fsc2: 6.25 Multi-Device Functions

6.25 Multi-Device Functions

Currently there is just one function that uses two devices at once. It uses the single-device functions (and thus will print error messages if the modules for the required devices aren't loaded or if the modules don't support the needed functions). The module they are defined in is automatically loaded, so it needs no special entry in the DEVICES section.

`get_phase_cycled_area()'

This function is for doing a complete measurement sequence in a phase cycled experiment. It goes through a complete phase cycle, setting the pulser, fetching the data from the digitizer and finally returning the measured data, i.e. the areas returned by the digitizer and added up according to the setting of the ACQUISITION_SEQUENCE.

The function needs both a pulser and a digitizer. It is not possible to use the function with more than one pulser or digitizer - if more than one pulser or digitizer is listed in the DEVICES section it will always use the first pulser and digitizer listed only.

The function can be used both for 1-dimensional and 2-dimensional measurements. In the first case there is just one signal channel, in the second two, e.g. a real and an imaginary part of a signal. Which kind of measurement has to be done is determined by the number of acquisition sequences. If there's only one it's a 1-dimensional measurement, otherwise a 2-dimensional one.

The first argument the function expects is a digitizer channel to be used for measuring the area of the signal, see above which channels can be used for the different digitizers. If the ACQUISITION_SEQUENCE is written in way that it is clear that two digitizer channels are needed, i.e. you have a line in the PHASES section like

ACQUISITION_SEQUENCE = +A, -B, -A, +B;

also the second argument to the function must be a digitizer channel. The first channel is used for fetching the A data, the second for the B data. This is, of course, only relevant when you have two different signals, e.g. the two outputs of a quadrature mixer and the measured data consist of adding up signals from both channels.

The following arguments are as many window identifiers (as returned by digitizer_define_window() as there are needed. If no window argument is given always the area of the complete curve is returned!

The type of the return value depends on the number of window identifiers passed to the function and the number of acquisition sequences. If there is only one window identifier (or none) and only one acquisition sequence a floating point value with the result of the measurement is returned. If, on the other hand, there is more than one window identifier and a single acquisition sequence an array will be returned with as many elements as there are window identifiers, the first element of the returned array containing the result for the first window, the second element the value for the second window etc.

If, in contrast, there are two acquisition sequences an array of twice the number of windows is returned. The first value in the array is the result for the first acquistion sequence for the first window, the second the result for the second acquistion sequence and the first window, then follow the results of both acquisition sequences fort he second window, etc.

As an example here parts of an EDL script for a 1-dimensional stimulated echo experiment with phase cycling. The parts with the definition of the pulses etc. are left out for sake of brevity.

DEVICES:

dg2020_f;
tds754a;


VARIABLES:

Num_points = 256;
raw_data[ 2 ];
data[ Num_points ];
Win_ID_1;                // signal window
Win_ID_2;                // background window
I;

...

ASSIGNMENTS:

...

PHASES:

PHASE_SEQUENCE_1     = +x, -x, +x, -x;  // sequence for 2nd pulse
PHASE_SEQUENCE_2     = +x, +x, -x, -x;  // sequence for 3rd pulse

ACQUISITION_SEQUENCE =  +,  -,  -,  +;


PREPARATIONS:

init_1d( 1, Num_points );
Win_ID_1 = digitizer_define_window( 388 ns, 4 ns );
Win_ID_2 = digitizer_define_window( 620 ns, 4 ns );

...

EXPERIMENT:

FOR I = 1 : : Num_points {
    raw_data = get_phase_cycled_area( CH1, Win_ID_1, Win_ID_2 );
    data[ I ] = raw_data[ 1 ] - raw_data[ 2 ];
    display( I, data[ I ] );
    pulser_shift( );
}

...

The first thing the function does is to do a phase reset to be certain the pulser starts with a pulse pattern for the first phase as defined in the PHASE_SEQUENCE declarations. Then it will measure the signals areas for both digitizer window areas. In the next step it switched the pulser to the pulse pattern for the next phase and repeat the measurement of both the signal areas and subtract them from the values measured in the first step (because in the ACQUISITION_SEQUENCE command requires subtraction of the data). Then, again the pulse pattern is switched to the third phase and a third set of data for both windows is measured. Also these data are subtracted according to the settings of acquisition sequence. Finally, the fourth and last phase settings are send to the pulser and a fourth set of signal areas is measured. These data now must, according to the acquisition sequence, be added to the previous accumulated data. The result, an array with two elements for the first and second window is returned by the function.

You may note that in this script pulser_update() isn't called after pulser_shift(). This is possible because get_phase_cycled_area() internally calls pulser_update() before it starts doing the measurement.

Two acquisition sequences would, for example, be used in an inversion recovery experiment with FID detection and phase cycling. Parts of the EDL script would look like this:

DEVICES:

dg2020_f;
tds754a;


VARIABLES:

Num_points = 256;
raw_data[ 4 ];
data[ Num_x_points, 2 ];
Win_ID_1;                // signal window
Win_ID_2;                // background window
I;
...

ASSIGNMENTS:

...

PHASES:

PHASE_SEQUENCE_1       = +x, +x, +x, +x, -x, -x, -x, -x;
PHASE_SEQUENCE_2       = +x, -x, +y, -y, +x, -x, +y, -y;

ACQUISITION_SEQUENCE_1 = +A, -A, +B, -B, +A, -A, +B, -B;
ACQUISITION_SEQUENCE_2 = +B, -B, -A, +A, +B, -B, -A, +A;


PREPARATIONS:

init_1d( 2, Num_points );
Win_ID_1 = digitizer_define_window( 388 ns, 4 ns );
Win_ID_2 = digitizer_define_window( 620 ns, 4 ns );

...

EXPERIMENT:

FOR I = 1 : Num_points {
    raw_data = get_phase_cycled_area( CH1, CH2,
                                      Win_ID_1, Win_ID_2 );
    data[ I, 1 ] = raw_data[ 1 ] - raw_data[ 3 ];
    data[ I, 2 ] = raw_data[ 2 ] - raw_data[ 4 ];
    display( I, data[ I, 1 ], 1, I, data[ I, 2 ], 2 );
    pulser_shift( );
}

We have two acquisition sequences and two digitizer windows, so the function returns an array with 4 elements. The first and third element of the array are the results for the first acquisition sequence for window 1 and 2, the second and fourth are the ones for the second acquisition for both windows. Since the data are measured with baseline correction, i.e. the result for the second, off-resonance window must be subtracted from the first windows result, to obtain the value for the first acquisition sequence from the first array element the third must be subtracted, and for the second acquisition sequence the value if the fourth array element from the second.

This document was generated by Jens Thoms Toerring on September 6, 2017 using texi2html 1.82.