I am using a flowmeter that gives AC sing waves. How can I connect it to my DAQ-9178 unit ??

[Mario8]

I am using a flowmeter that gives AC sing waves. How can I connect it to my DAQ-9178 unit ??

[johnsold]

In English the waves are called "sine" waves.

The cDAQ-9178 is just a chassis. You also need I/O modules to make the actual measurements.

What characteristic of the sine wave represents the flow? Amplitude, frequency, something else? What is the range of amplitude and frequency generated by your flowmeter? You need to know those things before you can select a DAQ module.

Lynn

[Mario8]

Unfortunately the DAQ module was selected prior the flowmeter, therefore I need to find a way to use the selected one.

The frequency given by the sine wave is the one that represents my flow.

p.s : I am using an Omega FTB9503 flowmeter .

Thanks in advance. ( also thanks for the correction. I haven't even noticed that I wrote sing instead of sine )

[johnsold]

Do you have just the flowmeter or do you also have some of Omega's signal conditioning equipment (such as the FLSC-64)?

You still did not specify which DAQ module you have. Is it an anlog input module, a digital input module, a counter module, or something else?

Lynn

[Mario8]

I do have only the flowmeter. As I have read this flowmeter should be followed by a signal conditioning system as you have already mentioned

but I don't have one.

( I was thinking of using an Op - Amp follower before connecting it to the DAQ system. )

The module I am using is NI 9205 and I am using the differential mode. ( all the other sensors that I am using

have 3 wires ( + voltage , ground , signal ) so I am connecting the signal wire to the DAQ system and the rest

 2 wires to the power supply.

As I have already mentioned this specific flowmeter ( ftb9503) has 2 wire AC signal. 

[johnsold]

OK.

Connect the two flowmeter wires to the NI 9205 in differential mode. You may need to connect resistors to ground to establish a suitable common mode condition. Check the manual for the 9205. Sample at at rate more than twice as high as the highest frequency from the flowmeter.  I looked at the data sheet earlier but do not recall the exact frequency, perhaps 1100 or 1600 Hz? Sampling at 5000 Hz or higher should be adequate.

As long as the signal is not corrupted by noise you should be able to search for zero crossings in the data. Subtract the indexes of successive (positive-going) zero crossings then multiply by dt = 1/sampling frequency. That time will be the period of the signal. The frequency is 1/period.

The data sheet indicated that the frequency-flow relationship is non-linear.  I did not dig in to see if the specify the non-linearity or provide a calibration curve.

Lynn

[Henrik_Volkers]

The omega signal conditioner (the one I checked 😉 )  has an input impedance of 50k OHM. If you need precise measurements, have a look at the calibration data provided with the sensor. It should be noted which input impedance is used. 

Your DAQ input is >10G Ohm,  So my adwise would be to use the 9502 differential with additional 50k resitor across the inputs and a 1M from AI- to AGND. (Improved version: instead of the 50k use two 25k (or 27k 😉 ) resistors in series and connect the 1M at that joint to AGND)

Use the +-200mV Range, Samplerate 5k SPS  (as johnsold already mentioned)

frequency range is 40 to 1300 , so capture about 250ms (1250 sample) and apply a extract single tone vi. that should get you the sensor frequency.
 

In case of fast frequency changes this vi migth fail ...

Since the power line frequency is in the same range than your sensor frequency: Use a shielded twisted pair cable to connect the sensor.

Sample 1 sec of data at 100k SPS and apply a FFT Power spectrum to that signal: You migth find a small peaks at the your powerline freq. and multiple of that (2x, 3x 5x ...) and other noise. 

If your sensor signal is significant stronger, you don't have to care... 🙂