ARAG flow meter

Hi. I have problem with connecting ARAG flow meter to Arduino. It's working on 12Vdc. I have problem with signal. Technical data says: pulse output 0-12Vdc, 300pls/l and signal emitted only when the fluid is flowing. Now, when flowmeter is inactive, water don't flow in signal cable is 12V. When water is flowing, then there is about 5V. In my opinion, signal should be also 12V or i am wrong??

The sensor may be a plain-vanilla hall-effect device and, at 10l/min, it is effectively producing a 50Hz AC signal, while you are trying to measure DC. The 5v is about the average you might expect.

If it is an electromagnetic meter, I imagine much the same applies.

Hi. This flow meter is electromagnetic. From technical data i assume that the signal is digital - signal = 12Vdc pulses (300 pulses per liter). I can't understand why the meter showing me 5V. Is it a normal behavior? Because of pulses, which looks like this 0V,12V,0V,12V,0V,12V....? Sorry, I'm a electro noob :P Can you explain me what should i do to handle it with Arduino? I found this in Arduino Playground : http://playground.arduino.cc/uploads/Learning/Level_shifting_4_arduino.pdf

Yes, I think it is normal behaviour.

The "0V,12V,0V,12V,0V,12V." you allude to is essentially an AC current, as I mentioned above. I believe you are trying to measure DC current and the 5v is simply the average of what is available. If the digital off was truly 0v and the on was truly 12v, and the on/off ratio was 50%, and the rise and fall times were 0ms, then the average would be 6v, and perhaps more easily understood.

You have other options to measure what is going on.

  1. Use a meter with some sort of peak-to-peak facility.
  2. Use a meter with a sample and hold facility
  3. Use an oscilloscope to see the waveform
  4. do nothing

I recommend item 4., as there is no suggestion there is anything actually wrong.

I don't know anything about level shifting as I use simple turbines that operate happily from 3 to 18v. It thus follows that I don't know about electromagnetic devices either, but I suspect the first thing you should do is check how your devices work at 5v and, since I understand you have one of the devices in your hand, you could start by ignoring any advice from the manufacturer that you must have a minimum of 12v. The arduino is only interested in a change of state to do its counting, and I don't think there is anything very critical about it, and besides, the normal procedure is not to look at the voltage but to look at the non-voltage, i.e. the off-time, 0v.

Thank you very much. You really help me. I already get it to work. Thank you again, you have beer from me :)

Hi. I have succesfully connected sensor to Arduino, but there is another problem. As i mentioned before sensor gives 300 pulses per liter. In any value below 300 pulses per second (= 1 liter per second = 60 litres per minute [flow meter max is 200l/min]) it's everything ok. Strange behavior starts after reaching this value. Arduino stops counting pulses. I don't know what is causing this. Is it can be Arduino fault(but i think 16MHz is enough to handle 300Hz), or maybe some electric elements fails above 300Hz? To connect flow meter i use level shifting schema from arduino playground, Method 2 with optoisolator.

I take it that you did not succeed in getting the sensor to run on 5v. I don't know anything about level shifting but I'm sure you are right in that arduino should be able to handle a 300Hz pulse rate. My stuff works at about 100Hz, but I ultimately expect to run at 500 Hz. It is possible that, while not actually failing, your level shifting is changing its characteristics at a higher frequency, like capacitors becoming de facto timing circuits, or something. (pure speculation)