What amplitude on power spectrum if analog input is 7.3V,sine,80hz?

I have an analog input of 7.3V, sine wave at 80 Hz feeding thru PXI-4475 (I have a PXI-1042 Chasis and PXI-8176 Controller and I am programming my application in Lab Windows-CVI). I see a sine wave with an amplitude of 7.3V in the time domain but I see an amplitude of 13.3V at 80Hz in the power spectrum. Should I see 7.3V in power spectrum display? My HP FFT Analyzer showed 7.3V at 80 Hz in power spectrum display. Please help. My email: [email protected] or my phone: 215-897-8766/7370. Thanks in advance.

There would appear to be a mathematical relationship between the 7.3 V sine wave and the 13.3 V amplitude as follows:
a) rms value of a sine wave at 7.3 V = 5.1619 V
b) square that result = 26.645
c) half the result = 13.32
The power spectrum should be expressed in terms of voltage squared. The power spectrum should produce a result that is a second order function of the initial amplitude. Are you sure the settings on the HP were for "power" when you read the output of 7.3V? The 13.3 V number appears to be the better of the two.

Similar Messages

What is the power spectrum unit for Unevenly Sampled Signal Spectrum.vi if the input signal unit is Volts?

The Unevenly Sampled Signal Spectrum.vi has two outputs, Power Spectrum FFT(X) and Power Spectrum FFT(X) Frequency. Can anyone tell me what's the unit for Power Spectrum FFT(X) if the input signal unit is volts. Also, is this VI equivalent to producing a PSD output?

Hi,
The power spectrum will be in units of Vrms^2 which are power units. There is a very usefull VI that you can use to easily transform the units of your spectrum; the VI is called Spectrum Unit Conversion.vi. You select the type of spectrum that you have and the units that you want it to be converted to.
Here is a good document on spectral measurements in genereal:
frequency spectrum
I hope this helps.
Regards,
Juan Carlos
N.I.

Analog input to modulate triggered sine wave analog output

I'm new to Labview and having trouble getting my app to program correctly.
I would like to use an analog input (AI) to modulate the amplitude of a
100 kHz sine wave and output the results to an AO. This is a real
time application: the AI will change every few 10's of ms so during one
"cycle" the amplitude will be modulated many times. Plus, the entire AO
will be triggered on and off with a digital input TTL trigger. The
waveform "cycle" will run continuously and so will the AI.
I've used an example included with Labview to read
the AI and a separate one to generate the sine wave and trigger it on
and off, but cannot combine the two together. I assume what I need to
do is implement a loop properly but when I try I can only trigger the
AO on and off and the AI does nothing or is static. I assume that the
vi just takes one point from the AI and uses that to determine the
amplitude of the sine wave, but doesn't "redraw" the sine fast enough
to respond to the AI changes.
Thanks,
Ethan

Hal,
I do not think I have Labview Realtime (unless it comes standard with the full version of Labview ). Do I need to have that? I have a 6251 DAQ board.
I've enclosed my program- it has the name of the original included program in its file name so you can see that I didn't do much to change it. I made some changes today (to make it non regeneration) but now can't get the AI to read at all. And I have no idea how to modulate the sine amplitude using the AI.
The sine wave works fine and triggers as needed. The one problem is that the sine wave doesn't end at the same point (phase) each trigger period so during the times between triggers the DC level on the AO is variable (which I do not want). Is there a way to end the sine wave at the same phase (at the zero crossing) while still triggering it with a digital input.
Thanks,
Ethan
Attachments:
ERB6-Cont Gen Voltage Wfm-Int Clk-Non Regeneration.vi ‏157 KB

Compact daq multiple power supplies into analog input

I'm trying to read several values from different sensors into a 9205 voltage input module using a compact DAQ. My sensors use different power supplies, they all output voltage between 0-10Vdc. I can read the value off of any one sensor fine, but once I hook up another both values start to shift and osscillate, however either one by themselves gives me a steady DC value. I am taking differential measurements from the sensor's outputs... I'm not sure if it would be ok to tie the grounds of the two power supplies together and feed them to my ground reference input of the module, if I take a voltage measurement between the two power supply grounds I see about 1Volt difference.
Any ides/suggestions would be appreciated.
Thanks,
M.

