TB-2605, PXI-2503, how to read different Data-type?

[aerosimon]

I connected my TB-2605 to my PXI-2503. Thanks to the Labview example "Switch-Scanning with a DMM-Handshaking", I can read my 4wire resistance and my generator output voltage individually.

However, I can't figure out how to program the reading of 2 different types of data. That is, I would like to be able to read my resistance and my voltage on the same front panel, even if it is in two different graphs.

In concrete terms, the only difference in the two programs that allow you to read either the resistance or the voltage is the type of measurement. So I tried to link in many different ways the readings, the scans, the initializations... But nothing works, there is always something that doesn't work. Maybe I'm on the wrong track since the beginning?
Thank you in advance for your help.

[rolfk]

If you want to acquire data from multiple channels from the same DAQ device, they MUST be in the same DAQ task (unless you do VERY slow single measurement readings, where you read one channel value then the other and so on, but that is both slow and very inaccurate in timing, since the sample time will be whenever your program happens to execute that according read node).

But DAQmx allows you to apply different channel characteristics and scaling to different channels in the same task. It's a little bit more complicated than just running an example but it can be done. The basic principle is to setup a DAQ task with all the channels you want to read and then in a loop execute on this task the according configure channel functionality for each channel type. As long as the characteristic of the channels is not conflicting with the ability of the hardware (for instance if it would only support either current or voltage measurement for all channels and you want to mix and match it anyways) this does work.

[aerosimon]

My problem is that as I am connected, my TB-2605 output connects to the DMM from the outside. So I don't know how to use DAQmx when I am on the DMM. I have already tried but it is impossible to create a task. I don't know how to do it.

When I have an object created on Data Neighbourhood, select NI-DAQmx Task, Acquire Signals, Analogue Input, Voltage, I get this:

[rolfk · Accepted solution]

Aah well, your PXI-2503 device is simply a multiplexer. Sorry! You will have to do considerably more work then. Basically your DMM can NOT be synchronized with the multiplexer to apply different channel configurations depending on which channel it currently addresses. That is simply not possible. You need the two to be able to communicate with each other somehow and that only works if both are specifically designed to do so, and that is only usually an option if both devices are from the same manufacturer AND are specifically designed to do so.

Unless you can live with software scanning where you configure the DMM, then apply the multiplexer channel, take a measurement and rinse and repeat, doing everything in software, you are out of luck with this hardware setup. Do not expect sampling frequencies of more than a few Hz with this however.

[aerosimon]

Ok thank's for all your answer,

So I have no way of having both my measures on the same panel?

What equipment can I use to do this?

[rolfk]

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@aerosimon wrote:

Ok thank's for all your answer,

So I have no way of having both my measures on the same panel?

We can't know! You haven't told us anything about the actual requirements. What speed do you want to do this with? How many channels, what specific characteristics for each channel?

What equipment can I use to do this?

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If your measurements are very slow, you can use this setup but need to do all the programming manually. Otherwise a DAQ card would for instance work. Or a data acquisition unit such as the Keysight 34970A could work.

[aerosimon]

We should have an acquisition every 5 seconds minimum, we have 4 connections to make: 2 for pressure, one for humidity and a pt100 for temperature.
A DAQ card or a data unit should be connected to what level of my acquisition module? Neither a PXI-8232 or 8430 could replace this?

[rolfk · Accepted solution]

Well with 5 second scan interval it certainly should be possible to do this in software.

While (acquisitionActive)

    Configure DMM to pressure settings

    Switch Multiplexer to first Pressure channel

    Read Measurement

    Switch Multiplexer to second Pressure channel

    Read Measurement

    Configure DMM to humidity settings

    Switch Multiplexer to humidity channel

    Read Measurement

    Configure DMM to PT100 settings

    Switch Multiplexer to PT100 channel

    Read Measurement

    Display and optionally store somewhere all 4 values

    Wait until 5 seconds have elapsed relative to start of this sequence

Repeat

[aerosimon]

Do you mean that I will have to stop reading the first measure to access the second? Because that's what I think I have to do, since my playback is a loop and you only get out of the loop when you stop the bar.
If I'm not mistaken, this means that I can't have my two measures at the same time?

[rolfk]

You do not do automatic scanning anymore!

Each "Read Measurement" step is a single command to your DMM that triggers an explicit measurement (with averaginging, filtering and what else as configured before) and then returns the result.

Each "Switch to .... channel" is one or more commands through NI-SWITCH to route the according signal to your DMM.

Basically you program the entire scanning sequence completely yourself.