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Author Topic: OMEGA low flow meter wiring  (Read 800 times)
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I plan to use this sensor for a project. I needed a low flow sensor able not to break with high pressure (for safety it should withstand up to 500PSI, although during normal use it should be below 150PSI).

http://www.omega.com/Manuals/manualpdf/M5171.pdf

I read in the datasheet above that the output is "Output NPN Sinking Open Collector @ 20 mA, Max"
and

"The output signal is a square wave signal, whose frequency varies linearly with flow rate. An external pull-up resistor (user-supplied) is required to insure that the open collector will sink less than 20 mA."

Can I wire this sensor as in the attached image, or am I missing something?

Thank you
Med


* flow sensor to mega.jpg (753.69 KB, 1755x1254 - viewed 56 times.)
« Last Edit: May 05, 2013, 08:06:23 pm by medkhai » Logged

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Is that a 10k resistor ?
I think 10k or 4k7 is just fine. 10k is in the datasheet.

That datasheet is a lot confusing. The person who wrote that must hve been drunk.
Connect Arduino GND pin to sensor (-) / 0VDC / ground.
Connect Arduino 5V pin to sensor V+
Connect Arduino input pin (preferably a digital input pin) to sensor OUTPUT.

Connect the resistor from the OUTPUT to V+ (5V).

The output is a square wave, so you don't need an analog input. You can use the analog input as a digital input of course.

Did you understand this sentence : "Output NPN Sinking Open Collector @ 20 mA, Max" ?
NPN = NPN transistor inside
Sinking = if active the output is pulled to ground.
Open Collector = if not active the ouput is floating.
20 mA max = the maximum, so a nice value would be roughly 1mA.
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Thank you for your reply.
So I modified the connections as attached.

- The digital pin I think should be an interrupt PIN right? Like pin 3 on the arduino.

- Changed the resistor value to 4.7KOhm to limit current to 1mA
- and moved it as pullup between +5V and OUTPUT

Thank you for point out the mistakes to me :-)
Med



* flow sensor to mega2_bb.jpg (553.48 KB, 1329x1410 - viewed 52 times.)
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Looking good.

But now the sketch.
You need a frequency counter or something like that.
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Hello, do you know what the output voltage of this device is? Thank you.
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Hello, do you know what the output voltage of this device is? Thank you.

Being open collector output, it's whatever voltage you wire it to. The easiest way to wire that to a arduino is to just wire it's output pin to a arduino digital input pin, then ground wire to arduino ground pin. Then just enable the internal pull-up resistor for the digital input pin you use.

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great, thanks for the reply. I am using http://www.omega.com/Manuals/manualpdf/M4172.pdf flowmeter. I am using an external 12V power supply for the flowmeter. So i think i can connect arduino gnd to flowmeter gnd and pwr supply gnd, flowmeter signal to arduino digital pin with internal pullup R enabled, and flowmeter power to external power.
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great, thanks for the reply. I am using http://www.omega.com/Manuals/manualpdf/M4172.pdf flowmeter. I am using an external 12V power supply for the flowmeter. So i think i can connect arduino gnd to flowmeter gnd and pwr supply gnd, flowmeter signal to arduino digital pin with internal pullup R enabled, and flowmeter power to external power.

 That should work fine. You could do without the 12vdc supply as that document says the flowmeter will work with down to +5vdc to the supply terminal which is available on the arduino 5V pin.

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