pressure sensor interface

[romesh]

Hi,

I am trying to building an application to test pressure leak on my instrument. I am using (30) MPXH6400A pressure sensors interfaced to NI USB-6218 DAQ card. I looked at the signal level compatability for the outputs from pressure sensor and input to DAQ and everything looks ok. I am a newbie in using Labview and I am trying to build a .exe for manufacturing to test my instrument on the line for any pressure leak. I figured there will be some starting point which I could use to build my application. The way that I envisioned the program would work: Interface each output from the sensor to a seperate A2D channel in DAQ and have a threshold in the software. If it passes the threshold light an LED with green showing the instrument has passed pressure leak test or if not light the led "RED". I would really appreciate if I could get some pointers to where I could start.

Thanks

[Dennis_Knutson]

There is the DAQmx Getting Started and the LabVIEW tutorials. LabVIEW also comes with a lot of examples. You'll want to look at those related to DAQmx analog input. When you install the driver for the DAQ card, you will have a utility program called Measurement & Automation Explorer (MAX) on your desktop. There will be test panels in MAX that you can use to check the connections and readings

You will be acquiring all measurements at the same time with a single DAQmx  Read or DAQ Assistant. An array of values can be wired to one of the comparision functions (i.e. Greater Than) and a scalar can be wired to the other input. You will get an array of Booleans as an output.

[ronke]

I have completed pressure test project recently, attached is the user interface.

ronke@163.com

[romesh]

Thankyou so much and I really appreciate it.

[romesh]

Hi,

Is it possible to get the vi file as I have to do some modifications. I have to monitor 30 channels and my sensor is MPX6400A.

Thanks

[romesh]

I looked at few examples on the forum and in Labview and I couldn't find any that samples multiple analog input channel. I would like to interface 30 pressure sensors in RSI mode using USB6218 analog input channels. I was thinking of setting the DAQ assistant to sample each channel in a round robin fashion (approx 10ms/channel) and convert the voltage output into pressure using a transfer function provided by sensor datasheet. After converting the voltage to pressure I have to compare it to a threshold pressure and if the captured input is below the threshold (with some leeway +-2psi) may be indicate the leakage using LED light, a very simple UI.Finally log the result into an excel sheet in a following format

channel No | Voltage | Pressure. How to implement the round robin fashion of sampling multiple channel using DAQmx?. I assume that inorder to implement the scaling (Transfer function) to convert the voltage to pressure I need to use the arithmetic function blocks in Labview instead custom scaling. I would really appreciate some reference to get me started.

Thanks

[Dennis_Knutson]

As I said, you will be acquiring all channels at the same time. Any number of exampes will do this if you just select the channels. If consecutive channels, the syntax with a DAQmx Create Channel function would be Dev1/ai0:29.

The DAQ Assistant is also pretty clear on how you can acquire multiple channels.When you create a DAQ Assistant, the information on selecting channels is right there. If you already have a DAQ Assistant, click on 'Add'.

Neither do I understand why you think you cannot use a DAQmx custom scale. Have you studied the information on DAQmx  that I gave the link to?

[Alain_S]

Help\Find Examples...\Hardware Input and Output\DAQmx\Analog Measurements\Voltage : will lead you to lots of examples 🙂

Pick this one: "Cont Acq&Graph Voltage-Int Clk.vi" as a start

On your computer, you should find it here C:\Program Files\National Instruments\LabVIEW 8.5\examples\DAQmx\Analog In\Measure Voltage.llb\Cont Acq&Graph Voltage-Int Clk.vi

Like Dennis said enter "Dev1/ai0:29" for 30 consecutive channels on a Device named "Dev1".

If you named your USB DAQ something else, use this instead of "Dev1" of course.

Process the "Data" output from the "DAQmxRead" vi as requested to turn your 30 led's red or green.

Attachment SNAG-002.jpg is just a very rough idea on what you could do.

Average 1 second data and compare it with some threshold levels.

Message Edited by Alain S on 01-03-2010 03:13 PM