Displaying multiple analog input channels using DAQmx READ commands.

I am using a NI USB-6009 module in a hydraulic load test stand. I want to read multiple analog voltage inputs and display them on my front panel. Using DAQmx commands or DAQ assistant, LabVIEW will only let you have one READ command for the analog inputs. Can someone point me to an example or give me some ideas on being able to display at least 3 analog inputs? Thanks.

With the DAQ Assistant, when you get a list of 'Supported Physical Channels', look at the bottom of the window. It says "<Ctrl> or <Shift> click to select multiple channels. When you use the DAQmx Create Channel and have a physcial channel control/constant, click the little arrow on the right side of the control/constant, select browse and use the same <Ctrl> or <Shift> click technique. If you want to enter the channels manually, the format is Dev1/ai0:2 for consecutive or Dev1/ai0,Dev1ai3 non-consecutive channels.

Similar Messages

Multiple Analog input channels affecting each other (DAQ_mx)

Hi, I use NI BNC-2110 / PCIe-6363 + Labview 2012 for my DAQ.
In out task, we acquire two analog samples(these two samples are timed by on board clock, 1000000 rate) from each analog input (AI_0 and AI_4) whenever DAQ receives a digital trigger from PFI0 (rising edge and retriggerable). We will receive 200 triggers and our program will finish until we receive 400 samples on each channel.
The interesting thing is that different analog inputs seem to affect each other. As shown in the figure below, the white curve is analog input AI_0 and the red curve is analog input AI_4. AI_0 is connected to a triangle input and the curve
below seems right. AI_4 is actually shorted (some result if open) but the acquired data is affected by AI_0.
However, this problem does not occur when only one channel is used in vi (Only the "create channel" and the "read" vi's are changed to be multiple sample and we repeat the experiment with everything else unchanged). So I believe it is not an actual voltage problem before the BNC-2110 board receives the analog input.
Any idea about how to solve this? Thanks in advance! Happy new Year.
Yang
Attachments:
Two Analog Inputs.vi ‏23 KB

I used a wire to connect the BNC core and BNC shell on AI_4 when I shorted it(it is set on floating source mode).
The effect happens even if I have some other kind of input in AI_4(the input is like a stair case but it is always modulated by AI_1). AI_4 always appears modulated by AI_0.
Actually it will not bother me at all if this only happens when AI_0 is open.
I guess the sample clock (1000000) is too high to cause this(Yep, probably it is Ghosting...). When this rate is 1000, it does not happen as I have just tried.

Writing more than 16 analog input channels into a single file

In DasyLAb 10.0, how can I WRITE more than 16 analog input channels (using WRITE DATA block) in one single file? I do not want to use 2 WRITE blocks, as I want all my data samples in one single file.

Another few questions:
In the merge block, what is the difference between Blockwise mode and Sample mode?
Also, now that I am using the Merge blocks (2 inputs to 1 output) to combine my analog inputs; how would I have to modify my WRITE block so that I can ultimately obtain both my inputs to be written in the same file in seperate columns. Could you please explain the settings I need to make on the WRITE block.
Thanks!

Usb 6009 multiple analog inputs

I am currently attempting to sample two different analog inputs at different sampling rates using a USB 6009. I keep getting the 'resource reserved' error and am wondering if this is not possible using this DAQ. Questions:
1. Does creating two analog input channels on the device cause this error?
2. Is it possible to sample at different rates on channels created in the same task? (i am trying to 'slow down' the second analog input to display switch points to a customer)
3. Running multiple analog inputs using independent timing would be better achieved by switching to a higher end DAQ? If so which would you recommend?
I have attached my vi. Thank you in advance for your help.
I surf therefore I am....
Attachments:
demo_nolvl.vi ‏27 KB

The DAQ boards only have 1 timing clock for the analog inputs/outputs. So you can only have 1 sample rate on a given card. I would recommend just sampling at the highest of the desired rates in a single task.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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Synchronizing two counter frequency inputs with multiple analog inputs

