Creating Lookup table in Labview 7.1

[Imti]

For a particular input voltage, the output is distance in cm. For example if the the voltage is 6.2mV the output should be 2.5cm, for 6mV the output is 6cm. Whenever an input voltage between any of these values is given, the output should be interpolated and displayed in cm. I would like to maintain a lookup table for this purpose in Labview 7.1. The graph between input and ouput is a linear graph. I would to know how to create a lookup table and configure it in Labview 7.1..

[johnsold]

A lookup table can be an array, either a diagram constant or a front panel control with vaules saved as default.

If the process is linear, you could enter the slope and intecept values and calculate the values from that. I think you can set custom scaling in DAQmx which would allow your readings to come out directly in distance units.

Lynn

[Imti]

my experiment is calculating linear displacement using photovoltaic cell. i have the experimental values. and according to the theory , the voltage and the displacement must vary linearly. but due to disturbances and errors, they may not vary linearly at some points. how should i proceed? please suggest....

[Ben]

Well since it is still AE Week here is an AE implementation of a LUT

Inititalize it with an array of raw values along with an array of the tranlsated values.

Use the Lookup action to translate raw to tranalsted.

Itr uses the threshold and interpolate VI to do the translation.

Ben

Message Edited by Ben on 04-12-2007 12:45 PM

[Imti]

 thank you for the solution. but i m just a biggener in lab view, and i couldnt actually get the concept of AE. could you please help me out in some other way. it will be fine even if interpolation cannot be done ie. it wil be fine if it displays one output for a range of inputs.

  voltage         distance

4- 4.2 mv          2 cm

4.3- 4.5 mv       1.5 cm

so if my input is 4.1 mv , it should display 2 cm

 please suggest me how to procede....

[Ben]

Here is an enhanced version complete with demo.

THe LUT has been updated as well.

I start by defining the Look-up table using the "Init" action.

After that I enter a loop were a random number simulate the measurement and the LUT is used to do the translation.

Have fun!

Ben

Message Edited by Ben on 04-13-2007 07:31 AM

[Imti]

i m actually confused.... for the LUT ypu sent, where do i enter my values of range of voltage and its corresponding displacement? what is the necessisity of random number generator? moreover i m not able to run it on my labview....

[Ben]

Are you using the ctl I posted in the previous post?

The left array passed in to the "Init" are the physical values.

The right array contains the translated values.

The random num just simulates a measurement.

Ben

[Imti]

yea i did include the .clt file.....

could u please tell me if look table is the only way to solve my problem?

i mean,  for the table i mentioned, if i give 4.1 as input, the output should be displayed as 2 cm.

[Ben]

For the limited info you have provided, it would also be possible to do this with a case structure.

Try running my demo in execution highlighting mode and watch how it works.

Ben