Measurement Considerations A-5February 2005Sample System GuidelinesA sample system is highly recommended for moisturemeasurement. The purpose of a sample system is to condition orcontrol a sample stream to within the specifications of a probe.The application requirements determine the design of the samplesystem. GE Infrastructure Sensing applications engineers willmake recommendations based on the following generalguidelines:• Typically, sample systems should be kept very simple. Theyshould contain as few components as possible and all or mostof those components should be located downstream of themeasurement probe. Figure A-1 on the next page shows anexample of a simple sample system consisting of an explosion-proof housing with a sample cell, a filter, a flow meter, a ventvalve and two-shut off valves, one at the inlet and one at theoutlet.• The sample system components should not be made of anymaterial that will affect measurements. A sample system mayinclude a filter to remove particulates from the sample streamor a pressure regulator to reduce or control the pressure of thestream. However, most common filters and pressure regulatorsare not suitable for sample systems because they have wettedparts that may absorb or release components (such asmoisture) into the sample stream. They may also allowambient contamination to enter the sample stream. In general,you should use stainless steel material for all wetted parts.Contact the GE Infrastructure Sensing PCI Division at 1-800-833-9438 (within the USA) or 781-899-2719 (outside the USA)for further instructions.
