How to measure CompactRIO system input voltage

[rbardsley]

Hello,

I would like to measure the voltage of the two 9-35V DC inputs going to the CompactRIO RT controller. I am using the 4-slot chassis due to space considerations and do not have a 24V analog input module on-board to be able to do this via a module. On the 9205 analog input module there is a hook for "chassis temperature" that works perfectly. I am trying to find a similar hook to read the voltage that the CompactRIO is running on.

I will be running this CompactRIO on two 24V batteries and wanted to be able to detect when the battery levels were too low to continue operation. When this state is reached, or hopefully prior to, I want to offload the data I have collected before running out of power to do so.

Any ideas?

Thanks,

Ryan

[Eric A.]

Hi, Thanks for posting
If I am not mistaken, the maximum voltage allowed on the NI 9205 analog inputs is around 10 volts.  Since you want to read the input voltage which you say is 24v, you could build a voltage divider with a high resistance to reduce the voltage you would have to measure and not waste too much current.  You would have to calculate what resistor values you wanted to use and figure out how low the new voltage could go.  This would be one way to do it.  Perhaps some other people on this board have some better ideas.

[Eric A.]

Hi,
I wanted to ask you if you found the information on this thread you posted earlier useful.  You might try to keep from posting the same question twice in the future.  Let me know if you found any of this information helpful.

[rbardsley]

Hi Eric,

I am not an electrical engineer, so trying to figure out a clever way to split the voltage and measure it on three different inputs would be a job for one of the other researchers here. This seems like a straightforward feature though. We are using the CompactRIO as an onboard controller for a robot, but I would imagine that other more "mission-critical" applications would benefit from knowing the voltage that is powering the C-RIO. Much like the on-board chassis temperature reading, it seems like an important piece that is missing from the basic feature list. I don't know if we even have the 3 inputs free on the AI module as they are used to control everything else.

Hmm.

Thanks,

Ryan

[Eric A.]

Hi Ryan,
That might be a good feature for us to add to our controllers.  I will submit a product suggestion for that.  If there is anything else you can think think of that you would like to change you can submit your own thoughts here.