Measured Voltage drops to zero for a few seconds periodically

[BF72]

Hello, I have an NI 9205 measuring the voltage drop across a resistor in a super-simple test circuit with a 12 VDC power supply. For some reason every 10-12 seconds, the measured voltage across the resistor drops to zero for a period of 3-4 seconds, and then comes back again. Screenshot attached (time in 1/10 sec).

I am monitoring the same voltage with a multimeter, and it shows a steady voltage. I have tried using different pairs of pins, same result. I am using the differential terminal configuration. I have an NI 9213 in same chassis measuring temperature with a thermocouple, and it gives steady continuous readings.

Many thanks for any suggestions, going a bit mad.

[Bob_Schor]

Hard to say what the problem is without seeing the code.  You've shown excellent evidence that either the module is very broken or the code is bad.

[billko]

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@BF72 wrote:

Hello, I have an NI 9205 measuring the voltage drop across a resistor in a super-simple test circuit with a 12 VDC power supply. For some reason every 10-12 seconds, the measured voltage across the resistor drops to zero for a period of 3-4 seconds, and then comes back again. Screenshot attached (time in 1/10 sec).

I am monitoring the same voltage with a multimeter, and it shows a steady voltage. I have tried using different pairs of pins, same result. I am using the differential terminal configuration. I have an NI 9213 in same chassis measuring temperature with a thermocouple, and it gives steady continuous readings.

Many thanks for any suggestions, going a bit mad.

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Sounds to me like you are getting intermittent read errors resulting in a "read" of 0 volts.  A picture is worth a thousand words, but actual LabVIEW code is worth a thousand pictures.

[BF72]

Sorry new to this, here's the VI code. Thanks for your help.

- Ben

[crossrulz]

You are setup for continuous samples, reading 1 sample at a time.  Since you are only sampling at 5Hz, I doubt there will be any timing issue.  But you are only reading 1 sample from 1 channel.  Why are you making the data type a 2D array?  It should just be a single double value.

Are you getting any errors?  Use the Simple Error Handler VI (in the Dialog and User Interface palette) with the error coming out of the DAQ Assitant.

[Sam2112]

hello

we are experiencing the very same problem with the very same hardware ( NI 9205) and the  same single circuit. ( 15V DC through a 20k ( 10+10 resistor) divider.

(we could post the very same screen shot than the original poster)

we measure the voltage in differential mode across one of the 10k resistor.

To avoid possible multiplexing "ghosting issue" we have disconnected all other ports of the module in order to try to resolve this issue: Only One port is used on the 9205

acquisition is made  with signal express 2015 : one sample at a time every second ( we tried several sampling frequency and always observed the problem)

1 Hz is the application need though.

also we have 2 different 9205 modules. we reproduce the problem on both.

we have changed all the wires in searc of possible faulty contact and the problem persisted.

we doubled the measure witn an oscilloscope and we know that the voltage never drop to Zero.

Is it a known problem that we have missed?

What we will be a troubleshooting strategy?

is itpossible that 2 modules apparently fully functionnal can be wrong at the same time and shows the same pattern?

any suggestion?

Thanks in advance

any advice welcome!

Sam

[QueenSelene]

Hi Sam,

Thanks for posting. While it is possible that two modules may both be wrong, it is pretty unlikely. It's more likely something is configured wrong on the acquisition side of things. Have you tried setting up a task in NI MAX to read the voltage? Can you observe the behavior there? Also just make sure that you're wiring the differential inputs correctly, a great way to do this is to use the connection diagram in NI MAX (tab at the bottom once you've created a differential analog input task). If you're still seeing the same issues after doing this, let us know.

Thanks,

Selene v

Applications Engineer

National Instruments

[JamesTriola]

Hey BF72,

We are expiriencing the exact same issue. We've used a labratory power supply to ensure a steady voltage. Did you ever happen to resolve this issue? 

It is also driving us insane.

Thank you,

James

[NIquist]

If you are using LabVIEW to sample the Analog Inputs of your 9205 please post the code.  

Did you try monitoring the voltage level through NI-MAX's test panels?   [Open NI MAX > open My System > Devices and Interfaces.  Click your NI 9205 device then go to the Test Panels... tab in the main window.  Go to the Analog Input tab in the new pop-up window and set your channel, etc.]  

Now click Start and you should see the voltage being charted.  Watch it for a while and see if it still exhibits the dropout behavior.

If it is steady there, you know the problem is your code.  I would be VERY surprised if this is a real hardware issue but with three people having the exact same issues it has to be a possibility.  I've never used that particular module but every time I've ever had problems of this nature it ends up being my error in the code I wrote.  

[GuillaumePunch]

I'm having actually the same issue.

We are using a module NI 9205. As proposed by NIquist I tried to use the NI-Max's test panels to troubleshoot.

We have two modules NI 9205, with both module we are facing the same problems, voltage drop to zero really often. Depending of the sample rate, those periods seem more or less long. To avoid possible multiplexing "ghosting issue", only one port is used on the 9205.

Module informations and screenshots of the test panel :