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U6, Labview, and pump tachometer


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#1 4Strings

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Posted 17 September 2012 - 05:51 PM

Hi, I'm new to both Labview and LabJacks, and I have the following problem. I have a small water loop consisting of a small pump. The said pump is connected to my LabJack U6 with three wires: 1. A Control Signal In, 0-5Vdc or 4-20mA (I'm using 0-5V) wire connected to DAC0 on the U6. 2. A Common wire connected to GND on the U6. And 3. A Tachometer Out; 0-6V Square Wave wire connected to AIN0 Now in Labview I've set up a system where I should be able to manually control the speed of the pump using a virtual control knob through DAC0, and read the flowrate from the tachometer, through AIN0, on an indicator in Labview. Now my problem is that the voltage reading in Labview (both on a number indicator and on an XY Graph) from AIN0 is unreasonable. I'm getting near-zero when the pump is off, huge peaks when I run the pump at low voltage, and almost no reading when the pump runs at the full 5V. What must I do to get rational readings??? Thanks, 4Strings

#2 LabJack Support

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Posted 18 September 2012 - 07:04 AM

Do you have a link to technical details for the pump? In particular, details about the tach signal?

Sounds like perhaps the signal is a pulse output corresponding to motor speed? If so, you probably just want to measure the frequency of that signal, and so should use a U6 Timer. I suggest you use Mode 2 to measure the period of the square wave:

http://labjack.com/s...s-guide/2.9.1.3

First, try it in the test panel in LJControlPanel.

#3 4Strings

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Posted 18 September 2012 - 07:47 PM

Do you have a link to technical details for the pump? In particular, details about the tach signal?

Sounds like perhaps the signal is a pulse output corresponding to motor speed? If so, you probably just want to measure the frequency of that signal, and so should use a U6 Timer. I suggest you use Mode 2 to measure the period of the square wave:

http://labjack.com/s...s-guide/2.9.1.3

First, try it in the test panel in LJControlPanel.


Thanks for the reply!

Unfortunately, the manufacturer of the pump doesn't have any information on the specific pump.
What I know about it is that it's a Micropump HG0024, with it's wiring as I stated in my previous post.

I tried to use the LJ Control Panel, with the tachometer wired to FIO0, I tried to set the "Mode" to RISINGEDGES32 and RISINGEDGES16, and both give me weird numbers when I manually run the pump at different speeds.

I was just thinking, since the tachometer out is a 0-6V signal, and I plug it in to AIN0, shouldn't there just be something/things I could just place in the Block Diagram in Labview so that it reads the analog signal and displays it as a frequency???

Thanks again,
4Strings

#4 LabJack Support

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Posted 19 September 2012 - 09:08 AM

I was just thinking, since the tachometer out is a 0-6V signal, and I plug it in to AIN0, shouldn't there just be something/things I could just place in the Block Diagram in Labview so that it reads the analog signal and displays it as a frequency???

If you know the max frequency you will get, it is likely possible to stream the data (see Sections 3.0 through 3.2) at a high enough rate to get a waveform, and then to software processing to determine the frequency of that waveform ... but that would be the hard way.

I tried to use the LJ Control Panel, with the tachometer wired to FIO0, I tried to set the "Mode" to RISINGEDGES32 and RISINGEDGES16, and both give me weird numbers when I manually run the pump at different speeds.

RISINGEDGES32 is the only one you need to use. The test panel will display clock ticks and period. So if your signal is 10Hz, period will show 0.1.

Run a jumper from FIO0 (where you have the tach signal connected) to AIN0. Then instead of other software run LJStreamUD. Set #channels=1 and scanrate=10000 and start streaming so you can see what the signal looks like, and let us know what you see (post a screenshot and/or data file).

http://labjack.com/s...t/ud/ljstreamud

#5 4Strings

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Posted 12 November 2012 - 06:12 PM

Hi,
I've been trying some things out with the tachometer...
First of all, I've exchanged my U6 for a UE9... And if I open the "UE9 Frequency Measurement and Analog Input.vi" Example VI, plug the Tachometer output of my pump into FIO2 (as stated in the example VI in order to take frequency readings), and run the VI while adjusting the speed of the pump manually, I get an accurate frequency reading!
Now, how would I go about building a simple frequency measurement system using any of the FIOs on my UE9 to use in a larger system in order to get the RPM (by converting the frequency of the tachometer) of the pump?

Thanks,
4Strings

#6 LabJack Support

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Posted 13 November 2012 - 07:50 AM

The UE9 has 6 timers, so if you will have 6 or less tachometers then use the timer method like you are now. That means FIO0 to FIO5 on the UE9. "UE9 Two 32-bit Frequency Measurements.vi" shows 2 mode 2 timer inputs, so that might be a good example to start with.


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