Appendix A. Measurement Considerations
Model PM880 Portable Hygrometer User’s Manual
179
A.3 Sample System Guidelines
A sample system is highly recommended for moisture measurement. The
purpose of a sample system is to condition or control a sample stream to
within the specifications of a probe. The application requirements
determine the design of the sample system. GE applications engineers will
make recommendations based on the following general guidelines:
•
Typically, sample systems should be kept very simple. They should
contain as few components as possible and all or most of those
components should be located downstream of the measurement probe.
Figure 79 on the next page shows an example of a simple sample system
consisting of an explosion-proof housing with a sample cell, a filter, a
flow meter, a vent valve and two-shut off valves, one at the inlet and one
at the outlet.
•
The sample system components should not be made of any material that
will affect measurements. A sample system may include a filter to
remove particulates from the sample stream or a pressure regulator to
reduce or control the pressure of the stream. However, most common
filters and pressure regulators are not suitable for sample systems
because they have wetted parts that may absorb or release components
(such as moisture) into the sample stream. They may also allow ambient
contamination to enter the sample stream. In general, you should use
stainless steel material for all wetted parts.
Contact the GE PCI Division at 1-800-833-9438 (within the USA) or
781-899-2719 (outside the USA) for further instructions.
