To measure the pressure using a pressure transducer which provides analog current output 4mA-20mA

[Amala]

I wanted to acquire the current analog signal which ranges from 4-20mA using NI 9207. I have tried in 2 ways.

1st method--- Created an analog current input channel & used a read Vi to acquire it.How should I give the channel connections in this..

2nd method-- By means of NI-DAQ Assistant,I set the channel connections and I got Amplitude versus time graph. Also it was giving negative values .Can I do this way which is much simpler?how can I resolve the issue

First attachment belongs to 1st method

Second attachment belongs to 2nd method

[Pete.Dunc]

Hi Amala,

Thanks for joining the forums! 

It sounds like you are on the right track, you can use either of the methods you mentioned to acquire from the NI-9207.

If you are getting negative readings I imagine you have your physical connections the 'wrong' way round.  The pin assignments are included in the NI-9207 Operating Instructions and Specification.  You can also view the expected connections for a specific channel from the DAQ Assistant dialog box.  Are you having any other issues?  Are your sampling rates set up as you require?

[Pete.Dunc]

I notice in your code for the DAQ Assistant that you have specified to read 10 samples at 2 Hz.  This will take 10 seconds - if this is desirable then great, however you may look to increase your sample rate or reduce the number of samples to read to slow this down.

Additionally, in you lower level DAQmx program - you have specified to read a single sample.  What are your general requirements in terms of sampling?  What is the overall aim of your program.

It may be worth having a read of some of the articles contained in the Introduction to LabVIEW - to help with the bigger picture of the application.  One of the articles explains the Example Finder:  this is a great resource when you are getting started with your program and can be located in "Help > Find Examples..." - I'd have a look at "Hardware Input and Output > DAQmx > Current Measurement" if you would like some examples using the DAQmx API.

[Amala]

Thanks for your reply Peter. My purpose is to measure the pressure of hydrogen gas produced by my reaction at various time intervals( 5 sec interval or so).The results I obtained using my DAQ assistant is attached below. Mine is a 3 wire pressure transducer having +ve wire, -ve wire and an output.I connected the output cable to AI8 channel and +ve to Vsup and -ve to COM in NI 9207 as per the manual instructions.Gave an external power supply of 500mA and 9V to Vsup(+ve) & COM(-ve).

Please have a look at the graph and the table . It is showing -5.24 in the table.How can I interpret this in terms of current?

[Pete.Dunc]

One thing I notice is that this is in nA - so a reading of -5 nA is basically nothing.  Have you checked your connections?  Try getting in with a DMM and having a check.  Does your transducer definitey output a current?

[Amala]

How to properly connect a 3 wire pressure transducer to NI 9207. My pressure transducer ( omega PX41CO -1KGI) possess red, black and a white wire. Can you please provide me a wiring diagram.I have an external power supply which output 9V & 500 mA.I connected the +ve of the power supply to Vsup of NI 9207  and -ve of power supply to COM. How the pressure transducer need to be wired to NI 9207. .

[Pete.Dunc]

Could you link to the product page?  Or the datasheet?  I found another pressure transducer in the PX41 family that produces a voltage output, which could be the issue.

[Amala]

Below attached is the spec sheet of pressure transducer from omega. Right now I contacted omega. They told it is a 2 wire transducer not a 3 wire.I was confused as I could find 3 wires from it.red, black and silver wire.But it seems I should not consider the silver wire. So I think I should proceed with connection of 2 wire pressure transducer.Can you assist me regarding the connection of it to NI 9207 with power supply specifications. The chasis which I have is  NIcDAQ 9174.

[Pete.Dunc]

Here is an exert from the NI-9207 Operating Instructions and Specifications:

[Amala]

Power supply connection is fine. What about the positive (red) and negative (black) wire connection of pressure transducer.To which terminals I need to connect both in NI 9207.