Hi,
I have been looking at the sensors you are using and the pins seem to be correct so I just want to make sure that we are on the same page with the connections you are making. This is assuming you have a spring terminal on your daq card rather than a DSUB.
Humidity Sensor - Pin 3 or 4 (CHn+) to AI0 (Pin 1) and Pin 6 (SGND) to AI8 (19)
CO2 Sensor - V to AI1 (pin 2) and 0 to AI9 (Pin 20).
In your software you should then be taking a differential voltage reading on AI0 and AI1.
Assuming that is all correct then this is very strange. The wiring diagrams suggest that the signals are ground referenced so this should be sufficient however the 1V difference in the ground lines is perculiar if they are plugged into the similar place. although the differential reading will eliminate error due to this one consideration is that if they are floating you may need to add bias resistors. You can find out more about this here. As I said it doesn't appear that this should be required but is worth a go if you have the kit to try it.
Otherwise it might be useful if you can send me some screenshots of the behavior on the graphs and perhaps your code and we can see if that helps. Also if you are able to verify the functioning of your sensors some other way would also be useful i.e. with a multimeter.
Regards,
James Mc
========
CLA and cRIO Fanatic
wiresmithtech.com/blog

What is the difference between power spectrum and PSD?

Hi all,
I input a time domain signal to the FFT power spectrum VI and FFT PSD VI seperately, and got two outputs in frequency domain with similar shapes but different magnitudes.
I refer to some signal and system textbook, and find PSD(w)=1/pi*Power Specrum or equivalently PSD(f)=2* Power Specrum.But as I observed from the LabVIEW outputs, this relation is not correct. I input a 1KHz sin wave with amplitude=1, Fs=512KHz, #s=2048 , the PS peak is 0.5 and the PSD peak is around 0.013.
So I wondered what's the real formula LabVIEW is using to calculate PSD?
Sunny

PSD is related to spectrum resolution, thus related to sample rate.
df= Sample rate/ #samples
I think they follow this relationship:
Amplitude FFT power spectrum = Amplitude PSD * df * 1.5

What is the equation for a Low-Sidelobe Window Function (in Power Spectrum VI)?

I am trying to find out what is the equation for the Low Sidelobe Window which is mentioned in the Power Spectrum VI. Hanning second sidelobe is around -32dB of the first. What is that for Low Sidelobe?

The CWT is not equivalent to the discrete dyadic wavelet transform. In theory, the CWT can compute the wavelet coefficient at any positive real scale and any real shift, while the discrete dyadic wavelet transform only includes the dyadic scales (2,4,8,16...). So the formula used to describe the CWT can be referred to the equation in pp.80 in S. Mallat's book.
In SPT's implementation, the time interval controls the shift in number of samples. The scales indicate the wavelet coefficients at integer scales 1,2,3,...,"scales" are contained in the output scalogram.
NISH DSP
Medical ultrasound and signal processing

What is the Fieldpoint analog input interchannel skew time?

I need to know what the interchannel skew is on Fieldpoint analog input modules because I need to aquire samples fairly close in time to one another simily to the typical MIO PC-based card. Also, I am wondering if the aquisitions can be externally triggered.

