DAQ reading error analog input voltage

[leo_tf]

Hello NI,

please help me,,

Actually, I'm quite new with Labview, so please forgive me if there is something wrong with my explanation and what I've done.

I'm working my final project using Labview, PCI 6221, and SCB 68.

I need 4 inputs of voltage to control 2 outputs of voltage too.

So I use AI0 to AI3 to read my sensor which is range 0 to 10 volts.

And AO0 to AO1 to generate voltage of 0 to 9 volts.

The problem is that MAX or DAQ Assistant does not read the proper value of voltage of all 4 inputs.

All the inputs show the value of -10.6 volts.

Even if the voltage of the sensor vary from 0 to 10 volts, the MAX and DAQ assistant give the value -10.6 volts.

What's wrong here?

is it my sensor or the SCB 68 or PCI 6221?

I try to recheck with multimeter.

The reading of sensor is good. It varies linearly and good.

Then I check the screws of all inputs of SCB 68.

It's all good too.

So why the PC read that value??

It is error.

are the devices damage?

But, when I generate a signal to AO0 and AO1, it gives the correct value.

I have tried all the AI but it gives the same result.

What should I do??

Give me an advice, please....

Thank you for your help..

Leo

[Dennis_Knutson]

Something could be defective or you could have the DAQ card configured incorrectly. What are the exact connections you are using and how did you configure the DAQ Assistant - Reference Single Ended, Differential, etc?

Also, have you run the self-tests in MAX?

[leo_tf]

I have installed PCI 6221 exactly by the manual book. even if it's installed incorrectly, how can I generate output voltage and get the right value. The fact is the output voltage is correct, but not the input.

Differential, RSE, NRSE, I have tried all the three, but it gives the same result.

Self-tests in MAX, I have run it everytime I open the MAX or DAQ assistant.

and also Reset, and Refresh.

When I change the min-max value, for instance 0-5volts, it will give the result minus 5. ....

but no vary.

When I change 0-1volts, it gives -1.0......and no vary.

What should I do??

please...

thank you

[Dennis_Knutson]

What I asked was exactly how you had everything connected. That means what pins of the connector block are connected to what pins of the signal. In the DAQmx help file are recomendations for field wiring. Which of those schemes did you follow? It sounds like something is open so also double check the cable between the DAQ card and the SCC-68. Try doing a loopback of AO0 to AI1 as well as grounding the AI inputs. See what those read.

[ColeTrain]

Hello Leo,

Dennis is absolutely right when he says that it sounds like something is open in your system.  When you are reading a value that is slightly outside of the range that you specify (say -10.1 when reading from ±10 V), it indicates that you are either reading a value that is outside of your range, or that the channel you are reading does not have anything attached to it.  

As a general rule, if you have a two wire sensor, you should configure your system to read differential (unless one of those is your grounding reference).  Otherwise, refer to the Field Wiring Guide and Noise Considerations document to determine if you need RSE or NRSE.  Dennis's suggestion of detailing how each of your wires is attached to your card will help us offer more suggestions.  Hope this helps.

[leo_tf]

dennis and cole,

thank you for all your suggestion.

 I've tried loopback. I connect a wire of AO0 (pin 22) as Vout to AI0 (pin 68) Vin

and AO ground (pin 55) to AI ground (pin 67) and connect AI0 to AI1 (pin 34) as V-

then I give the range 0-5volts.

in the test panels, I test it.

I generate 3.023 volts, but the input read -5.31 volts.

then I take the jumper off (the connection between pin 67 and 34), and it gives the same result -5.31v

even when I change the output, the input gives the same result.

maybe in my sensor hardware I misconnect the wiring.

but, with the loopback I've done above??

but, thank you,,

I will read and study more for the document you've given to me.

Enlighten me more....

regards,

leo

undergraduate student

[leo_tf]

Dennis, Cole, and everyone,,,

I've read the document you've given before.

Correct me if I'm wrong, that in my opinion my sensor is floating source, because its source is transformer which I use computer power supply.

My sensor is only spectrol which is similar with potensiometer. I try rewiring to SCB 68.

I try DIFF.

I connect V+ to the AI4 (pin 28) and V- to AI12 (pin 61) and connect R 10kOhm from AI4 to AIGND and AI12 to AIGND.

 same result as before, it gives -5.31 volts, even though I vary the input.

I try NRSE.

same connection as before but R connected to AISENSE not AIGND.

same result too.

there is no variance at all.

please,,, what's wrong here?

is there anymore ways to test the devices??

I'm desperate...

I need your help,,please...

thanks for your reply

Leo

[Dennis_Knutson]

Forget about the sensor for a while. If you can't get a loopback to work, then it's a waste of time trying to read the sensor.

Let's go back to that for a while. Your loopback should have pin 22 connected to pin 68 and pin 55 to 67. Nothing else. Set the analog output to the 1V default. Set the analog in RSE. Acquire the analog input. If you still see the -5 volts, double check the cable with an ohmeter. For one last check, connect 67 to 68. You should read 0 volts. If the voltage is still bad, then I suspect the card is defective.

[ColeTrain]

Hey Leo,

I'm with Dennis.  As you are an undergrad, I would say it's probably a safe wager to say that someone else has probably used this card before you and (forgive me) undergraduates I have dealt with have not always treated the cards the best.  At this point I have seen everything from someone trying to measure the wall voltage to pulling the PCI card out of their computer with the computer still on.  You would notice a bad card pretty quick from either of those, but less noticeable things like connecting your card to a 15 V source over night could damage it to the point you can't take good readings.  If you are still reading bad values with the loopbacks, create a service request and call in for an RMA.  

[leo_tf]

I've done all,,,,

and the result is the same as before.

nothing is different.

do you think that it's positively damage???

which one? the PCI 6221 or SCB 68??

what should I do?

I still have to finish my final project, which is I need to gather 4 inputs voltage and then connect with vi that I've built in labview and then generate 2 output voltage as my manipulated variable.

The only hardware that can connect to labview which our department has is the two above.

can you share your idea?

and then what should I do with the broken one??

thank you very much for your help.

warm regards,

leo