VTI Instruments EX1629, Руководство пользователя

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EX1629 Command Set 161
vtex1629_get_IIR_filter_configuration
F
UNCTION
P
ROTOTYPE
ViStatus vtex1629_get_IIR_filter_configuration (ViSession vi , ViInt32 channel , ViPInt32 filterType , ViPReal64
cutoffFreq , ViPInt32 transform , ViPInt32 filterOrder , ViPReal64 groupDelay );
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.
channel = an integer input value that specifies the channel for which the IIR filter configuration will be returned.
Valid input values: 0 to 47.
filterType = an integer return value indicating the type of filter that is currently configured to be used for the given
channel. See Description below for more information. Valid return values: 0, 1, or 2.
cutoffFreq = a real return value indicating the current cutoff frequency, in hertz (Hz), currently configured in filters
on the given channel. This parameter is only relevant for Bessel and Butterworth filter types. Valid return values:
0.001 to 4005.
transform = an integer return value indicating the type of filter transform currently configured for the given
channel. This parameter is only relevant for Bessel and Butterworth filter types. Valid return values: 0 or 1.
filterOrder = an integer return value indicating the order of the filter on a given channel. This parameter is only
relevant for Bessel and Butterworth filter types. Valid return values: 1 to 10.
groupDelay = a real return value indicating the group delay, in number of samples, of the currently configured filter
for the given channel.
D
ATA
I
TEM
R
ESET
V
ALUE
Not applicable to this function.
D
ESCRIPTION
This function queries and returns the IIR filter configuration parameters for a given channel. 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
A value of “None” disables the IIR filters. Note, however, that the FIR filter is always enabled and is not user-
configurable.
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 command.
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 command.