PtByPt derivative of an analog signal

Hello,
I'm using crio and NI 9215 to collect analog data. How should I use the Derivative x(t) PtByP.vi to calculate the derivative of the acquired signal in a loop that reads the samples?
Solved!
Go to Solution.

You could manually compute the derivative using a few primatives.
Esentially, all a derivative is composed of is delta-y divided by delta-x.
So you could just do something like this:
Assuming you have a 2D array of data, with the first column as X values, and second column as Y values.
You can find the instantaneous derivative for each point.
Edit: That image came out kind of strange. Those two orange wires that seem to go to the right of the for loop but dont connect to anything, they are supposed to feed into their respective shift registers.
Message Edited by Cory K on 08-11-2009 11:20 AM
Cory K

Similar Messages

Input analog signal with trig signal on DAQPad6020E

I would like to record an input analog signal in continous with trig signal on falling edge. The frequency trig is 3.87hz (258ms)with 5V level. In fact I want to record the input analog signal every 258ms.
I use a DAQPad6020E and the VIs "AI-Config", "AI-Start" and "AI-Read" with a "digital A" trigger type (PFI0/TRIG1 on block connectors) and record datas in a file.
I use the following configuration:
- sampling rate= 100000 S/s (max rate DAQPad6020E)
- minimum scan= 25200 pts
When I read the datas I notice that the gap between the first point of the first acquisition and the first point of the second acquisition is 1016ms and not 258ms like the trig.
I change the configuration:
- sampling rate= 10000 S/s
- minimum scan= 2520 pts
The gap is now 516ms (it correspond to two trig)
An other configuration:
- sampling rate= 155 S/s
- minimum scan= 40 pts
The gap is 516ms (it correspond to two trig)
I use also the VI "AI-Wave" but the results are the same.
I don't understand what happend. Maybe it's due to the card limits ?
Thank you for your answer.

Hello,
A trigger is an external stimulus that initiates one or more instrument functions. Trigger stimuli include a front panel button, an external input voltage pulse, or a bus trigger command. The trigger may also be derived from attributes of the actual signal to be acquired, such as the level and slope of the signal.
A trigger is not a clock.
If you want acquire with a specific clock, I advise you to use external clock. Instead of using your signal as trigger, use it as external clock.
Have a look at "Cont Acq & Graph Ext Scan Clk - D trig.vi" example. This example is provided with LabVIEW (Help >> Example Finder).
Here a tutorial about external clock acquisition :
http://zone.ni.com/devzone/conceptd.nsf/webmain/7d8eaea1d87cfb2686256802007b8c52?OpenDocument
Regards,
Isabelle
Ingénieur d'applications
National Instruments France

How to input/output a digital signal and acquire an analog signal at the same time?

Dasylab, version: 8.0.04
Acquirement Card: PCI1002L
When I use DasyLab to acquire the analog signals is no problem without digital inputs and outputs,
and when I use DasyLab to input or output a digital signal is no problem also, but when I do that at the
same time, DasyLab tell me the rate is too high and stop.
so, I searched the manual book1 (user guide) for that, it showed me :
To internally equalize measurement time and system time in the analog input, digital input and counter
hardware modules, use the following settings:
   Synchronization: PC Clock
   Sampling rate: <= 5Hz
   Block size: =1
the problem is, if I set the Sampling rate to 5Hz, the speed of the acquirement datas is not enough for my
application.
so, how to improve it? who can give me a example programm for me. thanks!
by the way, I come from China, my English isn't good, I'm sorry.
Allen, China.

Hi,
Have things changed over the years?
I need to syncronise a digital output (Modul NI9474) and an analoge input (AI-Modul NI9203) module. I need to measure time intervals from a flank in signal A to a flank in signal B. I would like accuracies of the order of 1 ms. Currently, the signals are not synchronised, with errors of the order of 2 times the block length (block size x sample rate), sometimes much higher. The best I got so far was a block size of around 20 with a sample rate of 1 kHz.
If I use the master and slave settings on the RTSL settings, my program doesn't run properly.
If I use digital signals for input and output, I can syncronise them with RTSL settings and everything is good, but I can't always do that.
Also, if I do anything in the GUI (such as scrollowing something or going to another window), my output gets screwed up properly.
1. What can be done to synchronise AI with DO?
2. Is there something that can be done to avoid messing up the output when something happens in the user interface? (I know that I am messing up the outputs as they make some valves switch and that is loud).
Thanks in advance!