The FieldPoint IO modules are designed to continually sample all (4/8/16) channels and write the data to shared memory. FieldPoint controllers then read the shared memory and make the data available to the user (serial/ethernet) or controlling program (RT). There are no provisions for external triggering of ADC conversions. Nor are there provisions to prevent the user from oversampling or undersampling the shared memory (e.g. the controller reads the shared memory 5 times in-between the ADC updating a channel). The interchannel skew can be determined by taking the IO Module All Channel Update Rate (e.g. 1.08 seconds for the FP-RTD-122)and dividing it by the total number of channels (e.g. 8 for the FP-RTD-122). Thus, the delay in between any two adjacent channels
is 135 ms for the FP-RTD-122.
Ultimately, FieldPoint was designed for single point measurements and not for waveform or simultaneous measurements. The capability for triggered, simultaneous or deterministically sampled readings is not currently available in the FieldPoint system.
Regards,
Aaron

What are the 4 analog inputs of my umi-7764 (on the analog input terminal block)

I would like to known what are and how connect the 4 analog inputs of the anolog input terminal block of my umi-7764. I am french, so if you want to answer in french, it will be easier for me .

Sébastien,
Selon la carte de contrôle d'axe que vous utilisez (7344, 7334 ou autre), vous pouvez disposer d'entrées analogique.
Si votre carte possède des lignes analogiques (voir la documentation de celle ci), cela signifie que vous pouvez les utiliser pour 2 choses:
1. Utiliser ces lignes analogiques pour le feedback (retour en position) de vos servo moteurs. Cela veut que vous travaillez avec un servo, et que vous êtes en boucle fermé. (Pour informations, un servomoteur peut aussi asservi avec un retour en position).
2. Si vous ne faites pas d'asservissement en tension ou que vous controliez un moteur pas à pas, alors ces lignes d'entrée analogique, peuvent être utilisées comme des lignes classiques. Pour les utilisez dans ce cas, vous devez cabler
votre signal sur l'UMI (qui n'est qu'une interface entre vos signaux et la carte) de la manière suivante:
- Le point chaud du signal sur "Analog Input X"
- Le point froid du signal sur "Analog Inout Ground"
De plus si votre carte de contrôle d'axe intègre des entrées analogiques, vous pouvez configurer leur gamme dans MAX (Measurement & Automation Explorer) le range de ces voies (+/-10, +/-5, 0-5 et 0-10 V).
(Comme l'UMI est un bloc générique, assurez vous bien que votre carte possède des entrées analogiques)
Finalement, pour lire le niveau de tension sur ces entrées, il existe dans le driver NI-MOTION, la fonction "Read ADC".
sur http://www.ni.com/manuals
vous trouverez la documentation de votre matériel.
A l'adresse ci dessous, vous trouverez de l'aide concernant la configuration de votre system motion dans max:
http://zone.ni.com/devzone/conceptd.nsf/webmain/081957EE013C7A4586256B92007818E0?opendocument
Raphael TILLET
Ingénieu
r Application
NI FRANCE
Cordialement,
Raphael T

When using the analog inputs and analog outputs of the PCI-7344, what is the conversion between the voltage entering the card to counts? Similarly, what is the conversion between counts to voltage at the output of the card?

I am using the PCI-7344 to control my system. The analog inputs are connected to the output of my system while the analog outputs serve as feedback to the system. The system is a servo. I want to know what is the conversion between the voltage read at the input, to card counts, and finally to the voltage output to the system.

Carole,
If you are trying to do analog feedback with a servo motor, Chapter 14 of the manual talks about how to set up the torque feedback. Also linked below is a LabVIEW example of analog feedback.
Chapter 14
NI-Motion User Manual
Automatic Analog Feedback with FlexMotion example
A. Talley
National Instruments

What is the needed analog inputs to UMI 7764

Do these signals need to be 0-10 V? +/- 10 V or what?

National Instruments motion controllers (and therefore the UMI), accept analog inputs in the -10 Volt to +10 Volt range. This means that your analog signal cannot exceed these voltage levels, but it can be anywhere within this range. You then specify the input voltage range over which the analog to digital converters (ADCs) will convert the input voltages to digital values, according to the voltage range returned by your analog signal. You can choose from any of the following ranges:
0 to 5 V
-5 to +5 V
0 to 10 V
-10 to 10 V (default)
Voltages outside of the range will clamp at the extreme values.
For more information on setting the range of your ADC channels in Measurement & Automation Explorer (MAX), please refer to the following tutorial:
Developer Zone Tutorial: ADC Settings for Motion Controllers
Hope this helps!
Best regards,
Dawna P.
Applications Engineer
National Instruments

What are the units for the power spectrum output? (units in)^2/Hz?

