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Publicado: 16 de octubre de 2012
Document Type: Tutorial NI Supported: Yes Publish Date: May 10, 2010
Pulse Width Modulation (PWM) Using NI-DAQmx and LabVIEW
Table of Contents 1. 2. 3. 4. 5. Introduction to Pulse Width Modulation National Instruments PWM Hardware Programming PWM in LabVIEW Using NI-DAQmx Advanced PWM Applications in LabVIEW Related Links
The National Instruments Getting Started with NI-DAQmx Series isaimed at helping you learn NI-DAQmx programming fundamentals. Through video and text tutorials, this series will take you from verifying your device's operation in Measurement & Automation Explorer (MAX) to programming data acquisition applications using LabVIEW. It is intended for both the beginner who wants to learn how to use the DAQ Assistant, as well as the experienced user who wishes to takeadvantage of advanced NI-DAQmx functionality. Introduction to Pulse Width Modulation Pulse width modulation (PWM) is a technique in which a series of digital pulses is used to control an analog circuit. The length and frequency of these pulses determines the total power delivered to the circuit. PWM signals are most commonly used to control DC motors, but have many other applications ranging fromcontrolling valves or pumps to adjusting the brightness of an LED. The digital pulse train that makes up a PWM signal has a fixed frequency and varies the pulse width to alter the average power of the signal. The ratio of the pulse width to the period is referred to as the duty cycle of the signal. For example, if a PWM signal has a 10 ms period and its pulses are 2 ms long, that signal is said tohave a 20 percent duty cycle. Figure 1 shows three PWM signals with different duty cycles. For a more thorough look into pulse width modulation, visit the link at the bottom of this page.
Figure 1: PWM Signals with Different Duty Cycles National Instruments PWM Hardware PWM signals can be generated as a digital signal, using counters or digital output line(s), or as an analog signal, using forinstance, an arbitrary waveform generator or an RF signal generator. Several National Instruments multifunction data acquisition (DAQ) devices are capable of producing PWM signals. This includes the E, S, B, M and the new X Series devices, which represent the next generation of multifunction DAQ from National Instruments. In addition, NI 660x counter/timer devices, as well as NI 653x digitaldevices can also be used. Although the remainder of this article focuses on using counters to generate PWM signals, it's worth noting that National Instruments hardware and software also supports generation of PWM signals using digital line(s) or analog output options. Programming PWM in LabVIEW Using NI-DAQmx
NI LabVIEW is the graphical development environment for creating flexible and scalabletest, measurement, and control applications rapidly and at minimal cost. With LabVIEW, engineers and scientists interface with real-world signals, analyze data for meaningful information, and share results and applications. The LabVIEW graphical development environment, combined with NI-DAQmx, gives you the tools needed to easily construct applications using counters to generate PWM signals. The firststep to create a PWM signal is to produce a simple digital pulse train. Below is an example of using LabVIEW to program a counter on an M Series device to create a digital pulse train signal using NI-DAQmx. Each step of the program, indicated by a number at the bottom of the figure, is described below.
1/3
www.ni.com
Figure 2: Block Diagram of LabVIEW Pulse Train Program using NI-DAQmx1. Create and initialize a counter output channel to produce a pulse in terms of frequency using the DAQmx Create Channel VI. Select appropriate inputs for Duty Cycle, Frequency, Counter(s), Idle State and Initial Delay. 2. Use the DAQmx Timing VI to configure the duration of the pulse generation. The Implicit instance should be used when no sample timing is needed, such as in counter tasks...
Pulse Width Modulation (PWM) Using NI-DAQmx and LabVIEW
Table of Contents 1. 2. 3. 4. 5. Introduction to Pulse Width Modulation National Instruments PWM Hardware Programming PWM in LabVIEW Using NI-DAQmx Advanced PWM Applications in LabVIEW Related Links
The National Instruments Getting Started with NI-DAQmx Series isaimed at helping you learn NI-DAQmx programming fundamentals. Through video and text tutorials, this series will take you from verifying your device's operation in Measurement & Automation Explorer (MAX) to programming data acquisition applications using LabVIEW. It is intended for both the beginner who wants to learn how to use the DAQ Assistant, as well as the experienced user who wishes to takeadvantage of advanced NI-DAQmx functionality. Introduction to Pulse Width Modulation Pulse width modulation (PWM) is a technique in which a series of digital pulses is used to control an analog circuit. The length and frequency of these pulses determines the total power delivered to the circuit. PWM signals are most commonly used to control DC motors, but have many other applications ranging fromcontrolling valves or pumps to adjusting the brightness of an LED. The digital pulse train that makes up a PWM signal has a fixed frequency and varies the pulse width to alter the average power of the signal. The ratio of the pulse width to the period is referred to as the duty cycle of the signal. For example, if a PWM signal has a 10 ms period and its pulses are 2 ms long, that signal is said tohave a 20 percent duty cycle. Figure 1 shows three PWM signals with different duty cycles. For a more thorough look into pulse width modulation, visit the link at the bottom of this page.
Figure 1: PWM Signals with Different Duty Cycles National Instruments PWM Hardware PWM signals can be generated as a digital signal, using counters or digital output line(s), or as an analog signal, using forinstance, an arbitrary waveform generator or an RF signal generator. Several National Instruments multifunction data acquisition (DAQ) devices are capable of producing PWM signals. This includes the E, S, B, M and the new X Series devices, which represent the next generation of multifunction DAQ from National Instruments. In addition, NI 660x counter/timer devices, as well as NI 653x digitaldevices can also be used. Although the remainder of this article focuses on using counters to generate PWM signals, it's worth noting that National Instruments hardware and software also supports generation of PWM signals using digital line(s) or analog output options. Programming PWM in LabVIEW Using NI-DAQmx
NI LabVIEW is the graphical development environment for creating flexible and scalabletest, measurement, and control applications rapidly and at minimal cost. With LabVIEW, engineers and scientists interface with real-world signals, analyze data for meaningful information, and share results and applications. The LabVIEW graphical development environment, combined with NI-DAQmx, gives you the tools needed to easily construct applications using counters to generate PWM signals. The firststep to create a PWM signal is to produce a simple digital pulse train. Below is an example of using LabVIEW to program a counter on an M Series device to create a digital pulse train signal using NI-DAQmx. Each step of the program, indicated by a number at the bottom of the figure, is described below.
1/3
www.ni.com
Figure 2: Block Diagram of LabVIEW Pulse Train Program using NI-DAQmx1. Create and initialize a counter output channel to produce a pulse in terms of frequency using the DAQmx Create Channel VI. Select appropriate inputs for Duty Cycle, Frequency, Counter(s), Idle State and Initial Delay. 2. Use the DAQmx Timing VI to configure the duration of the pulse generation. The Implicit instance should be used when no sample timing is needed, such as in counter tasks...
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