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Many experiments involve sending or reading waveforms from instruments like arbitrary waveform generators, digitizers or digital oscilloscopes. For example, imagine an

experiment where we want to control the amplitude of a sine signal outputted using an arbitrary waveform generator. The process can be divided into two tasks: The first task is to numerically calculate a waveform with the correct amplitude, the second task is to send that waveform to the output of the arbitrary waveform generator. Another example would be to measure a waveform with an oscilloscope, and then apply some function to extract the signal’s amplitude or frequency, which would allow us to record only a single or a few values characterizing the signal instead of saving the whole waveform to the log file.

Fig. 6.7. A Measurement configuration with signal connections for pulse generation and signal demodulation.

The Measurement program provides Signal Connections for managing situations like this. The idea is to separate the signal generation or signal analyzing from the instrument communication, to make it possible to develop generic Signal Generator or Signal

Analyzer drivers for creating or analyzing waveforms, which operate independently of the specific hardware that is used to output or measure the waveforms. In this way, the waveform generation/analyzing functions can be used interchangeably with instruments from different vendors. For more information on how to create your own Signal

Generator or Signal Analyzer drivers, see Section DriverINI.

The Signal Connections button in the toolbar of the main Measurement configuration window is used to show/hide a list of signal connections defined in the current setup. The button is only enabled when the setup contains instruments that allow waveform

generation/analyzing. The Signal Connections control contains a list with all the instrument quantities that can output or analyze a waveform. To make a connection, double-click one of the outputs and select the source signal from the dialog that pops up, or simply drag a

channel that represents a signal source from the main Channels list onto the correct output in the Signal Connections list. Figure 6.7 shows an example of

a Measurement configuration with a few signal connections.

Note that signal connections are also possible for scalar-valued channels. To make a signal connection between two scalar-valued channels, click the “Show scalar-valued signals”- checkbox below the signal connection list. Scalar-valued channels are listed in italics in the signal connection list, to distinguish them from the waveform signal connections.

As mentioned earlier in this section, two types of signal connections can be made: The first type is when a Signal Generator driver is used to generate waveforms that will be sent to the output of an arbitrary waveform generator, for example. The second type of

connection is when a waveform that is acquired using an instrument such as a digitizer or an oscilloscope is sent to a Signal Analyzer driver. The example in Fig. 6.7 illustrates both examples: The signals generated by the “Pulse Generator” Signal Generator driver are configured to be sent to various output channels of a Tektronix Arbitrary Waveform Generator (labelled “AWG” in the figure), whereas the waveforms acquired by the “Acqiris U1084A Digitizer” will be sent to the of the “Signal demodulation” Signal Analyzer driver that will extract the amplitude of the waveform at a specific frequency.

When running a Measurement that contains Signal connections, for each step in the step sequence the program will perform the following sequence:

1. Update step values: Update the values of channels defined in the Step sequence. 2. Generate and output signals: If present, calculate signals with Signal Generator drivers

and send the resulting waveforms to the corresponding instruments outputs.

3. Wait: Wait for the time specified in the Timing section in the lower-right corner of the main Measurement configuration window.

4. Acquire and analyze signals: If present, measure instrument channels that acquire waveforms, and send the acquired waveforms to the corresponding Signal

Analyzer drivers.

5. Log results: Measure the channels specified in the Log channels list and save them to disk. If a Signal Analyzer driver is in use, the Log channels list is where the user defines what quantities to store in the log file.

“Pulse Generator” driver will calculate new waveforms that will be sent to the “AWG” output channels. After that, the program will wait for 0.1 second to give the sample time to settle, before acquiring two waveforms (“Ch1 - Data” and “Ch2 - Data”) with the “Acqiris U1840A Digitizer”. The measured will waveforms will be sent to the “Signal demodulation” Signal Analyzer driver, which will analyze the waveforms and return the result in the channel named “Value”, which will be stored in the log file.

When running an experiment that contains Signal connections, it is possible to look at the measured waveforms in real-time as they are being acquired and processed. In the window that is visible when an experiment is running, mark the channel to investigate in the step sequence list in the left-hand part of the dialog (see Fig. 6.8).

Fig. 6.8. The measurement window during an experiment with signal connections, showing a measured waveform.