Sampling Lines - GE Optica Operator's Manual

Sensor Information
(cont.)

Sampling Lines

Installation
When selecting a location for installing a sensor, consider the
following criteria:
•
Locate the sensor as close as is practical to the source of the gas to
be measured, to keep the sampling lines as short as possible. This
minimizes the system response time and reduces the error rate at
low frost points due to sample line outgassing.
•
Choose a sensor location that provides access to the dewpoint
sample cavity cover, to facilitate periodic mirror cleaning.
Never place the sensor in a location where temperatures
rise above the maximum rated temperature for the device.
See Appendix D for complete sensor specifications.
Keep the length of sample tubing between the source and the sensor
short, for quick response and highest accuracy.
All sampling line compression fittings provided with the sensor are
for ¼-inch diameter tubing, unless otherwise specified at the time of
order.
The material used for the inlet lines can have an important effect on
the validity of the readings. Do not use rubber hose or plastic tubing
such as PVC or Tygon, because of their hygroscopic nature.
When measuring frost points below –30°C, sample gas leaving the
sensor outlet should be vented through an additional line three to six
feet long, since backflow of ambient moisture into the sensor can take
place even under positive pressure. Use stainless steel tubing and
fittings, and ensure that all plumbing is completely free from leaks.
At dew/frost points above –20°C, tubing material is not as critical.
Copper, Teflon, polypropylene, aluminum or brass tubing and fittings
may be used. The sampling system should allow for periodic
cleaning. It may be helpful to install a tee and closing valve on the
inlet side, to permit the sensor to be shut off while the sampling lines
are flushed. At very low humidities, even a trace amount of
contamination can alter measured frost point, so cleanliness is
particularly important.
Caution!
January 2006
2-13