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SCXI-1520 Null-Offset Calibration for Full-Bridge

I am using an SCXI-1520 and 1314 to record data from full-bridge load cells in SignalExpress and I need a way of progrmatically removing any offset.  Is there a way that I can do this using signal express or Measurement & Automation Explorer?  I am using SignalExpress version 2.5.  Thank you.
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carlmill,

 

I'm assuming you are setting up your DAQmx task as a voltage task, is this correct?  If so, when you set up your voltage channel settings, switch to the device tab and try turning Auto Zero on.  I've attached a screenshot of the necessary option.

 

Turning on Auto Zero 

Message Edited by Seth B. on 11-19-2008 01:31 PM
Seth B.
Principal Test Engineer | National Instruments
Certified LabVIEW Architect
Certified TestStand Architect
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Seth,

 

 I am setting it up as a task in DAQmx, but as a voltage source with excitation.  I tried setting Auto Zero to Once (on), but this seems to have little or no effect on the signal.  Some of the load cells have offsets of a couple hundred Newtons after applying a scaling factor and amplification, regardless of the Auto Zero setting.  I am not sure if it matters or not, but I am also using SCXI-1121s cascaded to SCXI-1141s in the same task.

 

Thanks for the help,

 Carl

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Carl,

 

While there isn't a function that will programatically remove any offset, what we can do is determine what our unloaded offset is, then apply a custom scale to the DAQmx task that will correct this offset.  First we will need to use the Test Panels in MAX for your device to determine what value you are reading when the load cells are unloaded.  Then, in the configuration window for your DAQmx Voltage with Excitation task, Select "Create New" from the Custom Scale drop down menu.  Choose a linear scale  Then, apply the negative of your unloaded offset in the y-intercept and 1 for the slope.  This should correct the offset that you are seeing.

Seth B.
Principal Test Engineer | National Instruments
Certified LabVIEW Architect
Certified TestStand Architect
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Seth,

 

I would similary like to programatically remove offset from a Custom Voltage with Excitation source using an NI-9237.  I am trying to use the Offset Nulling VI to do this but am running into some issues.  Any thoughts on if this should work and why not for the above post using the SXCI-1520?

Thanks

Dan

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What issues are you running into?  The firs thing that came to mind is that this is a DSA module which is not specifically made for accuracy but rather dynamic range.  This means that the 9237 is good for measuring relative to something else, and not an absolute value.
Doug Farrell
Solutions Marketing - Automotive
National Instruments

National Instruments Automotive Solutions
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Doug,

 

I found a workaround to my problem through a different post:

"Why do I receive Error 200378 "Custom scale specified does not exist"?

 

Thanks

Dan

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I am having a problem when trying to apply a new scale with a programmatically-reset y-intercept value. Using scale property nodes and the save scale Vi, I am able to update the scale shown in MAX while my VI is still running. However, I cannot get my VI to apply this new scale without stopping and starting the entire VI (not an option for my testing scenario). I tried programmatically stopping and starting the task, as well as reseting the device, but this does still not apply the new scale to my continuously sampled data stream.

 

Any ideas how to make the new scale work without restarting my VI? 

 

Thanks

Eric

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This post is several years old and is focused more on Signal Express.
You may have better luck posting a recent thread in the LabVIEW discussion group.

If you are in fact looking for SigEx help for Nulling any offsets, there have been a few improvements since this OP's first thread in 2008.
One of which is the Zero Offset step which handles this quite nicely.
I prefer to use a custom scale slope and add my own y-intercept however.

SCXI- 1000 Chassis w/ 1346 adapter
PCI 6281 DAQ card
SCXI- 1520 Bridge Board w/ 1314 Terminal Block (x2)
SCXI- 1180 Feedthrough Panel w/ 1302 Block
Signal Express 2014.
Win7 Enterprise
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Thanks for the help. I'm not interested in Signal Express specifically, so I'll repost as you suggested. 

 

 

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