Remove channel from DAQmx task - reconfigure open tasks and Calibration

[bestware]

Is there still no way to remove an AI channel from an existing DAQmx task? I know that it's possible to add a channel to a task using DAQmxCreateAIVoltageChan.

Removing seems to be possible only by clearing the task and creating a new one, but this ends up in error -50103 (The Specified Resource is Reserved.) at creating and clearing a task continuously (after ~ 100 - 1000 iterations).

Measuring device is USB-6225.

Any idea ?

[thomas.weskamp]

Dear bestware,

the 6225 device is a multiplexing device. In every case of changing the channels of the task, the multiplexer has to be reconfigured. The best idea of having a lot of fast aquisition channels may be a simultaneous sampling device. Maybe this link will assist you in choosing the best device for your application:

https://www.ni.com/en-us/shop/category/multifunction-io.html?productId=118688

Regards

Thomas

[JDubb007]

I have a similar question so I figured I would start here.  I am using a NI PXI-4330 8-Channel Bridge Input Module to take torque measurements from seven of the eight channels.  The problem is that I may not have all seven sensors connected to the PXI 4330 once I start my VI and need to be able to add channels to a task that is already running w/out disruption.  The help manual indicates that there are internal channels (typically used for calibration) that can be used instead of the external channels.  Is it possible to use the onboard analog gnd (internal channel) as the physical channel input then sometime later switch over to the external sensor w/out stopping my task?

My second question is regarding an error that I receive while attempting to calibrate a channel.  Everytime I attempt to do this, either using the VI in LabView or through MAX, I get the following error:

Bridge Calibration

Error -200077 occurred at Bridge Calibration

Possible Reason(s):

Requested value is not supported value for this property.

Property: AI.Bridge.ShuntCal.GainAdjust

You Have Requested: 460.140823

Valid Values Begin with: 500.0e-3

Valid Values End with: 1.500000

Thanks

[escalator]

Hello  JDubb007,

referring to your second question there is a knowledgebase entry:

Error -200077 When Performing a Calibration in LabVIEW or Measurement & Automation Explorer

http://digital.ni.com/public.nsf/allkb/440EB533229211CD8625711C007E61B3?OpenDocument 

If it does not help, it would be useful to get more information on installed hard- and software.

As for your first question I might need some more time.

[escalator]

Hello JDubb007,

changing channels generally requires restarting the whole task. On the other hand there should not be any limitation if you connect the unused channel to the ground at the beginning of your measurement. Later you can connect your signal to those channels.

[escalator]

Hello JDubb007,

this case is going to be closed after 5 workdays automatically, if you do not have further questions.

Best regards

[JDubb007]

Hey llja,

     Thanks for the informaiton regarding this problem.  I have been running my VI with the calibration disabled and had forgot that this was an issue.  The good news is that I was able to add all the channels that I need at the beginning.  I believe the problem I was experiencing with adding the channels was due to the fact that I was trying to calibrate each channel.  Now, my VI is set up such that, I create a Channel then use a Case Structure w/in a While loop to perform my calibration.  Everything works fine that way (as long as Calibration is disabled) regardless of whether I have anytype of sensor actually connected to my NI PXI 4472B DAQ or NI PXI 4330 card. When I actually connect a device to my DAQ I can immediately sample and view the data on my Front Panel.

     However, I am still experiencing the calibration issue.  The link that you posted was useful, but I think that I may have something else setup incorrectly.  The error suggest that my minimum and maximum input ranges are setup incorrectly.  Attached are screenshots of the error.  You'll notice on the third slide the Requested Value is 127.684456e3 while the Valid Value Begin is 500e-3 and Valid Value Ends is 1.5.  Based on these values I can understand why it's giving me this error, but I don't understand where the Requested Value is coming from? This occurs regardless of whether I'm using Simulated I/O or have a device actually connected to my 4330.  I noticed that the Requested Value changes whenever I change Minimum and Maximum  values to the Create Channel VI, but the value itself doesn't make sense.  I also don't know why it believes 1.5 is the maximum value. 

Thanks

Jeff

[Brad_K]

Hi Jeff,

The requested value for AI.Bridge.ShuntCal.GainAdjust is calculated by DAQmx when you call DAQmx Perform Shunt Calibration.vi, based on the calculated bridge value with the shunt resistor connected, the measured bridge value with the shunt resistor connected, and the assumption that the bridge's offset has been nulled. When this calculation results in AI.Bridge.ShuntCal.GainAdjust being used to compensate for an enormous amount of gain error, that usually indicates that there is a wiring problem, such as if the shunt resistor terminals are not actually connected, or they are connected to a different leg of the bridge than was specified for the "shunt element location" input. If this happens, then when DAQmx tries to enable the shunt calibration resistor, there is no change in the bridge deflection, which looks like a giant amount of gain error.

How do you have the QTR/SC terminal connected (as well as the others)? Here's the wiring diagram from the manual.

(Note: DAQmx simulated devices currently do not simulate "correct" data for shunt calibration, so they have the same effect as if the shunt calibration resistor was disconnected.)

Brad

[JDubb007]

Hey Brad,

    That explains everything!  My shunt resistance and QTR/SC terminals were not connected.  I added wires to jumper AI+ to QTR/SC, EX+ to RS+ and EX- to RS- and that seems to have done the trick.  Thanks a lot for your help!