Measuring 220VAC with CompactDAQ?

[chuggins143]

Hello all,

I'm building an automated test stand where I need to measure both single phase (120 & 277VAC) and two phase (208/240VAC... I'm aware that no one calls it two phase, but that's what you're actually measuring... anywho)  I have the single phase working properly as seen in VI "DAQ_Sample3", but when I try to apply the same logic to two legs of power my output is only giving me data for one leg.   I've gone in and added the other two channels so it is measuring both legs and both amp clamps... I can hook the DAQ assistant to a graphical output and it shows all four readings, but when I try to transistion to the power VI it'll only calculate a single leg.  I've attempted to combine the signals several different ways, but haven't had any luck getting a result that passes the reasonablilty test... can someone that knows a little more about this take a look at the VI I have for two phase (DAQ_Sample4-2ph) and point me in the right direction?  

Thanks!

Chad

[EEsRULEtheWORLD]

Hi Chad,

I opened your VI, and I noticed that you are using a polymorphic subVI called  EPM_Power in both of your applications.  Could you attach this VI to the next post.  From the grayed out image of the subVI, it looks like it's configured for 3 phase in both applications.  Is this correct? 

[chuggins143]

Hi Sara,

The Power Vi I'm using is the one in the "Electrical Power Managment (EPM) Palette for LabView", I did not create it by any means... it can be found here... http://zone.ni.com/devzone/cda/tut/p/id/8652  I've attached the VI that seems to be running... there's six different EPM_Power vi's in the file.  I'm assuming that there's a "master" vi that decides which one to use.

The configuration I have set to the "automatic" setting... so I'm not sure why it wants to go to the 3ph setting when I only have one phase wired into it.  Unfortunatly, I'm not an EE so I'm at a little bit of a disadvantage when it comes to this subject.  As I've mentioned I have the single phase portion working fine, but am at a loss as to how to get the "two phase" hooked up properly.  I'm more than willing to learn what I'm doing wrong, but just don't know where to look.  I've searched the knowledge base and tutorials, but still haven't found a clear cut way to get from the 4 signals I have coming from the DAQ Assistant to the two signals the Power VI requires.

Thank you very much for taking a look at this!

C

[chuggins143]

Ok, as an update, I used the calculations found here.... http://zone.ni.com/devzone/cda/tut/p/id/8216  and this gets me closer, but it's still not on the money.  Any thoughts?

THX

C

[EEsRULEtheWORLD]

Hi Chad,

Ben (NI Applications Engineer) had told me that you were communicating with him through email, and he had sent you a VI that should solve this issue.  Have you had a chance to try this VI?  Let us know the results of this VI, so I can either post this VI on the forum as a solution to this issue or continue troubleshooting with you.

[chuggins143]

Hi Sara,

First of all, thank you for taking a look at this, I really do appreciate it!

Ok, I hooked it up Ben's way and ran it... what I found is that since I now have two voltages and two current readings I have to combine them otherwise I get too many data fields feeding into my DAQ loop.  So I'm calculating my voltage, which is close to what I'm measuring (235V calc vs.. 240V measured, anyone have a better way that'll give me better numbers?) and if I just take my max amp draw between the two lines I'm good.  I am, however, noticing that my power readings are off when compared to the Fluke power quality analyzer... ??  For example... I'm showing a measured VA of 440 on the Fluke and 488 in my VI.  Likewise, my power factor is showing a .53 on the Fluke and .47 in the VI.... Could these differences be due to a conversion I'm doing or am I miscalculating something? 

For reference, when I run single phase (120VAC), the measurements are dead on when compared to the Fluke power quality analyzer.

I've attached an updated VI that shows what I'm doing... If you guys/gals see an error, please feel free to point it out.  I'm not proud and will take knowledge anywhere I can get it.  I'll also forward this to Ben and see if he can shed any light on what I'm doing.

Thanks!

Chad

[Henrik_Volkers]

Here is some more food 😉

http://www.zes.com/download/application-notes/zes_applicat_105_leistungsmessung_e.pdf

[chuggins143]

Thank you Henrik!  ...I'll have to do some digesting on that for sure!

Thanks!

Chad

[chuggins143]

Ok, back at this problem.  I'm now conversing with an application engineer from NI but thought I'd keep this going so others could benefit from my learning experience!

A quick recap, before I left for vacation I was having a problem with the numbers I was getting from the Power VI's when measuring single phase 208/240VAC.  My equipment is a CompactDAQ with a 9225, and a 9239 module.  I can measure 120VAC and my numbers are dead on, but with two legs of power my numbers are off... more so the higher the voltage goes.  At 208 my voltages are closer than they are at 240, but with either one my power factor, VAR, and VA are all off.  I'm validating my numbers with a Fluke 435 Power Quality Analyzer, and have double checked the voltage and amp numbers with several freshly calibrated DMMs so I know what I'm supposed to be getting.

When Benjamin and I last conversed, the consensus was that I wasn't taking enough samples... so I set up a stand alone VI just to read the voltage and amps. I set no limit on the loop speed and just let it run full tilt.  I have the DAQ Assistant running at 25KHz taking data in "N Sample" mode.  This should be enough samples to get a good read, but still the numbers are off...

The following are the last questions I sent to B...

Do the calculations in the VI assume that the voltages are exactly 120 degrees out from each other?  I ask because I threw in the phasor output for  each leg and am only showing they are out about half that.  This is could be due to the fact that I'm using a variac to adjust my voltage.  I also was  digging at one point and it seemed to me that the polymorphic VI that's picking which case to use is only picking from two of the list... ?? (that's been a couple of weeks ago and I don't really remember how I got to it...) 

If anyone else has an idea about what's running afoul here, I'd really appreciate hearing about it! 

Thanks!

Chad

[chuggins143 · Accepted solution]

Ok, well I finally figured out what was going on... Apparently if you hook up single phase (either one leg and a neutral (120/277VAC) or two legs (208-240VAC) you must measure between a0 and a1 (differential measurement) and not from each leg to ground as is depicted here... http://zone.ni.com/devzone/cda/tut/p/id/8216  For whatever reason if you measure single phase 208-240VAC and try to measure from each leg to ground the numbers don't come out right. I'm now measuring across one channel and my numbers are dead on with my analyzer. 

As a side note, the powers that be might want to add some other information to this video series... http://sine.ni.com/nips/cds/view/p/lang/en/nid/208111  and comment that the power measurements for all single phase (120/277VAC and 208-240VAC) should be taken across a single channel on the 9225 module.  ...or include a wiring diagram specific for various applications.

A big Thank You to all that tried to help!  Hopefully this thread will save someone else some time and frustration.

THX

Chad