Problem in getting the flow meter output in g/sec

[Rawoof]

Hello santosh,

You mean like this?

[StevenD]

These devices are usually only calibrated for a few select gas/liquids and they have to be told what the gas or fluid is to report correctly. They have a LabVIEW driver for serial communication. Doing an analog read will only give you values for whatever gas/fluid the device is selected to report. 

https://www.bronkhorst.com/en-us/products-en/accessories-and-software/flowware/labview/ 

[santo_13]

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@Rawoof wrote:

Hello santosh,

You mean like this?

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yes, that works if the full-scale signal of the sensor is 1 g/s and outputs a 0-10V analog signal

[rolfk]

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@StevenD wrote:

These devices are usually only calibrated for a few select gas/liquids and they have to be told what the gas or fluid is to report correctly. They have a LabVIEW driver for serial communication. Doing an analog read will only give you values for whatever gas/fluid the device is selected to report. 

https://www.bronkhorst.com/en-us/products-en/accessories-and-software/flowware/labview/ 

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Definitely need to watch out here. It does depend on the type of mass flow meter but if it is a thermal mass flow meter, then the calibration will be specific to a certain medium, be it gas or liquid, since the thermodynamic properties of the medium that is measured can change significantly depending on the gas or fluid.

If it is a flow meter that uses the Coriolis or ultrasonic measurement method, the measured mass flow is independent of the thermodynamic properties of the measured medium and you don't need to recalibrated the meter for the new medium.

Bronkhorst offers calibration services for specific gas sorts when you purchase a flow meter and you can have it recalibrated for specific gasses later on. You can also use conversion factors if you want to measure a different gas than what the meter is configured for, most Bronkhorst controllers allow to configure a built in gas selection which will actually correct this already inside the meter in software. However you need to watch out as the specified range of a meter only is valid for the specified gas. With a different gas the actual possible range can be quite different to the specified range according to the conversion factors.

[Rawoof]

Hello Santosh and Gerd,

Many thanks for the response now got a clear idea and went a little further to add two more sensors but I have another problem in getting the output in equal intervals.

I have a problem getting the output of my two thermocouples(T1 and T2) and the flow meter(m.dot) outputs at equal intervals as shown below.

I have used the sample clock to set the sample rate at 20 Hz and samples per channel along with the sample mode.

I'm getting the outputs at random intervals but not at every 50 milliseconds, as shown in the output data.

I want the outputs at every 50 milliseconds as 0.050,0.100,0.150 etc.

Here I'm attaching the code along with the supporting figures. 

Thanks in advance

 Rawoof

[Rawoof]

@Rolf K

Thanks for the info, as I'm measuring the mass flow rate of the oxygen. how exactly do I use these conversion factors? can you please elaborate.

Note: calibration certificate is enclosed.

[GerdW]

Hi Rawoof,

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@Rawoof wrote:

but I have another problem in getting the output in equal intervals.

I have a problem getting the output of my two thermocouples(T1 and T2) and the flow meter(m.dot) outputs at equal intervals as shown below.

I have used the sample clock to set the sample rate at 20 Hz and samples per channel along with the sample mode.

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You still didn't say which DAQ hardware you are using!

Usually I recommend not to put channels from different IO modules into the same task: are you using a cDAQ chassis with several modules? (If yes: which ones?)

You also measure the time in parallel to your DAQmxRead function: this might not be as accurate as expected…

[rolfk]

Well you can see that your device is actually calibrated for N2 or Air, which both have the same conversion factor of 1.0. O2 has a conversion factor of 0.98 so is almost equivalent and unless 2% accuracy is a problem for you, you would not necessarily have to do a numeric correction of  the measurement values.

The Bronkhorst devices usually have a register in which you can select from a number of gasses for the one you want to measure, which applies the conversion factor from that table. Or you can apply that conversion factor yourself after reading the value. And if you want to be really completely accurate you can send in your device and have it calibrated for the gas that you want to measure. That is of course not a free service.

[Rawoof]

Hello GredW,

I use the following

chassis-NI-SCXI-1000 

Modules-NI SCXI-1125, NI SCXI-1102B

Terminal blocks-NI SCXI-1320, NI SCXI-1303.

So it is better to put two parallel channels?

Also is there any other better way to give the sample rate instead of using a DAQmx timing(sample clock)?

Thanks,

Rawoof

[Rawoof]

Hello RolfK,

Thanks, got it, probably I may need to recalibrate it for the oxygen.