A Fluke 435 is a good data logger that has a PF feature. Check on it.

Find the phase difference between voltage and current waveforms in terms of samples and then find out powerfactor, which is cosine of this phase difference.

One important issue to check is the harmonics level. Usually PF correction has implications on harmonics and it is recommended to monitor them as well. Moreover, the presence of harmonics means that the Power Factor is different from Cos Phi (the previous post about phase shift ignores the harmonics). There are many good meters, both handheld and permanent installation. If this is long term installation, I would consider permanent power factor measurement.

This is called effective power factor and equal to = real power / apparent power at input terminals

Real power is the average of instantaneous input power which is a multiplication of instantaneous of both input voltage and current.

Apparent input power is the multiplication of total effective rms of both input voltage and current.

This is the way how to determine the exact effective input power factor for any kind of sinusoidal and non sinusoidal waveforms.

Therefore you have to monitor exactly the iput current and voltage waveforms and then you may use DAQ CONNECTED to PC

THEN YOU DO THE REQUIREMENTS .

Try to see the following paper which is related to PF

The investigation of power distortion in a three-phase modified controlled converter circuit

B.M. Saied, R.Kh. Antar

Conference Proceeding: 07/2010; DOI:10.1109/SSD.2010.5585595In proceeding of: Systems Signals and Devices (SSD), 2010 7th International Multi-Conference on

Abstract

Power system and its installation utility suffer from harmonic pollution due to the nature of non-linear load applications. The most reliable and significant approach, in order to contribute to minimize the harmonic pollution, is to treat each type of load autonomously. Therefore, this paper is investigating all types of power components for a filter circuit which is designed and used to reduce the harmonic amplitudes of the ac supply currents of a three phase six pulse controlled converter. The simulation results show that the filter circuit is active and reliable in the rectification and inversion modes, where dc machine is used as a load or prime mover in order to fulfill both rectification and inversion modes. The suggested method compared with the conventional type shows that a considerable improvements in effective power factor, minimizing harmonics and power distortion. Also different approaches have been presented for all types of power components.

What have been by Basil are correct. If you have no DAQ, you can use digital oscilloscope and download the numerical results into PC for further processing

To make good PF measurements, you have to be able to simultaneously measure line voltage (TRMS), line current (TRMS) and active (real) power. To measure active power, you need to measure the average of the instantaneous product of voltage and current. Unless you want to reinvent the wheel, I advise you use an instrument made for this purpose.

It looks like the Fluke 43B would have all the features you need for power analysis on a single phase load.

http://www.fluke.com/Fluke/usen/Power-Quality-Tools/Troubleshooting-Power-Meters/Fluke-43B.htm?PID=56080

It will record data and has many other features. It's very expensive (>$3k).

I agree that reinventing the wheel is not required for one project. A more cost effective option is to use permanent installation meters that may not give the ease of use of the handheld (such as the two Flukes offered above) but at fraction of the price and usually more accurate. A highly reliable product with high accuracy is SATEC EM133. See http://www.satec-global.com/eng/products.aspx?product=95. It would cost you 5%-10% of the cost of the Fluke devices with better accuracy (yes, 90-95% discount). You will get accurate power factor, both true and displacement (the difference between with or without harmonics), harmonics measurement and much more. You will not get the other power quality parameters, such as voltage flicker, that the Fluke has. SATEC do has similar products to Fluke, as well as less expensive devices than this one, but as far as I understand you needs this is the perfect solution for you.

Thanks your replies.we dont want to use the ready made device we want to design a circuit.

We got the idea to measure the displacement factor. Can any one help me how to measure the distortion factor. Power factor is the product of both distortion and displacement factor

by using dynamometer type wattmeter we can measure power factor.

Better use zero crossing detector which is even simple to design

It is useful only for displacement power factor how to measure displacement powerfactor

That actually gives the phase difference u cosine it then u will get the power factor

It is useful only for displacement power factor how to measure distortion powerfactor ratio of I1(rms)/I(rms), product of distortion and displacement power factor equal to total power factor

what is the device that you are using ? If you will make a device you can measure voltage and the currant and use instantaneous power theory for measurement both active and reactive power and then get power factor

When there is non linearity, there will be distortion in the Currents and Voltages and Harmonics will be present.

When Harmonics are present ,the

R.M.S.value of E = Sqrt ( sum of (Erms ^2) of all the Harmonics present including Fundamental)

.

So is the case for Current also.

Hence Knowing the total Real Power consumed we can calculate the over all Power Factor. using RMS Values of Voltage and Current.

Dr.P.S.

Try to see this paper, "

The investigation of power distortion in a three-phase modified controlled converter circuit"

It gives you an idea how to determine the effective power factor, the reactive power , real power and the distortion power , which can be used for any non-sinusoidal supply voltage and or current.

Mr.Yadhunandana,R.K.,

The following Link and the contents of the paper give you a clear idea on Displacement P.F and Distortion P.F.and how to calculate them.

