Appendix A LabVIEW Data Acquisition Common Questions. NI LabVIEW Data Acquisition Basics

LabVIEW Data Acquisition

Common Questions

Appendix

A

Where is the best place to get up to speed quickly with data acquisition and LabVIEW?

Read the LabVIEW Data Acquisition Basics Manual and look at the run_me.llb

examples (in examples->daq ) included with the package.

What is the easiest way to address my AMUX-64T board with my MIO board?

Set the number of AMUX boards used in the configuration utility

( wdaqconf.exe

on Windows or NI-DAQ control panel on

Macintosh). Then in the channel string inputs specify the onboard channel. For example, with one AMUX-64T board, the channel string “ 0:1 ” will acquire data from AMUX channels 0 through 7, and so on.

What are the advantages/disadvantages of reading AI Read's backlog rather than a fixed amount of data?

Reading the backlog is guaranteed not to cause a synchronous wait for the data to arrive. However, it adds more delay until the data is processed (because the data was really available on the last call) and it can require constant reallocation or size adjustments of the data acquisition read buffer in LabVIEW.

How can I tell when a continuous data acquisition operation does not have enough buffer capacity?

The scan backlog rises with time, either steadily or in jumps, or takes a long time to drop to normal after an interrupting activity like mouse movement. If you can open another VI during the operation without receiving an overrun error you should have adequate buffer capacity.

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National Instruments Corporation A-1 LabVIEW Data Acquisition Basics Manual

Appendix A LabVIEW Data Acquisition Common Questions

I want to group two or more ports using my DIO32F, DIO24, or DIO-96 board, but I do not want to use handshaking. I just want to read one group of ports just once. How can I set it up in software?

Use Easy I/O VIs (Write to Digital Port or Read from Digital Port) or

Advanced Digital VIs (DIO Port Config, DIO Port Write or DIO Port

Read), and set multiple ports in the port list. For Easy I/O VIs, you can specify up to four ports in the port list. Whatever data you try to output to each port of your “group” will correspond to each element of the data array. This also applies for input.

I want to use the OUT1, OUT 2, OUT3 and IN1, IN2, IN3 pins on my DIO-32F board. How do I address those pins using the

Easy I/O Digital VIs in LabVIEW?

These output and inputs pins are addressed together as port 4. OUT1 and IN1 are referred to as bit 0, OUT2 and IN2 are referred to as bit 1, and OUT3 and IN3 are referred to as bit 2. Only the NB-DIO-32F has

3 pins for each direction. If you use the Write To Digital Port VI, you will output on the OUT pins, and if you use the Read From Digital Port

VI, you will input from the IN pins.

I want to use a TTL digital trigger pulse to start data acquisition on my DAQ device. I noticed there are two types of triggers: Digital Trigger A, and Digital Trigger A&B. Which digital trigger setting should I use and where should I connect the signal?

You should use Digital Trigger A, which stands for “first trigger," to start a data acquisition. Digital Trigger B, which stands for “second trigger," should only be used if you are doing both a start AND a stop trigger for your data acquisition. Connect your trigger signal to either

STARTTRIG* (pin 38) if you are using an AT-MIO-16,

AT-MIO-16D, NB-MIO-16X, or EXTTRIG* or DTRIG for any other board that has that pin. The only analog input boards on which you cannot do a digital trigger are the PC-LPM-16, DAQCard-700, and the

DAQCard-500. Refer to the AI Trigger Config description in

Chapter 6, Advanced Analog Input VIs , in the LabVIEW Data

Acquisition VI Reference Manual for more information on the use of digital triggers on your DAQ device.

LabVIEW Data Acquisition Basics Manual A-2  National Instruments Corporation

Appendix A LabVIEW Data Acquisition Common Questions

Note: The NB-MIO-16 has an EXTTRIG* pin, but cannot support start and stop triggering.

When are the data acquisition boards initialized?

All data acquisition boards are initialized automatically when the first

DAQ VI is loaded in on a diagram when you start LabVIEW. You can also initialize a particular board by calling the Device Reset VI.

(Windows) I open a VI that calls a DAQ VI, or drop a DAQ subVI on a block diagram, and crash.

The first time a DAQ VI is loaded into memory in LabVIEW,

LabVIEW opens the library ( dll ) that controls data acquisition. A crash at this time indicates a problem in communicating with the driver. This may indicate that there is a conflict with another device in the machine.

