Getting raw voltage from NI 9237

[RobertUWM]

Hello,

I have a Load cell plugged into a NI 9237 and it is excited with 10V. I would like to read the voltage back from the load cell without scaling to get the voltage at the output.

Thank you for your time

[MarkGrot · Accepted solution]

Hi Robert.  The short answer is that you can't.  The NI 9237 returns a ratiometric value which means the data you get back is in mV/V, a unitless measurement.  The device does the division in hardware which allows for a more accurate reading since it uses the actual excitation voltage in the calculation but this scaling cannot be disabled.

[tsrobison]

I'm also trying to hook a load cell up to a 9237, if you wouldn't mind, could you outline exactly how you wired up that connection? I'm at a bit of a loss myself.

[Eric-E]

Hello,

You might want to create a new thread for this question to keep the records clean and get the best possible answer. 

The connection will depend on what kind of a bridge you wish to use and what accessory you are using.

Connecting Strain Gauges and Shunt Resistors to the NI 9237

http://ae.natinst.com/public.nsf/webPreview/892C84122A6501AE86257547007E5C53?OpenDocument

NI 9945 or NI 9944 with an NI 9237 Connection Guide:

http://digital.ni.com/public.nsf/allkb/F47EFDB8B1992282862572AD007CE9C3

Thanks,

Eric E.

[LC3]

Hey, I have a follow up question. Does that mean that if you have an excitation voltage of 10 then to convert to a physical unit we would multiply it by excitation voltage? This is what I have been doing in my calc from electrical to physical units but this is the first good answer I have seen that seems to confirm that. 

Also, does the NI 9237 actually know what voltage the sensors are actually receiving or is it based off of what you set the excitation voltage to be in the program. For example, excitation might actually be 9.96 or maybe 5 and is/should that be included in the ratio mv/V that is output or is 10 V included.