How do I zero 4 load cell channels with Signal Express?

[La-Z-Man]

I am using an NI9237 with Signal Express. I have 4 load cells each with there calibration data entered into the tables. They each are reading different data with no loads being applied. One is reading 130lbs another is reading 320lbs. etc. How do I zero these out. I have a 0 calibration point of zero but this doesn't seem to matter.

Can anyone offer any assistance as to how to correct this issues.

I was on tech support and they walked me through "devise" calibration but upon hitting the calibration button it give me an error of conflict.

La-z-Man

[La-Z-Man]

I am using an NI9237 with Signal Express. I have 4 load cells each with there calibration data entered into the tables. They each are reading different data with no loads being applied. One is reading 130lbs another is reading 320lbs. etc. How do I zero these out. I have a 0 calibration point of zero but this doesn't seem to matter.

Can anyone offer any assistance as to how to correct this issues.

I was on tech support and they walked me through "devise" calibration but upon hitting the calibration button it give me an error of conflict.

La-z-Man

[LVbum42]

This forum post seems to be very similar to the issue you are having.  They were able to calibrate the load cell to zero by adjusting the linear scale of their load cell in Measurement and Automation Explorer.  The applciations engineer in this forum has step by step instructions verifying that the DAQmx drivers are present first off.  It seems you can adjust linear scale with the sensitivity of your load cell as the slope and the offsets you are receiving as the y-intercepts.  Hope this helps.

How do I condition and zero (null offset) a load cell in Signal Express using SCXI 1520 & 1314?:  http://forums.ni.com/t5/SignalExpress/How-do-I-condition-and-zero-null-offset-a-load-cell-in-Signal/...

Regards,

Isaac S.

[OKors]

A custom linear scale with your signal offset as your y-intercept is a common method but you have to do this for each channel separately.
There is a Zero Offset step that you can drop right into the step setup. Be sure if your saving data that your saving the post offset signal.

[La-Z-Man]

Okars,

Thanks for all the help, sorry for the delay-been on vacation.

I have placed the cal information for each channel as it correlates to each load cell.

I don't understand what you mean signal offset.

How do I put a Zero Offset step into the step setup? Where?

I apologize, NI is totally new to me. My previous equipment had a low scale setting that you would zero and a high scale and your done....

Thanks,

Ted  

[OKors]

Let me ask you this...

• How are you conditioning your load cells? In other words, when you add the DAQmx Acquire step are you selecting Custom Voltage with Excitation or Force (Bridge)?
• What are you entering as your cal info for each load cell? Slope or mV/V Sensitivity?

If using the Force (Bridge) option, I'm pretty certain you HAVE to use the mV/V sensitivity and the only way to zero the offset is to add a Zero Offset step found under: Processing> Analog Signals> Zero Offset

If using the Custom Voltage with Excitation, you'll need to create a Custom Scale (Linear). In this custom scale you'd enter the Slope if you have that info available. Within this custom scale window is also where you'd include the Offset (or y-intercept).
You can use the Zero Offset step with Custom Voltages also but I prefer to use the y-intercept if I'm working with low channel counts and signals that do not require a re-zero all the time... its personal preference really, and makes for a tidier step setup panel without all the extra zero steps. The Zero Offest step and y-intercept accomplish the same thing.

Provide those details and we'll go from there.  

[La-Z-Man]

I am using Force Bridge Full and am set to mV/V.

Where do I find Processing>Analog Sifnals> Zero Offset?

[La-Z-Man]

OKors,

I am also now getting an error messege telling me I need to choose Newtons instead of lbs. However when I do this I get the same error. Any clues?

[OKors · Accepted solution]

Are you setting the Units to Pounds in  BOTH the Force Bridge setup screen AND the Configure Scale screen?

In the Force Bridge Setup screen under Signal Input Range set your Scaled Units to Pounds. Then click Configure Scale... enter your mV/V sensitivity as your Electrical "Second" Value and the full scale range of the load cell under Pysical Second Value. Also set the Units to "Pounds". After you click OK GO BACK INTO THE CONFIGURE SCALE WINDOW TO BE SURE THE NEW SETTINGS SAVED This is a known bug that's being worked on.

The Zero Offset step is found under Add Step> Processing> Analog Signals... Zero Offset (sixth one down).

Are you running the full licensed version of Signal Express or Trial? If a trial you may need to unhide the licensed steps in the Options settings under General.

[La-Z-Man]

The scaled units is greyed out and will not let me make any changes to it.

I am doing a full bridge with 4 load cells. All cells are listed in a sub group, do I need to do anything else?

I am running the LE version of SE.

[OKors]

It sounds like you're using a Custom Scale.

Under Custom Scaling select "No Scale" from the drop down list. This should allow you to toggle the Units in the signal input range.

BTW, you're not using the Custom Scale AND the mV/V sensitivity from the Configure Scale screen are you? it should be one or the other, not both. Custom scale is for a y=mx+b slope calibration scale, the Configure Scale settings are for when you're using the mV/V sensitivity as is commonly found on the mfg's datasheet.