Type C thermocouple measurement and compesation with DAQmx

Need to make type C thermocouple measurment using DAQmx. Analog thermocouple channel configuration VI has spot for custom scales in the units box but nowhere to wire the scale. Want to use cold junction compensation so is the only option to use a voltage input then subtract the cold junction voltage and then run that value through a conversion formula?

That does not work. The program seems to already try and apply a scale since I get an error from start task that says the prescaled units are already Deg C, and the scale of course goes from volts to degrees. When I try to change the custom scale name after start task I get an error that says the units are invalid for this measurement type. So there seems to be some coding that won't allow you to replace the scale for a thermocouple measurement. I'll probably have to take voltage readings and apply the scale after I subtract the junction value which is unfortunate I have to do things that way.

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Control Simulation and Design with DAQmx

Hi all, thanks in advance for any helpful direction you can provide.
I was recently setup with Labview 2013 Developer Suite and the Control and Simulation Design add-on and was hoping to get a little nudge in the right direction.
I have used Labview and the NI DAQmx setup for regular external measurements before but never integrated with the Control and Simulation toolbox. I am trying to use the Control and Simulation Toolbox to model a simple system (to start) in conjunction with the DAQmx setup I have, and am somewhat at a loss.
For example, I want to use Labview Control and Simulation to simulate a simple integrator (1/s). The input for the integrator is an external analog voltage (from separate electronics) coming in through the DAQmx setup and the output of the integrator is also and external analog voltage going back to the external electronics. In essence, a very simple control loop.
I have been digging through tutorials and searching for examples, of which there have been many excellent ones. However, I have yet to find an example whereby the control and simulation loop is talking to the outside world through the DAQmx interface. I do not believe the RT module or RT target is necessary for timing as the fastest we are running the loop is around 10Hz. I have found some small examples discussing how the Control and Simulation Toolbox timing can be controlled by the RT target or even the DAQmx but I am still struggling on how to pass data in and out of the loop and how to set the timing parameters. How do you get it to simply run endless, for example.
Again, thanks for any information or direction you can provide.

Hey Cabala,
Based on your description this would be a great starting example.
https://decibel.ni.com/content/docs/DOC-11521
Depending on your hardware you may or may not be able to use hardware timed single point for acquisition but you could set it up for continuous as well and use the same structure of 1 read and 1 rate for each cycle of the loop.
You can replace proportional gain function with the CD and Sim Loop and place a Integrator function with in that.
Sorry it appears one of the dependencies for that example is missing so you can't run it off immediately.
Please let us know if you have any other questions.
Kyle Hartley
RIO Product Support Engineer
National Instruments

How to measure and fill with the same transparency?

for example creating a fill using Edit > Fill with a random Color and Opacity in the Fill dialog, then later without the original information about the Color and Opacity but just the file, how can I make exact same fill and opacity again?

White represents 100% opacity, so, yes, 100 minus the black (K) percentage of gray in the mask is the equivalent of opacity. The Info panel can tell you colour and opacity of the displayed composite of visible layers under the pointer/cursor at any time.

RPM and Angle with PIX 6221

I am working on student project where we are controlling position of dc motor shaft. On the rotor of the motor there is optical encoder which is connected to PIX counter. But for best results of control we must measure speed and angle in same time. In attachment is the vi which we used. In the vi angle measurement is solved with DAQmx, but speed measurement is obtained with taking difference of angle in certain time. This type of speed measurement is sensitive to speed of loop and suffers from overflow of registers. Precise speed measurement is needed because of controlling dynamics of dc motor.
So is it possible to measure speed/frequency and angle from same CTR in DAQmx?
Sorry if solution is obvious, but we are new to LV.
Attachments:
RPM_ANGLE_DC.vi ‏30 KB

Hi weky,
actually it is possible if you use an absolute encoder. Please read this both links and tell us if it is helpful.
This link is basic information to use Encoders
http://www.ni.com/white-paper/7109/en/
This one can be helpful for you. There explains how to use absolute encoders
http://www.ni.com/white-paper/14964/en/
Regards!

