Phase measurement

Hello,
I would like to know if anyone has got a sample code to showcase phase modulation in LabVIEW. I have installed modulation toolkit but that has examples only for demodulation. If you have an example VI of phase modulation with simulated signal, I kindly request you to share the same.
Thank you.
Herok

Hi Herok,
Below is a sample VI to generate a phase-modulated signal using a NI-FGEN waveform generator. This program is a shipping example VI included with the Modulation Toolkit-
http://zone.ni.com/devzone/cda/epd/p/id/5601
The example about will need to be modified for simulating the device. The NI-FGEN driver allows you to simulate a device so that you can run your application without the hardware present. Details of how to simulate this are available on -
http://digital.ni.com/public.nsf/allkb/07A1DC2A64B4F0A38625729A00065771
To demodulate PM with simulated data , you can use the following example VI and build upon it for your application.
http://zone.ni.com/devzone/cda/epd/p/id/5648
As you said that you do not have hardware, you cab simulate the device using the NI FGEN Driver. The steps for this are given on the second link.
Please revert for further clarifications.
Regards,
Kanchan Bhakoo
Applications Engineer | National Instruments

Similar Messages

How to do carrier phase measurement of any RF signal and Phase Noise measurement of any RF signal?

Hello,
Can any one give some idea to do carrier phase measurement and Phase Noise measurement of any RF signal?
Regards,
Vijay

Vijay,
A great example for measuring RF phase noise can be found in the LabVIEW Example Finder. The name of the VI is "MT RFSA Phase Noise.vi" This example performs phase noise density measurements on I-Q data acquired using RFSA. You may also want to take a look at Performing Modulation Measurements on Real-World IQ Data With Carrier Frequency Drift to see if phase measurement could be implemented: http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=EEAFD63A09CD3B79E0340003BA7CCD71&p_node=200054&p_source=External
What type of RF signal would you be analyzing? Are you trying to measure phase shift of a carrier frequency that is varying with time?
Shea C
Applications
NI

Phase measurement RFSG RFSA

Hello,
Currently, I work with RFSA and RFSG to analyse signal wich is generated by the RFSG. I would like to measure phase in my RFSG module to do the AM/PM characteristics. For now, i didn't find any functions to measure this phase. Moreover, i found a function for phase measurement for RFSA but it did not work. This function is Get Frequency where we can have phase too.
So i would like help to measure phase in RFSG and RFSA .
Thanks for your help

You should be able to measure phase directly from the IQ samples returned fro the RFSG ( arctan(Q/I) ). However, there is a simple polymorphic VI that you feed in IQ samples....and out comes magnitude or phase. I can't remember the exact name of the VI, but it's easy to find.
Note...if you don't lock the RFSG and RFSA together via the 10MHz reference....the phase you measure may be corrupted due to clock drift. Locking the two via the 10MHz reference will eliminate the frequency drift between the clocks....though you may end up with some constant phase offset that you could then subtract off. However...this constant offset would likely be different every time you turned the devices on and off.
Brandon

Phase measured by two tone measurement have different dt

Dear all;
I write a labview program for isolated a signal from the mixture of two signals by using a reference input. I choose to use butterworth filter and apply it in bandpass mode. To determine the band width of the filter, I also use two tone measurement vi to detect the phase of the reference signal and the signal I want to outcome. Unfortunately, when I run my program, warming with message "waveforms have different dt value" is always show. How can I fix this problem?
Regards
Attachments:
lock-in test.vi ‏88 KB

Well you got a bad case of the DDT's and dt's
If you get rid of those express vis and use a vi from the waveform measurments pallette you won't get fooled by that dt that does not exist coming out of your filter
Of course you COULD use the Digital IIR Filter vi off the Waveform conditioning palatte and keep your dt info but that doesnt get rid of your DDT's
Here is one quick mod
Jeff
Attachments:
lock-in testmod.vi ‏36 KB

Phase-measurement, PXI-4461

Hi
I would like to do a hydroacoustic measurement with a common signalsource and two hydrophones. The hydrophones are mounted in parallell (same direction) at a fixed distance, - and is directed towards the signalsource with a given angle. This means that if I give an impulse from the signal source, the soundwave will reach the two hydrophones in the same moment IF the angle is zero. If the angle is larger than zero, the soundwave will reach the nearest hydrophone first. I would then like to find the delay between "signal-aproach" on the two hydrophones, because this will give me the actual angel to the signalsource in the actual plane. Frequency is 20-100kHz, ane I need a lot of "dynamic space". Is 4461 the right alternative, and how acurate can I do this angle-measurement ? Can I do it this way at all ??
Svein Erik

