Flow Meter and with NI USB-6210 and LabView SignalExpress

[tallita_nunes]

Dear,

I am using a flow meter (manufacturer Omega, model FPR-303), NI USB-6210 and Labview SignalExpress.

The flow meter has three cables: red, white and black.

According of the Omega, the red is the sensor power supply (5-24 V DC and 2 mA current), white is the signal and black is a ground. The sensor`s output is current sinking pulse (6-24 Vdc) and the sensor output can be a sinking or sourcing pulse and the pulse production by flow meter is a continuous pulse.

My plan was use the NI USB-6210 to count the edge or frequency pulse and to determination the flow according with factor-k that i obtained by manufacturer.

I read the USB-6210`s manual and connected the red in +5V, white in FPI 0 for crt0 and black in DGND, all of the wires in Digital I/O side.

In Labview SignalExpress, i did: Connected the NI USB > Add step > Adquire Signal > DAQmx Adquire > Counter Input > Edge Count. I choose the falling active edge and Sample On Demand.

I have tested the NI USB-6210 and flow meter, but i do not have success.

My questions are:

1) Is NI USB-6210 applicable in this case? If it is not, please, tell me the appropriate equipment.

2) How I connect the cables, is it correct?

2) Does NI USB-6210 take a sinking or sourcing pulse signal?

3) Does NI USB-6210 take continuous pulse signal?

4) In this case, do you recommend the edge count or frequency count?

Omega answer me that i can use the NI USB-6210, then i need by other Omega`s equipment to use with NI USB-6210.

Regards

Tallita Nunes

[johnsold]

Tallita Nunes,

In typical Omega fashion the electrical output is very poorly specified. After doing a little reading between the lines, it appears that the output is generated by an open collector NPN transistor with the emitter connected to ground. At minimum you will need a pull up resistor to +5 V. The USB-6210 has in internal pull down resistor of ~47000 ohms. So the pull up resistor should be no larger than 1/10 of that. The lower limit is set by the current sinking capabillity of the sensor (which Omega does not specify).  Figure 2 of the manual you posted shows a 2200 ohm resistor used with a 24 V power supply. The current in that is just under 11 mA. At 5 V a 470 ohm resistor would provide similar current.

Next. NI does not specify a rise time for timing input signals on the USB-6210. Open collector sensors can have rather slow rise times (by digial logic standards). The debounce filter settings may allow the device to tolerate slow input signals. The 2.56 ms filter is too slow for the upper end of the flow rate. Try the 6.425 us filter setting. If you see spurious counts (or no counts at all) you will probably need to add a Schmidt trigger between the sensor and the DAQ device.

Lynn