Problem of measurering wrong resistance on DMM with scanner

[Kazu]

Hello.

I want to be taught the way for measuring correct resistance on DMM with scanner.

Now,  I have connectted DMM and Scanner and use GP-IB for measurement.

The measurement program is for mesureing tenperature using Pt100 and it set scanning 30 chanel.

First turn, It is correct resistance but second turn, suddenly, the resistance decrease.

Instruments turn off for a while, this program sometime good performance so I don't think instruments is wrong.

Please tell me good advie for me.

I'm looking forward to your response.

thank you.    

[K.Saha]

Hello Mr Kazu

Thank you very much for your question in discussion forum.I have some questions about your problem.What type of DMM and programming language are you using?If you are using any instrument driver, could you please inform me the details of your driver?

I have studied about the accuracy of PT100 and it sounds that the accuracy varies due to many reasons.What is the range of your temperature you are trying to measure?According to your mail, the resistance is correct when your start the program.What do you mean by the second turn when the resistance becomes incorrect and please tell me the value (both correct and incorrect).

Waiting for your kind information.

Thanks in advance.

saha | AE | National Instruments, Japan

[Kazu]

Thank you, K.Saha

I have used R6561 of DMM and The language I use is LabVIEW 7.1 and driver is NI-488.2 of version1.70.

The tenperature range I want to measure is from 80K to 275K.

Generaly, The resistance at 273K of Pt100 is almost 100Ω but DMM show sometime from 10 to 50Ω. Clearly, it is incorrect.

According to some information, It is good for DMM and scanner to delay mesurement interval until their instruments are stable.

but I can't know where to debag this program.

Hope your advice.

Thank you.  

[K.Saha]

Hello Mr Kazu

Thank you very much for your promt reply with important informations.

I would like to make sure that resistance value from 10 to 50 ohms are shown whether on your DMM or in your LabVIEW program.So far I think you are collecting resistance value from your DMM through GPIB and converting it to temperature in your program.I want to know where the problem is occuring.For this I would like to request you to check the resistance value on your DMM when it is not connected with your PC through GPIB cable and device.If the resistance value changes even at the constant temperature, then it seems that there is some problem on your DMM.But if the resistance value is always correct on DMM and it becomes incorrect only in your program, then it will be helpful for me if you attach your VI.

Waiting for your kind reply.

Thanks in advance.

saha | AE | National Instruments, Japan

[Kazu]

Hi, K.Saha.

Thank yoy for your reply.

I try to measure the resistance without using GP-IB(I set the hand-change mode)

so DMM shows correct value in one cycle(from first to last channel)

But when DMM and scanner are contoroled by PC with GP-IB, The value of resistance is always incorrect.

therefore,　I attached VI and Please check where the It is wrong.

I am looking forward to your good advice.

Thank you.

[K.Saha]

Hi Mr Kazu

I have seen your VI.As there are some sub VIS are absent and I have no DMM just like yours, I could not run your VI.You are using two instruments(DMM and the Scanner) together.If you use only the DMM, what about the result.you told that resistance value on DMM is correct for the 1st cycle.What about the next cycles?

Your problem is a little bit complicated to debug.So I suggest you to perform a simple test to read resistance value from DMM.

You can do it in MAX(NI Measurement & Automation Explorer).Just open MAX and you can see your GPIB interface under "Device and Interface".Right click on GPIB interface and select "Instrument scan".Your DMM should be detected.right click on DMM and select "Communication with instrument".It will open "NI 488.2 communicator".Just input command and click query.Let me know the result.

Another way for simple test is to use "Instrument I/O assistant(block diagram→Input→Instrument I/O assistant).

Would you please tell me whether there is any error sign on DMM when you start your program?

Thanks in advance.

saha | AE | National Instruments, Japan

[Kazu]

Hi. K.Saha

Thank you for your advice!

I had tried to What  you told me yet but The program isn't good peformance ・・・.(DMM and Scanner are detected the query of DMM shows "error 10")

Error 10 means that  DMM can't understand the code. You may think It seem to be due to broken DMM but I may thinnk this DMM is so old that this can't do.

Is it correct?

DMM can be operated and the resistance value of 2nd cycle is correct.

Now this program has been run in my laboratory at once.( the program I attach is not perfect.)

What part of program is to debag, If the reason DMM can't show corecct resistance isn't due to mechanical(DMM and Scanner) nor defect subVI  

Thanks in advance.

[Kazu]

Hi.K.Saha.

In Addtion, When I input command in NI-488.2 comunicate,  it shows " iberr=EABO"

but this program had been normaly run before・・・.

recently, It is too bad!

Hope your help!!!

[K.Saha]

Hello Mr Kazu

Thank you for performing experiment according to my request.I think you did it in MAX.Am I correct?Make me sure that you get error 10 every time you query on NI-488.2 communicator.what type of command did you use to query?I suggest you to use the most simple command like "*IDN?" and inform me the result?If error 10 occurs,then I request you to see the help of NI-488.2(Start→All Programs→National Instruments→NI-488.2→NI-488.2 help).Search the "EOIP error code" under  Index  tab.Here you will see the solve for this error.

I think your LabVIEW program is not bad.there is something wrong in communication with the DMM.

Please try to solve the error 10 and let me know the result.

Thanks in advance.

saha | AE | National Instruments, Japan

[Dennis_Knutson]

Do you get the "error 10" displayed on the meter/scanner or is it from the LabVIEW error out cluster? If it's from the error cluster, then it does not mean the DMM cannot understand the code. It means "New I/O attempted with old I/O in progress." To test to see whether you are scanning to fast, run your VI with highlight  execution mode turned on or set a breakpoints at the VISA Read/Write functions in your sequence structure. If you get the correct readings, then add delays. In your case, this is simply done by adding additional frames in the sequence structure with a Wait (ms) function.

I also question whether you really need a GPIB Initialization function as the first step in the first sequence. Also, since you've got all of the error in/error out connections made, you don't need the sequence structure at all.