Why are my results correlating with each other?

[Ellen_Ward]

Hi,

I'm using LabVIEW 7.1 to read data from several RTD-01's on an SCC2345.

I have two pt100 sensors wired to each RTD-01, every 10 minutes I collect 100 readings at 100Hz and average the results to give me one value - a crude filtering method I know, but it works reasonably well. However, I am finding that the readings from each pair of pt100's correlate with themselves (e.g. 1.1 correlates with 1.2, but not with 2.1 & 2.2). This is not worrying me too much, however my boss wants an explanation and I must confess I can't provide him with one other than by saying that because 1.1 and 1.2 are on the same module block there must be some affect from the signal conditioning unit.

Can anyone provide me with a better insight into this?

Many thanks

Ellen

[RobSims]

Hi there Ellen,

Thanks for your post.

If I have interpreted your post correctly you are taking the average of 100 samples on each Pt sensor? Giving you two values (one for each sensor) for each sample 'session' every ten minutes? With several sample sessions completed you now wish to correlate these session values together for further manipulation?!

I've seen several possible interpretations within your post, but I've assumed this one. If I've picked the wrong one could you clarify a little further your desired method of data processing, and at what point in the process the system deciding to misbehave. That should help me get more of a handle on things.

Having said that, it sounds to me as if there may be an issue within the LabVIEW code you are using, rather than the signal conditioning and data acquisition hardware itself.

The signal conditioning unit will simply pass voltages/values back to the calling program when triggered. So, provided that you are getting a value returned from each Pt sensor at each sample intance, you should simply get an array of data fed back for multiple sampling instances (your array for each 'session'). From here on those values should be stored in memory allowing you to manipulate that data within software as you see fit.

If you would like me to take a look at your LabVIEW code please feel free to upload it in your reply.

Many thanks,