Chapter 4 Example Measurements

Figure 4-32 shows what the IIR filter specifications look like on the front panel. This is where you choose the design parameters for your filter.

Figure 4-32. Front Panel IIR Filter Specifications

In this example, the fifth order lowpass Butterworth filter is used with a cutoff frequency of 250 Hz. The order determines how steep the transition region will be. A higher order yields a steeper transition. However, a lower order decreases both computation time and error. In the case of our chosen filter, the Upper cut-off frequency, Passband ripple, and Stopband attenuation inputs are ignored. Refer to Chapter 16, Digital Filtering, for more information about software filtering.

Frequency with software filtering can also be measured using an instrument. The instrument control system setup is the same as Figure 4-26. Figure 4-33 shows the block diagram for this measurement. Notice that the IVI subVIs called are like those of Figure 4-27. The only difference is that IviScope Read Waveform Measurement [WM] VI has been replaced with IviScope Read Waveform VI in order to read an array of data. The outputs of this subVI are built into a waveform data type. The Digital IIR Filter VI and Extract Single Tone Information VI are used as discussed earlier to determine the frequency.

Chapter 4 Example Measurements

Figure 4-33. Measuring Frequency after Filtering Using an Instrument

Part II

DAQ Basics

This part contains information you need to use LabVIEW for data acquisition.

Part II, DAQ Basics, contains the following chapters:

•Chapter 5, Introduction to Data Acquisition in LabVIEW, contains all the information you should know before you start learning about data acquisition with LabVIEW.

•Chapter 6, Analog Input, contains basic information about acquiring data with LabVIEW, including acquiring a single point or multiple points, triggering your acquisition, and using outside sources to control acquisition rates.

•Chapter 7, Analog Output, contains basic information about generating data with LabVIEW, including generating a single point or multiple points.

•Chapter 8, Digital I/O, describes basic concepts about how to use digital signals with data acquisition in LabVIEW, including immediate, handshaked, and timed digital I/O.

•Chapter 9, SCXI—Signal Conditioning, contains basic information about setting up and using SCXI modules with your data acquisition application, special programming considerations, common SCXI applications, and calibration information.

•Chapter 10, High-Precision Timing (Counters/Timers), describes the different ways you can use counters with your data acquisition application, including generating a pulse or pulses; measuring pulse width, frequency, and period; counting events and time; and dividing frequencies for precision timing.