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Data Acquisition Idea Exchange

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So I have a cRIO with a 9203 mA input module. I also have sensors etc that are 4-20mA. So when it came to using the scaling feature of the shared variable as below see if you can spot the bug.

So I was thinking in mA from sensor to mA input to the 9203 which is a mA module - but the RAW scale is in Amps! (Which is obvious once your colleague points it out!) Consequently I wasn't seeing any signal readings from the cRIO as 20mA << 4A.

Since there is an error if you get Full and Zero around the wrong way... can there also be an error or warning if its outside the range of the module?

Regards

Nick

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Hi All,

In my post on the LabVIEW board I asked if it was possible to have control over the DIO of a simualted DAQ device. Unfortunately it seems this feature is not available. Once MAX is closed the DIOs run through their own sequences.

If there was a non-blocking way to control a simulated DAQ device through MAX it would permit much simpler prototyping of systems before they need to be deployed to hardware. For example if you want to see how a program responds to a value change simply enter it in the non-blocking MAX UI. Or as in my original case can make an executable useable even if you don't have all the necessary hardware.

I think this feature should only be available for simulated devices.

Thanks for reading - and hopefully voting,

Dave

Multiple people have requested that there be a natural way for Labview and SignalExpress to do a rotational speed measurement using a quadrature encoder. An express VI under "Acquire Signals>>Counter Input>>Rotational Speed" that asks you basic quadrature encoder type questions and computes the rotational speed would be very useful. The information it asks would be things such as Ticks per Revolution, Decoding type (x1, x2, x4) would be useful in computing rotational speed. In addition, this can be then converted into a shipping example for DAQmx relatively easily. I have had multiple people ask this question and believe that especially within SignalExpress, this would be very useful.

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Currently when streaming analog or digital samples to DAQ board, output stays at the level of last sample received when buffer underflow occurs. This behavior can be observed on USB X Series Multifunction DAQ boards. I have USB-6363 model. The exact mode is hardware-timed, buffered, continuous, and non-regenerating. The buffer underflow error code is -200290 “The generation has stopped to prevent the regeneration of old samples. Your application was unable to write samples to the background buffer fast enough to prevent old samples from being regenerated.”

I would like to have an option to configure DAQ hardware to immediately set voltage on analog and digital outputs to a predefined state if the buffer underrun occurs. Also, I would like to have an option to immediately set one of PFI pins on buffer underrun.

I believe this could be accomplished by modifying X series firmware and providing configuration of this feature in the DAQmx API. If no more samples are available in the buffer the DAQ board should immediately write predefined digital states / analog levels to outputs and indicate buffer underrun state on PFI line. Then it should report error to PC.

Doing this in firmware has certain advantages:

It can be done quickly (possibly within the time of the next missing sample – at 2Ms/s that’s 0.5us).
Handles all situations (software lockups, excessive CPU loading by other processes, loss of communication do to bus traffic, interface disconnection…)
It does not require any additional hardware (to turn off outputs externally).
Buffer underrun indication on PFI line could provide additional safety measure (it could be used for example to immediately disable external power amplifier connected to DAQ AO).

Doing this using other methods is just too slow, does not handle all situations, or requires additional external circuitry.

Setting outputs from software, once error occurs, is slow (~25ms / time of 50000 samples at 2MS/s) and does not handle physical disconnection of the interface. Analog output does eventually go to 0 V on USB-6363 when USB cable is disconnected, but it takes about half a second.

Using watchdog timer would also be too slow. The timer can be set to quite a short time, but form the software, I would not be able to reset it faster than every 10ms. It also would require switching off analog channels externally with additional circuitry, because watchdog timer is not available for analog channels.

The only viable solution right now is to route task sample clock to PFI and detect when it stops toggling. It actually does stop after last sample is programmed. Once that occurs, outputs can be switched off externally. This requires a whole lot of external circuitry and major development time. If you need reaction time to be within time of one or two samples, pulse detector needs to be customized for every possible sampling rate you might what to use. To make this work right for analog output, it would take RISC microcontroller and analog electronic switches. If you wanted to use external trigger to start the waveform, microcontroller would have to turn on the analog switch, look for beginning of waveform sample clock, record initial clock interval as reference, and finally turn off the switch if no pulse is received within reference time.

