Chapter 4 _______________________________________________________________ Installation
VAISALA _______________________________________________________________________ 27
Sampling from a Process
Sampling is needed when direct measurement of the air or gas is not
possible or desirable. This may be related to, for example, a high process
temperature, protecting the sensor from water spikes, the need to easily
detach the instrument from a pressurized process without running the
whole process down, or wanting to make the measurement at a more
convenient location.
Make sure there is sufficient flow of gas to the sensor (for example,
1 l/min) to give a representative sample.
You can use the Vaisala Humidity Calculator to simulate the effect of
pressure change to dewpoint. The Humidity Calculator can be found at:
Sampling Accessories
DMT242SC Sampling Cell
DMT242SC is a basic sampling cell with only the main sampling cell
body. The inlet and outlet are female threaded sample connectors (inlet
G3/8", outlet G1/4" ISO). Refer to Figure 13 on page 28.
DMT242SC is suitable for users requiring only a sampling cell to fit the
transmitter into and doing further assembly (piping into inlet and outlet,
valves, possible flow meter) by themselves.
DMT242SC2 Sampling Cell with
Swagelok Connectors
DMT242SC2 is similar to DMT242SC, but connections are made easy.
The sampling cell includes welded Swagelok connectors at both the inlet
and outlet that fit directly to 1/4" tubing.
To fit 6 mm tubing to the connectors, an adapter such as Swagelok®
Reducer SS-6M0-R-4 (not supplied by Vaisala) can be used.
DMT242SC2 is the suitable choice in, for example, plastics drying
systems, where the measurement is made by tapping off the dryer system
and bringing a small air stream to the sensor. The Swagelok connectors
of DMT242SC2 easily connect to a cooling coil or tubing providing the
essential function of cooling the dry air to ambient temperature before it
reaches the sensor.
