Data Acquisition Idea Exchange

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When I drop a DAQmx Task constant on my LabVIEW block diagram, I have the right-click menu option to Generate Code >>Configuration

This scripts out a sub.vi that creates the Task by adding each channel with channel specific properties sequentially, one channel at a time, to repeated calls of DAQmx Configure Channel.vi.

I have a hard time saving that vi output! I have not really learned how to name it properly without Using: "BLEEP_BLEEP_BLEEP_Configuration_that_cannot_be BLEEPING_scaled.vi"

I believe that an autoindexing loop would be much nicer.

My grandmother thanks you for improving my manner of speach.

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As far as I'm aware there is no current way to export the quadrature conversion clock from an encoder task. It would be great to be able to export that signal to use for other things.

For example, you could use this signal to perform an analog acquisition each time your encoder passed a mark, giving you position vs. signal. This would be useful for something like a roughness tester where you drag a stylus across a sample and get roughness vs. position. Or a pressure sensor reading pressure versus crankshaft angle.

Why is there no way to determine Trigger Status in NI-Scope?

No, "Acquisition Status" is NOT the same thing. As Acquisition Status only tells you if acquisition is complete. I suppose you could say if it's not complete then it is still waiting for trigger, but you could be wrong. Specially in the case of a slow acquisition (seconds/div).

Any modern DSO I have used had a VI to determine Trigger Status and would return several states.

Such as:

Stopped

Ready, Armed, or Waiting (pre-trigger acquisition complete, ready and waiting for trigger)

Pre-trigger (pre-trigger acquisition in process)

Triggered (post trigger acquisition in progress)

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Note: this might only be relevant & useful for multiplexing AI devices.

It was an important technique used to investigate channel-to-channel ghosting influence on a multiplexing device. For example, suppose you had a large signal A and a small signal B. You could set up a channel list to read "A,B,B,B,B", and thereby *investigate* the trend of these successive readings of the same channel and use *evidence* to determine when the ghosting influence had dissipated. THIS WAS IMPORTANT!

I recall hearing of others use the capability to be able to get faster sampling for one of their fast-changing channels, using a channel list along the lines of "A,B, C,B, D,B, E,B".

The feature that used to be supported on multiplexing MIO devices as far back as I could remember working with NI DAQ products. I only recently discovered that such support was inexplicably removed from DAQmx sometime in the last few years, now producing a fatal task error. I tested a few available systems and found that it was still supported under DAQmx 16.0, not supported by DAQmx 18.1, and not yet restored as of DAQmx 20.1. (All verifications were done with desktop or PXI X-series devices.)

Why was this ability taken away? Stop being so overzealous trying to protect us from ourselves! Multiple readings of the same channel is a legitimate and sometimes almost necessary technique. Maybe you lacked the imagination to understand why we'd want this, but guess what? We knew what we were doing. So stop stopping us.

-Kevin P

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Attempting to add a channel (Ch8) to an existing task which already uses that channel as a result of having already assigned its paired differential channel (Ch0) results in that channel correctly not being added to the task but also does not generate a warning or error. Thus when attempting to configure a task with 2 channels as Ch0 differential and Ch8 RSE, the resulting task only contains 1 channel. This may be not be apparent because the channels 0 and 8 appear as different from each other. Having a warning could give notification of this fact.

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019KxoSAE&l=en-US

The use of NI DAQmx Global Virtual Channels is the best way that I have found to configure and manage parameter scaling to provide measurement data directly in engineering units. The software architecture of our data acquisition applications is centered around the use of Global Channels (aka Virtual Channels). Configuring Global Channels using NI MAX (Measurement & Automation Explorer) is convenient for a small number of measurement channels. However, in system configurations with hundreds of channels, to create and manage them effectively, you need to build your own application for this task. We have built custom Global Channel creation VIs in LabVIEW for each type of analog input or sensor type that we use. These VIs are designed to read a configuration table in CSV format, and then loop through creating a Global Channel for each table row of information. This process allows for more flexibility in naming the channels as well as setting different scaling and storage of other channel-specific metadata.

We employ multiple networked data acquisition systems with Linux-based NI controllers, and we manage those DAQmx Global Channels across our network. Currently, to create DAQmx Global Channels on these systems, we must directly connect to the NI controller in the LabVIEW Project View and run our suite of Global Channel creation apps on that particular controller using their accompanying, locally-stored CSV configuration file. Currently, our networked distributed data acquisition system has grown to 10 controllers, each with their own set of common I/O. The creation of those Global Channels has now become cumbersome because we have five I/O types to manage and hence five custom LabVIEW applications each with a specific configuration file to run on 10 controllers individually.

A potential simplification to the process would be to run our custom LabVIEW applications on a Windows host PC and create the DAQmx Global Channels remotely. That would eliminate the need to directly connect to each controller from the LabVIEW Project View and copy a common set of config files to each controller and run the same applications on individually on each controller. However, the current version of DAQmx makes no provision for remotely creating DAQmx Global Channels. Note that NI-MAX is able to create DAQmx Global Channels remotely, but this functionality is not exposed for LabVIEW programmers to utilize. My idea/suggestion is that NI make this functionality available in LabVIEW.

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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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Data Acquisition Idea Exchange

Change DAQmx Generate Code >> Configuration output vi

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1U Rack Mount cDAQ

Allow export of "Quadrature conversion" signal

NI-Scope needs a way to determine trigger status

When data is transferred from CRIO to PC by network stream, LabVIEW prompts to disconnect from CRIO terminal?

Restore ability to include multiple instances of same AI channel in a task

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DAQmx adding RSE Ch (0) to existing Diff paired Ch (8) should give Warning

FlexLogger Automatic Shunt Resistor Value

Programmatic Remote Creation of DAQmx Global Virtual Channels To Facilitate Distributed Networked Data Acquisition

C series CAN interface module without external power supply

Analog/Digital Outputs using NI DAQ

FlexLogger: Let me cancel / revert channel modifications

Use a NI cDAQ 913x chassis with integrated controller (WES7 OS) like a normal cDAQ Ethernet chassis

Shared Variable - Validate Scale

Develop a PCIe network card able to provide TSN sync