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Basic Operation
Adjusting the Span 2
2-9
Adjusting the Span
The full temperature span of the Imager is -10 °C to 350 °C (14 °F to 662 °F). The LCD
display shows about 256 shades of color for whatever pallet you select. Adjusting the
temperature span allows you to see more subtle temperature gradients in a captured
image.
For example, if you are viewing an image with a temperature span from 10 °C to 30 °C
and are using the Imager at full temperature span, the image will be concentrated into
only about 15 of the 256 shades that could be shown. Reducing the temperature span to
10 °C to 30 °C allows you to view the display with the full range of about 256 shades.
1. Press G (
HOME) one time from the Home display to access the set Mode menu.
2. Press F (
MANUAL) to manually set Level and Scan mode or H (AUTO) to
have the Imager automatically set Level and Scan.
3. Press H (SPAN) to access the set Span function.
4. Press F (5 4) to close the range window or H (4 5) to open the range
window. The minimum temperature span setting is 5 °C.
Manually Activating the Calibration Flag
When the Imager is first turned on, the image freezes briefly from time to time and an
hourglass icon appears briefly on the display. This is a normal process that happens when
the unit momentarily shuts down the optical channel to eliminate offset errors. This is a
recalibration sequence that begins immediately after the unit is turned on.
Recalibration intervals occurs at 15, 30, 45, and 60 seconds and continues every
60 seconds unless a change in ambient temperature occurs. A change in the internal
temperature of 0.2 °C (0.4 °F) forces the Imager to recalibrate before the 60 seconds are
up and the new calibration cycle starts at that time.
To manually activate the calibration flag, press H (
FLAG) from the Main or Home menu
to start the recalibration sequence.
Using Distance to Spot Size Ratio (D:S)
The Ti20 imager views a portion of the scene that is 15 º high by 20 º wide (the Field-Of-
View (FOV), of the Imager) as shown in Figure 2-3. This scene is displayed on the LCD
on the back of the Imager. The single temperature displayed numerically at the lower
edge of the display, however, corresponds to a measurement of a much smaller part of the
scene. In particular, it corresponds to the average temperatures of the area seen through
the “hole” in the center of the reticle on the LCD display (see Figure 2-3).
The actual diameter of the measurement spot at the object is calculated by dividing the
distance to the object by 75 (the D:S for the Imager). If the Imager is properly focused on
a target 100 inches away, the diameter of the measurement spot on the object will be (100
inches) ÷ 75 = 1.33 inches. If the Imager is focused on a target 24 inches away, the
diameter of the measurement spot on the object will be (24 inches) ÷ 75 = 0.32 inches.
To achieve the smallest measurement spot (D:S = 75:1), the imager must be properly
focused on the object being measured.