Somat eDAQlite, Руководство пользователя, Страница: 114 / 228

Somat eDAQ
lite
114 I2773-4.
4
en
Output Data Type
Select an output data type of 16-bit signed, 32-bit float or 8-bit signed. The
fundamental data type for bridge channels is 16-bit signed, which consumes the least
amount of data storage while maintaining full 16-bit data resolution. The 32-bit float
data type adds a great deal of computational overhead and is not recommended for
high rate data collection. Use the 32-bit floating point option only if the input channel
is to be used in subsequent computed channels or DataModes that require the input
channels to be 32-bit floating point. The 8-bit signed data type adds some
computational overhead, but may be useful when only a rough picture of the
transducer data is required and/or data storage limitations are a major concern.
Digital Filter Type
Select the desired type of digital filtering for the channel. Digital filters ensure that
aliasing of the input signal does not occur. Always use a digital filter unless absolutely
certain of the frequency content of the input signal. The filter options are an eight-pole
Butterworth filter or a linear phase filter. For more information on digital filtering, see
“Digital Filtering” on page 213 .
Break Frequency
Specify the break frequency in hertz for the selected digital filter. For a Butterworth
filter, this is the approximate frequency at which the signal attenuation is 3 dB or 70.7%
of the unfiltered signal voltage at that frequency. For a linear phase filter, the field is
named the roll off start frequency and is the approximate frequency at which the signal
starts to attenuate.
The eDAQ
lite
automatically selects a default break frequency value to ensure that no
aliasing occurs. The selection is based on the A/D converter rate and the choice of
digital filter type.
NOTE
The check box field labeled “data is protected from aliasing” indicates whether the
current digital filter selection ensures no aliasing. TCE automatically updates the field
when the digital filter configuration changes. For example, the 100-kHz sample rate
option precludes aliasing because it is well over the Nyquist frequency of two times the
25 kHz analog guard filter. However, the 50-kHz sample rate option does not fully
preclude against aliasing because the guard filter only attenuates about 30% of the
25-kHz input signal content.
Excitation Range
The excitation range setting determines the magnitude of the bipolar voltage applied
to the red +EXC and black -EXC wires of the transducer cables. Note that a range of
X volts DC results in + X /2 to - X /2 pin out voltages. Select one of the following discrete
ranges: 10, 5, or 0 volts DC. The maximum current which can be supplied is 51
milliamps at either 5 or 10 volts DC.
If signal excitation is required for the transducer, which is always the case when using
an actual bridge, consult the transducer manufacturer's specifications and/or
suggestions for excitation settings. If signal excitation is not required for a particular
transducer, leave the excitation in the default initial state and set the excitation
proportional parameter to no.
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