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Teledyne API Model T360/T360M Operation Manual Principles of Operation
209
Reference
Pulses
Measurement
Pulses
IR Beam
Pulses
Segment Sensor
Pulses
MR Sensor
Pulses
Figure 7-14: Segment Sensor and M/R Sensor Output
Schmidt Triggers
To ensure that the waveforms produced by the Segment Sensor and the M/R
Sensor are properly shaped and clean, these signals are passed through a set of
Schmidt Triggers circuits.
7.4.3.4. IR PHOTO-DETECTOR
The IR beam is converted into an electrical signal by a cooled solid-state
photo-conductive detector. The detector is composed of a narrow-band optical
filter, a piece of lead-salt crystal whose electrical resistance changes with
temperature, and a two-stage thermo-electric cooler.
When the analyzer is on, a constant electrical current is directed through the
detector, The IR beam is focused onto the detector surface, raising its temperature
and lowering its electrical resistance that results in a change in the voltage drop
across the detector.
During those times that the IR beam is bright, the temperature of the detector is
high; the resistance of the detector is correspondingly low and the its output
voltage output is low. During those times when the IR beam intensity is low or
completely blocked by the GFC Wheel mask, the temperature of the detector is
lowered by the two-stage thermo-electric cooler, increasing the detectors
resistance and raising the output voltage.
07272B DCN6552