Aquisition of parts of large signals with ni scope

Hello
I am trying to aquire large data with ni scope.
The aquisition time is about 2 seconds with a sampling frequency of 50 MHz.
I figured out that this amount of data is too large. The NI USB 5133 does not have enough memory.
Actually I do only need some parts of this 2senconds signal thus it would be possible to aquire only some parts of the signal.
Moreover I need to average the signal to reduce the noise.
I am trying and trying but couldn't make it out so far.
Maybe you could help me with some ideas....
Thank you very much

This type of question would be more visible on the High Speed Digitizers Forum.
The USB-5132/5133 is a finite acquisition digitizer. The record size is limited by the total amount of memory on the digitzer. A 32MB/ch memory option for the USB-5132 and USB-5133 has just been released, which increases the maximum record length by a factor of 8 in comparison to the 4MB/ch option.
If you need to acquire more data, you must re-initiate the task to take a second record. There will be some "deadtime" where no samples are acquired during this initiate step. Some benchmarks have been provided to show what equivalent data rate can be achieved using this method. For continuous acquisition, consider a PCI, PXI or PXIe digitizer.
Jennifer O.

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Acquire Signal with NI-SCOPE 5102

Hello. i'm a beginner in LabView. I have to acquire signal from a NI-Scope 5102 and I have absolutely no idea how to do that in LabView, I instaled the drivers but in my computer I don't have the acquisition boards. I tried to see the examples and I can´t find nothing that can possibly help me. I need a step-by-step explanation of what to do.

FilipeV wrote:
All right I will tell you what I have to do. In college we built a printed circuit board that produces a triangular and square signal. In the second part of the work we have to build a virtual instrument capable of selecting only of both signal or both of them at the same time, display in a graph the selected signal and saving the values in a file. The signals generated in the circuit will be read with a NI-Scope 5102. If you wanted to do this what would you do?
I will see the examples and try to understand what I should do.
I only had one lesson of LabView and we didn't do anything like this. We only worked with some waves and learned to control the frequency and other parameters, and to view the waves on a graph. That's why I'm so confused with this.
I'd cheat. You haven't been properly trained with the tool.
Use Signal Express Set up measurement step and data logging. Configure the OI with a boxes for chanel selection. test it. Generate LabVIEW code
The context aware help you'll have in SE will probably teach you a bit about scopes too.
(I can't believe I just said that but if the profs won't teach the tools that only leaves bad practices to get'r'done) Don't think that your programming that way though
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Hello LabView Gurus,
Being a power engineer and having just a little knowledge of signal processing and labview, I have been pulling my hair out for the last couple of days to get a better estimation of phase difference between two signals.
We have two analog voltage signals; 1. sine wave (50Hz ± 1Hz) and 2. a square wave with exactly half of sine wave frequency at any time.
At the starting point of operation (and simulation/acquisition) both signals will have no phase difference. However, the square wave's frequency changes unpredictably for a just a few millisecond but then it gets synchronized with sine wave's frequency again. This means that the square wave will be phased out from its original position. The task of the labview is to find the phase difference between the two signals continuously.
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As this part is just a small block of a big project, I can only allow 5000Hz sampling rate each for both signals. I read 500 samples (which means I read data from 5 cycles of sine wave and 2.5 cycles of square wave).
Now the problem is, as long as the frequency of sine wave stays constant at exactly 50Hz, I get a good estimation of the phase difference but when the frequency changes even a little (and it will happen in the real scenario i.e 50Hz ± 1Hz and the square wave's frequency is dependent of sine wave's frequency), the estimation error increases.
I have attached my labview program. From front panel, you can set the phase of square wave (between -180 and 0) and you should see the labview's calculated phase in the indicator box named 'Phase'. Then you can press 'Real Frequency' switch that would cause the frequency to change like it would in real operation.
You can observe that the estimation error increases after you push the button.
All I need to do is to reduce this estimation error and make it as close to the actual phase difference as possible. Any help would be greatly appreciated.
I am using LabView 2009 for this task.
The application is for electric machines and the stability/performance of machines under different faults.
Thank you for reading this far!
Regards,
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Attachments:
v603.png ‏320 KB
v603.vi ‏186 KB

Jeff Bohrer wrote:
Basic math gives me a bit of pause on this approach. You are sampling at 50 times the frequency of interest so you get 50 samples per cycle. your phase resolution is 1/50th cycle or 7.2 degrees +/- noise. You will need to samlpe faster to reduce phase resolution or average multiple readings (at a time cost that is signifigant)
Jeff- (Hardly Working)
I am sampling at 100 times the sine wave's frequency and 200 times the square wave's frequency. Increasing the sampling rate completely solves my problem. But since I am acquiring several other inputs, I cannot afford a sampling rate higher than 5kHz.
F. Schubert wrote:
I'm not a signal processing expert, but here my basic understanding.
If you simulate sampling with 5kHz and a frequency of 50 Hz (and both are 'sync' by design), you always get an exact 5 periods. Any variation of your signals frequency gives you a propability to get 4 or 6 'trigger' events. That's an up or down of 20%!
The one measure to reduce such problems is using 'window functions'. They don't fit your current approach (counting instead of a DSP algorithm), so this needs to be reworked as well.
My approach would be to use the concept of a Locki-In amplifier. You need to phaseshift your ref-signal by 90°. Then multiply your measurement signal with the ref signal and the phase shifted ref signal. The obtained values for x/y coordinates of a complex number. Calculate the theta of the complex number (with the LV prim). Feed this in a low pass filter.
The trick on this is, that the square wave has harmonics in it, in this you are interested in the second harmonic which is the sine wave.
To get rid of the effect that the sync between sampling rate and ref signal frequency gives an error, you then can use the window I mentioned above (place it before the lock-in).
For a design that really plays well, use a producer-consumer design pattern to get the calculations done in parallel with the DAQ.
I suggest you to check on wikipedia for some of the keywords I mentioned. Go also for the external links which lead to great tutorials and AppNotes on the signal processing basics.
Sorry, it's not a simple solution I offer and we will have quite some conversation on this forum if you follow this path. Maybe someone else knows a simpler way.
Felix
www.aescusoft.de
My latest community nugget on producer/consumer design
My current blog: A journey through uml
An interesting view. the sine wave can indeed be looked as a second harmonic of the square wave. I will implement your idea and get back to you as soon as I get some results. But since I have very limited knowledge of signal processing, it might take me a while to get my hear around the solution you mentioned.