Hello all,
I'm fairly new to LabVIEW and I'm trying to collect data from multiple sources with synchronized timing on the acquisition but I'm having trouble figuring it out. My problem is that I've got two counter frequency inputs, one optical tachometer reading one pulse per revolution, and a max machinery flow meter with a k factor of 12000. I can't seem to figure out how to sync the timing with my multiple analog inputs. I've been attempting to get the tachometer to sync with the analog inputs first by following the example linked here. (https://decibel.ni.com/content/docs/DOC-10785) So far each time I run it I either get a timeout error on the DAQmx read or a "Multiple sample clock pulses were detected" error (see attached image). It seems if I slow the sampling rate way down to say 10 hz and ensure that the tachometer signal is over 800-1000 RPM (13-17 Hz) before starting the VI then the program will run without errors until the RPM drops below that threshold then the "Multiple sample clock pulses" error occurs. The code is attached below.
Does anyone know of a more effective way of syncing counter frequency inputs with analog inputs? I'd like to have a VI that can show 0 RPM (and eventually 0 flow as well, but I think I need to figure out the timing of one counter before I add another as it seems I can't have two counters in the same task). Any help on this would be greatly appreciated.
LabVIEW version 13.0
cDAQ-9178 Chassis with NI 9401 for the two counter inputs and NI 9205 for the analog inputs.
Thanks!
Richard
Solved!
Go to Solution.
Attachments:
SimpleDAQ.vi ‏44 KB
LV_Error.JPG ‏31 KB

Maybe third times the charm?
So I've finally got a good handle on why the VI is having problems at low RPM though I'm somewhat embarassed how long it took me to do that
Because I have the counter time synced to my Analog input task if it doesn't see at least two pulses between the two clock pulses set by the analog input task I get the -201314 "Multiple sample clock pulses" error. This seems fine at first as it just sets a minimum RPM that I can measure and it's well below the area I'm interested in so no problems there. I tried a simple error handler that would clear the error when it happend assuming the loop would keep iterating until the RPM went above that minimum at which point I would get a signal again. This is not the case, the read function just continues to spit out the -201314 error even after the RPM is back in the readable range. So then I tried adding two case structures so that when the error occured it would stop the task, clear the error, and then start the task again on the next loop iteration (Code Attached). This also doesn't work as the error shows up again on the stop task and then AGAIN on the start task on the next loop iteration. It seems this error is not actually being cleared and once it happens it stays with the task regardless of what the error cluster is carrying.
Anyone have any ideas? The only solution I can think of is to just clear all tasks and recreate them each loop iteration until the RPM is readable again but that strikes me as a horribly clunky solution.
Richard
Attachments:
SimpleDAQ_1_Start Stop.vi ‏48 KB

How can I get properties of global virtual channels using DAQmx?

I'm using DAQmx with VB6. In my app, I would like to be able to present the user with a list of available predefined channels to select from. I can use DAQmxGetSysGlobalChans to get a list of the channels, but I need a way to sort out which of these channels are defined as inputs, and which are outputs. It would also be nice to be able to query other properties of the virtual channel (for example, the device and physical channel being used). These all seem very simple things, but I haven't found anything like this in the documentation so far.
Thanks.

Try using DAQmxGetChanType(TaskHandle taskHandle, const char channel[ ], int32 *data)DAQmxGetChanType(TaskHandle taskHandle, const char channel[ ], int32 *data). This will return one of the following types:
DAQmx_Val_AI
10100
Analog input channel.
DAQmx_Val_AO
10102
Analog output channel.
DAQmx_Val_DI
10151
Digital input channel.
DAQmx_Val_DO
10153
Digital output channel.
DAQmx_Val_CI
10131
Counter input channel.
DAQmx_Val_CO
10132
Counter output channel.
Let me know if this works.
Regards,
L. Allen

How to display multiple tables from database using netbeans swing gui

plz reply asap on how to display multiple tables from database using netbeans swing gui into the same project

Layered Pane with JTables or you can easily to it with a little scripting and HTML.
plzzzzzzzzzzzzzzzzz, do not use SMS speak when posting.

Connector block 16 analog input channel for 6036E

sugesst me connector block of 16 analog input channels compatible with 6036E daq card

Thanks for contacting National Instruments.
You really have two choices in connector blocks: the SCB-68 and the CB-68LP. The CB-68LP is inexpensive, but unshielded. If you are concerned about introducing noise into your signal, or if you are talking small measurements (mV range), then the shielded option, the SCB-68, will be better for you.
Regards,
Mike G.
National Instruments Support

How to create multiple physical channels using DAQmx?