Thermocouple Measurements using an RTD for CJC

I am using an SCXI 1001 chassis with SCXI 1102 cards attached to TBX 1303 units and also SCXI 1121 cards attached to TBX 1328 units. I need to measure a number of K and T typre thermocouples in this system (using 1102 cards), and was hoping to use a PT100 RTD for my Cold Junction Compensation. Is it possible to achieve this by using the excitation current from an 1121 card and measuring the RTD value with the 1102 cards. It seems that when trying to select the CJC source in Max in the 1102 setup screen, there is no capacity for reading values from cards other than 1102 cards i.e I can't read the 1121 values.
What is the best way to achieve this using the setup I have?

James,
On the virtual channels of SCXI 1102 MAX configuration if you have not set-up any additional channels at this point then the CJC selection will only offer the internal Thermistor for it's CJC reference or a user value defined one. If you wish to use a PT100 you will need to set this up in MAX first using the Virtual Channels. Once you have that working go back to the SCXI 1102 and configure the CJC reference as User Defined, you should then be able to use the PT100 channel that you have just created.
Side note: The 1102 has been designed to thermocouple measurements and the internal CJC should be accurate enough for general measurements.
Kind regards
Joe
NI-UK

Can I measure pulswidths with daqmx base and NI-USB6501

Can I measure pulswidths with daqmx base 1.4 and NI-USB6501? I can measure edges width this function: DAQmxBaseCreateCICountEdgesChan. But, when using DAQmxBaseCreateCIPulseWidthChan I always get an error message back (DAQmxBase Error: <err>Value passed to the Task/Channels In control is invalid).
I also cannot find any examples about this topic in the software on CD nor on the internet.
I also don't know what values to use for the float64 minVal and float64 maxVal arguments when using the pulse width function of above (see the NI-DAQ™mx Base 1.x C Function Reference Help).
Maybe my device (NI USB6501) cannot measure pulse width's and when it does measure pulse width's, what value will it give back? Seconds or ticks and what is the accuracy?
Ok, enough questions for now. Thank you in avance for answering.
D. Stollman

The USB-6501 counter is capable of falling edge edge counting
measurements only, so the type of measurement you wish to do is not
possible with that device. The data sheet for the USB-6501 can be
found at the following link:
http://www.ni.com/pdf/products/us/20054920301101dlr.pdf
I believe the DAQPad-6015 and DAQPad-6016 USB devices are capable of
measuring pulse width, as well as many of NI's PCI data acquisition
devices.

SCXI 1001, SCXI-1102 and SCXI-1303 not working correctly with DAQmx

I have recently upgraded from Labview 6.5 to Labview 8.2 and now my SCXI 1001 with a SCXI 1102 and SCXI 1303 terminal block no longer reads the correct voltage. Using the old version of labview thermocouple measurements are correct at 0.5mV; however using the new version of labview and DAQmx the thermocouples are reading 5V. Everything is installed correctly as it still works with the older version of Labview, is there something that needs to be reset or change so that teh SCXI will function properly with DAQmx?

Hello ilabtech,
From my understanding you are using an SCXI 1001 chassis with an SCXI 1102 and 1303 terminal block to perform thermocouple measurements. You are upgrading to LabVIEW 8.2 and DAQmx. I am assuming you were using LabVIEW 6.1 since there isn’t a LabVIEW 6.5. You mentioned that are able to get a correct reading of 0.5 mV with LabVIEW 6.1 but you see a rail of 5V with LabVIEW 8.2 and DAQmx.
My first suggestion is that you ensure that the SCXI is set at the appropriate range and for the correct thermocouple type. You can also configure these settings in MAX as detailed on page 27 of the SCXI 1102 User Manual and Specifications Guide.
My second suggestion is for you to start off using an example program to see if you see the same error. When you are in a LabVIEW 8.2 VI you can go to Help>>Find Examples to open the NI Example Finder. You then choose Hardware Input and Output>>DAQmx>>Analog Measurements>>Temperature>> Cont. Acq Thermocouple Samples-Int CLK.vi.   This example program is supported by your hardware and is a good resource to use to troubleshoot.
If these suggestions aren't helpful please answer the following questions in your reply.
1.       I would like to know what range you have set the SCXI 1102 to read.
2.       What version of DAQmx are you using? You can find the version my opening Measurement and Automation explorer (MAX), expanding the “Software “and clicking on NI-DAQmx.
3.       What operating system are you using?
4. Does your Traditional DAQ program work in LabVIEW 8.2?
Regards,
Ima
Applications Engineer
National Instruments
LabVIEW Introduction Course - Six Hours
Getting Started with NI-DAQmx

