Vaisala DM500 - Manual (Page 28)

User's Guide ______________________________________________________________________
26 __________________________________________________________________ M210205EN-D
- Sample tubing shall be as short as possible, the surface area should
be minimized by using the tubing with the smallest diameter that
the flow conditions shall permit
- Surface finishing of wetted surfaces is important, polished or
electropolished steel is recommended for best results
- Avoid hygroscopic materials in the sampling lines, use stainless
steel membranes instead of rubber membranes
- Choose impermeable materials to avoid inward diffusion of
moisture through sampling tubes and enclosures, such impermeable
materials include high quality stainless steel and metals. Avoid
PVC or nylon tubes !
- PTFE (Teflon) tubes are not suitable for dewpoints below -40 ºC.
Measuring in Overpressure
When sampling in pressurized processes, the pressure difference
between the gas inlet and outlet ensures gas flow to the sensor.
However, please take into account the following:
- The dewpoint is measured always in the actual pressure. The
pressure is released at the flowmeter valve after the sensor
chamber. When measuring at overpressure, it must be taken into
account that the volume flow rate decreases under pressure,
whereas mass flow rate remains constant.
- The pressure ranges of the optional parts are:
- Integrated pressure sensor: 0...2 bar or 0...20 bar
- Integrated flow sensor: 1.7 bar