Large Network with mulitple buildings

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Note on Fixed LAN IP addresses:
When assigning fixed LAN IP addresses, remember that they must be outside the DHCP server range, and they cannot end in 0, 1, or 255. Since the DHCP server range is typically 192.168.1.100 thru 192.168.1.149 then your fixed LAN IP addresses would need to be in the range of:
192.168.1.2     thru 192.168.1.99    or
192.168.1.150 thru 192.168.1.254
Obviously, all your fixed LAN IP addresses must be different. And none of them should be in the DHCP server range. Fixed LAN IP addresses are always set in the device that is using that address, not in the router connected to your satellite modem.
Message Edited by toomanydonuts on 01-25-200703:37 PM
Message Edited by toomanydonuts on 01-25-200704:52 PM
Message Edited by toomanydonuts on 01-25-200704:54 PM

Large signal output capacitance measurements

Hello everyone,
I am working on a power amplifier and I want to measure output capacitance under large signal condition. I use nonlinear model of GaN power transistor.
Output power is around 36 dBm, f=8.2 GHz
I tried two methods:
1) I changed Vgs bias from -6V to 1V, Vds=28V. I use C_PRC solver under Linear Tab to find parallel capacitance at the output. I obtained a graph which changes 0.3pF to 0.5pF. In this simulation I dont use impedance tuner, just ports (50ohm) and biasing sources.
2) amplifier is biased at 28V and 125mA. Then I drive amplifier with from 20dBm to 30dBm input power. In this simulation I used HBTUNERs for maximum power output (25dBm input power) at the input and output. I can see there is a change for capacitance at the input vs changing input power. however at the output, output capacitance is constant and 0.52pF. I am measuring the capacitance from transistors drain, before tuner. I use large signal Y parameter measurement solver and calculate the capacitance.
The interesting thing, I can meause input capacitance change easly for large signal, but output capacitance is constant!
I have two questions:
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2) For large signal measurements, for example; 30dBm output means 30V peak to peak, 40dBm output means 50V peak to peak. So there is a big capacitance change during a period. When I measure the large signal solver, does solver use high peak values? if yes, can I change it to low peak value?
3) can we use gamma probes for large signals?
Thanks
Solved!
Go to Solution.
Attachments:
cout.jpg ‏80 KB

Thank you mohi_kh and ryanawr.
You are totally right and example is very good, but for these measurements can only be carried out from a PORT. I need the capacitance at the transistor output. There is a tuner between PORT and transistor. As you know if I dont use impedance matcher, gain and input impedance change...
When I remove the tuner and change PORT's impedance as same impedance seen from tuner to PORT, gain changed because of harmonics terminations.
I also tried YCOMP measurement at MainFrequency+0.001 (I selected transistor output pin for measurement) and convert it to capacicante by equations. As you see, graph is irregular around 24dBm input power. May it be correct?
I tried to measure S22 from output port as attached, and S22 is positive maybe I am doing something wrong, I am still working on it. anyway it isnt useful for me. I need the impedance at the transistor output.
Attachments:
circuit.jpg ‏133 KB
Ycomp and output cap.jpg ‏93 KB

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Sensor_Configuration_Test.vi ‏60 KB

Good afternoon MiamiVipul,
Thanks for contacting National Instruments with your issue, we'll try and get you up and running as quickly and efficiently as possible.
Look like you've got the right approach to your problem.
In order to integrate a property node into your code, you simply have to wire the task reference and error cluster in line with the rest of your code. I.e. after you create the task, you will have the purple task reference out as well as the pink error cluster out, wire those to the corresponding intputs on the property channel node and then wire the task and error out of the property node into the DAQmx Create Channel vi.
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Mixed signal with same index :p

Hi
I try to draw multiple signals with same index x
I built it but it can not draw
what part that is missed from this vi
best regards
m.s
hi ?Q>
Solved!
Go to Solution.
Attachments:
mixed signal.vi ‏94 KB

Hi,
I have no mathscript licence, but I think this should work :
let me know...
Best Regards,
V-F

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Nice, can you point me to the solution please ?
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Details please
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i tried to rebuild my files from folders that had the pics in them.
Exactly what did you do and how did you do it? this ay be the cause of your issue but without details we can n=ony guess
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originally all the photos had a large delta with a question mark.
Ok - this usually has a simple solution - do you still have a copy of the library that has this problem?
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How to add the Note board web part to a page with powershell

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I've been looking around everywhere but haven't seen it explicitly mentioned.
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Linda Li
Linda Li
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http://www.mdelectronic.fr
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Aquisition of parts of large signals with ni scope

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