Temperature measurement usb 6008 with Thermocouple

Hi,
I am trying to measure temperature with type k thermocouple on USB 6008. I set max for measuring voltage, and got 0 voltage with noise. It would be appreciated if you can help me to wire up properly.
Cheers,

Hi,
You are doing the right thing by acquiring your thermocouple data as a voltage. From there, you can convert it to temperature data after the acquisition.
There are two configurations that you can use to connect your thermocouple to the USB device: Differential and Reference Single Ended (RSE). If you use differential, then you would connect one wire to the + channel and the other wire to the - channel. For example, to use AI 0, you would make connections to AI0 (+) and AI4 (-). If you use RSE mode, then you would connect one wire to an analog input channel and the other wire to ground. So for AI0, you would connect the + to AI0 and the - to ground.
More information about these connections is available in the USB 6008/6009 User Guide. Also, here are two links about the different types of configurations you can use as well as thermocouple polarity:
Field Wiring and Noise Considerations for Analog Signals
How Can I Determine What Kind of Thermocouple I Have and the Correct Polarity of Signal Connections ...
Regards,
Hal L.

Sampling local variable and synchronize with DAQmx

Hello,
I made a small change in the set-up I used with labview and now when I wanted to change the code I'm having a rather complicated problem.
In my old set-up I was measuring three variables: x and y with a QPD and the power of a laser with a power detector. I was using the DAQmx and I was getting a matrix with three columns with n (sample rate) values. Now, for various reasons I had to take out the second detector. So now I want to build the same matrix as constructed before, but instead of putting the measured values of the laser power I want to put the theoretical values (they are in a local variable) as I cannot measure them. The problem is that this local variable, in general, changes during the DAQmx acquisition time and I would need to sample it at the same rate as I acquire the data from DAQ and then combine all them. How I could sample this variable and attach it to my DAQ results? DAQmx doesn't accept local variables.
Thanks

A local variable is not something standalone. It is always associated with a control or indicator. Hows is it updated?
From your description, it is not clear what you are doing. Can you show us some code instead?
(Also be more clear when using acronyms. QPD cound mean many things)
LabVIEW Champion . Do more with less code and in less time .

Error -200141 when doing buffered events with DAQmx and PCI-6602

When doing buffered events with DAQmx and PCI-6602 I get error 200141 - Data was overwritten before it could be read by the system.
This error is generated ONLY with random inputs >200/sec.
My setup is :
DAQmxCreateCIVCountEdges(taskhandle,"Dev1/ctr3"....
DAQmxCG+FGSampClkTiming(taskhandle,"/Dev1/FPI35",...
DAQmxSetCICountEgdesChan(taskhandlem,"", "/Dev1/80MHZTimeBase")
DAQmxSetChanAttribute(taskhandlw,",",DAQmx_CI_DataXferMech,DAQmx_Val_DMA,0);
Can somebody help ?

i'm getting the same Error-200141, while reading semiperiods. (Meas_Buffered semiperiod continous)
while loop ex.rate seems to be pulsewidth*no.Samples to read. in my case PW=60ms
Input buffer size measured with Property node= 10000
why this error happens?? i cant use any mode other than implicit timing for semi-period measurement right??
more info: all the ai channels are used ~ 16 differencial.
i found one solution which is _ reinitializing the whole task if an error occur. is this the right way??
Kudos always welcome for helpful posts
Attachments:
Counter_1_Meas Buffered Semi-Period-Continuous_main_lv09.vi ‏34 KB
SemiPeriod_Reconnect Counter on Error.vi ‏35 KB

