How a DAQ card acquire resistance/position/frequency?
I don't understand a thing...
how a DAQ card can acquire (directly)
a position, a frequency and so on.
I had a look at examples folder (ANSI C)
and found examples to read
frequency, position.
An ADC can acquire only voltage.
How with a DAQ card I can acquire
linear position, resistance and so on?
Thanks in advance.
Yes, normal DAQ ADC read voltages, However most DAQ-Cards provide some supply/exitation voltage/current you can use together with an sensor that deliver a voltage or a current, with thanks to Ohms law can be transposed to a voltage
linear position -> potentiometer -> voltage
frequency is measured with timers
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Henrik
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Similar Messages
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DAQ Card is inducing noise on an external clock signal resulting in false triggering
I am using an optical encoder as an external clock source for analog measurements with a PCI 6036 card. The optical encoder signal is "filtered" using a Schmitt Trigger circuit and proper shielding practices are used on the encoder cable. I am using a recent version of Labview.
When the TTL square wave signal from the encoder is viewed on an oscilliscope (without the DAQ attached) it is a picture perfect square wave, nothing that would cause any problems.
When I then connect the encoder output to my PFI line (with or without the oscilliscope) I get false triggering due to intermittent (seemingly random...) high frequency noise "blips". Out of 360 expected samples, I will typically get between 2 and 6 "bonus" samples... When captured on a scope, the noise looks like a decaying sine wave and lasts for only a few us. the peak magnitude is tyically around 2 V or so as shown on the scope, which is apparently just enough to make my card grab a sample.
Since the noise is only present when the encoder signal is attached to the DAQ, it seems that the DAQ is somehow inducing noise into the signal.
I have been fighting this problem for a while now and tried the following:
1) I first tried the raw encoder signal, but then added the Schmitt trigger, increased the signal strength of the encoder lines by adding resistors to ground, double checked my shielding, etc...
2) I verified that my ground potential between my card and my conditioning circuit were not causing problems. The conditioning circuit and encoder is now powered of the card itself, which should resolve any possible problem with grounds.
3) Cursed at various inanimate objects (made me feel better but didn't help the situation)
4) Checked if I could set a minimum pulse width required to trigger off of an exernal scan clock (I can't with my hardware.)
5) Swapped my card with a card of a different type (problem is still there)
If anybody out there has some recomendations, I am open to anything.Hello OSU_Mech_Eng,
I'm not quite sure how the DAQ card could be inducing glitches into
your digital signal. Digital signals from mechanical devices like
quadrature encoders can often be glitchy or bouncy, but your schmitt
trigger should act as a debouncing filter to clean up that digital
signal. It sounds like you have thoroughly troubleshooted this
problem, and I would recommend moving on and trying to use a counter on
your DAQ board to generate the digital signal, rathar than using the
raw signal from your encoder/schmitt trigger.
You were correct when you stated that the best way to do this is by
configuring your counter to perform retriggerable pulse
generation. You can use the signal of from your encoder to gate
the internal clock on your DAQ card, creating a clean digital
signal. By setting the minimum pulse width of the signal, you
will be able to ignore the small glitches in your signal. Here is
a link to some Knowledgebases describing how to do this:
How Do I Remove Glitches or Add a Debounce Filter to My Digital Signal?
How Do I Define the Parameters for Pulse Generation in NI-DAQmx?
For further reference, on all of NI's new M-Series DAQ cards (PCI
625x), the PFI circuitry contains built in debouncing filters to
protect against small glitches in digital signals. If you have an
M-Series card lying around, it might be helpful to give that a try.
I hope this helps,
Travis Gorkin
Applications Engineering
National Instruments
www.ni.com/support -
How to control two 6011e daq card to acquire eight signals simultaneously.
I use two 6011e daq card to acquire eight signals simultaneously .I use labview function to realize it,but the data graph show that the signals aren't acquired simultaneously,why?how to do it?
Hello;
You need to use the RTSI bus to route one board's clock signal to be the second board's clock signal. By doing that, you will have the same signal clock timing both boards, which will make the synchronization hardware timed.
You will need to have a RTSI cable connecting both boards together also.
The best way to go about this is to open the Labview examples that show how to synchronize multiple devices. You can apply the same idea to your board.
The examples can be found at Search Examples->I/O Interfaces->Data Acquisition->Multiple Device DAQ Examples.
Hope this helps.
