Справочник Пользователя для Teledyne gfc 7000ta

 

Teledyne Analytical Instruments 

202 

Reference 

Pulses 

Measurement 

Pulses 

IR Beam 
Pulses 

Segment Sensor 
Pulses 

MR Sensor 
Pulses 

 

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. 

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. 

While the photo-detector converts fluctuations of the IR beam into electronic signals, the Sync / Demod 
Board amplifies these signals and converts them into usable information.  Initially the output by the photo-
detector is a complex and continuously changing waveform made up of Measure and Reference pulses.  
The sync/demod board demodulates this waveform and outputs two analog DC voltage signals, 
corresponding to the peak values of these pulses.  CO2 MEAS and CO2 REF are converted into digital 
signals by circuitry on the motherboard then used by the CPU to calculate the CO

2

 concentration of the 

sample gas. 

Additionally the synch/demod board contains circuitry that controls the photo-detector’s thermoelectric 
cooler as well as circuitry for performing certain diagnostic tests on the analyzer.