How to acquire analog signal and send a TTL pulse at the same time based on PXI 6123

Hi,
I am using a PXI-6123 data acquisition card, as the picture show in the attachment ,I want to acquire the analog signal of ai0 through reference analog window and at the same time send a TTL signal to trigger my camera. I have tried two methods, one is using the DAQmx Export signal.vi another is using DAQmx connect terminals, but when the data acquisition card acquire the analog signal, the DAQmx Export signal.vi and the DAQmx connect terminals sometime can send an TTL pulse ,sometime can not.
I don’t know why? or some other method that can achieve my arm is appreciated.
Regards
chunlei
Attachments:
method export signal.vi ‏21 KB
method connect terminal.vi ‏36 KB
Send a TTL pulse.JPG ‏288 KB

Hi,
Have things changed over the years?
I need to syncronise a digital output (Modul NI9474) and an analoge input (AI-Modul NI9203) module. I need to measure time intervals from a flank in signal A to a flank in signal B. I would like accuracies of the order of 1 ms. Currently, the signals are not synchronised, with errors of the order of 2 times the block length (block size x sample rate), sometimes much higher. The best I got so far was a block size of around 20 with a sample rate of 1 kHz.
If I use the master and slave settings on the RTSL settings, my program doesn't run properly.
If I use digital signals for input and output, I can syncronise them with RTSL settings and everything is good, but I can't always do that.
Also, if I do anything in the GUI (such as scrollowing something or going to another window), my output gets screwed up properly.
1. What can be done to synchronise AI with DO?
2. Is there something that can be done to avoid messing up the output when something happens in the user interface? (I know that I am messing up the outputs as they make some valves switch and that is loud).
Thanks in advance!