Hi, I am new to Labview.
Can anyone please help me on how to create multiple physical channels? I am following the LabVIEW examples in the NI example finder but they are only for acquiring signals from one channel.
Actually, I am using the channels of an SCXI 1520 to measure voltage signals. And one more thing, in the NI Example Finder, they are sample codes there for setting the filter in SCXI 114x.
Will this example work with an SCXI 1520, too?
Thanks!

There are many ways to read multiple channels in LabVIEW. First, if you look at that example that lets you set the filter setting on the 114x and you click on the 'Physical Channel Listbox' then click 'Browse' you can see that you can select multiple channels. After you select the channels and hit 'Ok' it will build a multiple channel string. This is one way to read multiple channels.
Next, you can create a 'Task' in Measurement and Automation Explorer(MAX). When you create this task select all the channels that you need to read then back in LabVIEW simply select a 'DAQmx Task Name Constant' Select the task you just created and wire that to an Input of your first DAQ VI. If you do this you do not need to have a 'DAQmx Create Physical Channel' VI or create
Task because it is already created in MAX.
When looking at example VIs you can tell if a multi-channel read is acceptable by looking at the 'DAQmx Read' and if it says NChan that means it will do a multichannel read. There are tons of example programs that will display the multichannel read capabilities.
This example may not work for the 1520 because the properties that are set could possibly be specific to the 142x. When using the 1520 though it is very likely that the properties will be very similar if not exact. You will simply put a DAQmx Channel property node on your block diagram and then look for the Lowpass filter settings properties that will most likely be in the same location. Now another way todo this without using a property node would be in MAX when you create a task set the filter settings from the Device tab in the task configure window.
Let me know if you need anymore help with reguards to this issue! Have a great day!
Allan S.
National Instrument
s
Applications Engineering

DAQmx: Numerical indicators go blank intermittently using DAQmx Read

Hello everyone,
I was wondering if anyone else has ever fought this issue and won. I have a loop (I will attempt to attach an image of the block diagram) which performs a DAQmx Read operation. The loop employs a 200 millisecond wait. The loop scales the data, sends all of the values to little indicators in an array, picks out a few critical values to display on duplicate large indicators, and optionally logs the data by streaming it to disk. The task will usually (99.9% of the time) be run at 100Hz. So, I was figuring I could do a "Read All", since at 200 ms of wait time due to the millisecond multiple wait function, I should always have around 20 points to read in the buffer the next time around. This would allow me to have very current readings in my displays. I could do a partial read, but then I figure I would have a lag between the displayed values and the reality of what's going on in the test. Having current readings, as current as can be, is highly desirable for this application.
I figured everything was good with what I was doing, especially when I tested it with a simulated device (I know a simulated device behaves much differently than a real device, especially at start up). Everything seemed to work well. When I go to the real hardware, though, I intermittently get blank indicators. Actually, it is more like intermittent numbers in my indicators. Most of the time, the DAQmx Read operation returns a null, empty array (no data available in the buffer). I must be missing something, because I figured that a 200 ms wait would allow another 20 samples to be collected.
If someone could please just ease my conscience and let me know that I haven't done something very fundamentally wrong in this code, even if you couldn't help me with a solution, I would very much appreciate it. I feel that this code should work, keeping data in the indicators at all times, and don't know why it doesn't work. If you could offer me the solution, even if it is to point out that I did something very wrong, I would much appreciate it.
I am just writing this code, and still have some icons to make, so the sub VI's still have the default icons. Sorry about that. Basically all those do is get array subsets, or scale data, or write data to the data files. If you need to ask questions about the code, I can understand. I am not the greatest yet at writing self documenting code yet. And if you need to know what that event structure does, it watches the two boolean button controls to determine what state in the state machine to go to next, and the time out case of the event structure highlights a data value if it goes out of bounds.
Sorry if I am too wordy. I have been accused of that before. I just notice a lot of "Help! DAQ doesn't work. How do I fix?" posts, and I don't see how I or anyone else could help that person at all.
I am using LV8.2, with DAQmx 8.3.1, on Windows XP, 1GB of RAM, and a fairly healthy Duo core processor. I have a workaround where I throttle back the read operation, only reading 55% of the available samples, as reported by a DAQmx Read property node (the highest percentage I found that prevents the indicators from going blank). This introduces a small lag between the real world and the data on display, however. Also, it seems like a processor dependent solution. I would have to tweak this percentage for every machine I run this on.
If I have left anything important out, please let me know, and I will do my best to clarify, and thank to anyone who reads this, and a big thank you to anyone who takes the time to reply. Again, I would be real happy with a "That code looks good to me, and your thinking is correct", if that indeed is the case.
Thanks.
Attachments:
Log Monitor Block.JPG ‏292 KB

