Thermalert ET Series Operator's Manual
3-1
3.0
OPERATION
3.1
THEORY OF OPERATION
This type of infrared thermometer is a sophisticated thermal transducer utilizing
modern digital logic circuitry but does not include a microprocessor. A thin film ther-
mopile detector along with a spectral filter is used as the infrared sensor. A simple
lens designed to transmit infrared energy is used to focus the energy onto the detec-
tor. Special baffling techniques are used to avoid any stray radiation from sources
both inside and outside of the sensor. Besides the optics and IR detector, an ambient
temperature sensor is used to detect varying ambient conditions.
Both the IR detector and the ambient sensor are summed, the signals are modified by
the panel settings and fed to a comparator. They are then digitized to a 12-bit level.
An EPROM is used to linearize the signals according to the required output task (e.g.,
thermocouple or current). The 12-bit signal is then fed to a digital-to-analog converter
followed by a sample and hold circuit and an output amplifier.
Figure 3-1: Theory of Operation