Contributions incorrect in a continuous model with lags when selecting non-contiguous observations (Q893)

Summary:

Contributions in SIMCA^®-online 15.0 are computed incorrectly for a continuous (non-batch) project that uses lags in the model.

Symptoms:

This happens when:

Selecting observations that are non-contiguous (not consecutive). For example: selecting observations 1 and 3, but not 2.
Selecting two blocks of observations to compare them, if the first selected block is older (has earlier time stamps) than the second block. For example: selecting observation 1 first in one block, and then selecting observation 2 (resulting in that observation 1 is blue and observation 2 is red in the plot).

Cause:

SIMCA^®-online doesn't include all data needed to be able to compute the values of the lagged variables, causing errors in the contributions.

Workaround:

If contributions are very important, SIMCA^® can be used to compute them: Use the Update SIMCA^® project functionality in SIMCA^®-online to add the relevant process data to the project file. Then you can predict this data in SIMCA^® (offline) with the original model, and finally create the contribution plot in SIMCA^®.

Note that you can still create contributions to average in SIMCA^®-online by selecting a single contiguous block of observations (no gaps in time). And you can still select two blocks of observations and create a contribution plot when the first block is more recent than the second block, and the blocks are contiguous (and next to each other).

More Information:

Internal Sartorius bug number: 21001.

Status:

This problem is fixed in SIMCA-online 16.1.2.

SIMCA^®-online 15.0.1 includes a fix in the client so that erroneous contributions will never be displayed, but instead a small message is displayed alerting the user of the limitation.