Teledyne 6200E - Sulfides Analyzer - Manual (Page 50)

Optional Hardware and Software Model 6200E Instruction Manual
50 M6200E Rev: A1
The state of the IZS valves can also be controlled:
• Manually from the analyzer’s front panel by using the SIGNAL I/O controls located under
the DIAG Menu (Section 6.9.2),
• By activating the instrument’s AutoCal feature (Section 7.9 ),
• Remotely by using the external digital control inputs (Section 6.12.1.2 and Section 7.7.1),
or
• Remotely through the RS-232/485 serial I/O ports (see Appendix A-6 for the appropriate
commands).
Sources of zero and span gas flow must be capable of supplying at least 600 cm 3 /min. Both supply
lines should be vented outside of the analyzer’s enclosure. In order to prevent back-diffusion and
pressure effects, these vent lines should be between 2 and 10 meters in length.
External Zero Air Scrubber
The IZS option includes an external zero air scrubber assembly that removes all H
2
S the zero air
source. The scrubber is filled with activated charcoal.
The Permeation Source
Span gas is created when zero air passes over a permeation tube containing liquid H
2
S under high
pressure, which slowly permeates through a PTFE membrane into the surrounding air. The speed
at which the H
2
S permeates the membrane is called the effusion rate. The concentration of the
span gas is determined by three factors:
Size of the membrane: The larger the area of the membrane, the more permeation occurs.
Temperature of the NO
2
: Increasing the temperature of the increases the pressure inside the tube
and therefore increases the effusion rate.
Flow rate of the zero air: If the previous two variables are constant, the permeation rate of the
calibration gas into the zero air stream will be constant. Therefore, a lower flow rate of zero air
produces higher concentrations of H
2
S. The M6200E usually has a constant flow rate and a
constant permeation rate, hence, variations in concentration can be achieved by changing the IZS
temperature.
NOTE
The permeation tube is not included in the IZS Option and must be ordered separately.
See Section 5.4.3 below.
Permeation Tube Heater
In order to keep the permeation rate constant, the IZS enclosure is heated to a constant 50° C
(10° above the maximum operating temperature of the instrument). The IZS heater is controlled
by a precise PID (Proportional/Integral/Derivative) temperature control loop. A thermistor
measures the actual temperature and reports it to the CPU for control feedback.