Analog Signal to Digital a Primer

Many users have analog material sitting around, and they would like to get it into digital form, so that it can be edited. As this material is below SD (Standard Definition) quality, I will address the methods for digitizing it, so that it can be best edited in a DV Project. The output can be a DVD-Video, or other format, depending on what one wishes.
The process of getting this analog material into a digital form, is referred to as Capturing, and it is digitizing the analog material and writing it to a file, that can be edited.
One will need some method of getting the analog signals into digital form, and for connecting the analog output from their analog playback device to the computer. Though the analog signal could come from all sorts of devices, I’ll use a VHS tape deck in this example.
Since a VHS tape deck does not have an A-D (Analog to Digital) processor, and also does not have a a digital signal Out, one needs something in between it, and the computer. That “something” serves two needs: mechanical connection of cables and the ability to convert the analog to digital for use in an NLE (Non Linear Editor). That “something” can be a digital video camera with pass-through capabilities, a device, called a “bridge,” or a capture card inserted into a bus slot in the computer. All three have pluses and minuses.
The first two methods rely on one having a FireWire connection on the computer and will use the Capture module in the NLE software.
The digital video camera route is good, as one already owns it. Having one with pass-through capabilities is getting more difficult. The camera also has to have FireWire (FW, IEEE-1394a, or iLink) output, and the computer must have a matching connection.
An A-D bridge will do the same thing: allow one to connect the analog cables to one end/side, process the analog signals to digital and then output via FW to the computer. There are various such bridges available and two of the most often recommended makes/models are: the ADS-Pryo, and theCanopus/Grass Valley ADVC-110. Products, like the Dazzle lineup, just do not seem to work, or work well. I would avoid such.
A dedicated capture card performs the same task, with one exception. The card will mount into an empty PCI slot on the MoBo, and have inputs for the analog cables. The card will have chips on it, to digitize the analog signals and feed these to the computer via the PCI slot. These do not connect via FW, but have one drawback: they must, in virtually every instance, use additional software to do the actual Capture, as most NLE’s cannot directly see and work with them. Some of the included software Capture programs are better, than others. One common issue with many of these cards is a loss of sync, between the Audio and the Video. This is usually static OOS (Out Of Sync), in that it is usually off by a fixed number of frames, and does not drift over time. This can be fixed in the NLE, but is extra work. This ARTICLE will give you tips on correcting OOS.
Now, we are ready to begin the Capture, as our equipment and cables are all ready to go. We have a big decision in front of us - what format/CODEC do we use to Capture our digital files? Since we are doing an SD Project with non-HD (High Def) material, there is one fine choice: DV-AVI Type II w/ 48KHz 16-bit PCM/WAV Audio, using the DV/DVC CODEC. These files will be approximately 13GB / hour of Duration. Storage will need to be considered. These files are also I-frame, meaning that each “Frame” is rendered and available, so that frame-accurate editing is possible. The NLE will not need to do any processing, or conversion of these files, as even the Audio is ready for DVD-Video. Note: there will still be Conforming and the generation of PEK (Waveform Display) files, but the NLE will be able to do this quickly and efficiently.
Using AVI Uncompressed will get you nothing that you can see, other than larger files. Do NOT use any compressed format/CODEC, like MPEG-2, WMV, MOV, etc., as these will loose data from an already inferior source, and will then need conversion to be used, either with a stand-alone conversion program, or internally by the NLE. You loose quality and then have more work to be done. Do not let the temptation of smaller files lure you into using anything but DV-AVI Type II, and just accommodate the larger file sizes.
With the file format/CODEC decision made, the cables and devices hooked up, we’re ready to start the Capture. The exact operation will depend on what our equipment choice has been. See above for talk about additional Capture software, if one uses a capture card. Otherwise, we should be able to use the Capture module of our NLE. The first issue is that we will NOT have Device Control, as we would with a Capture from a miniDV tape-based digital camera, where we can control the mechanical aspects of the camera, during this process. As our VHS deck is hooked up to the A-D bridge, or digital camera w/ pass-through, via analog cables, our control signals cannot be sent to it. One would cue up the tape in the VHS deck, and then choose Record/Capture in the NLE’s Capture module, starting the Capture. Instantly, they would hit Play on the VHS deck, or via that deck’s remote control. This is easier the second time that one does it. I sit with the mouse in my right hand, poised over the Record/Capture button, and the VHS deck’s remote in my left hand, finger hovering over Play. It’s then a 1 - 2 push, and all starts. One can stop the Capture, if an unwanted section of tape comes up. The Capture module of the NLE will direct us on how to proceed from there, should more Captures be wanted. Some will just start up at a later point, and write an additional file for that portion of the tape, but some might require that one basically sets up a new Capture session One should investigate just what their NLE will require for doing multiple Capture sessions from one VHS tape.
When done, one closes the Capture module, and then navigates to the location that these DV-AVI Type II files have been stored in, and Imports them into the Project. This differs slightly from doing the Capture from a miniDV tape camera, as those Captured files are already in the Project.
Edit away, and Export/Share to the necessary output settings, file type and CODEC.
What about those VHS - DVD decks, the ones that will burn a DVD directly from the VHS tape? They seem so simple to use, and for the most part are. However, those DVD-Video discs, contain pretty heavily-compressed MPEG-2 AV streams. These MPEG-2's, besides being compressed, are in aGOP structure and are muxed (Multiplexed into one file with both a Video & Audio stream), plus there is often some Menus and navigation in the first VOB, the main container components of a DVD-Video. Many NLE’s can Import the VOB’s, and basically rip the MPEG-2 out of them, but that first VOB can be highly problematic, due to the way that most of those decks do the Menus and navigation. It is seldom 100% DVD-compliant by the DVD-specs. This can be a major problem. This ARTICLE will give you some background and tips on DVD VOB's.
Those dual-decks are good for doing one thing, regarding the DVD’s that they produce - provide one with an archival DVD-Video of the VHS tape, and not to be edited. However, the VHS side of these works well with an A-D bridge, just like a pure VHS deck does. I would strongly recommend that one does NOT use the DVD-Video portion of these, if editing will be desired. They cause many more problems, than they solve - just use them for an “archive” copy of the tape to a DVD-Video, for playback on a computer via DVD software or a set-top player, hooked to a TV.
What about film? Well, film is obviously analog, and one needs to digitize this to edit on the computer. The process of this digitizing is referred to as telecineing the film. While one can buy equipment to do this, it is expensive, and involves a lot of setup and testing to get the job done. There are many service bureaus, that offer telecining. Some are better than others. The main considerations are: care in handling of fragile film, how the telecining is done, i.e. frame by frame w/ a liquid gate, or just by straight projection, and then output format for the digitized files. Some of these services will offer a DVD-Video disc. Do not be tempted to do this. See above. Others will offer to write these digitized files to a miniDV tape, and this is just fine. One does then need a miniDV camera, or miniDV tape deck, to then do the Capture from, but the quality and editability will be preserved. The final delivery format would be to put these DV-AVI Type II files onto an external HDD. This saves one from having to do the Capture from miniDV tape, having to have a miniDV camera, or miniDV deck, and only Importing of those files would be required to get them into the Project. Many of these service bureaus will either sell you the external, or use one provided to them. Check out specifications for things like format of the external. FAT-32 will limit the file sizes to ~ 4GB max, and NTSF will have no such limitations. However, if the service bureau is on Mac, and you’re on the PC, their Mac’s can ONLY see FAT-32 HDD’s. Talk this over with the service bureau first, so that there are no surprises later on.
Hope that this helps,
Hunt
PS - also see this FAQ Entry for more detail.

