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 Post subject: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 4:52 pm 
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I hope this is the right place for this ---

I have a specification that specifies a pulse train with a 5 microsecond wide pulse and a duty cycle of .0005/4 kHz. I am trying to calculate the period --
I realize duty cycle = PW/period therefore period = PW/duty --- My question is duty is usually something like .01, .05 .1 (1%, 5%, 10%) -- How do I handle the .0005/4 kHz spec ?

Griz


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 6:08 pm 
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What is the thing requiring this spec? That would help put it in perspective. Or a picture of where it calls out that spec. Ive never seen a duty cycle called out like that.

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 6:13 pm 
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Maybe it means .0005 @ 4000 kHZ


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 6:17 pm 
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I have been doing this a while and I never saw this called out this way either. This is an attenuator we need to run a peak power test on -- Raytheon spec


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 6:56 pm 
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If the 4 Khz is the frequency of the pulse train, the period would be 250 uS.
But with a 5 uS pulse width, that makes the duty cycle of the pulse train 5/250=.02 or 2%?

I can understand the confusion. Now if the attenuator can't tolerate a continues string of 5 microsecond pulses, maybe there is a secondary duty cycle, where the pulses are completely off for some time period and then back on again?

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Last edited by processhead on Mar Tue 06, 2018 7:44 pm, edited 1 time in total.

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 7:21 pm 
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Nope -- that is the way it is written direct from their spec


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 7:45 pm 
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After some more thought, I revised my previous post.

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 8:00 pm 
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grizzly1 wrote:
I have been doing this a while and I never saw this called out this way either. This is an attenuator we need to run a peak power test on -- Raytheon spec


I bet that spec originated in Waltham? Im trying to decipher a couple nebulous specs they called out on something Im working on also. That usually results in acquiring some exotic testing setups.

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 8:18 pm 
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What processhead wrote makes sense but if you follow that thru it will now take 500 w peak and translate it into 10 w avg -- and we have a 2w part so that won't do -- we want no smoke :?


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 9:10 pm 
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Perhaps it's 1/.0005 x 5uS = 2000 x 5uS = 10,000uS

so 1 5uS pulse then 9,999uS resting ?

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Tue 06, 2018 9:29 pm 
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majoco wrote:
Perhaps it's 1/.0005 x 5uS = 2000 x 5uS = 10,000uS

so 1 5uS pulse then 9,999uS resting ?


This would great but where does the 1/.0005 come from ?


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 2:24 am 
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You need to go back to the customer for clarification. My experience in dealing with customer specifications was that they were sometimes complied by people who had no real understanding of what they were specifying. They just took part of a spec here and a part there and combined them. The larger the company the more often this happened.

RRM


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 2:56 am 
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Let us know when you find this out. I'll place my bet that it's specifying a pulse width that is equal to 0.05 % duty cycle (.0005) at 4000 Hz. So the specified pulse width would be .05 x 1/4000 = 0.0000125 sec. That's a 12.5 uS pulse every 1/4000 sec. Let us know!


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 11:31 am 
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Greetings to the Forum:

Yet another example of that humorous article about data sheets.... the only part of which I can remember is that units used will be the least comprehensible possible. "Velocity, for example, will be expressed in furlongs per fortnight." :lol:

Regards,

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 3:12 pm 
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Thank you all for your inputs --- while the mystery of the notation ".0005/4kHz" still remains -- (not only how to interpret it but also now where that notation came from), we have backtracked the specification to the original documents and found that it is currently specified as :

Peak power will be measured with a 5x10-4 duty cycle and 5 uS pulse width -- which translates into a 10 mS period --

So my problem is solved and I can test parts - the crazy notation is history at this point

Thanks again all that were scratching their heads --

Griz


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 3:30 pm 
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grizzly1 wrote:
Thank you all for your inputs --- while the mystery of the notation ".0005/4kHz" still remains -- (not only how to interpret it but also now where that notation came from), we have backtracked the specification to the original documents and found that it is currently specified as :

Peak power will be measured with a 5x10-4 duty cycle and 5 uS pulse width -- which translates into a 10 mS period --

So my problem is solved and I can test parts - the crazy notation is history at this point

Thanks again all that were scratching their heads --

Griz


Ok, just so it's clear to my thick head, is that scientific notation in your description?

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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 3:34 pm 
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yes


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 7:30 pm 
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grizzly1 wrote:
Peak power will be measured with a 5x10-4 duty cycle ...Griz

Is it correct to say that's .05% duty cycle?


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 Post subject: Re: Duty Cycle Calculations
PostPosted: Mar Wed 07, 2018 8:11 pm 
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yes


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