How do I eliminate noise in an analog signal using a filter?

[Joey Wood]

I have noise in a 0 to 5 volt signal. I am attaching a sample vi that when I run it Whatever My number is going in is different when it goes through the filter why is this?

[GabbyG]

I do not see your problem.
The nature of filtering is a modification of one value in accordance with the surrounding values. The alogrithm of how to "correct/modify" a certain value will change. But especially with floating point values it is most improbale to get the same value at input and output.
Gabi

[Joey Wood]

What kind of difference should I be seeing? I am measuring j type thermocouples and I am reading 74 deg F in and getting 5.1 out. What does a filter actually do? My Temperature is jumping 1 to 2 degrees and thats to much. Is there a better way of slowing down this fluctuation?

[GabbyG]

A correct filter type to get rid of noise is a low pass filter. Very basicly it takes the previous value(s) and calculates new value(s). So if the previous value is 0 and the next one is 100 it will probaly come out with something like 50, 50.
In your vi you take a single sample of several parallel channels into one array and present it as input to the filter vi. But this vi takes it as a sequence (in time) of one single reading and tries to compare them to each other.
You might rather want something like a sliding average.
Initialize an array (of e.g. ten) with zeros and in a loop replace one element after the other with a new reading. At the end restart from the beginning. Take an average of the readings and the result will reflect
the last (ten) samples.

Gabi