Amplifying Type K Thermocouple for high temp reading with USB 6008

I am attempting to amplify a type K thermocouple so that the signal can be read somewhat accurately by a USB-6008. I have looked at the AD595 chip but it states a maximum useful temperature of 100 C and I am going to need to be reading up to 700 C.
Is there another amplifier chip that would work up to this temperature, or should I resign myself to using the signal unamplified and getting a very inaccurate (~30 C/division) reading for temperature?
Solved!
Go to Solution.

A heads up- some people have ran into issues using the chip with the USB-600x devices, various solutions. You may want to browse of these posts ahead of time:
http://forums.ni.com/ni/search?board_id=170&submitted=true&q=AD595
-AK2DM
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

Problems with Measurement and Automation Explorer (MAX)

Hello LabVIEWers,
I have been having a serious problem getting MAX to start and to remain stable. Here are the specifics:I am running LabVIEW 8.5 Full Development System on a Dell PC with 1GB of RAM and plenty of hard drive space. The OS is XP Pro and I also have McAfee Enterprise Virus Scan software. MAX will start-up and appear to run for a few minutes and then the software bombs out. I get a "Measurement and Automation Explorer has encountered a problem and has to close" pop-up message. To fix the problem, I have uninstalled all NI software using MSI Blast. I have wiped the registry clean of NI keys as per instructions in previous posts. I have deleted any remaining NI software on teh hard drive including C:\program files\national instruments and C:\Documents and Settings\All Users\Application Data\National Instruments. I have then restarted the machine and did a complete fresh install from CD's, DVD's, and the harddrive (CD's written to hardrive and DVD written to harddrive first). I installed first the LabVIEW and then I installed the Device Drivers. I restarted the machine between installs. I have even installed the updated NIDAQ 8.6. After which I set protections on the NI directories to read/write. Ok, basically I have done all these things numerous times and I still cannot get things to work correctly.
I was able to get into MAX for a little while (it is somewhat stable immediately after a fresh reinstall). I defined 4 Simulated DAQmx devices and none of them acted like they were simulated. I received various errors saying that the device was not found or could not be started. So I basically could not run my software with the simulated devices. LabVIEW sometimes seems to work ok but just now, I got a "Error loading nidmm_32.dll, initialization routine failed" error. I also get the same error for nilvaiu.dll. Both of these DLLs are in the C:\Program Files\IVI\Bin and c:\windows\system32 directories respectively and prior to the last time I started the software, all worked ok with LabVIEW.
Is my computer failing? Are there any other options to getting this installed without probems?
Please help.
Michael Froehlich

Duplicate Post
Keep discussion here
National Instruments
WSN/Wireless DAQ Product Support Engineer

Problem with DAQmx and Real Time PCI-7041/6040E.

Problem with DAQmx and Real Time PCI-7041/6040E.
I have a problem with the Real Time card PCI-7041/6040E, I think it is properly installed because my software run with the traditional NI-DAQ. When I try to use the new DAQmx to acquire one signal, Labview doesn't see any device for de DAQ card 6040E.
Information, I work on Windows XP and LabView v7.0.0 (NIDAQ RT v7.0.0, NI-Serial RT v2.5.2, NI-VISA v3.0.1 and NI-Watchdog v2.0.0).
Could Labview RT run with new DAQmx ?
What can I do to use DAQmx with PCI-7041/6040E?
Thanks for your help !