Yeah, as you and Erik said, just specifying (Sample Rate / 5) as the '# to read' could do the trick. Then you can ditch the 'Wait (msec multiple)' function. I don't think I'd recommend the -1 = infinite timeout though. I'm pretty leery of stuff that can lead to an infinite wait or an infinite loop. Even a 1 sec timeout should easily be way more than enough. Note however that this method depends on all your processing code executing in under 200 msec on average. Otherwise, your reads will fall behind and you'll eventually get a DAQ buffer overflow error. My earlier suggestion to first query for # available samples and then read the MAX of (# available, SampleRate/5) will prevent cumulative fall-behind effects.
There's too many unknowns to speculate with any confidence on exactly why the software timing method didn't work. I can point out some additional things that bear greater scrutiny though.
1. You've got some sort of function dealing with file streaming that takes a path input and produces a path output. This probably means that every loop iteration you're using the path to open a file, write data, and close the file again. This actually may consume more than 200 msec, at least some of the time. Because this runs in parallel with the msec wait function, something like the following could be happening:
A. Iteration 1 proceeds as expected. The DAQ read collects 20 samples, the file write consumes only 100 msec, and the wait msec function ends after 160 msec in order to end on a 200 msec multiple. The wait function took longest, so your whole loop ends on a 200 msec multiple.
B. On iteration 2, the wait msec function ends after 200 msec on the next 200 msec multiple. The DAQ read collects another 20 samples (because it's been pretty much exactly 200 msec since the previous loop iteration started) right away. However, Windows was busy messing with the file cache so this time your file write consumes 375 msec. The file function took longest so your whole loop ends 175 msec into the next 200 msec multiple.
C. On iteration 3, the wait msec function ends after 25 msec on the next 200 msec multiple. The DAQ read collects 37 samples that have come in since the prior call 375 msec ago. The file function consumes only 50 msec this time, ending the loop 25 msec into the next 200 msec multiple.
D. On iteration 4, the wait msec function ends after 175 msec at the next 200 msec multiple. The DAQ read collects the 5 samples that have come in since the prior call 50 msec ago. Uh oh, not enough samples...
One possible fix is to open the file outside the loop and leave it open until after the loop is done. Opening and closing files has quite a lot of overhead. Inside the loop, you'd be passing around the file refnum. Doing this one thing alone might also be a way to fix your timing problem. Along similar lines, you could write the data to a queue and then do your file writes in an independent loop that reads the data out of the queue. You can search here for "producer consumer" for more info.
-Kevin P.

How to configure physical channel using DAQmx block(remote PXI6733)

I am trying to run the example in labview that use DAQmx. But I find I can't find the physical channel by browser or using DAQ assisstant. It reports "No supported device found". My PXI6733 is on a controller and communicate with host computer by TCP/IP. Could I use DAQmx in such environment? What I should do to find the physical channel?

Braver,
The NI 6733 is not yet support by NI-DAQmx. Thus, you will need to use Traditional NI-DAQ to program this device until this support is added. I would suggest that you examine the following Traditional NI-DAQ examples:
Examples >> Hardware Input and Output >> Traditional DAQ >> Analog Output
Good luck with your application.
Spencer S.

