using a custom scale?

[maxpower]

I have an application that will measure a barometer sensor connected to a USB-6008.  The voltage range and milliBar output relationship is as follows:

Baro Sensor Output

Minimum Voltage         -4.0 VDC      812.7 milliBar
Maximum Voltage       +4.0 VDC      1083.6 milliBar

I couldn't find any examples in LabVIEW Help.  Any ideas how I can use the custom scaling in DAQmx 7.5, specifically "DAQmx Create Scale"?  I'm using LabVIEW 7.1, DAQmx 7.5 on a Windows XP system.

Thanks for any assistance,
tsc

[Travis_W]

Max

Here [link removed; article no longer available] is a link that should help you out.  It describes how to programmatically create and utilize custom scaling with NI-DAQmx.

Sounds like you need slope = 33.8625 and y-intercept = 948.15.

One way to easily test this out it to create a NI-DAQmx Task in Measurement and Automation Explorer and choose to include a new custom scale.  After doing this, you can test the input and see the post scaled values all within MAX.  Its pretty cool.

One important thing to note is that the analog input limits (both in MAX and in LabVIEW) are post-scaled values.  When you include this scale you should change your limits to 812.7 - 1083.6.

Cheers,
Travis W
DAQ Enthusiast

[Simon GB]

I've also been trying to get custom scaling to work in Labview 8.2.  Unfortunately the maximum scaled value required for one channel is 240, and I discovered that the DAQmx 'Create Channel-AI voltage' VI for some reason will not allow a maximum above 98.  None of the other versions of the VI seem suitable, is there any way around this?  Scaling later on would be messy as in each loop I'm reading in a range of channels as a 2D array and want to display scaled results as they are collected.

Thanks.  

[Simon GB]

Ahh, I've just worked it out.  For the benefit of anyone else interested I think that the max and min voltages on the Create Channel VI are limited to the real world limits of the the acquisition card after the custom scale has been applied.  I thought that 98V was a strange number for an inbuilt limit.