Hi Svein,
Since you are wanting to find out time delay between two signals you will definitely want synchronization. So any of the DSA devices should work well for that since they use one ADC per channel and all the channels are synchronized. Additionally there are some S-series boards which can sample a little faster up into the MHz range. These S-series boards are lower resolution: 14-18 bits instead of 24 bits, however they are simultaneously sampled so you can maintain tight synchronization between channels. http://sine.ni.com/nips/cds/view/p/lang/en/nid/10955
I'm not sure how to quantify "a lot of dynamic space," but I will say that a 446x family is going to be one of the best options when it comes to dynamic range both because it has a high dynamic range and it has many input ranges. I don't know how much you really need however, so that's difficult to say. There are other higher channel count offerings in the DSA family that may have the functionality you want. http://sine.ni.com/nips/cds/view/p/lang/en/nid/12051
If you are considering eventually doing three-dimensional algorithms, then I suppose you will need more than two input channels. The 4462 shares the same architecture as a 4461 but has four input channels instead of two inputs and two outputs.
How accurately can you make the measurement? The DSA family generally publishes an "AI Interchannel Phase Mismatch" spec. It is on page 10 of the 446x specifications http://www.ni.com/pdf/manuals/373770j.pdf . So depending on which input range you want to use, you could have as good 0.08degrees or better. But it would depend on your application.
Hope that helps.
Daniel
Conditioned Measurements Hardware

Interchannel delay and phase measurement

Hi all,
Below is my latest vi, which I am using to measure the phase shift across the RC circuit. The values I am getting each time I run the program have an error of 0-0.3 radians. When testing for interchannel delay (i.e I put the two analog inputs at the same point on the RC circuit expecting the same readings). However the delay (measured also in radians of phase shift) varies 0-0.3.
It appears that error is related to the interchannel delay but they are not constant (each run the error is different). Can anyone provide me with insight on how to correct this?
If someone could also check the program to see if anything is amiss there.
Sorry the explanation is poor I am having trouble wording the problem. Please ask for any more details. Feedback/advice as always would be hugely appreciated.
Attachments:
RC Circuit Test Multiple AI.vi ‏265 KB

You can account for interchannel delay using the "AI Convert Rate" property available in DAQmx. Invert it (to get how long the interchannel delay is) and multiply it by the current frequency (in radians per sec) and subtract that from your phase calculation.
Attachments:
interchannel delay.JPG ‏10 KB

Chrominance Phase Measurement

Measure the chrominance phase of RGB color. Now I using Video analyzer to measure and would like to replace using NI.

Dr Spock 已寫:
RGB colour strictly speaking does not have chrominance, therefore you cannot measure RGB chrominance phase. Only PAL and NTSC Composite (CVBS and S-Video formats) video has chrominance.
To make this and many other detailed analogue video measurements you should consider VideoMASTER from microLEX Systems in Denmark - a National Instruments Alliance member. Their VideoMASTER product uses the NI 5122 digitiser card to acquire video signals and analyse them with their own special software.
I've seen the VideoMASTER of mocroLEX. It's really a successful solution of video analyzer. But I do not need all functions provided in mocroLEX's software package. The only one question to me now is to figure out how to measure the chroma phase by NI 5122. Does anyont know how to calculate it from a video line waveform (any mathematic equation) of a function to do it ?

Three phase Measurament

Hi everyone,
I'm trying to measure the phase and the power factor for a three-phase motor. The problemn is that the motor is running with 480V and the SCXI module that I have can only handles until 300Vrms. I'm thinking about using some voltage transformers to step down the voltage and then connect it to the SCXI module. If I do that, will it affect my phase angle and power factor?
Assuming that this configuration works, how can I find the phase in each wire? Is it possible to run all samples at the same time and then make some comparisson between their plots to measure that?
Thank you!
Kenny Caldas
Solved!
Go to Solution.

