Setting the sampling rate in SignalExpress

I am using a cDAQ-9172 with a strain gauge module and a thermocouple module and using SignalExpress. I want to acquire data at a pretty low frequency rate (2Hz), but I am unable to use 1 sample on demand in the acquisition setup. I get the following error.
Error -201087 occurred at DAQ Assistant
Possible Reason(s):
Measurements: Task contains physical channels on one or more devices that require you to specify the Sample Clock Rate.
Specify a Sample Clock Rate.
Device: cDAQ1
I am unable to setup a sample clock rate as it is 'blacked' out by the software in the 1 sample on demand mode.
When I try to use continuous or 'N' sample mode, the cDaq is sampling at a rate of around 1600 Hz, even though I am putting in a value of 1Hz on the seti[ screen. The large amount of data will prevent me from downloading the data to Excel for further reporting. I obviouisly don't need to sample my TC module at that rate either.
Is there anything I can 'easily' do to decrease the sampling rate down to a low level? Everything I have tried doesn't seem to work and I don't really want to go away from SignalExpress.
Jay

Hi Jay
I am assuming that you are using the NI-9237. This strain module has only a specific set of sampling rates. If you specify a rate that is not supported it will corers the rate to the next higher sampling rate. Also since you are using the cDAQ chassis, there is only sample clock so it must choose the highest sampling rate. So it is not possible to sample at a lower rate. Please see the following link.
If you have access to LabVIEW then I would suggest taking your readings at the fast rate and then average the samples before you write them to your file. The following link has some more information on this.
If you are limited to Signal Express, this task is tricky. If you select a N-Sample acquisition, set the samples to read to greater than two, and set the post acquisition delay under the execution control tab to 1000, you acquisition will acquire the two samples at the very fast rate, but it will wait 1000mS between each acquisition. This will slow the overall sample rate.
Chris_K
National Instruments
Applications Engineer

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[Q] How to set the sampling rate separately?

Hello,
I'm using LV5.1 in Windows98 with SCXI-1200.
I want to set different sampling rate in each input channel.
I've ever used "AI acquire waveforms.vi" only.
Anybody can help me?
Example codes are highly appreciated.
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Hyun-ho Lee
[email protected]

The inputs of the SCXI-1200 are multiplexed to a single Analog-to-Digital converter. Because of this, the only difference in sampling rates that are achievable would be integer divisions of a common high frequency. This is functionally identical to acquiring all channels at the highest rate, and decimating (throwing away) data from channels that need lower data rates.

FMLE won't let me set the sample rate with Blackmagic Decklink Studio 2 (Windows)

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I am trying to set the audio device on FMLE to the Decklink Studio 2's audio inputs. However,
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One thing you might try doing is trashing the preference file in your user directory:
~/Library/Preferences/com.apple.compressor.Compressor.plist
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How to coerce the sampling rate??

I think I found my problem with sampling rate.
I'm using a PCI-5122 scope card, and in many of my aquisitions, I'm setting the sample rate to 40MS/s. Apparently, this is not a valid number and the scope reverts to 50 MS/s
Later when I try to calculate cycles per second based on cycles per sample, I need the actual sample rate, and 40 MS/s ain't it.
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please,.

The digitizer coerces the sample rate because of how the sample clock is derrived from the Reference Clock. The following information is on page 13 of the specifications:
http://digital.ni.com/manuals.nsf/websearch/C6B059C1BDD70101862574C8005567F1
The sample clock is created by dividing down the Reference clock (internal reference clock is 100MS/s) by decimation, and it divides it by N, which is an integer between 2 and 65530.
Thus 50MS/s uses a decimation factor of 2, and 33.3MS/s is the next valid sample rate with a decimation factor of 3. So when you specify a sample rate that is not possible, the driver automatically coerces the requested sample rate up to the next valid rate. You can obtain the actual sample rate used in an acquisition using the NI-SCOPE property "Actual Sample Rate", or the LabVIEW VI "niScope Sample Rate.vi". Using this property, you can get the values you need for your calculations.
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How to set the sampling interval using DAQ device?

Now I have a capacity sensor and a 24 bit DAQ device (http://www.mccdaq.com/usb-data-acquisition/USB-2404-10.aspx).
The DAQ device has the maximum sampling rate of 50kS/s . My question is how to set the interval of data collection. For example, if I set the sampling rate to 2000, in continuous sampling mode, I use DAQmx read.vi in a while loop and set the 'number of samples per channel' to 100. I want to plot these data as a function of time by using a XY graph and also save these data. So I add a 'Mean' function to get the average of the 100 samples per each loop (than means, there are 20 data output per second). But when I set the 'number of samples per channel' much smaller (to get more data per second), there are some problems. It seems that the program cannot read so many data and get the average at a higher frequency. I don't know where the problem is. All in all, how to collect data more frequently?Maybe I didn't express my question clearly. I'll upload a simple program later if necessary. Thanks.
Solved!
Go to Solution.