I’m actually quite impressed how well USB-6363 handles streaming to outputs. This allows me to output waveforms with complexity that regular arbitrary generators with fixed memory and sequencing simply cannot handle. The buffer underflow even at the highest sampling rate is quite rare. However, to make my system robust and safe, I need fast, simple, and reliable method of quickly shutting down the outputs that only hardware/firmware solution can provide.

Thanks,

Sebastian

When it comes to documentation of an measurement, you need to report ALL settings of a device that effects that measurement.

From a core memory dump written as a hex string to a XML document.... anything that shows up a difference in the settings that affect the measurement would be fine for documentation.

Something like a big property node readout followed by a format into string .... but make sure not to miss a property.... and a bit more complicated when it comes to signal routing....

A measurement that isn't sufficiently documented is all for naught.

Just think of a nasty auditor 😉

It's so easy to make measurements with LabVIEW, please make it easy and consistent to document it.

Example:

A quick measurement setup with the DAQ-assistant/Express fills Gigabytes but after a certain time they are useless because nobody knows how they where taken. A simple checkbox could add all this information in the variant of the waveform. (or TDMS or ...) even if the operator don't have a clue of all the settings that affect his measurements.

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Basically, FlexLogger limits the range of readings to the values used in the 2 point calibration. For example, if your sensor has a range of -10 to 10 PSI, and the 2-point cal is done at +/- 10 PSI, FlexLogger will only display values within +/- 10 PSI (and will saturate otherwise).

I totally understand why this is done, but sensors in fact DO read above (and sometimes below) their stated ranges and have documented accuracy (i.e. 1% above 95% full scale) , so clipping the value to the scaling settings in the cal page is the wrong thing to do...the sensor can still be measuring correctly, but FlexLogger will only show the saturated value.

The scaling, however it is done, probably result in a Y=mX + b equation, and FlexLogger should display Y, whatever Y is, regardless of stated sensor range or 2-point cal/scaling.

A worse case is if the sensor has a range of +/- 10 PSI but your cal/verification system is only capable of +/- 5 PSI, you will be limited to +/- 5 PSI with the FlexLogger 2-point cal implementation.

Yes, there are way around this, but why should the user, usually technicians who don't necessarily understand the math or ins/outs of software, have to figure out a way around FlexLogger?

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I am using DAQmx Physical channel controls in user Interface to select the particular DAQ modules.I would like to display only the particular type (AI,DI,AO,DO.....) of modules which is connected in the system.For example i need to display only, DO-NI-9477 cDAQ modules in the physical channel not the other DIO models like NI 9403...IO name filtering option not useful to filter the other models which is same type.

That should be great if NI provides the option for filtering the modules name based on their product type or user configurable naming (for example, if cDAQ1 device renamed as "DEV1" means user can enter filter the device based on the string "DEV").

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It has come up a few times from customers, and I wanted to gauge interest and solicit ideas on how this should work.

Currently, with the built-in TDMS logging support, if you want to change to a new file in the middle of logging, you need to stop the task and start again. For some use cases, this isn't practical (for example, http://forums.ni.com/t5/LabVIEW/Why-the-TDMS-file-is-larger-than-it-should-be/m-p/1176139#M511099).

The question is: How would you like to specify the "new file" behavior and what are your use cases?

For instance, a couple ideas to get the ball rolling:

Add an interval attribute like "Change file after n samples". We would then auto-increment the file name and change to that file when we have logged "n" samples.
Make file path attribute changeable at runtime. We have a file path attribute for logging. The idea here would be to support changing the file path "on the fly" without stopping and starting the task. The problem here is that it would not suit very well a use case where you want a specific file size. Additionally, it wouldn't be as easy to use as #1; it would be more flexible though.
(Any additional ideas/use cases?)

Thank you for your input!

Andy McRorie

NI R&D

It has come up a few times from customers, and I wanted to gauge interest and solicit ideas on how this should work.

The question is: How would you like to specify the "new file" behavior and what are your use cases?

What I'm currently thinking (because it seems the most flexible to different criteria and situations) is to simply allow you to set the file path property while the task is running (on DAQmx Read property node). The only downside I can think of with this approach is that you wouldn't know exactly when we change to the new file. We could guarantee within (for example) 1 second, but you wouldn't be able to specify the exact size.

Would this be a good solution for you? Can you think of a better way to specify this behavior?