Just want to emphasise Lynn's point about 480 nominal volts and what you might actually have.
Get your design and wiring checked by someone certified to do so before connecting.
Some further points:
How is the motor being fed?
a. If fed by a Direct On-Line starter or a Star-Delta starter, there will be a big spike when the contacts open to turn the motor off, or during the star-delta transition.
b. If fed by a PWM inverter, then the inverter synthesises the AC 50 or 60 Hz wave form by chopping DC very fast, and relying on the motor windings to act as the low pass filter. Good luck trying to instrument that.
Fault Level: You must have fuses as close to the instrumentation pick-off point as possible. That way, if there is a fault in your wiring the instrumentation fuse pops, and you do not have the full fault current flowing through your instrumentation wiring. Fault current will probably be about 4 times motor start current if the motor is fused correctly, and if it is an induction motor.
I would use isolation amplifiers on the voltage inputs. That way you can use a simple potential divider on the input to scale to the voltage you want, but make sure that the isolation amplifier has a suitable frequency range.
So it would go something like:
Line voltage->Fuse(or other protection device)->Potential divider->Isolation Amplifier->SCXI module.
IF you sample each channel fast, e.g. 10,000 samples per sec., then the time difference between samples and hence sampling induced phase error will be small.
Also look at the safety issues with Current Transformers here:
http://en.wikipedia.org/wiki/Current_transformer

AM demodulation and carrier phase measurement of multiple signals simultaneously

Hello All,
I need to extract and compare the carrier phases from a number of
medium wave AM signals using a 5600 downconverter and a 5122e
digitizer. The signals are all real off air broadcasts, and so are in
the band 500kHz to 1500kHz. Since the transmitter frequency references
may all drift I guess the most sensible way to do this is to filter and
mix each signal down to the same IF and track their relative phases.
However I'm not sure what clever tricks can be done with current
Labview vis. I've had a dig through what I have (I have the modulation
toolkit amongst others) but can't use the features based around the
5660 due to my hardware. I can see the signals where they should be on
a spectral plot, but have not had much luck getting sensible looking
results using mt_niscope_demodulate_am.vi. I am currently tuning the
5600 to 15MHz rather than attempting to tune it to central frequencies
around 1MHz, I presmue this is the right thing to do? Could someone
point me in the direction of some good starting point? Any suggestions
welcome
Thanks
Ramsey

Hello Ramsey,
I assume you are trying to capture these AM signals and compare their relative phases all against each other. Sort of like saying the AM 1300 carrier is X degress in phase different from the AM 1530 carrier.
This is what I would do. I would use the full PXI-5661 RF analyzer and capture the entire AM band in the acquisition. This is roughly a 1 MHz bandwidth. At this low bandwidth, a low IQ sample rate can be used with the PXI-5661 (1.25 MSamples/sec gives the PXI-5661 a 1 MHz IQ data BW). With this low IQ rate, you could actually stream the entire AM band to hard drive for some time.
Since you have recorded the AM band to disk for a period of time, you can extract all the relative phase information you want. And the receiver reference is the same for all acquired data so the only variation will be due to the Tx side.
Look at this example:
RFSA Acquire Continuous IQ.vi
located at:
C:\...\<LabVIEW>\examples\instr\niRFSA
Regards,
Andy Hinde
National Instruments

How to measure the phase of a sinusoidal signal?

I need to measure the frequency and the phase of a sinusoidal signal. I tried to use the Advanced Single Tone Measurements.vi but the phase measured in each iteration (each second) keeps changing (the measured frequency is not in integral Hz, so the first point of the next iteration is at a location different from the location of the first point of the current iteration...I guess this is the reason). How can really measure the phase of a signal (not always changing with time)? When I change the phase of the input sinusoidal signal, the measured phase should be changed though.
I'm using LabVIEW 7.1 and PCI-6110.
Thank you very much!
Marlon

Marlon,
Without DAQ hardware I cannot run your VI. DAQmx is not supported on my platform (Mac OS X), so I cannot examine your VI in detail.
1. The AI VI will wait until it has the amount of data specified. So if you are collecting one second's worth of data at a time, it will wait one second before completing. The 50 ms Wait will run in parallel, so it has no effect on the timing in this case.
2. Continuous AO is possible, depending on the hardware you have. However, I have no experience with implementing it. Since your frequency is such that you do not end the AO data segment at the end of a signal cycle, you need to be careful to avoid discontinuities in the signal sent to the AO.
3. There is no data dependency between the AI and the AO. It is possible that the AO could run after the AI in any given iteration of the loop.
4. Your phase reference should be the excitation signal. The best method of evaluating the response of the beam would be to use two sensors, one at the shaker and one at the tip. Then measure the phase shift of the signal at the tip with respect to the shaker signal. If two sensors cannot be used, either measure the voltage sent to the shaker or use the simulated signal that you send to the AO as the reference. In either case you would need to compensate for the response of the shaker.
5. Consider the phase shift in the filter. The steady state phase shift is about 14 degrees. The initial transient lasts about 5 cycles of the input waveform.
6. Your simulation sampling rate is 1000 samples/second. While this satisfies the Nyquist criterion for a 379 Hz signal, it does not give you much data to work with for the phase information. If the hardware will handle it, I would go to 10000 samples/second.
Lynn

How can I measure the phase difference of two input signal?