Filipe -
How to acquire data from 2 chs of the same DAQ card at different sampling rate
I am using single DAQ card (either 6013 or 6014) in my system i want to acquire data from 2 (or more) channels with following requirements
1. sampling rate of each channel should be independant of each other (say one is 20 Hz and other is 15 kHz)
2. data from all the channels should be acquired simultaneously.
3. coding must be done using DAQmx VIs
I have tried out following things
1. I created separate task for each channel: i found out that two tasks can not run simultaneously even though the channels are different
2. I tried out single task with two channels included in it. and i used 'channels to Read' property to determine from which ch. i want to acquire data: this method works fine if the sampling rates are same. but if i change the sampling rate of one channel it gets reflected in other channels as well.
can somebody help me out to solve this problem.
i will appreciate if somebody can post the sample code as my deadline is approaching
Tushar Jambhekar
[email protected]
Jambhekar Automation Solutions
LabVIEW Consultancy, LabVIEW Training
Rent a LabVIEW Developer, My BlogHi Dennis Knutson
Thanks for your suggestion.
Tushar Jambhekar
[email protected]
Jambhekar Automation Solutions
LabVIEW Consultancy, LabVIEW Training
Rent a LabVIEW Developer, My Blog -
I'm using the MHDDK for analog out/in with the PXIe 6341 DAQ card.
The examples, e.g. aoex5, show a single Timer (outTimerHelper::loadUI method), but the example shows DMA data loaded with the same vector size.
There is a comment in the outTimerHelper:rogramUpdateCount call which implies that different buffer sizes per channel can be used.
(the comment is: Switching between different buffer sizes will not be used)
Does anyone know what the format of the DMA buffer should be for data for multiple channels with different frequencies ?
For example, say we want a0 with a 1Khz Sine wave and a1 with a 1.5Khz sine wave. What does the DMA buffer look like ?
With the same frequency for each channel, the data is interleaved, e.g. (ao0#0, ao1#0; ao0#1, ao1#1, ...), but when the frequencies for each channel is different, what does the buffer look like ?Hello Kenstern,
The data is always interleaved because each card only has a single timing engine for each subsystem.
For AO you must specify the number of samples that AO will output. You also specify the number of channels. Because there is only one timing engine for AO, each AO will channel will get updated at the same time tick of the update clock. The data will be arranged interleaved exactly as the example shows because each AO channel needs data to output at each tick of the update clock. The data itself can change based on the frequency you want to output.
kenstern wrote:
For example, say we want a0 with a 1Khz Sine wave and a1 with a 1.5Khz sine wave. What does the DMA buffer look like ?
With the same frequency for each channel, the data is interleaved, e.g. (ao0#0, ao1#0; ao0#1, ao1#1, ...), but when the frequencies for each channel is different, what does the buffer look like ?
In your example, you need to come up with an update rate that works for both waveforms (1 KHz and 1.5 KHz sine waves). To get a good representation of a sine wave, you need to update more than 10x as fast as your fastest frequency...I would recommend 100x if possible.
Update Frequency: 150 KHz
Channels: 2
Then you create buffers that include full cycles of each waveform you want to output based on the update frequency. These buffers must also be the same size.
Buffer 1: Contains data for the 1 KHz sine wave, 300 points, 2 sine wave cycles
Buffer 2: Contains data for the 1.5 KHz sine wave, 300 points, 3 sine wave cycles
You then interleave them as before. When the data is run through the ADC, they are outputting different sine waves even though the AO channels are updating at the same rate. -
1. My PCI-6036E card has a FIFO of 1024 bytes in AI. Maximum how many samples can be acquired with single trigger for digitizing a waveform?
2. PCI-6036E DAQ card has got a AO with 10ks/s update rate? Can I generate a pulsed output with the AO of this card? I need a pulse of, say, 5 V and 1 kHz frequency.Giri,
1.The trigger is usually for enabling the acquisition. I mean, when it is logic zero, you acquire nothing; however, when it is logic one, you start acquiring your waveform,and you can acquire continuously without having to worry about how many samples, unless you want to set your program for doing so. You can acquire continuously by implementing buffer acquisition. Finally, the FIFO that is in the board will not affect the buffer acquisition.
2.Yes, you can do that! You can generate your 5V signal with that specific frequency, and you should not have any problems, because the freq fits in the update rate.
I hope this information is helpful.
