So Ultraviolet Fluorescence - Teledyne T101 Operation Manual

Principles Of Operation
10.1.2. SO ULTRAVIOLET FLUORESCENCE
2
246
The chemical process is:
2 H S 3
+
2
The converter is a heated stainless steel core containing a catalyst across which the
sample gas passes just before induction into the reaction cell. The temperature of the
converter is maintained by a heater controlled by the CPU via the I
card. The converter is enclosed in high-temperature insulation and encased in a stainless
steel housing.
The converter is most efficient when it operates at 315°C, converting 95% of the H
into SO . Converter temperature is viewable via the front panel as the test function
2
CONV TEMP (see Section 4.2.1) and can also be output via the test channel analog
output (see Section 4.6.9). A warning message, CONV TEMP WARNING (see Section
4.2.2) will be issued by the CPU if the converter's temperature is below 310°C or above
320°C.
When the converter is operating at peak efficiency there is a nearly 1:1 relationship
between the amount of H
leaving it. Therefore, by measuring the amount of SO
converter, the amount of H
inferred. This is accomplished by measuring the ultraviolet fluorescence of the SO
the sample chamber.
The physical principle upon which the T101's measurement method is based is the
fluorescence that occurs when Sulfur dioxide (SO
by ultraviolet light with wavelengths in the range of 190 nm - 230 nm. This reaction is a
two-step process.
The first stage (Equation 10-1) occurs when SO
photons (hv) of the appropriate wavelength. (In the case of the Model T101, a band pass
filter between the source of the UV light and the affected gas limits the wavelength of the
UV light to approximately 214 nm.) The SO
light, causing one of the electrons of each affected SO
energy orbital state (SO
SO
2
The amount of SO converted to SO
2
average intensity of the UV light (Ia) and not its peak intensity because the intensity of
UV light is not constant in every part of the sample chamber. Some of the photons are
absorbed by the SO as the light travels through the sample gas.
2
O
  → 
2
S entering the catalytic converter and the amount of SO
2
S originally present on the sample gas can be directly
2
absorbs some of the energy from the UV
2
*).
2
+ 
hv
214 nm
* in the sample chamber is dependent on the
2
Teledyne ML - T101 Operation Manual
2 H O 2
+
2
2
C bus and the relay
in the gas after it leaves the
2
) is changed to excited state (SO
2
molecules are struck by ultraviolet
2
molecule to move to a higher
2
→
Ia
SO *
2
(Equation 10-1)
SO
2
S
2
2
in
2
*)
2