Covert analog input signal (NI 9203) to meaningful units

I'm very new to LabVIEW and I wanted to do something that I thought was fairly simple. Using the NI 9203 analog input module I wanted to measure pressure using a sensor that has an output of 4-20 mA. Altough I get some signal at the end on my screen, it's not realy the pressure. How can I convert this to a meaningful signal? I also took a look at the exeple VI's in the module specific file, but I don't have a clue how to use them.
Hopefully someone can help me out.
Jurgen

Hi Jurgen,
You have two possibilities. But you must first know the relation between the current created by your sensor and the pressure mesured by your sensor. Normally you should receive this kind of things with your sensor.
First one, you configure the scale in MAX (Measurement and Automation eXplorer) and you can associate this scale to a task. In this case, the value you will receive in LabVIEW will be automaticly converted into the right (scaled) units. If you are not familiar with MAX and creating scales, you can take a look at this article. or the attached file or yet the MAX NI-DAQmx Help (Start >> All Programs >> National Instruments >> NI-DAQ >> NI-DAQmx Help).
Second one, you create a subVI (VI into another VI) in LabVIEW that will make the conversion in LabVIEW itself. By this way, this is simply a VI that makes the correlation between the current and the pressure.
I Hope this will help you.
Regards,
Julien Roland - District Sales Manager
NI Belgium - Technical Support
Don't forget to rate a good answer

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Average_0411041_2.vi ‏77 KB

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Hi Marcus,
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On Thu, 25 Mar 2004 09:30:26 -0600 (CST), Marcus G wrote:
>Hello Johannes,
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Hi everyone,
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I would appreciate if you could provide me with the good tutorial which explains
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Best Regards,
Khassan
Solved!
Go to Solution.

This is my code in C++, you can optimize it if it looks too messy. This code reads signal from analog input and outputs it through analog output.
To make this code work additional include directories and library directories must be added from NI.
I hope it helps someone.
#include <stdio.h>
#include <conio.h>
#include "NIDAQmx.h"
#include <math.h>
#define DAQmxErrChk(functionCall) { if( DAQmxFailed(error=(functionCall)) ) { goto Error; } }
int main(int argc, char *argv[])
int32 error=0;
TaskHandle taskHandleRead=0,taskHandleWrite=0;
int32 read=0;
float64 dataRead[1000];
char errBuffRead[2048]={'\0'};
char errBuffWrite[2048]={'\0'};
bool32 done=0;
int32 written;
DAQmxErrChk (DAQmxCreateTask("",&taskHandleRead));
DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandleRead,"Dev1/ai0","",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandleRead,"",100.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,0));
DAQmxErrChk (DAQmxCreateTask("",&taskHandleWrite));
DAQmxErrChk (DAQmxCreateAOVoltageChan(taskHandleWrite,"Dev1/ao0","",-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandleWrite,"ai/SampleClock",100.0,DAQmx_Val_Rising,DAQmx_Val_ContSamps,1000));
DAQmxErrChk (DAQmxStartTask(taskHandleRead));
DAQmxErrChk (DAQmxStartTask(taskHandleWrite));
while( !done && !_kbhit() )
DAQmxErrChk (DAQmxReadAnalogF64(taskHandleRead,1,10,DAQmx_Val_GroupByScanNumber,dataRead,1000,&read,NULL));
DAQmxErrChk (DAQmxWriteAnalogF64(taskHandleWrite,read,0,10.0,DAQmx_Val_GroupByChannel,dataRead,&written,NULL));
_getch();
Error:
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DAQmxGetExtendedErrorInfo(errBuffRead,2048);
DAQmxGetExtendedErrorInfo(errBuffWrite,2048);
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Dear All,
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Message Edited by Jochen on 10-02-2007 08:37 AM
Attachments:
gearing.jpg ‏162 KB

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Covert analog input signal (NI 9203) to meaningful units

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