L Aguila
Applications Engineer
National Instruments -
I am using 6023E DAQ card to collect the signals, such as AE, Force, Torque from the machine. I want to collect only some part of signal for example between start triger and stop trigger. I'd like to know how I can creat those triggers in LabView from one of the channels that I am acquiring at the same time. I found one or two library file that is only for start trigger. I know that this is availabe in some of DIAdem functions. Please let me know if you have done some example for this requirement.
If you are wanting to create a software trigger based on an analog input voltage in LabVIEW, there are several options. One suggestion would be to compare the voltage values from one input channel to a number within a loop. If the input voltage crosses that threshold (is greater than the number), have a case statement that will acquire data from the other channels. This would simulate a software start trigger in LabVIEW.
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Hi
I ma using 6070E daq. I am generating a infinite pulse train using one of the counters. I want to generate another pulse train which should 90 degress phase shifted with respect to the previsously generated pulse. How to implement this using the counters in the DAQ card.Hi Gopal,
1) yes the frequency generator is programmable. You have 2 timbebases (10MHz and 100kHz) and you can divide down by any integer between 1-16. Those are the only frequencies you can use.
2) The way counters work is that you can apply a gate signal to the counter which will cutoff the output. Therefore, you can have a second counter generating a pulse train of an equivalent frequency to the frequency generator (fout) but you don't want it to start immediately. You want it to start only after a short delay (equivalent to a 90d phase). Therefore, you need to "gate" or prevent the output on this counter for that small delay period of time. The way you can do this is by using a second counter to create a delayed pulse. You would
connect the output of that counter to the gate of your pulse train function. That way, during the delay period of the pulse, you won't be outputing your pulse train yet. When the pulse (high-time) of your pulse reaches the gate, then your pulse train will start generating its pulse train (which is consequently delayed by the amount of delay used in the single delayed pulse counter). Since you don't want your pulse to go back low, you will have to turn off or clear your pulse counter while it is high. That way the signal on the gate will remain high forever.
Your better solution is to use a PCI-660x card to perform this action. You will have more counters which will give you a greater range of frequencies to choose from and you will have more accurate timing of the signals.
Anyway, hope that clears things up. Have a good day.
Ron -
How to arm channel 1 of a PCI 6133 DAQ card using labview?
Hi,
I am new to the Labview and I need some help. I have a PCI 6133 multifunction DAQ card and I'm using Labview 8.2 to capture five channels waveform data. I setup channel ai0 to be the trigger channel and I need to capture data from ai0, ai1, ai2, ai3, and ai4 when ai0 is trigger.
Question:
1) I am using DAQ assistant to configure my channels. How can I arm the channel ai0? I have an "execute button" and it should arm the scope when I click it.
2) Is there trigger ready signal, so I can save all the channels data when channel ai0 is trigger?
Can anyone provide some help?
ThanksHello wirte spreedsheet,
Thanks for posting to Discussion Forum. It looks like you are using the
PCI-6133 to acquire analog data from ai0:ai4. You want to use ai0 as
the trigger for the other channels.
Does your application need to be retriggerable?
Are you doing continuous acquisition?
Are you doing Analog start trigger or reference trigger?
Take a look the following shipping examples, found in LabVIEW click
Help>>Find Examples. On the browse tab, Hardware Input and
Output>>DAQmx>>Analog Measurements>>Voltage:
Cont Acq&Graph Voltage - Analog SW Trigger.vi
>> This example demonstrates how to perform an analog software
triggered acquisition. The example allows the user to specify the
triggering condition and the number of pre-trigger samples to acquire.
Cont Acq&Graph Voltage - Int Clk - Analog Start.vi
>> This example demonstrates how to continuously acquire data
(Waveform) using the DAQ device's internal clock and an analog slope
start trigger.
Take a look at these applications and let me know if you have any questions or comments.
Have a good day.
Regards,
Sandra T.
Applications Engineer | National Instruments -
PCI-6023E DAQ card maximum sampling frequency
Hello
I am using PCI-6023E DAQ card in pc-based ETS solution (and writing appilication in LabView 7.1 with RT module). The card has 200kS/s maximum sampling frequency, but it can be set for much higher sampling frequencies and the waveform acquired appears to be correct (i.e. i've tried setting it fo 1MS/s and sampling 400kHz sine, which is obviously above Nyquist frequency for 200kS/s card, but on spectral graph, main peak is at 400kHz). Is the card driver doing some kind of free/coherent sampling?
