USB-6218 not working with current loop

[dj_928]

Hello, 

I have a USB-6218 DAQ and I am trying to talk to a flow meter using an Omega FP90-1P. I have attached the data sheet for it. I am hooking it up like the attached picture which is pulled from the manual of the meter. 

My problem is, there does not seem to be any current flowing through the DAQ. The meter does not turn on, and I have confirmed no current flowing by breaking a lead and testing with the multi meter. 

I am using an external 24VDC power supply. 

Thanks for any help

[adena.l]

Hi dj_928 - 

Where are you hooking up the USB-6218? Is it taking the place of the PLC or Recorder?

Also, have you gotten the flow meter to power on and function previously? 

[dj_928]

Yes you are correct. The USB 6218 is taking the place of the PLC/Recorder. 

The flow meter works fine in the stand alone configuration where I just provide power to the meter itself. But once I try to do a current loop through the DAQ, the meter does not power on, nor does it work in my created task in NI MAX. I tried this in both the RSE and Differential configuration on the DAQ. Neither works. 

[AnalogKid2DigitalMan · Accepted solution]

The 6218 input is for voltage and not current and it has a high input impedance.

You need to put a 250 ohm resistor in parallel with the 6218 inputs. This will allow loop current to flow and you convert current from the voltage reading by dividing 250 (Ohms Law). Thus 1V equates to 4mA, while 5V equates to 20mA.

-AK2DM

[dj_928]

That did the trick putting a 250 ohm resistor in parallel. Thank you so much!