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U3-HV measuring 2 flow meters and 1 rpm signal?

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#1 srs14

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Posted 27 June 2014 - 11:08 AM

I am a grad student constructing a pump and heat exchanger lab for the undergrads to perform tests with. so basically I am trying to measure 2 flow meters and rpm of the pump (square wave and need the frequency of all 3) as well as 4 thermal couples and a differential pressure sensor. So i know that logud can measure and record the analog voltage signals of the thermal couples(with ljtic amp)  and pressure transducer. But the flow meters are rated with pulses per liter. Our university has labview on all the computers but i have no experience with it or much programming background other than matlab.


I have played with all the U3 examples and have an idea of how everything works with the different VI's used to find/call up/run the labjack but i still feel like im in over my head. 


over view of the experiment


--cold water flows through a heat exchanger(measuring the temperature in and out of the HX and also the flow rate)

--hot water is pumped from a reservoir through a heater ,through the heat exchanger(measuring temp in and out of the HX and also pump head/pressure and flow rate)


I have the working test setup with sensors in place, its just creating a user interface for them to record data in the correct units gpm/lpm thats getting me. Building a interface this large with all the different LJ vi's in labview is way over my head. can anyone help or point me in the right direction. I have to build and program 5 of these before the end of the summer.

#2 LabJack Support

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Posted 27 June 2014 - 12:56 PM

See the following for general information about frequency measurement:




The U3 has 2 timers you can configure in 32-bit Period mode to easily measure frequency, but for the 3rd frequency you will have to use a counter and look at count-change divided by time, so you might just decide to use counting for all 3.



LJLogUD can collect input data, write to file, and display on the screen.  It can even scale the readings, including the timer readings, but if you use the count-over-time technique LJLogUD will not be able to do that math for you.


If you are going to program in LabVIEW, you will have to learn about LabVIEW programming.  I suggest going through NI's tutorials.


If you like programming in Matlab, you can certainly use that.


Consider using DAQFactory for minimal or no programming requirements.

#3 srs14

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Posted 27 June 2014 - 01:54 PM

i was able to configure fio4 and fio5 as timers using risingedge32 and displayed the period correctly in the LJcontrolpanel but the fio4/5 shows the on/off state of the square wave rather than the period in logud. is there something i am doing wrong? I wrote the changes to the board .

#4 LabJack Support

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Posted 27 June 2014 - 02:19 PM

Make sure you use "Config Defaults" in LJControlPanel to set your desired configuration as the power-up default.


You have to use channels 200/224 and 201/224:





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