Caluculating Real Power

[Henrik_Volkers]

to get back to your question about REAL POWER

P(t)=U(t)*I(t) 

when you measure U(t) and I(t) fast and synchronus enough (your card will multiplex channels, so read them with 10kS/s and you should be fine)

Your 'real' energy is the integral over a time interval (10h or as small as one powerline cycle), so divide by that time and you get 'real' power   

Since electronic powermeter are more and more common, look up the application notes from TI, Freescale, NS, Linear ...(long list) about powermetering , you can do it with LabVIEW and your 6024 and you will learn !

Message Edited by Henrik Volkers on 09-10-2007 02:31 PM

[Gabi1]

i am surprised. even using Keitley instruments i could not get fast enough readings to measure "real" time U and I. you need an oscilloscope for that, and it is quite difficult to find some with 10KHz analog signal output

[Henrik_Volkers]

maybe we are talking about two different things....

most regular line powermeters sample U and I with 2kS/s to 8kS/s (some simultaneous, some  not) to get a 1%  power reading.

(I'm not talking about powerline analyzers or stuff like a Zimmer ZES-300(0) )

With a PCI-6024   you should be able to read 2 channels with 100kS/s multiplexed, sufficient to make ordinary line power measurements....

(0.18 deg Phase error @ 50Hz)

With some calibration it should be possible to use the soundcard input together with a a current and a small voltage transformer for galvanic isolation and get about 5% accuracy, to bad I haven't the time , the parts should be somewhere in a box  

[Gabi1]

this is true, if you have fast enough readings, then simply use Labview for measuring the phase shift between current and voltage, to get the power factor and real power.

but from what i understood he was using a simple current transducer, which could only measure average AC current.

[johnsold]

The original post mentioned a shunt, so no speed problems.

Lynn

[Gabi1]

true enough 🙂

i have overlooked his specifications. the thing is i had never expected somebody to hook up directly (i.e without some kind of protective electronics) to the DAQ card. that is why i assumed he was using a cheap DVM. 

Anyhow, a shunt with some optocoupler would do totally the tric, you are right.