daqmx custom scaling setup issues

[Guzz]

I'm trying to setup a custom scaling on daq mx to achieve the following

input 0-10v

scaled output -50 to 120 (degrees)

i set up a mapped range to scale it thou it sticks at just over 40deg (5.3v) whereas the raw voltage continues to rise as expected

is there a limitation on the custom scales? (i've also tried it as a table & linear range)

[John.P]

Hi Guzz,

There should not be a problem using the cusom scale with this sort of range.

The scale should be linear, with a slope of 17 and a Y-intercept of -50.  Can you confirm these are the settings you are using?

Also are you sure the raw voltage is rising about the 5.3 volts? How are you testing this?

Have a look at this Knowledge Base article for more information on custom scales.

I hope this helps,

Regards, 

John P

AE

NI

[Guzz]

yip, it shouldnt be a problem - yet it still is 😄

the input voltage is definatly working, if i turn off the custom scaling its fine and i've probed it with a meter

i originally had it set to 17x-50 as you would expect....thou no joy (or with any other scaling method)

i've currently got it scaling on the fly for displayed values thou this isnt suitable for logging the values to a measurement file as the values are read in as waveforms

i could use the waveform scale and offset vi thou this is avoiding the issue

thanks

[John.P]

Hi Guzz,

I can find no reason for the behaviour you are seeing and i am unable to replicate the problem.

As a workaroud i suggest simply applying the scale to the DAQmx output using nodes,(multiply by 17, minus 50).

If you use the ouput from the node (as opposed to the outoput from the DAQmx Read VI in the rest of your application the values will log correctly.

Hope this helps,

John P

AE
NI

[Guzz]

the workaround is possible thou doesnt address the potential issue with the driver

i'm using a pci-6221 (37pin) with the analog signal on ai 0

[John.P]

Hi Guzz,

Generally custom scale issues are just caused by a missing setting somewhere.

How are you setting up the custom scale? In LabVIEW or MAX? Are you setting a minimum and maximum range on the DAQ task?

Have you tried creating the scale in MAX and using a simply DAQ Assistant in a new VI, do you still see the same behaviour?

If this is the case can you please post the code so i can take a look at it?

What version of the DAQmx driver are you using? Have you tried repairing / reinstalling the driver?

Kind Regards,

John P

AE
NI

[Guzz]

hi

i'm using labview 8.6, max 4.5 & daq 8.7.2

i'm creating a daqmx task in the labview project to define the sampling and create the task

when i run this task from the daq assistant (double click on the task in the project view) it works with no scaling but sticks at the equivilant of 5.2volts with a custom scale set

[John.P]

Hi Guzz,

Can you please post your code so i can take a closer look at this for you?

Thanks

[Guzz]

There is no code involved at this level of investigation, i'm testing it using the task created in the labview project (daq assistant)

signal input range of 0-10, RSE terminal configuration

with custom scaling set to 17x - 50 it jams at the equivilant of 5.2v, with no scaling the value continues on past it

[John.P]

Hi Guzz,

I meant the VI with your daq assistant in, I wanted to check exactly what settings you were using.  I was unsure if you were creating the scale programatically using the DAQmx Create Scale VI, or if you were creating a custom scale in MAX and importing this into a DAQ Assistant Express VI.

I think your problem may be arising from your maximum and minimum values.  When you set a custom scale the max and min values relate to the custom scale,  not the raw input.  Take a look at this KB.

Also it is worth setting this up using DAQmx VI's instead of just testing with a DAQ Assistant.  Have a look at this KB which explains setting a custom scale using the DAQmx VIs.

 
I have tested the same custom scale using both a DAQ Assistant, and the DAQmx VI's and have had no issues with incorrect scaling.

I suggest playing around with your maximum and minimum values, and setting up a simple DAQmx task using the low level VIs to see if you still have the same problems.

Let me know how you get on.

Regards,

John P

AE
NI