How to wire self-powered current transmitter to 9207 analog input?

[wishiwasanindian]

Hi,

I have a gas mass flow controller that is 24VDC powered.  I would like to use the 4-20mA output with a NI 9207 analog input module.  When looking in the manual for this module, it shows the connection diagrams for loop-powered sensors(pg13), but I am wondering how I would interface with a separately powered sensor.  Can I just tie the positive terminal on the 4-20mA output to the Vsup, pin, or will this have negative effects on my mass flow controller?  I also have a few pressure transducers that are loop powered, so eventually I will tie the 24VDC supply to Vsup anyway.  Any thoughts?  The help is much appreciated.

Thanks

[Joel-P]

Hello wishiwasanindian,

I do not think that you should tie the positive terminal of the 4-20mA output to the Vsup pin, unless you have already tied in the 24 VDC supply. If you are going to be adding in more pressure transducers in the future, I believe that it would be best if you were able to tie into the 24 VDC supply and then wire the transducers as seen on pg 13.

http://www.ni.com/pdf/manuals/375206a.pdf

Thanks,

Joel

[wishiwasanindian]

I agree, the first idea would probably not work. 

The thing I am worried about is that my mass flow controller is powered by 24VDC - on seperate pair of wires than the 4-20mA mass flow reading output.  It seems that this 4-20 signal coming from the mass flow controller is not loop powered as it receives power from the seperate 24VDC wires fed to the controller. 

I guess I'm wondering how I would wire this to the analog input card (I also have a few pressure transducers that are loop powered that need to be wired to the same card).  Would I just take the positive terminal of the 4-20 mA output -> connected to AI10 for example and then connect the negative 4-20 wire from the mass flow controller to COM since it is self-powered?

I have attached a terrible schematic, this is how I am thinking about wiring it now, does this seem right?  Any feedback greatly appreciated.  Thanks 🙂

[Joel-P]

Hello wishiwasanindian,

Thanks for the schematic, and it is more than satisfactory to provide the necessary information.

My only concern with the current setup (no pun intended) is that the 9207 may be sourcing the 4-20 mA output of the Mass Flow Controller. This is still within specification for the 9207, but I am still a little concerned. If you could include the model of flow controller, or a spec sheet I would be more comfortable making a recommendation on the wiring.

Thanks,

Joel

[wishiwasanindian]

Joel,

Attached is the user manual for the mass flow controller in question.  Let me know your reccommendation about wiring configuration based on this.  The controller is configured for 4-20mA output and 24VDC operation.  Thanks again, it's great to get a second set of eyes.

[Joel-P]

Hello wishiwasanindian,

For testing, you should be able to connect both the 4-20mA+ and 4-20mA- terminals to analog inputs in the 9207 module. The 9207 can source and sink up to 21.5mA, and should be able to read both terminals in order to determine how you would like to configure the sensor.

Thanks,

Joel

[wishiwasanindian]

Is that 21.5 mA per channel, or for the entire card?

[wishiwasanindian]

I am guessing for each channel, but just want to be sure.  Thanks

[Joel-P]

Hello wishiwasanindian,

You are correct that it is 21.5 mA (max) per channel.

Thanks,

Joel

[Bennus]

Hi,

I'm also interested by this subject, and I'd like to know how you finally wired your sensor.