Measurement and Automation Explorer MAX's Test Panel's Analog Input provides a quick method to examine a signal and vary acquisition parameters. It would be useful to be able to zoom the time axis and have a cursor display so that for example noise level or rise time could be looked at in more detail. The time axis limits can currently be manually overwritten as a way to zoom but that is cumbersome. Assuming the graph being used in this test panel is built from a standard NI graph, it should have zoom and cursor capability already part of it and thus easily added.

Steve

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This is pretty trivial to achieve through LabVIEW itself, but...

Signal Express is a simple, stand alone data acquisition system that allows those with limited exposure to LabVIEW set up simple test and measurement routines. One area where this is ideal - at least, for me - is in environmental or long life testing. Instead of crafting a beautiful piece of custom software for my colleagues, I can hand them a DAQ, point them in the direction of the SignalExpress and DAQmx installers, and off they go. With a little fiddling, they can create a logger that suits their needs.

One thing I've noticed, however, is that when sampling with non-simultaneous cards such as the USB 6225, users will select 1-pt-on-demand, set to some big interval, and then come back screaming at the top of their lungs - "OHMYGOD THERE'S CROSSTALK BETWEEN CHANNELS!". With a little bit of fault-finding, it's easy to point out that it's not crosstalk, but ghosting between channels, because I would guess that 1-pt-on-demand uses interval sampling and rattles through the multiplexing as quickly as it can.

My idea: give users the option to either select round-robin mode with a sensible delay, or complete control over the interchannel delay.

I realise that the standard line is usually "use LabVIEW" - I do - but I'd rather spend my time working on the important stuff and empowering those with less experience and/or exposure to make accurate measurements.

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It seems the only indication in MAX that a device is simulated is that under the Devices and Interfaces section, the tiny glyph to the left of the device name is colored yellow instead of being white/transparent. I end up not remembering what color means what. It would be useful to add text "Simulated" next to the device name. It would also help to distinguish simulated devices by having the color of that glyph be green (instead of its current transparent/white) when the device is installed and detected. Have the color change to red (and keep the existing red X) if had been detected and a device number assigned but is currently not installed/detected. Then simulated devices being yellow may imply "warning/caution" or "not real". Perhaps also have a help-hint popup ("Detected" or "Not Detected" or "Simulated") when the mouse hovers over device names.

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I rarely have to set up hardware for a new analog measurement and always have to puzzle over the difference between RSE and NRSE modes. I think of the inverting input as the reference, so "Non-Referenced Single-Ended" doesn't make sense to me. And, if I run the AISense line to my remote sensor, isn't that a Referenced Single-Ended measurement?

Yesterday, I noticed that at least some on-line documentation now refers to GRSE (Ground Referenced Single-Ended); adding that single letter helps a lot. What about adding another single letter and referring to the other mode as RRSE (Remote Referenced Single-Ended)? One letter could save a lot of people a lot of time.

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We normally have a DAQ system consisting of several elements:

-Sensor

-Custom filtering/attenuation

-Signal conditioning

-NI-DAQ device

When we use scales in DAQmx we have to create a scale for every 'route' we use (sometimes we have to use a 4 kAmps sensor for a 100 amps signal).

If we could define a scale in a task consisting of multiple scales, we could directly pick the sensor and signal conditioning we use for each signal. A change in one of these elements could easily be adjusted.

Ton

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Data Acquisition Idea Exchange

Ability to switch a device from a real to a simulated one and vice versa

Shared Variable - Validate Scale

Post the NI-DAQmx base C Function Reference Help pages on your fora somewhere

Permit control over Simulated DAQ devices through MAX

DAQmx and Labview needs an Express VI and/or Shipping Example for doing a rotational speed measurement using a quadrature encoder.

Configurable DAQ Output Behavior on Stream Buffer Underrun

Documentation of all settings of a measuring device as a function of the driver

FlexLogger's 2-point calibration implementation is flawed

Build API for GPIB Analyzer to interact with LabVIEW

DAQmx Physical channel-I/O Name filtering based on module product type/device name

Ability to split between multiple TDMS files while logging

Add documentation about different channel properties

Zoom and Cursor capability in MAX Test Panel Analog Input

Allow Signal Express users to select between interval sampling and round robin sampling

Clearer indication in MAX that a device is simulated or not detected

Clarifying Single-Ended Measurement Modes

NI Digital Waveform Editor needs to allow cut and paste within signal name entry window

Ascii Sortable Naming Convention For PXI Cards

DAQmx: Allow stacking of multiple scales

Don't Show NI Device Manager Again Option