I can't seem to find the answer in the manual that came with the software or anywhere online. Maybe I am just looking in the wrong places.
Thanks
David

Hi David,
I assume you are referring to the step, "Power Spectrum", in Analysis»Frequency Domain Measurements
Per the help that I see, "This step can return the spectra in root-mean-square, peak, and peak-to-peak
units."
Also, in the configuration tab of the step, for magnitude you can select either dB or linear.
Hope that helps!
-Sam F, DAQ Marketing Manager
Learn about measuring temperature
Learn how to take voltage measurements
Learn how to measure current

Use analog input as sample clock

Hi,
I have a PCI 6115 DAQ card. I currently perform an
analog acquisition on ai0, with an external clock on PFI7. But
sometimes, my clock signal is not high enough and the acquisition does
not occur. At some NI show, I heard a trick to solve this problem :
plug the clock on analog input (say ai1), the clock signal gets
amplified by the card internal amplifiers, and then route this
amplified signal to the sampling clock. This seems to be a wonderfull
solution, but I cannot find out to actually redirect the amplified ao1
to the sampling clock. Does someone know how to do it ?
Thanks a lot,
Jérôme Lodewyck

I tested the attached example on a simulated device so hopefully it will work on a real one without any kinks. You didn't specify your programming environment, so I'm assuming you're using LabVIEW. If not, hopefully you can translate to the appropriate ADE based on the picture of the block diagram.
In the example, I'm using an AO task to program the analog trigger as specified. This has two consequences. First, you won't be able to perform hardware timed AO while the AI acquisition is running. If this isn't acceptable, you'll need to try the second approach described in the next paragraph. Second, you'll have to wire the signal to PFI0 instead of an AI channel. With this configuration, the signal will be seen with a +/- 10V range and referenced to AI Gnd. Since the trigger DAC is an 8 bit comparator circuit for this board, you'll have ~80 mV of resolution. You didn't mention what the amplitude or DC offset (if any) of your signal is, but hopefully this resolution will suffice. You can use the level and hysteresis properties for the analog trigger to filter out noise in the analog signal or account for DC offset.
If the constraints listed above aren't to your liking, you can try to use a second AI channel as a trigger channel. This has some advantages and disadvantages. The disadvantages are that this requires you to use a trigger with your AI task and it also requires you to acquire another channel of data. You mentioned the trigger wasn't a problem so this can probably be taken care of with simple analog start trigger. The data can easily be thrown away, but depending on your sampling rates, it might require a lot of extra bus bandwidth or processing power when scaling the data. On the positive side, it doesn't require you to use up your AO channels needlessly and you can apply gain to the input signal in order to effectively increase the resolution of the trigger circuit. You can also apply a low pass filter and different terminal configuration if desired. The gain, coupling, terminal configuration, filtering, and coupling applied to the signal is controlled by the values used in the Create Channel VI and the Channel Property node. To create an example that does this, simply start with one of the shipping examples for an Analog Start trigger, change the trigger source to one of the AI channels instead of a PFI or APFI pin, and change the clock source to the AnalogComparisonEvent as shown in the attached example.
That should do it. Good luck with your application and post back if you have additional troubles.
Attachments:
AI - External Clock Using Analog Trigger Circuit.vi ‏81 KB
AI - External Clock Using Analog Trigger Circuit.JPG ‏60 KB

Windowing and Power Spectrum

Hi,
I have a simple .vi that is attempting to calculate the total PSD over a 500Hz bandwidth. My question pertains to the Windowing function and
what affect it has on the power calculation. I have much on windowing etc. in the NI's help but cannot seem to arrive at the value I am simulating to. I have including my .VI and the associated input file. (this file represents Pulse Densisty Modulated data output from an ADC)
thanks for any help
Attachments:
PSD of PDM.zip ‏127 KB

You may want to try "FFT Power Spectrum and PSD.vi". it takes care of the compensation for the window effect automatically.
Be careful that "Amplitude" compensation is used for Power Spectrum, and "Energy" compensation for PSD. The difference is a scaling factor of 1.5 for Hanning window.
Attachments:
psd.vi ‏20 KB

Signal-to-Noise ratio from Power Spectrum?

