USER MANUAL | ICOS | INSTRUCTIONS | UM/ICOS-EN REV. B.2
Appendix F: External Dynamic Dilution
System (Optional)
The External Dynamic Dilution System (EDDS) is an optional accessory. This section
describes the EDDS and explains setup and operation.
Figure 94: EDDS Front & Back Panel
The EDDS:
Automatically dilutes the sample stream with zero-air whenever the concentration
rises above the target (2, 5, or 10 ppm). It maintains the target concentration at
that level.
Has a response time constant of approximately 2 minutes, so a sudden rise in
concentration will cause the concentration to over-range for up to 2 minutes while
the DCS adjusts the concentration to target.
The sample and the zero-air flow in through the gas inlets and are mixed in the EDDS. Both
the sample and the zero-air must:
Be pressurized to between 15 and 50 PSIG
Have a sample gas flow capability of 200 SCCM
Have a zero-air flow capability of 2.2 SLPM
When transitioning from a large concentration to a lower concentration of
gases, a memory effect may result from residual gas in the analyzer.
Verify that the gas from the previous sample has had time to exit the
system. Residual gas can also be removed by switching inlet lines, using
shorter line lengths, or flushing lines with zero-air.
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