Teledyne 7300a - NDIR analyzer - Manual (Page 30)

3 Start-up and Theory of Operation Model 7300A
3-4
Teledyne Analytical Instruments
These lamps are typically rated for 20,000 hours continuous operation when
run in the DC mode (+5VDC). This collimated energy is directed through
parallel infrared beams. The radiant energy passes through tubes containing a
continuously flowing sample gas. As the beam passes through the reference
tube, the energy of the beam is unattenuated and balanced which provides a
standard of source energy output for comparison. The gas of interest is
present in the measurement tube, however, the energy of the beam will be
attenuated at the specific absorption wavelength.
After passing through the two tubes, the radiant beams are reflected and
imaged by a second concave mirror onto a photon detector. A spectral filter,
located just in front of the detector, represents the precise “window” of the
absorption band for the specific gas of interest. Energy outside the band is
eliminated.
The detector converts the optical energy from the radiant beams into an
electrical signal which is modulated in proportion to the gas concentration.
Th erm istor
H eater
Temperature
Control
Fine
Adjustment
C oarse
A djustm ent
Auto-
R ang e
M
U
X
A to D
C onve rter
D ig itial to
A nalo g
C onve rter
(DAC )
0-1 V dc
C oncen tration
and R an ge
4-20 m A dc
C oncen tration
and R an ge
D iffere nce
A m plifier
Auto Z ero
A m plifier
C e n tra l
P ro ce ssin g
U n it
(C P U )
A larm 1
A larm 2
S ystem
Fa ilure
A larm
R S -232
R ang e
C ontacts (4)
E xtern al
Valve
C ontrol
R em ote Sp an
C ontrol
R em ote Zero
C ontrol
C al
C ontact
D isplays P rocessing
Pow er
S upply A to D C onv
To C P U
IR
S ource
P ream p
P ream p
D etecto r
D etecto r
Block Diagram of the Model 7300A Electronics