Setting The Infrared Light Sensitivity; Ir Light Sensitivity Levels - Northern Digital Polaris Vicra User Manual

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Setting the Infrared Light Sensitivity

7.1

The IR light sensitivity level determines how sensitive the Polaris Vicra System is to IR light.

Background IR Light

Background IR light is IR light that is not reflected (passive) or emitted (active) from a marker, but

is detected by the Polaris Vicra Position Sensor. Background IR light can be direct (light bulbs,

sunlight) or indirect (reflections off shiny surfaces or draping). In particular, IR light in the 800 nm

to 1100 nm range can interfere with the Polaris Vicra System's ability to track tools. For example,

some types of operating room lights emit IR light that is detected as background IR.

The IR light sensitivity level controls the Polaris Vicra System's ability to tolerate background IR

light.

Trigger Level and Integration Time

The integration time is the time in which the Polaris Vicra Position Sensor collects IR light.

The trigger level is the minimum IR light intensity considered to be valid marker data. The Polaris

Vicra System uses the trigger level to distinguish between marker data and background IR light. IR

light that falls below the trigger level is rejected by the Position Sensor. The trigger level increases

with the integration time. In general, as the sensitivity level increases, so does the trigger level.

During operation, the Polaris Vicra System makes adjustments to the integration time so that the

intensity of the brightest IR light detected is set to a maximum value, and the intensity of all other IR

light detected falls below this value. Changing the sensitivity level does not change this maximum

value. Thus, when the sensitivity level changes, the integration time does not change but the trigger

level does.

The relationship between trigger level and integration time for each sensitivity level is illustrated in

Figure

7-1.

Polaris Vicra User Guide - Revision 2

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