Problem in getting the flow meter output in g/sec

[Rawoof]

Hello,

I want to measure the mass flow rate of oxygen.

I'm struggling to get the output of my flow meter (Bronhorst model F-112AC)  in g/sec.

Is my output in mA or volts? How to convert the output into the mass flow rate? Is there any control law? or formula? to implement.

I'm sharing the instrument data sheet along with the calibration details.

Also, I'm sharing the simple code I have written and output

Can someone guide me?

Thanks 

Rawoof

[santo_13]

What is the output type of your flow meter? 0-5V or 0-10V or 4-20mA?

The measurements you are seeing in your VI are in Volts evident from the Units control on your Front Panel.

Yes, you need to scale it as per your sensor datasheet.

Your calibration report states these,

0% = 0 g/s

25% = 0.2498 g/s

50% = 0.5001 g/s

75% = 0.7501 g/s

100% = 0.9996 g/s

Now, you have to convert these % FS into electrical units by knowing your output type, if your sensor output is 0-5V, then these translate to 0V, 1.25V, 2.5V, 3.75V and 5V respectively.

here are some articles on how to use scales in DAQmx

https://www.ni.com/en-us/support/documentation/supplemental/18/ni-daqmx-custom-scales-and-usage-expl...

https://www.ni.com/en-us/support/documentation/supplemental/18/ni-daqmx-custom-scales-and-usage-expl...

Since you have multiple calibrated points, you can go with the table method.

[GerdW]

Hi Rawoof,

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@Rawoof wrote:

Also, I'm sharing the simple code I have written and output

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No you don't share any code!

All you attached are some images: we cannot edit/run/debug images using LabVIEW!

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@Rawoof wrote:

I'm struggling to get the output of my flow meter (Bronhorst model F-112AC)  in g/sec.

Is my output in mA or volts?

---

That question should be answered by the exact type marking found on your device. As we don't have your device at hand you need to read that on your own!

Does that device offer both kind of signals (voltage and current)? Then you need to choose the correct pins/contacts/wires - after reading the fine manual you got from the manufacturer!

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@Rawoof wrote:

How to convert the output into the mass flow rate? Is there any control law? or formula? to implement.

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You can implement simple formulas, commonly named as "scaling": there is a input signal range and a desired range of readings. It all boils down to very simple math…

You can also apply scales directly to your virtual channels in DAQmx, then you will get already scaled readings from DAQmxRead!

On your code image:

• Why do you define a "finite samples" task when the loop will run until you press the stop button? Why not use "continuous" mode?
• Why don't you close the DAQmx task? You should cleanup up that task after the loop!

Hi santo:

0% = 0 g/s

25% = 0.2498 g/s

50% = 0.5001 g/s

75% = 0.7501 g/s

100% = 0.9996 g/s

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The spec sheet guarantees an accuracy of 0.5% of reading + 0.1%FS.

This translates to ±0.001g/s (FS alone) and upto ±0.005g/s (0.5% reading at 1g/s), in sum ±0.006g/s at 1g/s.

So the device is calibrated with 0.04% accuracy at 1g/s, but its specs only guarantee 0.6% accuracy: there's a factor of 15 between both values!

IMHO it would be sufficient to apply a simple scale of 0%=0g/s and 100%=1g/s…

[Rawoof]

Hello,

Thanks for the response.

Please find the enclosed code.

There is nothing on the device regarding the output, but from the manual(attached below) I understood that the device offers both current and voltage as outputs.

Regarding the measurement scale, for example, if I choose linear scale what should I feed into the slope and intercept values?

Likewise if i choose polynomial what should i feed into the constants?

Actually, I wanted to add the thermocouples measurements to this existing code, so kept a low-frequency rate for limited samples as I perform the experiment hardly for a few seconds. I still need to develop the complete code, but I got stuck here.

Thanks,

Rawoof

[GerdW]

Hi rawoof,

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@Rawoof wrote:

Regarding the measurement scale, for example, if I choose linear scale what should I feed into the slope and intercept values?

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So you have an analog signal of 0...5V, which scales to 0...1g/s.

What is the slope and intercept here?

(This is basic math, just a linear equation of one multiplication and one addition...)

Btw. you can also define a DAQmx scale using min/max of input/output range, when my memory serves well...

[santo_13]

Please share your model number, your sensor model describes how to identify out the output type - https://www.bronkhorst.com/getmedia/257147fc-7f5d-4628-9a47-0533cf68ac08/917099-Manual-EL-FLOW-Selec...

@GerdW - I agree that just a linear scale will suit this scenario, I suggested a table scale so the OP understands how to use the technique if some other sensor is non-linear and has a calibration table instead.

@Rawoof

For the linear scale, the intercept will be 0 as 0V correspond to 0 g/s, the slope will be 0.2 as 5V correspond to 1 g/s.

[Rawoof]

Hello Santosh and Gerd,

Thanks for your response.

Please find the below model number.

[GerdW]

Hi rawoof,

please read my first message again, where I mentioned "exact type" and "read the manual"...

Is there a reason not to use the serial port?

[Rawoof]

Hello Gerd,

Please check the below figure. I have connected according to the first circuit(Marked in yellow),so it the output should be in volts(either 0-5v 0r 0-10v) if I'm not wrong.

[santo_13]

@GerdW, looks like the OP might want to measure the flow rate synchronous to some other signal and hence used the DAQ instead of the inbuilt RS232 port, maybe?

@Rawoof, since your sensor uses 0-10V (evident from the B in 'ABA' term in your model), it becomes quite simple, just divide the DAQmx waveform by 10 to get g/s units.