the_wine_snob wrote:
Products, like the Dazzle lineup, just do not seem to work, or work well. I would avoid such.
Although I now have a Canopus ADVC300 I previously used a Magix 'Movies on DVD' USB device. I found the results from this to be particularly good and, to my ageing eyes, I see very little quality difference.
I think this is because Magix use their proprietary high quality codec (from their Pro products) to capture the footage. Like DV-AVI it runs around 10GB+ per hour. This can then, very simply, be exported to DV-AVI Type 2 for use in PRE. Note that there are some sound synchronisation issues with the 'out of the box' settings - but the fix is quick and I posted details to the Magix forum.
Would I revert if I could return my ADVC300 bridge? Probably not - the firewire connection and the PC seeing the box as a camcorder adds to ease of use. In fact I am pleased to have both. There are some things Magix does better than PRE7 (batch exporting each scene as an individual DV-AVI file being just one) and it has smart-rendering which is handy for quick clip splitting/exporting.
Cheers,
Neale
Insanity is hereditary, you get it from your children

How do I set a threshold from an analog signal (4-20ma) coming in on a cfp AI 110, to trigger an alarm on my UI?

I have the alarm set, indicator set, just need a digital trigger from an analog input. I realize I could use an external switch into a digital input, but would rather use what we have. We are using this analog signal for other purposes as well. This application is for controlling a machine. Thanks.....

Hi Bob,
The way you have your Case structure setup now is that the “7” case will only get executed if the value from the wire is exactly 7. This same applies to the “8”. Also, there is no default case, so if value does not match any of the cases then your indicator will not change.
You indicated earlier that you need the indicator to be ON when the value is below 7mA and OFF when above 7mA. You will want some like this:
Alternatively could just use the Not function inside the Boolean palette to achieve the same functionality without the case structure.
You will want to check out the LabVIEW Training Page.
Message Edited by DiscoBall on 03-27-2009 12:12 PM
Message Edited by DiscoBall on 03-27-2009 12:13 PM
Joshua B.
National Instruments
NI Services
NI Support Resources
NI Training Resources
Attachments:
compare.jpg ‏27 KB

Problem when combinning PWM signal and Analog signal TOGETHER!

Hello everybody,
first of all i have DAQmx 6212, and i need to run a small water pump (9V-16V) which needs to be driven by a PWM signal; also i have a motor (5V-13V) for a water valve that needs to be driven by a analog signal and it has a built in a force feedback potentiometer, i connected on the extremeties of this potentiometer +5V from the DAQmx and used the output voltage from the third extremety as a diagnose value for knowing the position of the motor.
my VI shows:
1. is a normal Counter output to create my PWMout signal.
2. is an analog input i use it as a PWMin to the LabVIEW to diagnose what is happenning in my water pump through the duty cycle and the frequency.
3. is an analog input from the third extremety of the potentiometer.
4. is an analog output which i have used as a power supply for the motor valve and i have used an AC/DC amplifier to aplify the signal from the DAQmx and drive the motor, between (3. and 4.) i have made a feedback with some calculations i had a P-controller to know the actual position of the motor valve.
My Problem:
when putting 1. and 2. in the same VI alone, i am getting a clean PWM in/out with no problems mentioned;
also when putting 3. and 4. in the same VI alone i can control the motor valve without any problems;
but when i put all these 4 together as found in the attached VI, i have a problem that the motor valve is running continously without stopping even if i change the valve position between 0 and 100 %, i should mention that i am seeing a normal PWM out/in signal on my oscilloscope, one other thing that if i delete one of (1. or 2.) and run the VI the motor valve is working fine without any problems.
so this my problem, if you can think of any solution please let me know.
thanks in advance for your help.
Regards,
Alosh
Solved!
Go to Solution.
Attachments:
pwm.out.in.analog.out.in.vi ‏45 KB

