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USB-6343 DAQ with 24 single ended samples

Hello all, I have been working this semester on a project that entails taking data from 24 different pressure transducers that take single ended measurements. It seems that I will only be able to take 16 readings given my pinout? I am somewhat confused, the website says it is capable of 32 single ended readings but when looking at the pinout I believe only 16 will be possible. Pinout locations 1&3 will be used for transducer #1, pinout locations 4&6 will be used for transducer #2. Am I correct in saying that this DAQ unit is only capable of 16 analog RSE channels? Is there another way for me to use 24 RSE channels on this DAQ unit? 

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@GNorsten wrote:

Hello all, I have been working this semester on a project that entails taking data from 24 different pressure transducers that take single ended measurements. It seems that I will only be able to take 16 readings given my pinout? I am somewhat confused, the website says it is capable of 32 single ended readings but when looking at the pinout I believe only 16 will be possible. Pinout locations 1&3 will be used for transducer #1, pinout locations 4&6 will be used for transducer #2. Am I correct in saying that this DAQ unit is only capable of 16 analog RSE channels? Is there another way for me to use 24 RSE channels on this DAQ unit? 


1&3 for transducer #1

2&3 for transducer #2 , ...

 

You need to use both + and - for each RSE measurement.

 

1&2 would be for a differential measurement.

 

mcduff

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This article may help:

 

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019QRZSA2&l=en-US

 

In my experience, in a lab setting with low powers, short wires, etc. I can get away with the "not recommended" configuration in that article. I would not do this with long wires in an industrial setting where ground potentials could change slightly throughout the system.

 

If your sensors are grounded (which it sounds like they are) tie the + ends to AI0+, 1+, 2+, etc and tie the - ends to AI SENSE, not AI GND. If your sensors are floating, still tie the + ends to AI 0+, 1+, etc and tie the - ends to AI GND, not AI SENSE.

 

The only times you use AI0+ and AI0- (thus halving the number of AI's you can use) is for differential measurements. You'd use that if the sensors terminals are both non-grounded and changing. For example, say you're measuring the difference between two signals; you could hook the + of one signal into AI 0+ and the + of the other signal into AI 0- and measure between them.

 

Alternatively, say you have 10 sensors to measure across a giant industrial system and cannot guarantee that the ground potentials are the same absolutely everywhere; you could use differential signals to get good measurements despite ground floats.

 

Of course, you can also just measure both signals and subtract in software, but sometimes there are good reasons to take differential measurements. It doesn't sound like your system is one of them.

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So I am correct in saying that this DAQ unit is only capable of 16 RSE channels then? 

Your description is how I currently have it wired (and collected results verified with a manometer as they are pressure transducers) 

Pinout location #1 = output voltage coming from transducer 

Pinout location #3 = reference ground from DC power supply

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@GNorsten wrote:

So I am correct in saying that this DAQ unit is only capable of 16 RSE channels then? 

Your description is how I currently have it wired (and collected results verified with a manometer as they are pressure transducers) 

Pinout location #1 = output voltage coming from transducer 

Pinout location #3 = reference ground from DC power supply


No. It has 32, they're just laid out a little differently than you might expect. Pin 2 is the 8th input. Ignore the stuff in parenthesis. You have AI0, AI1, AI2, ... all the way up to AI 31 over on pin 59. That's 32 total input channels. There aren't 32 AI GND inputs, but you can share those. They're all connected internally anyway.

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Thank you for the reply, I hope that I can clarify my intentions in the following sentences. I have 24 Omega brand differential pressure transducers but output single ended measurements, exhibiting a 3 wire configuration (+ and - to supply excitation voltage and and output terminal that I have wired to the DAQ unit). As stated on another reply, on the DAQ units' pinout location 1, I have wired a single transducers output and in pinout location 3 I have a reference ground from the power supply. According to the link you attached this is a floating RSE signal.

 

With this configuration, only 16 allotted signals will be supported, correct? 

 

 

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So both pin 1 and 2 can be read as separate channels using LabView? I am conflicted with this idea because pinout location 2 reads "AI8 (AI0-)", this leads me to believe that pinout locations 1, 2, and 3 correspond to a single channel... I apologize if these questions sound extremely immature, the LabView VI I am working on for this project is rather foreign to me as a mechanical engineering student.    

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@BertMcMahan wrote:

 

Of course, you can also just measure both signals and subtract in software, but sometimes there are good reasons to take differential measurements. It doesn't sound like your system is one of them.


Actually, the DAQmx API lets you take RSE and DIFF measurements from the same set of channels. See https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000001DdfrSAC&l=en-US

 

mcduff

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@GNorsten wrote:

So both pin 1 and 2 can be read as separate channels using LabView? I am conflicted with this idea because pinout location 2 reads "AI8 (AI0-)", this leads me to believe that pinout locations 1, 2, and 3 correspond to a single channel... I apologize if these questions sound extremely immature, the LabView VI I am working on for this project is rather foreign to me as a mechanical engineering student.    


Yes. In RSE mode, pins 1 and 2 are totally independent. Completely separate. There is no relation between them at all other than they're sitting next to each other. Electrically they are 100% independent. When you switch modes, you switch pin functions. Yes, it is confusing until you learn the "DAQ lingo" but you'll get there 🙂

 

"AI8 (AI0-)" means this pin is considered "AI8" if you're in RSE mode or "AI0-" if you're in differential mode. It's telling you the "alternate mode" of the pin.

 

For your application, ignore the parentheses.

 

In summary:

-If you say "RSE read AI8" it will tell you the voltage potential between pin 2 and pin 3 (aka, earth ground). AI3, 6, etc are all connected together and to the earth ground.

 

-If you say "NRSE read AI8" it will tell you the voltage potential between pin 3 and pin 13 (AI SENSE).

 

-If you say "Differential read AI8" it will give you an error, because valid differential inputs are AI 0-7 and 16-23.

 

-If you say "Differential read AI0" it will give you the voltage potential between pins 1 and 2.

 

The pins are laid out that way to help with wiring. In other words, if you have a bunch of differential signals, you wire the two ends of the signal to pins 1 and 2, which are right next to each other. If you have a bunch of single ended signals, you can just go down the list.

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