Epson XDT manual Appendix H Sample Gas Filter Considerations, Tested Instrument ˚C

XDT User’s Manual Appendices

Appendix H: Sample Gas Filter Considerations

Sample treatment with pre-filtering may be a necessity in many instances. However the filter housing and element may affect the dewpoint reading and/or the response time of the system. Below is a graph comparing measurements from the same calibrated sensor with and without a filter utilizing a polycarbonate bowl. All other parameters, which may affect the measurement, were kept constant. Outside of the sample system, a rather hot and humid environment was cre- ated, to illustrate a worse case condition. As can be seen the filter does not cause problems for dewpoints greater than -50°C. However the systems' ability to make precise measurements quickly deteriorates for dewpoints below -55°C.

Tested Instrument (˚C)

-35	Effect of polycarbonate filter on dewpoint measurement
	Tests performed inside environmental chamber
-40	at 30˚C temperature and ~100%RH. Test gas
	flow rate 3LPM. Using XDTsn: 2007 and
	XTR-100 sensor sn: 18107

·Data with legend "ALL SS" was taken with an

-45	all stainless steel system.
	· Data with legend "Through Filter" was taken with
-50	same system but with the addition of a polycarbonate
	bowl filter
-55
-60
-65
-70
-75	MBW ˚C
-80	ALL SS ˚C
	Through Filter ˚C
-85
-90
-90	-85 -80 -75 -70 -65 -60 -55 -50 -45 -40 -35

Chilled mirror reference instrument MBW (˚C)

With this in mind the user should select the appropriate filter construction materials. It is impor- tant to note that a stainless steel housing filter will not cause measurement errors, however if the filter element inside the housing is made of hygroscopic fibers, then there will be a delay intro- duced in the measurement.

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