how to convert square waves to a physical data

[sgirgin]

Hi all,

I have omega ftb-1302 flowmeter sensor which gives a square wave as output.I wired it to DAQ.When i plug in the power supply i saw this image

When i open the valve it doesn not fluctuate.What am i supposed to do?

[johnsold]

How do you have your grounds connected? According to the flowmeter data sheet the output signal should switch between the positive supply and ground.  The image you posted shows it swinging between +5 V and -5 V.

That does not explain the lack of any variation as the flow changes but does suggest that something is not connected correctly.

Are you sure that the flow actually changes?

Lynn

[sgirgin]

Hi Lynn

According to datasheet i wired;

white cable to ai4 from DAQ. 

red cable to power supply +

black cable to power supply -

i saw your point you mean there must be only 2 cable connected with power supply + and signal and power supply - to analog input -?

[johnsold]

It is hard to say because the terminology is not precise.

Does the power supply have a ground connection or just + and - outputs? Something needs to connect between the power supply and the DAQ system ground. Analog Input - may not be the same as ground.  Some small current must flow from the signal output line through the DAQ input to DAQ ground to sensor ground to power supply. If you do not define that path by correct wiring, errors or damge to equipment can result.

What DAQ device are you using? What power supply?

Lynn

[Dennis_Knutson]

Why ai4? Why no ground connected to the DAQ device? What's your device? Why an amazing input instead of a counter that will directly read frequency? What do you see with an oscilloscope?

[johnsold]

Dennis,

The sensor uses an analog switch to connect the output to the positive power supply (10-24 V) or to ground. So the voltages are incompatible with most coutners and the edge rates may be too slow.

Lynn

[sgirgin]

I am using NI 6229 BNC DAQ.and 24V power supply. Power supply has 3 pins. +,- and the remaining must be ground.

What i understand from your saying is now;

white cable to ai4

red cable to power supply +

black cable to power supply ground

And there must be connection between power supply ground and DAQ.but where exactly?

[Dennis_Knutson]

Sorry, assumed a 5v supply.

[johnsold]

Guessing that the third pin on the power supply is ground is a good way to destroy something. Look it up. What is the voltage between + or - and the third pin?

Also, connecting the output of the sensor to the 6229 could damage the DAQ device.  The analog input specifications say that the input voltage must be within +/-11 V of AI ground. With a 24 V power supply the sensor output could be 23 V. 

DISCONNECT everything until you know what you have and how to connect it without damageing anything.

Lynn

[sgirgin]

i suppose that analog input range is about signal range not from power supply.

if so whats your suggestion assume that i have 10 V power supply and the third pin is ground.i am stuck in power supply ground and DAQ connection