Hello,
I'm trying to measure the phase difference of two input sine waves with the
same frequency.
Is there anybody how I can do this with labview?
Thanks,
Dae-han

This is my case! I have TDS3034 which can measure phase. However when I open Read Waveform Measurement vi that comes with tkds30xx.llb, I have a number of options under "measurement function" but not the phase measurement. May be I need another vi to do this?

How does Order Analysis measure phase lag, particularly super-sync amplitudes?

In recent testing of a high speed gear box, an 8X amplitude was observed (on the radial displacement probes) as the gear passed through a certain speed range. An NI4472 pci card and vi's written in 7 Express, w/ Order Analysis tool kit were configured with radial displacement probes and keyphasor as input signals. The behavior of the phase lag measurement is significant. If the phase lag of the 8X amplitude rolled as the gear passed through a particular speed range then this could suggest one particular problem, but if the phase lag remained constant then this could indicate a different problem. So, someone asked: How does the system measure phase lag of supersynchronous amplitudes?

See attached file for figure 1,2,3
The Phase measurement in the LabVIEW Order Analysis Toolkit uses the phase lag convention. Phase is defined as the angle difference measured from the peak of a vibration signal backward in time to the reference trigger point. This means the directions of numerically increasing angles are always set against the shaft rotation. The trigger point here is the tachometer pulses.
Figure 1 shows the relationship of the vibration signal and reference signal to zero degree phase. The shaft has a heavy spot and a keyway slot. When the keyway slot passes the tachometer, the tachometer detects a trigger pulse. The heavy spot causes the shaft to vibrate as the shaft rotates. When the heavy spot passes the proximity probe, the vibration reaches a peak. When the heavy spot passes the proximity probe and the keyway slot passes the tachometer simultaneously, the peak of the vibration does not lag or lead the reference trigger point. At this point the phase is zero degrees.
The other part of the convention dictates that 90 degrees means that the peak of vibration lags 90 degrees behind the trigger point. Figure 2 1illustrates the 90 degree phase. When the vibration signal reaches the peak, rotate the shaft backward (counter the rotation direction) until the keyway slot passes the tachometer. The number of degrees you rotate is the phase lag, or the phase value in machinery vibration measurement. Figure 2 shows the relationship of the vibration signal and reference signal to the 90 degrees phase convention.
For the 8x phase, the measurement is conducted in the similar way. The difference is that the 8x order component go 8 times faster than the trigger pulses. Figure 3 shows the 90 degree phases ( tacho pulse in rising edge) of the 8x order components. The phase measurement is still conducted through calculating the delay between the peak in the 8x vibration components and the trigger pulses and comparing the delay to one cycle of the 8x components. In figure 3, the signals between the two green grid lines are used to output one phase results.

Phase Locking the Up and Down Converter Modules

I am interested in phase locking the 5660 and 5670 modules, but from what I understand...this might not exactly be possible.
Using the 10MHz references...it seems that I can frequency lock the two together (i.e. - I can eliminate any phase error due to the two LO's drifting away from each other). However...am I correct in assuming that there is no way to actually access the individual oscillators such that I can remove the phase difference between them?
For example...if I want to measure the phase added by a DUT....I would have to measure the phase without the DUT...then meausre the phase with the DUT...then look at the relative difference in the two phase measurements (as calculated from the IQ samples). However, if I were to repeat this measurement by first measuring the phase without the DUT....then turn the generator off...then back on again....then measure the phase with the DUT...I'd expect to get a different answer, since by turning the device on and off, I have no idea or control over the phase relationship between the two devices.
Is this correct?
Finally...does simply connecting say, the 10MHz Out of the upconverter, to the Freq Ref IN of the downconverter automatically frequency lock the two together...or do I have to go into LabView and programatically tell the things which reference to use?
Thanks!
Brandon