Moreover, when sampling frequency is set to 200kS/s, the card seems to be doing same thing - i.e. for 200kS/s and sample block size of 200kS, graph should be updated once in a second, but it's updating slighty slower.
I'd really appreciate if someone could explain me (or gave me a link to materials) what exactly is happening here? Is driver doing some background work, or maybe it is problem with network latency/unstability ? What is the impact of this effect on real-time aquisition?
Thanks in advance
Jan KienigSince the fundemental is 4 times the nyquist, then what you are measuring is an alias of the fundemental. This works well as long as the fundemental is a repetitive signal. Sampling every other peak and every other node looks the same as sampling every peak and node. Tektronix exploited this on their 7S series sampling heads. Another use of this phenomena is the effective demodulation of high frequency signals as long as the bandwidth meets nyquist. As with your card, if the input amplifier supported it, I could extract modulation information from a 500 MHz signal so long as the the bandwith of that modulation did not exceed 100 kHz.
Parker -
How to use PXI 6071E daq card to complete multichannels scan with high sampling speed
I used pxi 6071E daq card to acquire 115v 400hz AC signals.when I use mutichannel scan function,I find that the voltage of waveforms have much more error.The voltage error is about 0~15v.please you can tell me why this happened?how to solve it.
Attachments:
多通道监测4.vi 199 KBSunny;
As you are scanning multiple channels and the signal range is high, you can try to set the interchannel delay a little higher. The interchannel delay is the time which the multiplexer will take to switch to the next channel. If that time is to short, the instrumentation amplifier can have problems to settle, and then an error at the reading will happen.
You can change the Interchannel delay at the AI Config.vi.
Hope this helps.
Filipe -
How to synchronize the data acquisition from both GPIB and DAQ card
I want to begin/stop acquiring the data from GPIB and PCI6024E card into Labview at the same time. Since the acquisition from GPIB is quite slow comparing to the one from DAQ card, I can not put both of them in the same loop structure. Is it possible to synchronize them?
Thank you!Hi,
I wanted to save data acquired from NI-DAQ (for example, NI 9234) in a file using the DAQ-mx ANSI C Code. The response I got was as follows:-
One way to do it is with TDMS logging. DAQmx comes with functions designed to log to a TDMS file. This is a special file type that is used for collecting data in a logical format. It can be displayed in a TDMS viewer where data is separated into groups and channels. NI-DAQmx provides examples for how to log to TDMS. Look at the TDMS examples in the C:\Users\Public\Documents\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Analog In\Measure Voltage directory.
However, now I want to know is there a way that using that same C code, can we save the data in a .txt file format (Text File) instead of a TDMS file? We actually want to access that file through MATLAB (that's why we want to save it in text format).
Also on an other note, is there a way we can access & open TDMS files by MATLAB?
Thanks,
Sauvik Das Gupta -
How to measure current and resistance if i only have DAQ using VB 6 and Measurement Studio
I want to do a remote lab for basic electronic lab. One of the task is to measure current and resistance. How to do it if I only have DAQ card and using Visual Basic 6 and Measurement Studio. Can anyone give me a clue.
If your DAQ device is supported by DAQmx, you can use it with VB6. Here's how: NI-DAQmx Support in Visual Basic 6.0.
Michael P
National Instruments -
How can I control a stepper motor drive using a DAQ card?
I need to control a simple CW/CCW stepper motor drive using a DAQ
card. I simply need to output a 5 volt signal and then a drop in
the signal, and so on 200 times or steps for 1 revolution. I have
desiigned the basic program, but do not know how to output the
appropriate signal.
Cheers,
MattWhat DAQ card do you have? Ideally, one with a counter output to generate the steps, where you can control frequency. If you try to start the motor too fast (acceleration or abrupt application of fast pulses) it may stall out. Search in Help/Search for Examples for 'frequency' and 'pulse' for example of frequency generation. You can also use a digital output on the DAQ card to control direction.
If DAQ card does not have a counter, you coul do a software timed loop to toggle a digital output to generate the pulse train. It may not be fast enough nor accurate for your application, do not know from info you have given
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
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Multi cam shoot using P2 cards. How to move clis to timecode positions
multi cam shoot using P2 cards. How to move clis to timecode positions. We were using free TC. I want to a large # of clips from both cams. and have them move to the correct TC position on the timline. In Nuendo eith audio u hit apple a or ctrl a right click move to orgin. Avid will take care of it for u. FCP???
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