The traditional optomechanical design of the IR temperature
measuring systems was shown to produce inaccurate results when
directly ported into handheld mobile devices. Traditional systems
were optimised for situations in which the device is thermally stable
and when the measured targets were significantly warmer than
the device. When these assumptions are not valid, the measurement
error can be several degrees. Based on first principles, an
optomechanical designwasoptimised for handheld mobile use. The
system performance was modelled and then tested by a laboratory
prototype. The attainable repeatability of the implemented sensor
prototype using correct calibration curves measured by 2.5 ◦C intervals
was better than ±0.5 ◦C in an operational temperature range
from +12.6 to +49.3 ◦C and a target range from +10 to +90 ◦C. Utilizing
the correct calibration curve is a necessity in order to attain
a repeatability of better than ±1 ◦C in the IR temperature measurement
with an operational temperature range of −40 to +80 ◦C and
a target temperature range of −40 to 120 ◦C required typically in
mobile devices.