Hi Brandon,
You are correct in what you are saying. The PXI-5600 and PXI-5610 Down/Upconverters each have their own synthesizers internally generating the LO signals for the mixers inside, and these LO signals cannot be exported from the modules. For these modules to be phase locked, they would need to share the same LO signals.
By sharing the 10 MHz reference you can achieve frequency lock where the phase difference between the two modules will stabilize, but the phase difference will not be zero - it will be some unpredictable phase offset which will not be increasing or decreasing (i.e. frequency lock). Whenever the 5600 or 5610 is retuned, the phase difference will also be different.
With regards to the 10 MHz signal, both use the same component for the reference so it doesn't matter which module you lock to the other as they are equivalent in quality. You do need to make a call in software to lock the destination module to the source module. If you are driving the PXI backplane with the source module, you'll also have to make a SW call to do this. This is very easy though, just look for VIs called Configure Reference Clock or something similar.
Regards,
Andy Hinde
National Instruments

Phase shift base signal

Hello,
I have two sinusoids which have a phase difference which varies slowly over time, the difference being indicative of position. To measure the phase difference, i have used a premade vi called "Graph and Calcuate Phase differece". I have also used an example online to somewhat sucessfully calculate the phase some of the time.  The example would be the code that was posted in this thread.
http://forums.ni.com/ni/board/message?board.id=170&message.id=6956&query.id=101197
These examples work great with theoritcal signals, but there is a problem (see figure below) I am having in practice.. Since the phase shift can occur in the range [-360,+360], i believe the index of the peaks are getting lost, causing it to pick up the next peak in the sequence, thus, causing a phase shift (see figure below, plot of phase shift) to be measured.  Another way of saying this is that after a small amount of phase shifting occurs, the lead peak begins to references the next peak in the comparison signal.
Im at loss on how to identify the peaks and track them so i can accurately measure phase shift. Any help is appreciated. Im sure this is soemthing that has been done before, esp since there is a vi just for measuring phase shift. I guess i just dont know the key words to find it...
Below is a screen shot showing the two signals. The bottom plot is showing there is a relative small shift in phase which periodically jumps.
many thanks
Jim from CT
Message Edited by JimmyinCT2 on 01-23-2008 07:17 PM

dahhh, okay, i think i finally figured out what is going on here, and i think im just being somewhat dumb or maybe just assuming to much.
Looking at matts example helped a lot as i see why.
with one of the old VIs for measuring phase shift, we were getting a phase shift range of [-360, 360] or more.    We were just assuming that was the range here with this new VI.
With the new dual channel measurement (or the example you posted), when phase is measured, there is an inflection point at some angle of phase difference.. The way your example works (and the express vi) is with an inflection at 180 degrees. So, lets imagine we have a measurement of phase shift that is 178 degrees, as this difference increases, the next is 179, and then 180.. Now as it continues to move, the next phase measurement will not bet 181 but instead -179.   As the signal continues to move in the same direction, its then 178, 177, 176.. So there is an inflection point at 180 degrees with two sinusoids, in simple terms, its because the phase difference of one sinusoid to the other has shifted and is now being measured in reference to the next peak in the series.
Its troubling for measurements are if you turn on a machine that is measuring phase, and it happens to be right near -/+180, it can cross that boundary often, creating substantial noise.   Also, that for certain types of peak detection, such as for motion, its desirable to have a larger range such as [-360,360] which should be theoretically possible (like the first vi we used) but i guess [-720, 720] could be done too assuming there is enough difference between the peaks. It would have been awesome to have a VI that measures peak movement outward to infinity.   We were originally using a VI that calculated out these larger differences, think it was doing the calcs in frequency domain (imaginary nums) rather then cross correlation like the example.
I think for now, we are going to have to work inside the range [-180,180] and initialize our hardware to 0 phase so we dont start near the inflection point and see if that works.
Message Edited by jimmyinCT on 01-26-2008 07:54 PM

What are the phase noise specifications for the 10 MHz internal reference in the PXI-5661?

Im looking for the phase noise specification on the 10 MHz internal reference for the PXI-5661.

Hello Bob,
As you may have noticed, and the likely reason for this post is that that spec is not readily available for the PXI-5600. You will however notice that the overall phase noise of the system is noted and my suspicion is that even though the 10Mhz reference helps improve the overall phase measurement, it won't necessarily dictate the measurement. I can ask R&D for this spec but they will likely inquire the need for this specification. Do you intend to use an external source instead of the built in reference?
Regards,
Glenn M
Application Engineer
Regards,
Glenn

Phase measurement

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