NI9237 measurements fluctuate

[RyanWu]

Hello,

     I am using NI 9237 to measure resistance. Please see attachment for my link. I set the mode as 'Full bridge'. The results shown a big fluctuation of ~ 0.005 Hz. Is this fluctuation from power line? How would I romove this fluctuation?

Thanks,

Ryan

[Margaret F.]

Hi Ryan,

In order to answer this question, I'll need some further informatiom. What resistance value are you expecting to meausure? What excitation are you providing? If you are provding one of the higher levels of excitation, have you tried 2.5 or 3.3V?

Please provide a screen shot of your code as well as a drawing of the full circuit that you have connected. Thanks!

[RyanWu]

Hi, Margaret

I am using the 2.5V excitation. The resistance range I want to measure is between 4000 to 20000 ohm.

Thanks,

Ryan

[Margaret F.]

Hi Ryan,

 I'm sorry to keep asking questions, but I still need more information. If you are using full bridge, are you providing the three necessary resistors and what are their values? If you are using quarter or half bridge, what accessories are you using?

Also, please post a drawing of the exact circuit that you have. Have a good weekend!

[RyanWu]

Hi Margaret,

     Please see the circuit figure attached with my question. I just used the EX+ and EX- as a power source. And then connected a big resistor (#1 in the plot,  ~100 times of the resistor I want to measure) with the resistor (#2 in the plot) I want to measure in series. Then using AI+ and AI- to measure the voltage (V2) across the resistor (#2) I want to measure.

You have a nice weekend too,

Ryan

[Margaret F.]

Hi Ryan,

I have looked at the circuit figure you have attached, but that does not indicate to me half bridge or quarter bridge as well as what accessory you are using. Please provide this information. Also, what kind of task do you have setup?

[RyanWu]

Hi Margaret,

     I am using the half bridge connections. Besides lead wires, I only have two resistors, R1 (=1 Mohm) and R2.

     I am want to measure the resistance of a resistor R2, which should be R2 = Vai+ /((Vex - Vai+)/R1). 

Thanks,

Ryan

[Margaret F.]

I am going to take this to our R&D Department and will post back when I have something.

[RyanWu]

Hi Margaret,

     Have your R&D people found the same phenomenon?

Thanks,

Ryan

[Margaret F.]

Hi Ryan,

I have spoken to R&D about this and we need to make this issue less generic in order to get to the root of it. I have attached a screen shot of a half bridge configuration. Please provide the values labeled R3 and R4 that the red arrows are pointing to as well as the model number of the accessory you are connecting to which is indicated in the picture by a green box. Thanks!