Data Acquisition Idea Exchange

Howdy!

I am trying to use a data acquisition system using python. There are thermocouple  modules and voltage modules that I would like to read from. It is set up and ran in 2013 LabVIEW and I am trying to put the test system into python for easy changing of the test and user control. 

I am wondering if the NI-DAQmx python library is kept up-to-date and if this is possible. I have been doing a lot of nitty gritty reading through the documentation on this library because there are not many examples of data collection using python to talk to the NI sensors. After trial and error attempts I have gone back to the basics to try and see if I can even change settings in the configuration of thermocouple channels. All I am trying to do is to take measurements from the thermocouple and I am changing the units from Fahrenheit to Celsius in separate runs. I can't even get this to work, even looking at example of this from Stackoverflow and the documentation where it specifically says how to configure the thermocouple channel (https://nidaqmx-python.readthedocs.io/en/latest/ai_channel.html and Ctrl-F to find thermocouples). 

Here is a snippet of the code I'm writing:

try:
    with ni.Task() as task:
        
        #Add the thermocouple channels to read from NI-9214's
        task.ai_channels.add_ai_thrmcpl_chan("cDAQ1Mod1/ai0:11", name_to_assign_to_channel='',
                                             min_val=0.0, max_val=100.0, units=ni.constants.TemperatureUnits.DEG_F, 
                                             thermocouple_type=ni.constants.ThermocoupleType.T)
        task.ai_channels.add_ai_thrmcpl_chan("cDAQ1Mod2/ai0:7", name_to_assign_to_channel='',
                                             min_val=0.0, max_val=100.0, units=ni.constants.TemperatureUnits.DEG_F,
                                             thermocouple_type=ni.constants.ThermocoupleType.T)
        
        #Set the thermocouple type to T
        #task.ai_thrmcpl_type = ThermocoupleType.T
        
        #Add the voltage channels to read from NI 9209
        task.ai_channels.add_ai_voltage_chan("cDAQ1Mod3/ai0:7")
        task.ai_channels.add_ai_voltage_chan("cDAQ1Mod3/ai9:12")
        task.ai_channels.add_ai_voltage_chan("cDAQ1Mod3/ai19:27")
        task.ai_channels.add_ai_voltage_chan("cDAQ1Mod3/ai29:31")
        
        #Set the rate of the Sample Clock and samples to aquire
        task.timing.cfg_samp_clk_timing(rate=Hz, sample_mode=AcquisitionType.CONTINUOUS)
        
        #Set the ADC Timing Mode to speed up the collection
        #task.ai_channels.ai_adc_timing_mode =  ADCTimingMode.HIGH_SPEED 
        task.ai_channels.ai_adc_timing_mode = ADCTimingMode.AUTOMATIC

This is a little frustrating to filter through the problems because there is not much out there that has the python use for help. If you search in the documentation search, the links of the results that you can click on are broken so that is another pitfall to this method.

Any help is greatly appreciated but I am curious if NI will keep the python library updated and running for future use.

NI-DAQmx python documentation: https://nidaqmx-python.readthedocs.io/en/latest/index.html 

Stackoverflow example help: https://stackoverflow.com/questions/47479913/python-nidaqmx-to-read-k-thermocouple-value

Thermocouple example: https://www.youtube.com/watch?v=NMMRbPvkzFs

This Topic is base on other topic in PXI Forum (Link).

The main problem is the Range passing the Min/Max limitation.

I would like to simulate a channels in "Nominal" Case.

1. The range should be based on the Min/Max limitation.

2. I could select input style (Sin Wave, Triple Wave, Random in sub range, DC with error range, based on external data,...)

3. Near to Real timing simulation include cases of sync between different channel rates.

Currently,

1. The range is limited to the Min/Max Values. Excluded the cases show below.

2. Only Sin Wave. Excluded an Odd Case show below.

3. I tried case of sync between 2 channel with different rates. the simulation is not close to the real DAQ case. 

Here are the cases from the PXI Forum (Link😞

1st problematic case

1. Define a Simulated Device - PXIe-4353 in MAX.

2. Open "Test Panel"

3. Use the default parameters of the test:

  a. Measurement type - thermocouple

  b. Max Input Limit - 100

  c. Min Input Limit - 0

  d. Units - Deg C

  e. Thermocouple type - J

  f. CJC Source - Built In

4. Click Start.

The result is Sin Wave.

The sample values range ~[-1030,-74.7], out of the Max/Min Limits.

=> BAD sample results, values lower than -273 C ?!?!?!?!

2nd Problematic Case

If I change the Max/Min Limits to other valid range like [-200,1200]

The sample values range is BAD

And, the result is some kind of Non-Sin Wave

3rd Non-temperature Case

If I change the Measurement type to Voltage.

The sample values range is based on the Max/Min Limits.

=> So it is OK

Tnx,

Raz

Today, we can create a DAQmx custom scale in MAX or Labview via the "DAQmx Create Scale" VI. This VI changes a pre-scaled value, e.g. 5Volts, to a scaled value in a physical unit, e.g. 100Newtons. This scale can be Linear, Map Ranges, Polynomial or Table.

For all of these four options, only a mono-channel sensor can be used.

However, multi-channel sensors are not so rare and there is actually no way to scale a 6-components load-cell, for instance. For this kind of transducer, F = M*U where F is a 6-components vector including the 3 forces in Newtons and the 3 moments in Newtons*meters, U is a 6-components pre-scaled vector including the 6 input channels in Volts and M is a 6*6 matrix. M is never diagonal, because the forces affect the moments.

Finally, what I'd like to have is an extension of the "DAQmx Create Scale" VI which could enable a multi-channel pre-scaled input to be scaled in physical units through a matrix.

Thanks.

Hi,

     i need to create a vi with 16 bit channel output to show a waveform graph and my point is i need to display a list and the user should select which channel they want to display in a graph.

For example, if the user wants to see a graph for the channel 1 & channel 2, whatever it is, up to 16 channel, is anybody got a idea? that what i was telling actually.