Module Configuration - Allen-Bradley 1444-TSCX02-02RB User Manual

Chapter 10 Operate the Module
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Module Configuration

After sensor and signal, module configuration has the greatest impact on
measurement accuracy. Considerations here include the specific measurement
that is applied. The measurement includes overall or tracking-filter magnitude,
the configuration of that measurement, and the higher-level signal processing
that is performed on the signal. For example, measurements such as the
hardware sample rate and any of the filtering or the resampling measurements.
This table provides guidance on configuration-related considerations that can
affect measurement accuracy for common acceleration or displacement
measurements.
Table 72 - High-level Signal Processing Considerations
High-level Signal Processing Considerations
Page Parameter
HW Configuration Xdcr Sensitivity
Measurement Type
Filters ADC FFT FMAX
Primary Path High Pass
Filter
Primary Path Low Pass
Filter
Primary Path FFT FMAX
Measurement Function Configuration Considerations
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018
Considerations
Enter the precise sensitivity of the sensor used.
Sensors are designed to a "Nominal" sensitivity, such as
100 mV/g. However, the sensors actual sensitivity can vary
from nominal by several percent, so it can be 105.6 mV/g
(for example). If accuracy is more important than the
ability to change out sensors easily, then enter the actual
sensitivity rather than the default nominal value.
Do not select measurement types that specify integration.
Integration creates a significant complexity to the
measurement as the frequency of a signal has a dramatic
effect on its magnitude (divides by frequency).
When amplitude accuracy is most important, or if the
signal of interest is not at a stable, fixed, frequency, set the
ADC (hardware) FFT FMAX to the highest practical value.
When frequency accuracy is most important, set the AFC
FFT FMAX to the lowest practical value.
Do not select measurements from the Post Filter signal
source if a high pass filter is applied.
Filters are designed so that the cutoff frequency specified
(on the Filters page) is the point where the signal is
attenuated by -3 dB. This design means that some
attenuation is applied on the pass band (higher
frequency) side of the filter. In all cases, the amount of
attenuation decreases rapidly at frequencies further away
from the corner. However, some attenuation can be
expected at frequencies more than twice the cutoff
frequency. How much and how fast is dependent on the
quality of the filter, which in the 1444 can be either -24 or
-60 dB/octave depending on the selected measurement
type.
Do not enable a low pass filter.
Do not select an FMAX lower than the ADC FFT FMAX if you
use any type other than the Aeroderivative Measurement
Type.
If the required measurement is an FFT or an FFT Band
measurement, and requires a reduced FMAX, then define
the FFT on the Alternate Path rather than the Primary
Path. The Anti-Alias filter (required when resampling) that
is applied on the Alternate Path is a higher quality than
the one available to the primary path.