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To use Dencytee Arc as an in-line total cell density probe, a relationship between the raw measurement signal (optical density) and the offline total cell density measurement must be established. The Arc Air software creates this offline correlation using a guided model.

Offline Correlation for a Total Cell Density Sensor

The optical density signal obtained with Dencytee Arc can correlate to many types of offline total cell density measurements. The correlation involves pulling and measuring a full series of offline samples at up to 6 time points throughout the duration of the bioprocess. Arcair software is used in tandem with offline sampling at each time point to capture the optical density measurement. The software establishes a correlation between the offline measurement and the in-line optical density signal. With this correlation, future measurements of the in-line optical density are displayed as an in-line total biomass measurement using the specified offline unit. This procedure is automated and user-friendly with ArcAir supporting the workflow and storing the correlation directly on the sensor.

For more information on the default offline correlation models and supported units for custom models, see the Dencytee Arc Measurement Units page.

The offline correlation model can be selected through the settings menu:

For assistance with using the ArcAir software, refer to the ArcAir Guided Tour.

For assistance creating a model, refer to the guide below.

Offline Correlation Guide:

When connected to a Dencytee Arc sensor in ArcAir, select the “Offline Correlation” tab at the top of the screen:

You can build a new correlation model:

Models can be paused while in progress and completed later using the “Continue on unfinished correlation models”. Correlation points can be added or modified with “Edit existing offline correlation models”:

All data used to establish a model is stored on the sensor head, meaning a sensor can be disconnected from ArcAir during correlation and reconnected later to complete the correlation.

When creating a new correlation model, refer to the Measurement Units page (link above).

Correlations must use between two and six correlation points with monotonic behavior (only increasing values). The first correlation point should have the lowest turbidity while the final point should have the highest turbidity. If possible, a correlation point at 20% transmission should be part of the data set. This point is 0.7 A.U. when measured with the default offline correlation model called “Transmission”.

The ArcAir software will guide you through each correlation point. The first step is an initialization:

Included in the initialization is a guided stabilization period (can be skipped if stable for 100 seconds by pressing Next):

During the initialization, the system verifies that process conditions are producing a stable signal.

When the initialization completes, there are options to reinitialize the correlation point (CP), continue to the next correlation point, or enter the offline value:

Offline measurements can be entered immediately or after process completion. If offline measurements are not entered immediately, the initialization stores the measured optical density at the sampling time point. When the offline measurement value is known, it can be entered into this correlation point.

The final step is offline value assignment, which can be entered after the process run:

Finalized correlation points will display a summary of the data, with the option to deactivate the correlation point or move to the next point:

A summary of all correlation points can be found under “Correlation Information”:

Once all correlation points have been initialized with offline values entered, the model will be saved and the offline-correlated total biomass sensor is ready to use.

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