NI9205-Voltage measurement accuracy is not accurate ？

[Xuxiaomiao622785]

Hello all!

I encountered some problems during using NI9205， two same resistors（2MΩ） in series  are connected with 5V,   in the middle of the voltage should be 2.5V. The actual collected value fluctuates about 100Mv, which is somewhat inconsistent with the 1% accuracy of the full range about product manual ？How should I smooth out voltage fluctuations？

Thank you very much!

[santo_13]

Ideally, the signal source should have a low impedance, 2M series impedance is substantial and could be causing the issue. Try to reduce the resistance to K ohms.

[Xuxiaomiao622785]

Thank you for your reply. Because the test sensor resistance cannot be reduced to K ohms，The attached manual shows that the resistance can reach MΩ, Can there be another method ？

THANK YOU VERY MUCH !

[Henrik_Volkers]

If you read the specifications of the 9502, you find a spcified  input bias current of +-100pA

(mean there is a current flowing out of the input into your resistors... )

SO. ALL IN SPEC 😄

(Read The F....antastic Manual  😉 )

2M Ohme are selected?  Usually they have some tolerances too 😉

Maybe add a chopper input amp?

Or analyse the offset voltage drift and if appropriate adjust the voltage divider (or simply do it in software 🙂 )

If you tell us more about your actual application , type of sensor, input schematic , a better help is maybe possible.

[Xuxiaomiao622785]

Thank you for your reply.I try the way you say，add a chopper input amp  in software. but I have a new problem.Hope you can give some advice.Single-channel can acquire accurate voltage, but multi-channel acquisition voltage error is large.

Measuring the voltage division between four series resistors （1MΩ） is actual application. I add 6V to both ends of the circuit, and collect the divided voltage. The real values should be 1.5V and 3V.

when i use NI MAX test panel,  1.5V and 3V can be measured, but voltage value collected by the NI labview analog input are 1.5V and 2.1V,voltage error is large.

Look forward to your reply.🤗

[Xuxiaomiao622785]

Hi,All

Some new problems I've encountered while using the NI9205. Measuring the voltage division between four series resistors （1MΩ） is actual application. I add 6V to both ends of the circuit, and collect the divided voltage. The real voltage values should be 1.5V and 3V. when i use NI MAX test panel, 1.5V and 3V can be measured, but voltage value collected by the NI labview analog input are 1.5V and 2.1V,voltage error is large.

Hope to get some suggestions for improvement~😄

[santo_13]

If you can measure 1.5V and 3V using NI MAX, then the instrument is good and capable.

Please share the code you developed that measures 1.5V and 2.1V for review.

[Xuxiaomiao622785]

Hi, thanks for your reply.

I didn't compile the code myself，I just create a new analog input in LabView and turn on the voltage acquisition of two channels, One voltage acquisition channel is 1.5V,another voltage acquisition channel is 2.1V, 2.1V is obviously not accurate.I am going to collect eight voltage channels, the same problem occurs, one is accurate, the other seven are not accurate.

[WUNAN]

Hello all

        I met some problems in the process of using NI9205. The chassis is NI9188, and the actual circuit is 4 1MΩ resistors in series, and 6V voltage is applied at both ends. The actual value of the collected voltage should be 1.5V and 3V.However, the acquisition values of NI LabVIEW analog input are 1.5V and 2.1V, with large errors.

                                                                                                  Thank you for your

[GerdW]

Hi Wunan and Xiao,

why did you create new threads for the very same topic?

(Why don't you join forces to tackle the problem together? You surely are from the same group of students!)

What's different now? You still use a voltage divider network of resistors and you still get the same explanation as has been given before…