How to trigger from analog input channel

I am using a BNC-2110 into a 6062E card. And I am sure this question has been posted several times but I was unable to find a clear answer. I am trying to use the devices ai0 channel as my trigger source. I tried using a voltage source in the trigger reference, and that almost works but it only works for several loops before coming up with an error. If someone knows what I may be possiblely doing wrong or where to find this information, any assistance would be great.
- there is always an easy way, but it is always the hardest to find

Hey Henry,
The BNC-2110 is just the connector block. What card do you have the is interfacing this block with your computer? (should be a PCI or PCI-express card). Are the GPS receivers outputting digital signals that conform to TTL compatible logic levels (are the signals 5V or 0V with no more than 1.6mA of current)? If they are outputting a digital signal, then you can send these signals into any of the PFI lines to act as a trigger (or to the trigger lines).
For example, if you would like to perform an analog acquisition each time the trigger hits and have an X series card, you can open up example finder (help»find examples...) and then open Hardware Input and Output»DAQmx»Analog Measurements»Voltage»Cont Acq&Graph Voltage-Int Clk-Retriggerable.vi. Then make sure your Trigger Source parameter is set to the same PFI line that you are sending your GPS signal to (on the BNC-2110, the trigger connections are really just PFI0 and PFI12, but these are common lines to use for triggers, but any PFI line will work). If you have an M series card, and cannot do retriggerable analog input, you can reference this example for how to use counters to workaround this limitation of our M series cards: https://decibel.ni.com/content/docs/DOC-6801
If your GPS signal isn't digital, and is some arbitrary analog square wave, you can use an example like this: https://decibel.ni.com/content/docs/DOC-4657 to use the analog value to trigger you're reading (you just need to set the appropriate window for your analog signal in the VI). I hope this helps!
-Nathan H
Software Developer
National Instruments

How do I get a list of configured channel using DAQmx

I would like to know how to read the channels in a task list or the global channels that are setup in MAX. I use to be able to do it in DAQ using the read channel VI. I can't find any equivalent in DAQmx. My new system works only with DAQmx. My program allows the operator to select from the channels configured in MAX.

Hi Benegin,
This can be found under the DAQmx System property node. I have attatched a picture to help you find it.
-Sal
Attachments:
system_property_node.JPG ‏359 KB

How to use a Time - Voltage Array to Control a Analog Voltage Output using DAQmx Write VI

I have an array of Time values associate with Voltage values that I want to use to control a Anolog Votage Out Device (PXI-6251) using DAQmx. The array contains 1,000 elements. The time values are NOT evenly spaced, the rate changes through the array. The array is output once, timed to other processes.
My problem is I haven't been able to locate a reference on how to handle the timing variability in the array. If time was equally spaced I could use a loop....
The attached showes the array, first row is time (ms) and the second row is voltage (volts).
Can someone point me in the right direction?
David
Attachments:
TimeVoltage.png ‏11 KB

David,
if you have only Base version of LabVIEW, this will be a time consuming task.
If you have either Full or Professional, you will find interpolation-functions in the mathematic palette.
I am not sure which ones serves you best, but i'd startexperimenting with Interpolate 2D.
hope this helps,
Norbert
[Edit]: You could also use a polynominal fit on your voltage values. You will get a function describing the voltage over time. But you will have to modify this function to take care of the variation of time spacing. If you have a function describing your voltage over your (nonconstant) timestamps, you can simply create values for constant timeslices for your voltage.
Message Edited by Norbert B on 11-06-2008 10:21 AM
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Read spreadsheet file for Analog Out Profile using DAQmx

I am trying to read a .txt file in, then output the Analog out profile (Daqmx) vs. time. The first column is time is (ms) in .001 sec increments. The second column is the Analog out voltage I want to output. I want to read the profile in, and ouput the a Analog out voltage incrementing in .001 sec intervals (or whatever the time increments are in the .txt file). The problem I am having is, it reads in the whole file and outputs it in a fraction of a sec, instead of incrementing by the time. I attached a screen shot of what I have. Any help would be great. Thanks
Attachments:
screen shot read.jpg ‏75 KB

You are reading the timing but not doing anything with it. You've specified Analog Wfm 1Chan NSamp for the DAQmx Write but you did not create the waveform data type. Use the Build Waveform function on the Waveform palette and wire in your array to the Y (waveform component) input and the time interval to the dt input.
Message Edited by Dennis Knutson on 04-06-2006 08:56 AM
Attachments:
Build Waveform.JPG ‏6 KB

Displaying multiple analog input channels using DAQmx READ commands.

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