Hello,
I refer to your posts because i am using the PCI 7041/6040E card as
well but without any success to make it work. The problem I have
already described in the following thread:
http://forums.ni.com/ni/board/message?board.id=170&message.id=120198
Would be nice if you had a look on it, maybe you can help me. BTW, the
thread starts with a problem of someone else, the difficulties I
encountered are to be found a little bit to the bottom of the thread's
page.
Thank you!
Dirk Völlger
Darmstadt
Message Edited by ratschnowski on 07-28-2005 07:14 AM

How to measure and log frequency with fieldpoint CTR

Hi,
I am developing a data acquistion and control system for an engine dynamometer using the fieldpoint modules and Labview. One of the most important signals is the engine speed, measured in RPM. The RPM signal is a 0-12V pulse where one pulse equals one revolution of the engine. As well as being an important piece of data for later analysis, engine RPM will also be in the input into a PID controller, so the signal must be both accurate and have a high measurement frequency.
Currently I am using the FP-CTR500 modules to measure the frequency of the signal. I am already aware of the included frequency measurement VI example, as well as the one posted before for low frequency measurements, and I have gotten both to work with my setup. I would be using the low frequency VI becuase the max frequency measurement would be in the 200Hz range.
The first problem I am having is with the structure of the VI and how the data is output. The case structure in the VI activates when the counter is read and resets the counter, then switches to the next case. I would like the RPM number to output out of the case structure into a write_to_file VI and PID controller input. The problem is that when the case switches, the counter is reset to 0, which will be recorded in the written file.
This is some example output data (RPM):
1232
0
2321
0
2400
0
2521
0
The data is being written correctly, but of course I can't have 0 readings when the case structure changes. This would be especially problematic when input into a controller VI.
The next problem I am having is with sampling rate. If I were to use the low frequency measurement VI, the sampling rate of RPM would be variable based upon the the speed of the signal. Or, the original frequency measurement VI has an adjustable sampling rate. Of course, in my system there are a number of other signals that need to be recorded at the same time. I have found that as I am collecting data, the "write to file frequency" is entirely dependent on the read frequency of the frequency measurement. Therefore, if I had set the read frequency VI to read at 1 Hz, data will be recorded only every 2Hz. Ideally I would like an overall measurement frequency of all channels (mix of analog and digital) to read between 20-50Hz, but if I am limited by the frequency measurement.
Any ideas on how to solve this problem, either through Fieldpoint or Labview?
I can post my VI if this help.
Thanks,
Huang

Thanks for your reply.
I should probably describe my current setup before I go into anymore details with the problem. As for my specific setup, I am using an FP-1000 connected with an AIO600, AI110, CTR500, and TC120 all running through the RS232 line to a desktop running labview 8. The actual counter module is reading a tachometer signal output from a separate engine controller. THe output is a 0-12V ON 50% duty cycle signal. As for data logging, i am simply using a "write to measurement file" Express VI. I have a while structure which holds all of the express VIs which access the fieldpoint IO, and these are all routed to the "write to" VI.
As for the specifics of the data logging problem, as I said, when I set the count frequency of the "Fieldpoint Frequency Measurement" VI to 1Hz, (which means the VI calls the case structure at 2Hz), the "write to measurment file" VI is called at the same rate (2Hz). Which means that the overall logging rate of the VI is only 2Hz. Is there someway to decouple this?
I was able to solve the problem of calling the frequency variable from the case structure by using a local variable which is called outside the case structure.
And now I have been having a lot of problems with reading the actual frequency from my engine controller. THe actual signal will only range from 0 to around 200Hz. I noticed, by comparing the actual signal to what was being read in my labview program, that after around 80Hz the signal increases by around 1.5times more than the actual signal. ie. Actual signal = 100hz, Read Signal = 150Hz. After trying to figure out what was the problem, I decided to change the Noise Filter settings to 200Hz. It actually worked for all the frequency ranges up to around 150Hz but after that the filter attenuates the signal to the point where the actual signal is 160Hz, but is being read at 100Hz. My question is if there is a way to change the actual filter setting outside of the 2 given setpoints (200hz and 40khz) or if you have any other suggestions on how to fix this problem? I was thinking of creating a noise filter input in MAX so that i could play with the values in Labview, but am i only limited to those two filters?
Thanks again for your help,
Huang

School photo with 25 kids and I have been able to name 17 on them - but the remaining 8 faces I am unable to name. I go through the process (done it thousand of times) and type in the name and it sticks, I close the photo and reopen I

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Type C thermocouple measurement and compesation with DAQmx

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