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AC peak current measurement

D

David N.

Jan 1, 1970
0
I am using a Valhalla Scientific digital power analyzer to measure
power current and voltage. Unfortunately, the instruction manual for
this unit has been lost, so I need some help understanding what this
thing is measuring.

The unit displays true power, amps in true rms and volts in true rms.

1.) What is meant by "true power"? How are the calculating this?
2.) I know that the current is not sinusoidal. Is there a way to
calculate the peak current using this meter?

Thanks,
David

--
 
E

Eeyore

Jan 1, 1970
0
David N. said:
I am using a Valhalla Scientific digital power analyzer to measure
power current and voltage. Unfortunately, the instruction manual for
this unit has been lost, so I need some help understanding what this
thing is measuring.

The unit displays true power, amps in true rms and volts in true rms.

1.) What is meant by "true power"? How are the calculating this?

http://en.wikipedia.org/wiki/Apparent_power
 
M

MooseFET

Jan 1, 1970
0
David said:
I am using a Valhalla Scientific digital power analyzer to measure
power current and voltage. Unfortunately, the instruction manual for
this unit has been lost, so I need some help understanding what this
thing is measuring.

The unit displays true power, amps in true rms and volts in true rms.

1.) What is meant by "true power"? How are the calculating this?

True power means the average value of the instantanious power. At each
instant, you multiply the voltage by the current and then you average
the results. Very often some of the values you are averaging are minus
because energy is actually being returned to the mains at that time.

If you merely multiply the RMS current by the RMS voltage, you get a
number that is often higher than the true power.
 
David said:
I am using a Valhalla Scientific digital power analyzer to measure
power current and voltage. Unfortunately, the instruction manual for
this unit has been lost, so I need some help understanding what this
thing is measuring.

The unit displays true power, amps in true rms and volts in true rms.

1.) What is meant by "true power"? How are the calculating this?
2.) I know that the current is not sinusoidal. Is there a way to
calculate the peak current using this meter?

Thanks,
David

Some references on true power, etc.:

http://groups.google.com/groups/search?hl=en&q=true+apparent+power
http://www.allaboutcircuits.com/vol_2/chpt_11/2.html
http://www.google.com/search?hl=en&lr=&q=true+apparent+power+

I think Valhallas do typically measure peak inrush current, for
instance. I would get the model number and use Google to see if you can
find the manual. You can also check the Valhalla website to see what
you can find or you could just call the company. I remember talking to
some people there years and years ago and they were helpful.

http://www.valhallascientific.com/calibrators/cal-2701c.shtml
 
D

David N.

Jan 1, 1970
0
In general, is there a way to find the peak current, given Vrms, Irms
and P (true power) when the V and I waveforms look as follows?
 
J

John Larkin

Jan 1, 1970
0
I am using a Valhalla Scientific digital power analyzer to measure
power current and voltage. Unfortunately, the instruction manual for
this unit has been lost, so I need some help understanding what this
thing is measuring.

The unit displays true power, amps in true rms and volts in true rms.

1.) What is meant by "true power"? How are the calculating this?

This is the averaged value of the instantaneous product of line volts
and load current. If both are sines, that would be equivalent to

Erms * Irms * cos(phase angle)
2.) I know that the current is not sinusoidal. Is there a way to
calculate the peak current using this meter?

Not unless you know the exact waveform.

John
 
E

Eeyore

Jan 1, 1970
0
David N. said:
In general, is there a way to find the peak current, given Vrms, Irms
and P (true power) when the V and I waveforms look as follows?

Nope. You have to measure it.

Graham
 
T

The Phantom

Jan 1, 1970
0
In general, is there a way to find the peak current, given Vrms, Irms
and P (true power) when the V and I waveforms look as follows?


.
. .
. .
. . .
V . . .
. .
. .
.
.
. .
. .
. .
. .
I ... ... ....
. .
. .
. .
. .
.
Is this a measurement you will have to make often, or is this a one time
need? How do you know the current waveform is as you have shown?
Normally, one would need an oscilloscope to know the waveform and if you
have a scope it can make the measurement.

If you will need to do this often, it might make sense to buy an
instrument for the purpose. I see a number of Fluke 189 meters for sale on
ebay; $250 buy it now or starting bid of $100 and take your chances. This
meter can make the peak measurement you need.
 
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