Scale NI cDAQ 9189 voltage to pressure

[himanshu25]

HI,

I have NIcDAQ chasis along with NI 9401 AI(0-10V). I want to scale these voltage signals to Pressure Signals(bar).

At 2 Volts the Pressure is zero bar and at 10Volts the pressure is 100 bar. After reading the signals I am scaling the signals in labview(calculating). Doing so I get a lot of spikes. Please help me in this.

I have attached a vi showing what I am doing. I am be wrong as I am new to labview. I tried DAQmx custom scaling but couldn't work it out.

Thanks in Advance.

[tvirag]

Hey himanshu,

The NI 9401 is a digital input module incapable of collecting analog data. You shall use one of the voltage input modules for this application: https://www.ni.com/en-us/shop/category/voltage.html

In case you are using a proper card I would recommend opening up an example VI from Help -> Example finder, I particularly recommend the "Voltage - Continous Input.vi" from the DAQmx library.

Once you can collect the data itself, and the example VI will do most of the job, you can create a scaling using the following equation:

return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;

 Of course you should implement it using some simple VIs and it is elegant to put this step into a subVI.

And thats it, done!

[tvirag]

Hey again,

I could not resist and made the scaling subVI, find the image attached:

Cheers!

[himanshu25]

I have one more query.

I am write the voltage Signals and the pressure Signals to a measurement file. And I want absoulte time and relative time in the same file. Please help

[tvirag]

If I were you I would use the TDMS file format to store the data. The collectd waveforms do have the starting time and the delta T embedded, thus the absolute time value can be calculated from there. Also you can make a simple channel for the relative time witch is basically a number starting from 0 and incrementing in every iteration with the periodic time.