Dear nathand thanks for your reply,
i have ran the vi again and i am have error no 50103 from the (AI, number 3. ) but it is not displaying the error message, the VI keeps running without any error notification.
adding to that, i have tested the VI again today by placing (1. and 2.for the PWM inout) together in one VI and (3. and 4.for the motor valve) in another VI and ran them one after the other, i had another problem. if i turn the motor valve vi, the motor will run smoothly but in the pwm vi i will have a problem in which the AI did not read any value. also doing this vice versa by running the pwm vi first it will work perfect but the motor vi will have problem in reading the measured voltage in AI during this the motor will keep on running without stopping.
so i think now the problem is in AI (2. and 3.) readings they are interfering on each other but i am not discovering where is my problem...
Q: does the AI's seems well build or i can do it in an another way so to get over the interfering?
Regards,
Alosh

Why use FIFO to read analog signal?

Why must we use FIFO to obtain analog signal from FPGA? I can use a normal method of calling the FPGA using Read/Write Control and the results in a waveform chart is much more smoother.

I've uploaded 2 real-time VIs with and without FIFO. MQ convert is the subVI in my computer. Do have a look at it...
My waveform chart is done that way so that I can easily export to excel ( i think) but this is a different problem in a different topic http://forums.ni.com/t5/LabVIEW/3-Waveform-Chart-to-a-Single-Excel-but-in-Different-Spreadsheet/m-p/...
Attachments:
Real-Time With FIFO.vi ‏397 KB
Real-Time without FIFO.vi ‏391 KB
MQ Convert.vi ‏19 KB

How to convert a analog signal to digital signal

Hello,
How to convert an analog signal into digital signal such that every sample of analog signal corresponding to 1.2V will be represented as '1' in digital signal and other samples of analog signal(that are not 1.2v) will be represented(converted) as '0' in digital signal.
And how to display both wavefroms or signals in graph indicators.
Thanks.
Solved!
Go to Solution.

If you have 1000 samples, and you want to convert to digital, you are going to get 1000 digital values. Attached is what I mean.
Unofficial Forum Rules and Guidelines - Hooovahh - LabVIEW Overlord
If 10 out of 10 experts in any field say something is bad, you should probably take their opinion seriously.
Attachments:
Analog_to_Digital Hooovahh Edit.vi ‏52 KB

How can I delay analog signal?

I have an analog signal, the frequency is less than 1kHz. I want to get a delayed analog signal. Is it possible to realize analog delay generator using labview (daq card is PCI-6115)? I hope I could specify the delay time.
Any suggestion will be greatly appreciated!
Stephen

Hello Stephen,
It is possible to institute a delay an analog output. This is best done by specifying a trigger and then beginning the output when that trigger occurs.
Below is a link to an example program developed for LabVIEW that waits a specified number of seconds and then triggers analog output to begin. This code performs analog input as well, but for your program you could remove that portion. The trigger that is used is RTSI pin 0. After a specified period of time, the RTSI pin 0 is set to 1 and then the analog output begins.
Analog Input with Delayed Analog Output
Take a look at this example and
try to build from it for your code. If you have any further questions on this issue, let me know.
Regards,
Scott R.
Applications Engineer
National Instruments

How do i send an analog signal to trigger another program

I am trying to send out an analog signal from labView that will start Bioware. How can I do this?

Hi Orbz,
There are 3 Send modes in Logic:
• Pre Fader (original signal is sent before it reaches the channel strip's fader etc.
• Post Fader (sent before volume fader adjustments)
• Post Pan (send before volume fader and Pan/Balance adjustments).
Click and hold on the Send slot in your synth channel strip and select Post Pan fro the drop-down menu.
Funnily enough I've just finished writing a tutorial about this very topic!! It's not published yet, but will appear on the macProVideo.com blog in the coming days...
http://www.macprovideo.com/blog/

Analog signal smoothing

I have a LVDT analog signal that I need to plot to a waveform chart for a test that is running at 5hz. The signal is very choppy and unreadable. If I slow it down to say 1hz or less the plot looks like a nice sine wave, which is what I am looking for. What can I do to acheive this at 5hz. Thanks in advance for help and advice.

tavwtby wrote:
And why should I be converting the Dynamic Data to an array of doubles, I am only reading a sinbgle scalar. I would have to index the array anyway wouldn't I?
No you're not. Your DAQ Assistant is getting 1000 samples from 4 different channels. You are throwing away 999 samples from channel 0 and all of the other channels.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
Unofficial Forum Rules and Guidelines

SONY Handycam DCR-HC19E, Capable of Passing Digital Analog Signal?

