User's Guide ______________________________________________________________________
52 __________________________________________________________________ M210667EN-C
The basic principle of LTD112 is shown in Figure 19 below.
Test LED
Detector
Narrow Band
Amplifier
Temperature
Measurement
EEPROM
Synchronous
Demodulator
20bit ADC
Main Receiver Signal
CPU
Main Receiver DC
CPU
Test LED
CPU
CPU
DC
Measurement
Main Transmitter
Main Transmitter Clock
0401-036
Figure 19
Block Diagram LTD112
Window Transmitter Module LTL212
The window transmitter module LTL212 (see Figure 20 below) is
mounted to the optics unit and is secured by two screws. It is connected
to the measurement CPU using two connectors.
1104-093
Figure 20
Window Transmitter Module LTL212
The window transmitter module contains a white, high-power LED as a
light source. Under the control of the measurement CPU, the light source
is modulated with a frequency of approximately 250 Hz. A monitor
photodiode measures the emitted light intensity, and a closed loop
regulator in combination with a LED driver achieves a normalized,
constant transmitter intensity.
The intensity signal and a derating signal, proportional to the applied
LED forward current, are connected to the ADC of the measurement
CPU for self-diagnostics.