Teledyne 7300A Operating Instructions Manual page 30

3 Start-up and Theory of Operation
These lamps are typically rated for 20,000 hours continuous operation
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.
D etecto r
IR
S ource
D etecto r
Th erm istor
D isplays
Block Diagram of the Model 7300A Electronics
3-4
P ream p
Auto Z ero
D iffere nce A m plifier
A m plifier
P ream p
H eater
Auto-
R ang e
C oarse
A djustm ent
P rocessing
Pow er
A to D C onv
S upply
Teledyne Analytical Instruments
A to D
To C P U
C onve rter
M
U
X
0-1 V dc
C oncen tration
and R an ge
D ig itial to
A nalo g
C onve rter
(DAC )
4-20 m A dc
C oncen tration
and R an ge
A larm 1
A larm 2
S ystem
Fa ilure
A larm
R S -232
C e n tra l
P ro ce ssin g
R ang e
U n it
C ontacts (4)
(C P U )
E xtern al
Valve
C ontrol
R em ote Sp an
C ontrol
R em ote Zero
C ontrol
C al
C ontact
Model 7300A
when