Hi
I wondered if my Sony Handycam DCR - HC19E (miniDV) is capable of sending an analog signal through firewire to my computer as I wish to monitor my progress on my tv.
And:
Should I be on record or play/edit mode on camera?
What to do if I wish to playback my videos on FCP 5?
Any help would be greatly appreciated.

I don't know what settings on the camera, but this is the playthru checklist:
#8 External Monitor Viewing.
Shane's Stock Answer #8:
A simple path is mac > firewire > camera or deck > rca cables > tv
Then start up your camera and tv, then open fcp.
Then go View > External video > all frames
Video playback should be Apple firewire NTSC (If you are using an NTSC set)
Audio playback should be Audio follows Video
Techinially, this should send synched video to your TV
If for some reason you can't view your timeline on your external monitor, there are a few things to try:
1) Make sure that the camera/deck is connected and powered on BEFORE you open FCP.
2) In the Final Cut Pro menu select AUDIO/VIDEO Preferences and make sure your signal is being sent out thru Firewire DV.
3) Go to the menu and select VIEW>EXTERNAL>ALL FRAMES.
4) Click in the % box above the image and select FIT TO WINDOW.
5) Go to VIEW->refresh A/V devices
6) Make sure the Log & Capture window is closed
If you want it to play in both the canvas and the external monitor you need to go to the FINAL CUT PRO menu and select AUDIO/VIDIO settings and make sure MIRROR ON DESKTOP is selected under the PLAYBACK OUTPUT section
Shane

Analog signal from PXI

Hi everybody,
I have a problem: I cannot acquire 6 analog signals with a PXIe 8135 with 4MS/s. I use two boards with 4 MS/s, 16 bits and 8 Analog Inputs. I use a subVI of SAMPLE CLOCK for configuration with this parameters, Continuous SIGNAL, SAMPLE RATE = 4MS/s ( see attachment ). With one signal is ok, but with 2 signals, i have an overload Memory Message.
Where is the problem in the VI?
Thanks for your help.
Attachments:
acq_and_graph.zip ‏165 KB
acquire&loggdata.png ‏230 KB

Quickly looking through your code now, try removing the "Number of Samples analog". Since you are using Continuous Samples, you are just limiting the buffer and also limiting how many samples you can read at a time.
But you might want to think about using Finite Samples. You know how long you want to log for and you know your sample rate. So why not just do the simple math and tell DAQmx to get that many samples? You can use the DAQmx Task Done? VI to see if it is done. That would be much simpler than checking the time that has elapsed.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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How to make a synchronous acquisition of two analog signals with a one channel DAQ ?

Hi !
It is the first time I use Labview. I have just made some easy VIs, and now, I do not know how to deal with my problem...
My problem : I have only one acquisition card (DAQ Ni 6034E) and I would like
to acquire simultaneously two analog signals. It seems to be possible, in a quasi-synchronous acquisition if the card acquires one point of the first signal, then the first point of the second signal, then the second of the first signal, and so on ... I thougth that I could made two sequencies with a VI of data acquisition in each sequency, with the AI MULT PT. But with this, I think that I will lose the precision of the sampling frequency. And I have to know the sampling fre
quency ...
Thanks for your help !
Carline

Hi Carline,
A PCI-6034E is a low-cost board, which only has one Analog to Digital Converter (ADC).
With only one ADC you can't acquire different channels at the same time. That's why you find a multiplexer before the ADC in this type of board. This enables you to acquire multi-channels at the same rate quasi simultaneously. The samples of the different channels will be interleaved as it is explained in the following knowledge base :
- http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/9379ea091c264b7c86256bc90082ca5d?OpenDocument.
With this method, the sampling frequency is the same for all channels. The sampling frequency of one channel is determined with the "scan rate" parameter. There is only a small delay between the samples
of each channels. When you perform an interval scanning acquisition, this delay depends on the "sample rate" that you specify. To have more informations about this terminology, please refer to the following KBs :
- http://digital.ni.com/public.nsf/websearch/4D1435DF82EF494186256D8A006DD6D4?OpenDocument.
- http://digital.ni.com/public.nsf/websearch/4D1435DF82EF494186256D8A006DD6D4?OpenDocument.
To easily perform such a multi-channels analog acquisition, you can use the VI named "AI Acquire Waveforms.vi". You also can use an example provided with LabVIEW. You just have to browse the NI Example Finder in "Harware Input & output >> Traditional NI-DAQ >> General".
Best regards,
Benjamin
National Instruments France

PtByPt derivative of an analog signal

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