Hi,
I have a feeling this is a basic issue but for some reason I'm not getting it. I hope this forum can help.
I have a Power Spectrum (freq on the x-axis and power on the y-axis) and I am trying to determine the signal to noist ratio of the rf signal live.
I am using LV 8.5 and have the spectrum toolkit and am using an RFSA in a PXI chassis.
Any suggestions?
Thanks
- rf curious

Hi Rf Curious,
This questions does not have a simple
answer but let me share my thoughts and you can decide what it makes
most sense for your application. For signal to noise ratio (SNR) you
should have ideally the power of the signal and divide it by the power
of the noise. The problem here is that you are looking at both at the
same time (rf live signal). Depending of what type of signal is it, you
can recreate it and substract it from the spectrum (you will need to
recreate the phase and magnitude and delete it from the phase and
magnitude of the spectrum). This is normally done with simple signals
such as a tone.
If you don't have access to the magnitude and
phase of the data, and you only see the spectrum, then you will have to
do things different. You can probably measure the power of the signal
by measuring the power of the band where the signal is located. Then,
you can terminate your input and measure the power of the noise of the
instrument (with same attenuation and RBW settings) and have a rough
estimate. This method should have better results when S >> N. You
can also take the adjacent channel (or further) noise reference.
Finally,
if your signal has a pretty flat spectrum, then you can only take the
difference between the noise and the signal since they both have the
same RBW.
If by now, you have found other methods, feel free to post your ideas here for any other person that come across this problem.
Regards,
Gerardo O.
RF Systems Engineering
National Instruments

Basic accelerometer-power spectrum readings

Hi all,
I'm new to Labview and am trying to create a simple power spectrum logger. I've had a look at multiple tutorials but am stuck getting to places (most of the tutorials require sound and vibration toolkit, are really old and incompatible with Labview 2011 etc). The program I'm trying to do is:
1) Collect signals from accelerometer (4kS/s)
2) Generate power spectrum
3) Save to disk (on board the cRIO)
My setup is:
- cRIO 9014
- NI 9234
- Labview 2011
So far, I've managed to get the signal readings (XYZ axis) and merge them, put them into a 'Collector' block and then output them to the power spectrum block. I've very crudely used a 'Time Delay' block to set the sample rate (which I know is probably not accurate, but I cannot figure out how else to do it). I'm having a problem figuring out how to input the sample rate into the collector, which is why my power spectrum is giving me 0 to 0.5Hz (it's likely assuming the sample rate is 1Hz). I've attached my .vi.
Would someone be able to point me to a tutorial/example/alternative solution? Thank you very much in advance.
Attachments:
accelero.vi ‏93 KB

I think what you want is the CompactRIO vibration data logger. It does not require the S&V measurement suite, though you will find it very useful.
Check this out!
http://zone.ni.com/devzone/cda/epd/p/id/6388
It has a waveform acquisition template for the FPGA. It has a data logging state design.
You can see a Video of it working here
http://www.ni.com/mcm/wind/
Let us know if this helps.
Preston Johnson
Principal Sales Engineer
Condition Monitoring Systems
Vibration Analyst III - www.vibinst.org, www.mobiusinstitute.com
National Instruments
[email protected]
www.ni.com/mcm
www.ni.com/soundandvibration
www.ni.com/biganalogdata
512-683-5444

What amplitude on power spectrum if analog input is 7.3V,sine,80hz?

Similar Messages

Maybe you are looking for