NI Elvis Read Current and Voltage Simultaneously

Greetings,
I'm trying to read voltage and current on an NI Elvis II to characterize the output of a TENS unit (currently using SignalExpress).
What I have worked out:
Thanks to advice on another question I asked earlier today, I've now got the timing worked out so that I can produce log data at 10kHz when measuring voltage through the CH1 Scope input.
I'm now moving on to the other have, and am trying to add current in as another task. It makes sense to me to try and read that through the DMM current input. However, I'm getting errors that will only allow me to read the value once, instead of at the 10kHz rate I measure the voltage at (and would prefer that they are read in sync).
This seems like it should be pretty straightforward to do, but I'm just not seeing it. It's really important (in a non-academic and non-job way) that I get this done tonight, and I really appreciate all the support this board has offered. If there's anything I need to provide to make the issue clearer, please do not hesitate to post.!
Would it be easier to run this through LV proper instead of SignalExpress?

The DMM that is onboard the NI ELVIS II is not specced to run at the rates you're requesting. In fact, the DMM is a software timed device, which means that it will only collect samples when your computer tells it to. I created a quick benchmarking code to see how many measurements that an ELVIS II could take per second and I came up with about 4 or 5. You can recreate the code yourself to see similar results.
After one second, the elapsed time Express VI will output a 'true' which will stop the while loop. The DMM will be constantly acquiring and writing data into an array. When the while loop has finished, an array of DMM data will be output. The size of this array will indicate the number of samples that can be read in one second.
Nathan M.
Applications Engineer
National Instruments

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As we said in the other thread, you need to talk to whoever is designing the microcontroller and decide on a specific format for it send you the data. Once we have that, then we can start talking about how to program this up.
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Message Edited by h_baker on 07-09-2009 04:54 PM
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Hello to all,
I'm developing a system of power analysis based on "Electrical Power Measurement Toolkit".
I think to use a system based a cRIO-9075 and a NI 9215 (simultaneous sampling).
I think to use this current and voltage trasformers:
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Have a nice day!

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Attachments:
block.jpg ‏140 KB
project.vi ‏76 KB

thanks for the tip Tim,
I wired up the stop button to the VISA close block, and now I'm able to run and stop it multiple times without freezing.
1) I know how to add shift registers, but why do I need one? It doesn't seem like I need to pass values from one iteration of the while loop to another...
regards,
imran
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project.vi ‏43 KB

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Since I don't know your exact configuration I will make some basic assumptions based on how it appears that you have configured the DAQ Assistant Express VIs.
Assumptions:
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[email protected] wrote:
Hi i want to read parameters with visa read, from three sensors related to pic16f877a, using module xbee ..but i want to make every one from those parameters (temperature, voltage and current) in a table ..it's the first time i use Labview so i don't know if ther is a solution for my problem so if any one have any idea please help me. thnx in advance.
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Hello lvuser,
In you code you are also measuring the voltage and current back into your program. You can make programmatic decisions based on these measurements, for example, stopping the program based off of a voltage that floats too high. Our devices make sure to try to maintain the voltages and currents you tell them by completing a closed loop system with measurements taken on the same inputs that are sourcing. Try taking the readings you get in your program and using some threshold to trigger a case statement that holds a function to close the resource and turn off the generation.
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Hi there,
As strange as this may sound, this is not a bug. OK, this sounds really funny, but I am totally serious, and I am going to explain why:
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An inductor is a purely reactive component, that is, it does not dissipate any power.
When simulation starts, Multisim assumes the inductor current to be 0, which may seem reasonable. The voltage across the inductor is also 0 at this point. This is the initial condition.
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E3631AERR.spy ‏7 KB

Hi neilchuang,
A read timeout error is usually caused by an error on the command string sent.
The first thing I would check is if the instrument requires a termination character at the end of each message (such as linefeed). I noticed in the Spy capture that the commands do not have a termination character attached. This means that the instruments never recognized that you completed the query command, it doesn't execute the requested action and as a consequence of that it doesn't have any data to return.
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DiegoF
National InstrumentsMessage Edited by Molly K on 02-18-2005 11:05 PM

NI Elvis Read Current and Voltage Simultaneously

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