Another question is in continuous mode, NI DAQmx uses Samples per channel to determine the buffer size. But according to the website you specified, it says if the acquisition is continuous (sample mode on the DAQmx Timing.vi is set to Continuous Samples), NI-DAQmx will allocate a buffer according to the following table. And for sample rate between 100 - 10,000 S/s, the buffer size is 10 kS. So if I set the sample rate to be 5000 S/s, and set the Samples per channel to be 20000, then what exactly the buffer size is? 20 kS or 10 kS?
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The first things we need to know in order to be able to help are what are your operating system and audio device?
Also the FAQ Setting the Sample Rate in Windows Vista and 7 may help.

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I've been playing around with the AudioQueue stuff for a few days and it's all working fine.
I was trying to build a low-latency playback system by making the streaming buffers the same size as the audio file and pre-loading the buffers (which works fine) but I've hit a snag.
I've been trying to get the streaming to work at different sample rates so that I can play back the same sample at different pitches. I managed to do it by modifying the sample rate in the AudioStreamBasicDescription structure but in order to actually make the stream playback at the new rate it seems you have to create a new output, reload the audio file into the buffers and re-enqueue the output queue before starting playback again, otherwise the sample rate change has no effect.
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Dan,
there is one point in your understanding, which i am not sure what you think about when talking about it: I understand E-series devices do not support this property change while the VI is running.
infact, you cannot change the sample clock rate during acquisition. but
this does not mean that you cannot change it while the VI is running.
you have only to interrupt the acquisition. since you want to acquire
continuous, this would have the same effect as stopping the vi, i asume.
so the best way to accomplish this task is to use an external clock.
this is e.g. often used for acquistion on rotating shafts. the
acquistionrate is always e.g. 24 points per revolution regardless of
the rotational speed of the shaft, except for a maximum frequency of
course.
Norbert B.
NI - Germany
Message Edited by Norbert B on 09-14-2005 04:16 AM
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Changing the Sampling rate

Hi,
May I know how do I change the sampling rate on a Thermocouple node dynamically through a VI on the host ?
I notice there is a Config node in the "Start" case where I can set the "Sample Interval Mode" to "Host Driven" but I do not know how to continue after that...
Thank you very much !
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A user message is created by simply right-clicking on the node and selecting "Create User-Defined Variable." Once you set it up, that variable will update over the network automatically.
Once you've got that setup, you need to figure out how you are going to use that variable. You should probably start here: The LabVIEW Wireless Sensor Network Module - Under the Hood
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ADjusting the sampling rate on a FIR filter?

How do I adjust the sampling rate on a digital FIR filter? Thanks in advance.
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You should really start a new thread instead of posting to one that is 5 years old.
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The sampling rate of FP-AI-110

How can I change the sampling rate of cFP-AI-110 in Labview 8.5?
And the filter settings of cFP-AI-110 (50,60 and 500Hz) is equal to the sampling rate?

Hi!
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I need to increase the sample rate to 50KHz to allow for arc detection

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capture data with a sampling rate greater than 10kHz. Would setting the 'samples per cycle'
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RT-Controller (permitting us to use the FPGA VI un-altered) at a sample rate greater than 50KHz?

The number of samples per cycle can be specified from 128 to 512 without having to recompiling the FPGA VI. But even with 512 samples per cycle, the sampling rate after resampling is about 512*50 or 512*60, still less than 50k Hz.
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Is the sample rate half with the snd read waveform.vi?

Hi Guys,
I plan to use the PC soundcard for data acquiring with the standard LV "snd read waveform" vi. During programming I found that the sample rate is the half of the adjusted value. For example when I set
- the format to 8bit mono
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- and the sample rate to 11025
then the operation takes 2000ms. I would expect 1sec.
Used system: LV7.0, WinXP SP2.
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Thanks,
Tomi
Attachments:
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To be more precise, that's the time take for the below mentioned finite cycle
SI config>> SI start>> SI read >> SI clear.
Its this 'entire' process which takes 1997 milli Sec
Now, what you really have to check is wheather your 'SI read' function is living up to the sampling rate you have set!
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Hope this helps
Regards
Dev

Conflict between the saved data and the sampling rate and samples to read using PXI 6070e

Hello, I am using PXI 6070e to read an analog voltage. I was sampling at 6.6 MHz and the samples to read were 10. So, that means it should sample 10 points every 1.5 um. The x-axis of the graph on the control panel was showing ns and us scale, which I think because of the fast sampling and acquiring data. I use "write to measurement file" block to save the data. However, the data was saved every 0.4 second and as 35 points data at the beginning of each cycle (e.g. 35 points at 0.4 sec and 35 at 0.8 sec, and so on) and there was no data in between. Can anyone help me how there are 35 reading points every cycle? I could not find the relation between the sampling rate and samples to read, to 35 points every 0.4 second!
Another thing, do I need to add a filter after acquiring the data (after the DAQ assistant block)? Is there anti-aliasing filter is built in PXI 6070e?
Thanks for the help in advance,
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I'm not seeing anything that points to this issue. Your DAQ is set to continuous acquire. I'm not sure if this is really what you want because your DAQ buffer will keep overwriting. You probably just want to set to Read N Samples.
I'm not a fan of using the express VIs. And since you are writing to a TDMS file, I would use the Stream to TDMS option in DAQmx. If you use the LabVIEW Example Finder, search for "TDMS Log" for a list of some good examples.
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Setting the sampling rate in SignalExpress

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