Duty cycle, frequency and pulse width--an explanation

I'm going to explain the difference between duty cycle frequency and pulse width these terms are often used together they're sometimes used interchangeably and they're often confused but they have different meanings and I'm going to take a minute and explain that now first I wanted to just make sure that we understand the difference between a digital and analog signal because all of these signals that we're going to be measuring are going to either be digital or analog a digital signal is when the switch is on and off or has finite increments an analog signal is one that has an infinite number of increments as it changes so start with the analog signal an analog signal could be a waveform of any kind where the voltage is varying or changing it has a an infinite number of different increments that it can change to it's not just on or off or high or low but it could be one two three four five or one and a half and two and a half and three and three-quarters and those increments can even be split smaller and smaller and it varies infinitely a digital signal on the other hand is given a set number or a finite number of increments typically on or off or high or low so if we have a zero to 5 volt scale here low may be near zero volt volts and high would be near five it looks like a square wave because it doesn't vary there is no 1 and a half it's either zero or five and nothing in between so often we have an analog signal that needs to be converted to a digital signal whenever we're using a computer or a data acquisition device we're collecting analog voltage measurements that vary we've got to be turn into some sort of a digital signal that the computer can recognize and interpret so the way that works is like this if this is our analog signals coming in and it's a waveform is varying like this we would set up some kind of a rule or a threshold and we might you might say if this is zero volts down here at the bottom and this is five volts so we're looking at a 5 volt scale the threshold may be 2.5 volts right here in the middle what happens is as as this signal goes into the analog to digital converter it monitors it and as long as the voltage is below two and a half volts it's considered low so moves along here at a low voltage until it reaches this two-and-a-half volt point and when it does it immediately switches to high and it stays high until it drops past the two and a half bolt level again and that continues every time every time it crosses that 2.5 volt level if it's above 2.5 volts it's considered on or high it's below it's off in a very basic way that's how an analog signal is converted into a digital signal it can be used now let's take a minute and explain how we measure those signals whether it's analog or digital we measure them in one of these three ways okay so if we have some type of an electrical signal and doesn't matter whether it's analog or digital but we'll just start out with a digital signal if we use digital because it's most universal there are three different ways that we can measure this signal I'm not talking about voltage the voltage level or amplitude right that's that's obvious we're always going to be able to measure that but as far as its time the time base there are three ways we can measure it one is in a percentage and that's called duty cycle we simply take one cycle which is from here to here and we ask ourselves what percentage of that cycle was this turned on for and here looks like roughly 50% so we could say it was on for 50% of the time and it was off for 50% of the time and when it comes to duty cycle we're simply talking about the on time so this has a 50% duty cycle I'll add a few more segments here I was continued to go down here I can see my cycles are all staying about the same width this looks like maybe another 50% or it's slightly wider we could call this at 55 percent duty cycle which would mean that is off 45 percent of the time this one looks like it's close to 50 again but over here we've got something that's much smaller during this cycle looks like maybe was on for only about 20 percent of the time which means it was off for 80 percent the 20 percent duty cycle at that point so that's duty cycle now the other measurements are frequency and pulse width frequency takes these cycles that we just marked off and says how many times did that happen per second that's measured in hertz Bri v8 is Hz how many cycles per second so if we look at this we would if if this happened to be one second from here to here we would say we had one two three four cycles per second if it happened that there were a hundred of those in a second we would say it had a hundred curves or the frequency was a hundred Hertz 100 cycles per second so frequency is measured in cycles per second duty cycle is measured in percentage upon time and finally pulse width is measured in actual time usually in milliseconds we're talking about a computer that's turning these things off and on so it's usually quick but it just is in time so of course on a lab scope our tie our base across the bottom the domain that we're measuring in is always time and so if we were to come along here and say this this was point five seconds here and each of these cycles is happening it say one second right three point five seconds here we would say well the distance between here and here the distance between here and here is the amount of time that it was on for and that is the width that pulls if it's 50% this would be 1.0 right here right we have point five one point oh one point five the difference between here and here is going to be 0.5 seconds that's the pulse width of course we're usually doing in much smaller increments of time than that and so we're talking about a fraction of seconds so we'll usually measure that in milliseconds but that's the that's the way we measure the time that the bolts was on for hopefully those all make sense not for that clarifies the difference between those three different terms they're all different different ways of measuring sometimes even the same signal it is possible to have an analog signal such as this and also measure its frequency how many cycles that happen per second it's kind of difficult though to measure duty cycle because there is no defined off-and-on unless we convert it into a digital signal it's also difficult to measure pulse width because there isn't you need to find poults here so so frequency can be applied to an analog or digital signal where the other two can only be applied to a digital signal and that's that's a brief explanation of the difference between those three and how they use to measure signals as you can see we took one signal we made it at three different ways and that's entirely possible so the question really is which these three do we want to measure your typical multimeter or lab scope can measure any of these or if not you can take the measurements that you make and calculate these things

Channel: Justin Miller

Views: 353,508

Rating: 4.9096746 out of 5

Keywords: Automotive, Engineering, Technology, BYUI, BYU-Idaho, duty cycle, duty, percent, percentage, on-time, on time, on, time, milliseconds, pulse, pwm, pulse width, modulation, frequency, hertz, cycles, per second, switching, switch, analog, digital, controller, pulse width modulation, data acquisition, voltage, signal, current, electricity, electronic, module

Id: rBQVfCUuhfs

Length: 8min 53sec (533 seconds)

Published: Wed Nov 11 2015