 / SRD
Low Limit = 32 / SRD
The following table shows the hard limits for selected SRD values:
Low Pass Hard Stop Limits (Hz)
ADC out 4578 3433
FMAX (SRD) (12)
(9)
Low 3.6 2.7
High 3556 2667
The number of orders is equal to:
Samples Per Revolution * 0.625
2.56
The order values are:
Samples/Rev Orders
8 2.0
16 3.9
32 7.8
64 15.6
128 31.3
Chapter 4
1717 1287 1144
(24) (32) (36)
1.3 1.0 0.9
1333 1000 889
127