programmatically creating linear scales

[hprd]

I think I am having trouble with a linear scale.

I am making displacement and load measurements that require each channel to have their own scale.  I loop through the channels in my configuration and use a linear scale to scale the data so that the VI acquires in engineering units. 

When just the displacement or load VIs are run in my main VI, they read correctly.  When I use both at the same time the load data and displacement data mix.  For example:  When I apply a -20lb load (compression) and move the displacement sensor 1 inch, the new load is -19lbs. 

I believe I've isolated the problem to the linear scaling.  I did this by using diagram disabling on each part of my code.  By disabling the linear scales, I no longer have a problem.

Has anyone experienced a similar situation before?

I'm using LabView 8.1

[Chris_Co]

Hi hp,

I have attached a dynamic task creater that scales individual channels in LV 8.0.  Ensure that all arrays are of same dimension and it should work for you.

Chris

[hprd]

Thanks for your help.

I finally traced the channel interference problem to poor settling time on the analog-to-digital converter.  I slowed down the convert rate to less than 25kS/s and the problem went away.  It was not the linear scales as I had thought.

HP

[SSAC-Smith]

Your comment that you solved your "channel-interference" problem (that is normally called crosstalk) points up a potential problem with all multiplexed data acquisition systems (and some others but these are the worst).

The specified performance of the systems assumes that the source (transducer and cabling) impedance is essentally zero. If this is not the case, the resistence combined with the capcitance of the multiplexer buss will produce a low-pass filter that "slows" the slew of the voltage when the channels are switched. The voltage read will be a mix of the earlier and present channel.

The solution is to put an amplifier ahead of the channel. But this is expensive. You don't get something for nothing... ss