Different Excitation values in the Same Task

[wisjaf12]

Hello

I am trying to acquire pressure signals from two pressure transducers simultaneously using DAQ Assistant. I am using NI DAQ Ethernet Chassis with NI 9237 Module. One of the transducers requires an excitation voltage of 10 vdc while the other transducer requires 5 vdc excitation. I created a DAQ Assistant task with two channels (one for each transducer). When I run the VI it returns the following error:

Error -200257 occurred at DAQ Assistant

Possible Reason(s):

Excitation property must be the same for related physical channels.

Refer to the documentation for information about setting excitation across related physical channels.

Conflicting Properties

Property: AI.Excit.Src
Corresponding Value: Internal

Property: AI.Excit.Val
Corresponding Value: 10.0

Channel Name: Pressure_1

It looks like using different excitations is causing the problem. Can you please help me solve this problem to be able to acquire simultaneous measurements from the two sensors and provide the required excitation for each one.

[Aaron_W.]

wisjaf12,

I believe the problem you are seeing is because there is only one bank of channels on the 9237 and they all share the same EX+ / EX- signals. From the Operating Instructions and Specifications:

"The NI 9237 is isolated from earth ground. However, the individual channels are not isolated from each other. The EX+, EX–, and T– signals are common among all channels."

The explanation for the 9237 is similar to this KnowledgeBase document. Hope this helps, looks like you might need another 9237 if you are going to have sensors with different excitation values.

[wisjaf12 · Accepted solution]

Aaron_W

Thank you for your reply. Based on what you posted and as I expected the diffrent excitation values are causing the problem. However, I am still looking for another solution rather than purchasing an additional module as it is quite expensive for a student like me.

[Aaron_W.]

Since all of the Excitation Channels for each channel are tied together I think your only other option is to find transducers that use the same excitation voltage.

[wisjaf12]

Yes, thats right and this is what I am working on now.