If the period is set to a value less than 1 millisecond (a setting of less than 1000), only one PWM output will be active. That means that the PWM period can range from 100 microseconds to a little over 65 milliseconds. Timing is in microseconds (1 million microseconds = 1 second). The period is set by selecting the “Set Period” radio button, then either selecting a ui16 tagnamed variable, or entering a number between 15. The Period is common to all PWMs in the PLC. With this dialog box, you can Set the PWM Period, Start (continue/adjust) PWM operation, or Stop the PWM. When you place a PWM block in your program, a dialog box, like that shown below, will pop up. However, the Period is common to all PWM signals on the PLC unit. Each active output has its own “on time”. Branch Expansion units that are used a expansion IO, cannot output PWM signals.Īny combination of digital outputs, contained on the PLC with the program, can have PWM output signals. Any Branch Explansion PLC which has its own program (embedded subroutine) can output a PWM signal from the embedded subroutine. That means that any Ace or Branch digital output can programmed to output a PWM signal by the application main program. PWMs Application Limits : PWMs can be applied to any digital output that is physically present on the PLC module that contains the application program. If you want to output another pulse, your program must execute another “Start PWM pulse” block. A single pulse PWM output is active for its defined “on time” within the PWM period. The next figure show a standard PWM on the top, and a single pulse PWM output on the bottom. Most Velocio PLC digital outputs are “sinking” transistor outputs – so when the output is on, the output sinks, pulling the signal low. The figure, on the right, illustrates a PWM output signal. Standard PWM signals repeat every period increment.
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Partial (5%, 10%, 53%, etc.) opening is generally controlled by an “on time” pulse purportionate between to full open and full closed limits. The valve may be controlled to a fully closed state with a 1 millisecond pulse on time and fully open with a 3 millisecond pulse (actual times are defined by the valve manufacturer). Valve position is controlled by the “on time” of the output pulse, within this period. For example, a typical servo valve control might have a 20 millisecond period. The single pulse feature of the function is applicable to any single pulse output need.Ī pulse width modulated output signal is one that has a period and an output “on time”, or duty cycle, within that period. It is also used for laser pulse control, motion control, light intensity controls and other other applications. Pulse width modulation is a very powerful function that is commonly used to control the positioning of servo valves.
PWM is the acronym for “Pulse Width Modulation”.