Self-Cal NI 9205

[Jafor]

How do I self calibrate an NI9205?  I downloaded the manual from the NI website and tried to follow it, but I'm missing some essential information and have no idea what it is.

[CarlaU]

Hi Jafor,

Which manual did you download? Did you look at the NI 9205/9206 Calibration Procedure? What essential information are you missing? When you open this manual, look at page 6. This is where is talks about self-calibration. Basically, you just need to find the device in Measurement and Automation Explorer. Right-click on the device and select Self Calibrate. It should walk you through the steps there. Also, have you looked at ni.com/calibration? This page has a lot of information regarding calibration of devices. I hope this helps!

Carla

[Jafor]

Yes I have the NI 9205/9206 Calibration Procedure and I did look on page 6 and created the vi.  The procedure does not tell you where to put the vi.  I assumed that it would go in the RT part of the project.  But is dev1?  The procedure says this refers to the device.  Which device?  The cRIO, the FPGA the IO module.  I assume its the IO module.  Since I've been using MAX I have never seen an IO module listed there.  It only shows the cRIO devices on the network.  So its kind of confusing when you say to bring up a device in MAX that I've never seen listed there.   And if I right-click the cRIO or whatever is in the MAX list there is a menu that comes down and there is NO self-calibrate.  We have NI-DAQmx 8.5, Labview 8.2.1

Thats why I say that something is missing here.  What am I not doing?

[CarlaU]

Hi Jafor,

The procedure in the manual is for the 9205/9206 module used with a CompactDAQ chassis. From your previous post, I’m assuming now that you are using this module with a CompactRIO chassis instead. The calibration procedure is different for this case. The calibration information for that particular module, such as the offset and the LSB, should come with the module information. If you open up one of the examples in the NI Example Finder (for instance, NI 9205 Basic IO.lvproj), you can see that there are property nodes that get the calibration coefficients in the FPGA code. These coefficients are then used in the RT host VI to convert the data from binary to a nominal value.  So essentially, the self-calibration is already done for you. You can actually not go into Measurement and Automation Explorer to do the self-calibration for the cRIO. In addition, that VI that the calibration procedure says to create is also used for CompactDAQ and not CompactRIO. Any other type of calibration you are going to want to do on the module will have to be sent in to National Instruments. I hope this helps clear up things! Have a great day.

Carla

[Jafor]

Thanks for the reply, Carla.

But it seems that we have no recourse here but to replace a bad module.  While doing some testing we ran into a problem in which one of our modules was measuring twice the value of the other.  I looked at the code and could not find where this was happening until we monitored the calibration coefficients for the two modules concurrently.  We noticed that the two offsets were way off.  So barring having to replace the (scarce) module, we thought we would attempt to "self-calibrate."  I did not see the documentation that says we need to have a CompactDAQ.

[CarlaU]

Hi Jafor,

Thanks for your reply. Can you clarify a bit more of the problem you are having with the NI 9205 module? Were you testing the two modules with the same signal? What type of values were you getting with each of the modules? Did the module use to give you different values? If so, how far off are they and when did this occur? The offsets of the two modules could be very different. Essentially, the offset and LSB Weight differ per module since they are used to convert analog input values to calibrated engineering units. One thing that could be interesting to try would be to run the example NI 9205 Basis IO.lvproj and see what sort of values you get for each of the modules. This could help us determine if it is truly the module or if there is something in the code that we could change. I hope this helps!

Carla

[Jafor]

We have 2 cRIOs that are currently recieving the same physical signal (DC voltage level).  Each RT takes it, encodes it to TCP then sends to another system via ethernet.  The other system receives the two messages, decodes them and display on a labview OMI.  Our first indication was that one of the signals was twice that of the other.  We traced the problem to one of the cal coefficients in the bad module.  LSB weights are very close but the offsets are very different.  We swapped the 9205 modules from cRIO chassis' and the problem followed the module.  Now we need to get another module or send it back to NI for cal (if this will fix it). 

We have probed the RT code in debug mode and then brought up the FPGA code which displays the coefficients.  As I mentioned before, we most likely have a bad 9205 module.  We don't have the means to calibrate.

[Bassett_Hound]

Jafor,

Have you used the 9205 module with the Shipping example and seen the same results?  Its a little unclear in the posts if your using the LSB Weight and Offset values to calibrate the Integer values returned from the modules.  Typically this would be done by passing the Binary value, LSB weight, and Offset values into the Binary to Nominal.vI in order to convert the data to calibrated engineering units. I would suggest the 9205 Basic IO example as a starter that can be found with the NI Example finder.  The path to the Binary to Nominal VI can be located at the following directory or in the example:

C:\Program Files\National Instruments\LabVIEW 8.5\examples\CompactRIO\Shared\Binary to Nominal.vi

 Its very possible that different modules will have different LSB Weight and Offset values as these values are calculated at the factory and depend on the ADC on a particular module.

Also, NI RIO 2.4 now inclucdes support for Returning Calibrated Engineering units in Fixed Point out of the I/O nodes.  If your able to upgrade I think you might like it.

Bassett Hound

[Jafor]

Yes we are using Binary to Nominal.vi and yes we are selecting the 9205 case

Our FPGA code waits until coefficents are valid before we use them in the RT code.  We use the Read/Write property node and pull out the coefficents to use in the Binary to Nominal.vi.

I think this is irrelevant as we have traced the problem to a bad 9205 module.  This is because when we run the FPGA code ONLY for both modules and read the coefficents the offsets aren't even close. 

My original question was "How do I self-calibrate," and we don't have the means to do that in our lab.  So we have a bad module and it must be replaced.

[CarlaU]

Hi Jafor,

If you have tried the example mentioned above and  are still getting incorrect values for that particular module, then I think that in this case the best method for National Instruments to help you would be through email or phone support. Please go to ni.com/support and click on the link under request support in order to find more information about this. Have a good Monday!

Carla