To determine the source of the problem, quit LabVIEW and Windows, re-launch Windows, and run wdaqconf.exe

. Run a simple configuration test with the NI boards in the machine. If this results in a crash, there is probably a conflict with another device in the machine or the driver’s file versions do not correspond for some reason. If not, you need to obtain the latest version of the DAQ driver from NI BBS,

World Wide Web, or FTP site.

We have also seen cases where the video driver conflicts with both

WDAQCONF and LabVIEW. You can obtain the Error Messages and

Crashes Common Questions document from the NI FaxBack system.

(Windows) I am having problems accessing ports 2 or higher on the AT-MIO-16D or PC-DIO-96.

A problem was found in version 3.0 with addressing the highernumbered ports on these boards. To fix the problem, get the updated version of atwdaq.dll

, and use the updated DIO Port Read.vi

.

These updated files are included with LabVIEW for Windows version

3.0.1. LabVIEW for Windows version 3.0 users can obtain these files by downloading the file win30up2.zip

from the NI BBS or FTP sites. The file is in the directory support/labview/windows/

LVWin3.0/updates .

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National Instruments Corporation A-3 LabVIEW Data Acquisition Basics Manual

Appendix A LabVIEW Data Acquisition Common Questions

(Windows) While performing analog input, I get memory allocation errors (-10444) even though I have a large amount of memory on my machine.

Buffers for data acquisition arrays, unlike arrays for LabVIEW buffers, must be available in physical RAM, not in virtual memory. For example, assume the machine has 32 MB of RAM, and LabVIEW is allocated 8 MB of RAM. The memory allocated to LabVIEW wires will come out of the 8 MB; however, data acquisition buffers will be allocated out of the remaining 24 MB of RAM.

On an AT style machine (ISA) using DMA, the DMA controller can only address the first 16 MB of RAM. If you get "out of memory" errors on your machine, try setting the board to use programmed I/O

(interrupts only) with the Set Device Information.vi

(in

DAQ->Calibration and Config ). An alternative is to switch to an EISA bus machine. The DMA controller can address up to 4 GB of

RAM on EISA machines.

(Windows 3.1) I am having problems running Windows for

Workgroups with my data acquisition program.

Remark out nivisrd.386

in the [386 Enhanced] section of your system.ini

file. To mark out the line, place a number sign ( # ) at the beginning of the line which reads: device = c:\windows\system\nivisrd.386

nivisrd.386

normally improves performance by reducing interrupt latencies in Windows enhanced mode.

(Windows 3.1) I bought LabVIEW for Windows and also have a slightly older DAQ device from National Instruments. I installed the entire LabVIEW package, but should I go ahead and install my NI-DAQ for Windows drivers that I originally got with the board?

In most cases, the answer is no. The LabVIEW installer installs a set of DAQ driver files that are guaranteed to work with LabVIEW, whereas if you happen to install an older version of the drivers, you may run into many problems. You may even end up crashing your computer every time you do any data acquisition. If you buy a new

DAQ device and if you already have LabVIEW installed, it is safe to

LabVIEW Data Acquisition Basics Manual A-4  National Instruments Corporation

Appendix A LabVIEW Data Acquisition Common Questions install the NI-DAQ for Windows drivers from those disks. In any case, make sure you install and use the latest version of the NI-DAQ drivers.

(Macintosh) My analog input VIs returns error -10845 (buffer overflow). What is the problem?

If you do not have an NB-DMA-2800 or NB-DMA8G board in your

Macintosh and are trying to acquire at sampling rates (not scan rates) greater than 8 kHz, you may get this error. Even at sampling rates under 8 kHz, depending on the type of machine, you may run into overflow error problems if there is a lot of other interrupts that need to be serviced. This is all due to the long interrupt latencies. If you do have either DMA board in your Macintosh, make sure that you have a

RTSI cable connecting your DAQ device and the DMA board. Even after you connect a RTSI cable, restarting LabVIEW may help.

Also, if you have a Quadra, your errors may be caused by prolonged network interrupt latencies, which prevents the NI-DAQ driver from copying the data in the DAQ device resident memory to the memory on your computer. In this case, you can either disable AppleTalk in the

Chooser and disconnect your AppleTalk cable or contact National

Instruments and ask for the newest revision of the NB-MIO-16X

(which has a larger device resident memory) if you are using either of those DAQ devices.

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National Instruments Corporation A-5 LabVIEW Data Acquisition Basics Manual