average value of current pulses?
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Posted by acannell@wwc.com on December 15, 2006, 2:44 pm
Please log in for more thread options i am trying to figure out the average current consumption of a pump. it draws 13ms pulses of about 500ma about 15 times per second at randomly spaced intervals. i put a 0.1ohm sense resistor in the positive lead of the battery which powers the pump, and i put an rc integrator across this resistor (10k and 1000uF capacitor). does this make sense as a way to average out these pulses and get a voltage which represents the long term (relative) average of the voltage across the sense resistor? | ||||||||||||||||||||||
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Posted by Andrew Holme on December 15, 2006, 3:02 pm
Please log in for more thread options Yes, but the time constant doesn't need to be so long. With those values, it's going to take almost one minute to fully charge the capacitor. I would try 10k and 100uF. | ||||||||||||||||||||||
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Posted by Bob Eld on December 15, 2006, 6:00 pm
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> i am trying to figure out the average current consumption of a pump. it
> draws 13ms pulses of about 500ma about 15 times per second at randomly > spaced intervals. > > i put a 0.1ohm sense resistor in the positive lead of the battery which > powers the pump, and i put an rc integrator across this resistor (10k > and 1000uF capacitor). > > does this make sense as a way to average out these pulses and get a > voltage which represents the long term (relative) average of the > voltage across the sense resistor? This will work but it may give difficulty. The peak voltage is only 50mV across the .1 ohm resistor and the average voltage will be less than 10mV. That's a small number prone to errors with an electrolytic capacitor. I would use a film capacitor of several microfarads with hundreds of "k" in the resistor to get a time constant about one second. It is now 10 seconds, longer than necessary. You may want a little more sense voltage to work with by making the .1 ohm resistor .2 or even .5 ohms. What are you going to do with the average value for current? If it is going to feed any type of processor or controller for indication or control, you might consider doing A to D conversion and numerical averaging in the digital domain in that processor. It could be a single chip solution without any analog integration, large caps or other parts. | ||||||||||||||||||||||
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Posted by Phil Allison on December 15, 2006, 9:24 pm
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** Groper alert ! >i am trying to figure out the average current consumption of a pump. it
> draws 13ms pulses of about 500ma about 15 times per second at randomly > spaced intervals. ** How ambiguous. What exactly are these " randomly spaced intervals " ?? Every other Tuesday afternoon if it rains ?? ...... Phil | ||||||||||||||||||||||
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Posted by John Larkin on December 15, 2006, 9:59 pm
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On Sat, 16 Dec 2006 13:24:02 +1100, "Phil Allison" >
> > >** Groper alert ! > > >>i am trying to figure out the average current consumption of a pump. it
>> draws 13ms pulses of about 500ma about 15 times per second at randomly >> spaced intervals. >
> >** How ambiguous. > >What exactly are these " randomly spaced intervals " ?? > Random intervals can't be described exactly. That's because, I think the theory goes, they're random. John | ||||||||||||||||||||||
> draws 13ms pulses of about 500ma about 15 times per second at randomly
> spaced intervals.
>
> i put a 0.1ohm sense resistor in the positive lead of the battery which
> powers the pump, and i put an rc integrator across this resistor (10k
> and 1000uF capacitor).
>
> does this make sense as a way to average out these pulses and get a
> voltage which represents the long term (relative) average of the
> voltage across the sense resistor?
>