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  #1  
Old 08-08-2002, 11:29 AM
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Question What the heck is "duty cycle"

That's what I hear when I call up the stores and ask if they have a digital multimeter with 'duty cycle'? Is that the same as 'voltage event', 'auto ranging', 'data hold' or 'bar graphing'? No one seems to recognise the term 'duty cycle'. Can someone just reccommend a decent model?
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  #2  
Old 08-08-2002, 11:38 AM
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Cap'n - do yourself a favor and look on ebay for a Fluke dmm with duty cycle. You can usually find one at a good price.
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  #3  
Old 08-08-2002, 11:39 AM
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<< but I use analog meters only)>>

Another "Simpson 260" guy ???

In love w/my 260 ... [ all 5 of them]
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  #4  
Old 08-08-2002, 11:46 AM
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I know what you mean..
I have them all, but have been using Simpson 260/s for 35 years and you just get to know how to read them without even looking at the scales, if you know what I mean..
Deflection Vibe, I call it....
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  #5  
Old 08-08-2002, 11:51 AM
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Excuse me, but I don't have an answer yet

Anything at Radio Shack, Sears etc.?
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  #6  
Old 08-08-2002, 12:03 PM
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This is decent for the $$$$

http://www.thetoolwarehouse.net/shop/FLU-78.html
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  #7  
Old 08-08-2002, 12:26 PM
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I found two Flukes at WW Grainger. 6T087 for $70 and 6TO88 for $80. Both have duty cycle. They don't appear to have much else but I have a Beckman Industrial 360 to use for everything else. BTW, can duty cycle, in this case Lambda, be measured with a Snap On automotive occiliscope? I have access to one.
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  #8  
Old 08-08-2002, 12:44 PM
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A scope is the "BEST"!

check out Stevebfl's article complete with pics: http://www.peachparts.com/Wikka/EngineControls

Here's a pic showing '50%' DC from Steve's article:.
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  #9  
Old 08-08-2002, 12:50 PM
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You can use the old style analog meter to measure duty cycle. Duty cycle is defined at the ratio of "on" time to "off" time. On is defined as when the voltage is high and off time is defined as when the voltage is zero. If the on time is equal to the off time the duty cycle is 50%.

So given that as a basis for discussion one can read duty cycle using an old style meter. Here is how to do it.

It is important to know the voltage level during the "on" and "off" times. Knowing that allows one to make a simple reading and then calculate the duty cycle.

Lets assume that the voltage during the on time is 12v and zero during the off time. When we read a duty cycle voltage the meter will average or integrate the voltage between the on and off times. So if we were at 50% duty cycle then the meter would read 6v or half of the voltage during the on time. If we read 5v then we can calculate the duty cycle to be 41.55%. If we read 4v then we have a duty cycle of 33.33% and so on.

The formula is ---- duty cycle = Vread * 100 / Von

in our example 41.666 = (5 * 100) / 12

where;

Vread = voltage read my the meter
Von = voltage during the ON time

Hope I have not confused the issue. No need to go buy an expensive meter just to read duty cycle.
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Old 08-08-2002, 12:59 PM
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Dave I love to read your posts. I just wish I could understand them!
Jim, I read the article and that's why I need the "duty cycle". SB used a multimeter but if a scope will do it I won't have to buy anything.
I going to print Dave's reply and put it under my pillow tonight and see if I understand it tomorrrow!
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  #11  
Old 08-08-2002, 01:05 PM
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Since you have a scope you are all set. Just display the waveform and measure the ratio of on and off. And your done.
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #12  
Old 08-08-2002, 01:19 PM
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To expand on the previous good definition of duty cycle: The period of the event that duty-cycle represents does not have to be any set time-length. The first event to monitor is thus frequency. When asking about the meter, looking for duty-cycle, with salespeople that don't know what about the electronics being tested, frequency is something they usually understand. Frequency tells you how long the event takes. How much of that time is on or off is the duty-cycle. Equipment that measures frequency will usually do duty-cycle.
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  #13  
Old 08-08-2002, 02:30 PM
LarryBible
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I bought a GREAT little DMM from the Sears Craftsmen tool catalog with Duty Cycle for $30. Actually they were having a 10% off sale so it was only $27.

It works great! All you have to do is look at the table showing various functionality for the meters they have. It can't be beat for the money.

Have a great day,
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  #14  
Old 08-08-2002, 02:58 PM
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Thanks all.
Larry, do you know the model number of your meter?
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  #15  
Old 08-09-2002, 12:31 AM
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I bought two from Sears 3 days ago. on sale for $17.99 each(close out?). By Craftman...Sears item#34 82040.
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