Also,the full paper can be accessed

http://www.ijetae.com/files/Volume3Issue2/IJETAE_0213_60.pdf

The paper cited by Basil Saied has to be obtained from I.E.E.E.Explore on payment..

Dr.P.S.

You can use a Power analyzer. This will directly give you the power factor including harmonic factor and displacement factor.

If you do not have a power analyzer, use a spectrum analyzer and find the voltage and current harmonic values. use the same and find the harmonic factor. Find the displacement factor either using dynamo meter type watt meter or using low pass filter and getting fundamental values. Then you can get the power factor.

Prof. Madhava Udayagiri has given the Practical way of measuring the power factor including harmonic factor and displacement Power Factor, compared to the Theoretical method of calculating them, which is really useful.

Dr.P.S.

There are ics available form analog devices. These ics take input voltage and current signals and calculate real, reactive powers, power factors and many other parameters of interests. You can use such an ic in your project. Check Analog devices website for more details.

Muhammad Abbasi is right in his suggestion. One such interesting paper can be accessed through the link given below.

290

PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 6/2012

Sabir RUSTEMLI, Muhammet ATES

University of Yuzuncu Yil

Measurement and Simulation of Power Factor using PIC16F877

Link :

pe.org.pl/articles/2012/6/68.pdf

The paper referred below will also be of interest on the subject using Digital Ics

Link :

http://go.galegroup.com/ps/i.do?id=GALE|A278403097&v=2.1&u=siast&it=r&inPS=true&prodId=EAIM&userGroupName=siast&p=EAIM&digest=748cebd2e4b067b82de8740b4b5be7ee&rssr=rss

An adaptive scheme for power-related measurements and power-factor correction

Author(s): Muhammad S. Adeel and Muhammad A. Saqib

Source: Australian Journal of Electrical & Electronics Engineering. 8.3 (Oct. 2011): p211.

Document Type: Article

Full Text: COPYRIGHT 2011 The Institution of Engineers, Australia

http://www.engineersmedia.com.au/journals/ajeee.html

Abstract:

This paper presents a fast, low cost and accurate instrumentation scheme for power-related measurements and power-factor correction. These measurements include the root-mean-square values of current and voltage, the active and reactive powers, the total harmonic distortion and the true power factor. It is a microcontroller-based digital sampling system which runs a fast algorithm for displacement power factor measurement. The controlling system monitors and senses any variations in power factor, and accordingly switches the appropriate capacitor combination across the load. The scheme presents an economical and efficient solution to the power distribution companies for its customers.

Dr.P.S.

As "power factor" is defined using sinusoidal voltage and current waveforms then irrespective of load it would require one to determine the fundamental sinusoidal components of the voltage and current waveforms.

Many systems ( as mentioned above) use FFT's on both the voltage and current waveforms from which they determine the "conventional" power factor using the fundamental components only. This is why there are now various definitions such as power factor, true power factor and displacement power factor. Others like distortion power etc arise when doing harmonic or non-linear load compensation.

For non sinusoidal waveforms using just the fundamental components one may determine the "conventionally" power factor. By including harmonic components one may arrive at the true power factor and if there are large switching delays then displacement power factor comes into play; the latter really applies to thyristor or naturally commutated devices rather than self commutated or PWM devices and a good example of the former is a thyristor supplying a resistive load with a firing angle of 90 degrees, which creates the appearance of an inductive load due to the displacement of the current relative to the voltage due to the firing delay.

In the end power factor is defined by what the utility measures and charges one for. All are identical if the voltage and current waveforms are symmetrical and sinusoidal as mentioned at the outset.

You could use your analysis of the ability to measure the possibility of change or the stability of the power factor (power quality analyzer fluke 430) is good device

I would like to understand your word "accurately". For a measurement point of view it is a matter of uncertainty of the measurement chain and post-processing that you use, but there is a definition of power factor behind this , that is more related to power systems discipline, to what the utility bills you for (as G. Diana said above), to what you can compensate with your static converter.

On the measurement side "accurately" reflects in the uncertainty (the term class is old, but you can relate the two) of the voltage and current transformers, or probes, that you use; Then on the uncertainty of the digital acquisition system (e.g. sampling oscilloscope, DAQ board, micro with ADC on-board). The first two may be in the order of 0.1 to 1% all together and even better.

Finally on the post-processing that you use: FFT? it depends on integer or floating-point FFT, on how accurately you represent the phase angles (granularity in phase reflects in teh estimate of the displacement factor), on which harmonics you include for the calculation of the total power factor.

Pay attention that then also the frequency response of your probes becomes relevant, so 0.1 to 1% is normally declared at the fundamental and slightly beyond, but if you need to go up to the 40th or 50th harmonic you could have some surprise, especially for inductive dividers (voltage transformers). Current transformers are normally much more accurate.

Please, share some more info.