VTI Instruments EX1629, Руководство пользователя

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EX1629 Command Set 261
vtex1629_set_IIR_filter_configuration
F
UNCTION
P
ROTOTYPE
ViStatus vtex1629_set_IIR_filter_configuration (ViSession vi , ViInt32 _VI_FAR channels[] ,ViInt32
numberOfChannels , ViInt32 filterType , ViReal64 cutoffFreq , ViInt32 transform , ViInt32 filterOrder );
F
UNCTION
P
ARAMETERS
vi = contains a session handle to the instrument. This handle is obtained by the function and remains valid until the
session is closed.
channels = an input integer array containing a list of channel numbers for which the IIR filter configuration will be
set. Valid input values: 0 to 47.
numberOfChannels = the size of the channels list. Valid input values: 1 to 48.
filterType = an integer input value indicating the type of filter to be used for the indicated channels. See Description
below for more information. Valid input values: 0, 1, or 2.
cutoffFreq = a real input value indicating the filter's cutoff frequency in hertz (Hz), which is only relevant for
Bessel and Butterworth filter types. See Description below for more information.
transform = an integer input value indicating the type of filter transform to be employed , which is only relevant for
Bessel and Butterworth filter types. Valid input values: 0 or 1.
filterOrder = an integer input value indicating the order of this filter. Valid input values: 1 to 10 for the Bessel
filter, 0 to 10 for the Butterworth filter.
D
ATA
I
TEM
R
ESET
V
ALUE
filterType = 1 (Butterworth) cutoffFreq = 10
transform = 0 (bilinear) filterOrder = 6
D
ESCRIPTION
This function configures the IIR filters for a given list of channels. The filterType parameter has three allowed
values:
Decimal
Value
Hex
Value
#define Symbol filterType Description
0 0x00 VTEX1629_IIR_FILT_NONE None
1 0x01 VTEX1629_IIR_FILT_BUTTERWORTH Butterworth
2 0x02 VTEX1629_IIR_FILT_BESSEL Bessel
The cutoffFreq parameter defines the cutoff (-3 dB) frequency for the low-pass filter indicated above. The EX1629
will locate this parameter in the range [ f
s
/1000, f
c
max] (see Table B-1), where f
s
is the current sampling frequency.
Note that this value can change if the sampling frequency is altered. The actual value can be queried with the
vtex1629_get_IIR_filter_configuration function.
NOTE If the user sets the filter frequency a value below f
s
/1000 or higher than f
c
max, the EX1629 will
automatically set the filter frequency to f
s
/1000 or f
c
max, respectively. No error or warning is
provided when this occurs.
The transform parameter provides for two modes of transformation:
Decimal
Value
Hex
Value
#define Symbol transform Description
0 0x00 VTEX1629_TRANSFORM_BILINEAR Bilinear
1 0x01 VTEX1629_TRANSFORM_MATCHEDZ Matched-Z
The filterOrder parameter defines the desired order of the filter. When the filterType is set to Butterworth, there is
an additional option of 0. This corresponds to an automatic option, whereby the EX1629 will assign an order based
on an analog prototype Butterworth design given the sampling frequency, cutoff frequency, and a -200 dB
attenuation at the Nyquist frequency. The actual order can be determined using the
vtex1629_get_IIR_filter_configuration function.