HT HN000100, User Manual

Page: 43 / 52

THT100 - THT200 - THT300
EN - 42
5.6 CHARACTERISTICS OF THE LENS
The instrument is provided with a 9mm focus lens (THT300) or 7.5mm (THT200,THT100).
The theory of operation is reported below, based on the 9mm lens.
Definitions

FOV (Field Of View)

Visible range

represents the maximum angular opening
(expressed in degrees) the instrument is capable of managing at a certain distance.

IFOV (Instantaneous Field Of View )

represents the smallest detail within the FOV,
that the instrument can detect at a certain distance. It is expressed in radians by the
following formula:
IFOV (theoretical) = (size of sensor's pixels) / (focus length of the lens)

D:S ratio

Ratio Distance / Cross-section of the target object

it provides
information on the maximum distance between the instrument and the target having a
certain cross-section (spot) in order to obtain correct temperature measurements. It is
expressed as:
D:S (theoretical) = 1 / IFOV (theoretical)
Case of instrument THT300
FOV = 41.5° (Horizontal) x 31.1° (Vertical)
Focus lens = 9mm
Size of sensor's pxls = 17µm
IFOV (theoretical) = 17µm / 9mm = 1.89mrad
D:S (theoretical) = 1 / IFOV (theoretical) = 529:1
Fig. 48: Representation of the instrument's field of view FOV

Typically, the IFOV parameter (real) is always considered as approx. 3 times higher
than the theoretical one, therefore the D:S ratio (real) is approx. 3 times lower than the
theoretical one. This means that, for THT300: D:S (real) ~ 176:1