ABB PGC5007 - Detector

PGC5007
PGC5007 Operating Instructions 3 Operation
10 OI/PGC5007-EN, Rev C
3.4 Detector
The detector for the Fuel Sulfur Analyzer is the flame photometric detector (FPD). The detector cell is located in the electronics
housing and the burner block is located in the oven.
Flame photometric detection works on the principle that when sulfur is burned in a hydrogen-rich atmosphere, luminescence
(light) characteristic to sulfur is produced. The FPD cell consists of a burner chamber equipped with a spark ignition system, and
a photomultiplier tube which is thermoelectrically temperature controlled. A narrow bandpass filter optically connects the
burner chamber and the photomultiplier tube. An exponential amplifier conditions and amplifies the
photomultiplier tube output to provide a linear output over a wide dynamic range. Sulfur addition permits accurate
measurement of low-level sulfur compounds. Figure 3.6 shows a typical FPD cell.
Photomultiplier Tube
Burner Block
Fig. 3.6. Flame Photometric Detector
When a sulfur compound passes through the hydrogen-rich flame, strong luminescence occurs between 320 and 460 nm. The
narrow band-pass filter allows a sulfur spectra-centered transmission at 394 nm ± 5 nm to achieve a specific ratio of sulfur to
non-sulfur compounds between 10,000 and 30,000:1. A photomultiplier tube views the filtered light and outputs a voltage
proportional to the intensity of the filtered luminescence. For maximum sensitivity, the detector is optimized with respect to
temperature, gas flow rates, and bias voltage on the photomultiplier tube.
Because the amount of sulfur in the sample is very small, a sulfur addition module provides a standard level of sulfur. This
keeps the sulfur readings above the noise level of the method. When the analyzer processes a sulfur compound, the sulfur in
the sample adds to the standard sulfur, providing a level more easily measured by the photomultiplier tube.
The FPD Electrometer PCB, located inside the Electronics compartment of the isothermal oven, digitizes the detector output
signal for processing. This assembly also provides energy for FPD flame sensing and ignition.