pressure measurement

[beechmont]

I can not find 400 Ohm resistor in the store. Can I use 300 Ohm 1/2 W resisitor? check the link http://www.radioshack.com/product/index.jsp?productId=12554233

Thanks!

[GerdW · Accepted solution]

Hi beechmont,

as long as you keep Ohm's law in mind you can use any resistor you like...

I would suggest to use a resistor with

- atleast 1/4W capability (P=I^2*R, so you could use upto 500Ohm resistors to measure 20mA)

- high accuracy (1% or less)

- maybe you should sort out resistors with bad temp coefficients.

Btw. I think the Radioshack website is a very bad designed online-shop. Nearly to no filters for the kind of tool you look for. I cannot even filter for certain resistor value ranges. Gosh... Don't you have any reasonable electronics distributors in the US?

[beechmont]

THANKS A LOT!  

I also wonder how to calibrate the transducer. I asked the support of transducer before. They just told me to zero it following the maual. What I want to know how to display pressure reading in labview, not current reading.

[GerdW]

Hi beechmont,

so now you ask for some basic math? Like the math tought in school - for me it was in 5th or 6th year?

Look up for things like "linear scaling", "offset and gain": it's a simple formula as "y = mx+b"...

Or to put it in more clear words:

What kind of calculations are needed to convert a value from 4-20mA to 0-x Pa, when 4mA = 0Pa and 20mA = xPa? Come on...

[beechmont]

I connect the pressure measure system to the computer and try to configure it. When I open the signalexpress and add a step/DAQ/pressure (bridge). I was told the device is not supported. What is wrong with the wiring or my operation?

[NIquist]

We don't know since you didn't post an actual error message or a diagram of your connections. You can press Alt-PrtScn to capture an image of the error pop-up or just copy the message.  At least post the error number.

Can you see your 9205 in NI MAX (Measurement and Automation Explorer)???

[beechmont]

I can see 9205 in Measurement and Automation Explorer but it is not identified as a pressure measure device. I guess only module, like NI 9237, can be identified. Maybe I have to choose add step\DAQ\acquire signal\voltage. Then I add a step to process the voltage signal with formula.

[GerdW]

Hi beechmont,

NI9205 is a generic AnalogInput module, so yes: you have to create a DAQmx task to read the signal and a DAQmx scaling to convert voltage to Pa...