Reading Data through LabVIEW from a Flowmeter connect to U&

9 posts / 0 new

Wed, 06/28/2017 - 02:18

Swati Poduval

Hello,

I have a flowmeter from Kobold http://www.kobold.com/Electromagnetic-Analogue-Output-MIK-L4-with-AUF which is a 10-500mL/min with 10 bar max pressure. I want to connect this to a LabJack U6, as I want to read the flow value displayed on the device through LabVIEW.

I have 2 main concerns:

1. How to i correctly connect this flowmeter to the Labjack U6 ?

2. How to i read this data from Labjack using LabVIEW. I am already aware of some of the Drivers that are available for LabVIEW, but i do not know how to fill in the correct value to the Inputs in the front panerl of LabVIEW. e.g. Address that needs to be given in the Labjack ''LJUD Open S.vi'' etc.

Could some one help me by explaining this as I am new to labjack and flowmeters.

Please do ask me if you Need some more Information.

Thanks!

Wed, 06/28/2017 - 15:12

LabJack Support

I'm having trouble following their datasheet and determining exactly which model you have, but I'm guessing it has a 3-wire 4-20 mA output? Best solution is to use the LJTick-CurrentShunt in which you would follow figure 4:

https://labjack.com/support/datasheets/accessories/ljtick-currentshunt

You would want the 1 connection from the negative of your power supply to SGND or GND.

If you don't have an LJTCS you can often just use a resistor:

https://labjack.com/support/app-notes/measuring-current

To get started in LabVIEW with the UD library (U3/U6/UE9), see the "Getting Started" steps here:

https://labjack.com/support/software/examples/ud/labview

The example in step #7 calls eAIN and that is likely all you need.

For the open call, it is defined in 4.2.2 and more info is in 4.3.1:

https://labjack.com/support/datasheets/u6/high-level-driver/function-ref...

https://labjack.com/support/datasheets/u6/high-level-driver/example-pseu...

If you just have 1 U6, you can just use FirstFound=TRUE and then address and connectiontype are ignored.

For the eAIN call it is defined in 4.2.17 and more info is in 4.3.3 and 4.3.9:

https://labjack.com/support/datasheets/u6/high-level-driver/function-ref...

https://labjack.com/support/datasheets/u6/high-level-driver/example-pseu...

Fri, 06/30/2017 - 05:03

Swati Poduval

Thank you. I took your advice

Thank you. I took your advice and used the LJTick and the example Vi seems to help. I am now able to read the voltage values. However I need to convert these voltage values into flow meter units mL/min or liters/min; as my ultimate aim is to display the flow meter output in LabVIEW.

I have sent my query to the manufactures of kobold and am waiting for the reply.

Thanks again!

Fri, 06/30/2017 - 08:56

LabJack Support

Is the hardware working? Do

Is the hardware working? Do you get the voltage you expect for different flows?

Tue, 07/11/2017 - 02:59

Swati Poduval

Yes I am getting different

Yes I am getting different voltage readings for different flows. But I am still waiting for a reply from the company for the formula/characterization details so that I can convert voltage to mL/min units.

Tue, 07/11/2017 - 11:59

LabJack Support

Lets say they tell you that

Lets say they tell you that 10-500 mL/min corresponds to 4-20 mA. That means your slope is 30.625 mL/mA and your offset is -112.5 mL.

For the LJTick-CurrentShunt, you know that I = V / 118, or Amps = Volts / 118, or mA = 1000 * Volts / 118, or mA = 8.475 * Volts. So the LJTCS gives 8.475 mA/volt.

Mon, 07/17/2017 - 07:46

Swati Poduval

Thank you so much.

I am now able to read the flow and display the same using LabVIEW.

however I do notice some difference(+/- 3 mL), I am guessing this is due to the offset. Could you tell me how -112.5 mL was derived.

PS. May be it is something I am over looking

Thanks!

Mon, 07/17/2017 - 11:11

LabJack Support

In my example I assumed that

In my example I assumed that 10-500 mL/min corresponds to 4-20 mA.

mL = (30.625 * mA) - 112.5

If the measured current is 4 mA:

mL = (30.625 * 4) - 112.5 = 10 mL

If the measured current is 4 mA:

mL = (30.625 * 20) - 112.5 = 500 mL

So why might you have a 3 mL error? Here are a few of the more likely reasons:

1. According to Kobold does 10-500 mL/min correspond to 4-20 mA? I was just guessing.

2. Error in the sensors conversion of flow to current.

3. Error in the LJTick-CurrentShunt's conversion of current to voltage.

Do you have some sort of reference that gives you the known flow? If you have 2 points of known flow, say 100 mL and 400 mL, you can note the measured voltage at those 2 points and then come up with a slope/offset that relates voltage to mL. That is an in-system calibration that accounts for all errors in the system at once.

Tue, 07/18/2017 - 07:06

Swati Poduval

Hello!

Yes I am currently trying to calibrate the difference, at any 2 given points the difference is not always the same.

I am guessing its due to the flow meter itself, as the support team says 0-500 has more linear characteristics than 10-500. However for the current set of tests that we are doing, the error seems within the acceptable range.

Thanks again for all the wonderful support provided by you.

Helped us finish few important tasks on time!

Cheers:)