09-15-2011 02:48 PM
This must be very basic for most engineers except I'm not an engineer! .
I plan to buy Dac Card USB-6356 to read four analog inputs. I need to read those input in-phase.
So I need to get those four inputs read in-phase and do some simple calculation.
I have not purchased the card because I want to make sure I will be able to read accurate data.
Now we use North Atlantic Instruments Digital Analyzer Model 2251 to read voltage in-phase.
What VIs do I use to make sure what ever voltage in the range of 0.8 to 2.6 is read in-phase?
This is the formula I will perform after I get the in-phase voltage: V1 - V2 / V1 + V2
Solved! Go to Solution.
09-15-2011 02:57 PM
if by "in phase" you mean "simultaneous sampling", the USB-6356 should be able to do what you want.
09-16-2011 12:48 PM
This is Andrew Brown, an Applications Engineer from National Instruments. I agree that the USB-6356 simultaneous sampling module should be able to read the voltages in phase. The normal DAQmx Read function should work to take in those in-phase voltages, though the DAQ Assistant would also work if you are interested in simple set-up of your program. To help you get going, here is a good Getting Started with NI-DAQmx guide.
Please let me know if you have related questions.
09-21-2011 07:10 AM
I got a bit mor information and this is what it means to read in-phase voltage.
We have a primary Coil on the LVDT which is read for reference and a secondary 1 and secondary 2.
When we read the secondary we must not read RMS voltage we must read it in-phase with the Primary signal.
Please see image attached.
Here is the equipment we use not but it only reads one of the secondary at a time. We must be able to read four inputs since this LVDT has two channels. and also read the Primary for reference.
In the manual it explains in-phase as follows:
IN PHASE MODE: The in phase mode is selected by pressing the front panel FUND key. The in phase mode measures the rectangular vector voltage component which is inphase with the input to the reference channel A. A negative indication on the display indicates the in-phase vector component is 180 degrees out of phase with the reference. Since the OFFSET function rotates the rectangular vector coordinate system, it will affect the values displayed in the in-phase mode. A reference input of at least 0.2 millivolts is required to provide a phase reference and to synchronize the in-phase-locked loop.
We only read one secondary at a time with the model number 2251 but we want to read four sec 1 and sec 2 for channel A and channel B.
Anyone worked with and LVDT that was read IN-PHASE USING NATIONAL INSTRUMENTS DAQ CARDS AND LABVIEW?
09-22-2011 12:54 PM
I was able to locate several excellent examples about reading LVDT measurements using LabVIEW. The first of these is LVDT/RVDT/Resolver Measurements, which provides background about your LVDT measurement and numerous related links. The second, more specific link is Measuring Position and Displacement with LVDTs, specifically the section on SCXI for LVDT Measurements. It provides information about how you would wire up your LVDT and recommendations of what modules to use. In brief, the recommended set up from the page is:
PCI-6052E DAQ card
SCXI-1349 cable assembly
SCXI-1540 LVDT module
SCXI-1315 terminal block
This should absolutely match up with your in-phase application and meet your requirements. Please let me know if you have related questions.
08-17-2012 11:51 AM
I figure I post this solution to my problem since I t may help someone else.
In order to read the in-phase RMS voltage of two signals (A reference and the actual output signal) one must get the Phase Angle, convert to radians and then use the cosine function. This results must tehn be multiplied by the RMS value to get the actual in phase voltage.
example: Phase angle = 8.67 cosine of that is : 0.98857 X RMS voltage in this case 0.8852 equals final RMS in-phase voltage of : 0.8751
If anyone needs more detail infor please let me know.