Using arduino with electrical power suite

Question

I am using an arduino to measure voltage and current and eventually get the power readings . But however when i am getting  the readings from the analog input  and connect it to my power VI the  power factor remains 1or -1 . I am measuring single phace power. I am using an SCT- 013 -000 current transformer for the current . and apower transformer for the voltage 240 - 6V . below is my vi and screenshots . Can you help me troubleshoot why my powerfactor isonly flickering between 1and -1 . for all loads including resistive , capacitive and inductive loads . 
Attachments:
Power from Wall Socket.vi ‏45 KB
VI outlook.PNG ‏58 KB

Answer 1

OK. Let's try to define some terms.
Phase resolution: The smallest difference in phase angle between the voltage and current waveforms that can be measured. 
Example: At 50 Hz one period is 20 ms. If you take a sample every millisecond (1 kHz), you will get 20 samples per cycle of the 50 Hz signal. That is equvalent to 18 degrees between samples. Since power factor is proprtional to the cosine of the phase difference you would get possible power factor values of 1, 0.95, 0.81, and 0.59 for phase differences of 0, 18, 36, and 54 degrees or time differences of 0, 1, 2, 3, and 4 milliseconds.
If the sampling rate is 120 Hz, the period is 8.333 ms and the phase resolution is 150 degrees. That is meaningless for power factor measurements.
Next, the Arduino LINX software cannot achieve anywhere near 120 Hz as you have the VI set up.  Open up the LINX VIs and look at what they are doing. It sends an 8-byte packet to define a channel. Then it waits for 2 bytes to return. One of those bytes tells the next VI how many data bytes are coming. It appears that you get 2 bytes of data from each read. That is a total of 24 bytes for two channels. The digital write also sends 8 bytes although that runs in parallel with the reads. With the standard settings doing two one-channel analog reads takes at least 25 ms. That is equivalent to a sampling rate of 40 Hz. The Nyquist criterion specifies that the sampling rate must be greater than twice the frequency of the signal you want to measure. So your sampling rate needs to be >100 Hz.
If you use the N Channel version of Analog Read for two channels (as opposed to the two separate Reads you have now), it sends a 9-byte packet and receives 6 bytes. The maximum rate it could achieve is ~64 Hz, which is still far too slow.
Lynn