Sensor Information; Sampling Lines - GE Optica Operator's Manual

2.5 Sensor Information

GE Measurement & Control produces a variety of sensors compatible with the Optica, ranging from one to five stages
of thermoelectric cooling. A comparison chart listing specifications of each sensor is given in Appendix D. "Chilled
Mirror Sensors". The following sections provide information on installing the following GE dew point sensors:
•
Model 1111H — Single-stage sensor
•
Model 1211H — Two-stage sensor; for high pressure and temp.
•
Model D-2 — Two-stage sensor
•
Model SIM-12H — Two-stage heated sensor
•
Model 1311DR — Four-stage heated sensor
•
Model 1311XR — Five-stage water-cooled sensor
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.
CAUTION!
temperature for the device. See Appendix D. "Chilled Mirror Sensors" for complete sensor
specifications.

2.5.1 Sampling Lines

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, PTFE, 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.
Optica™ Operator's Manual
Never place the sensor in a location where temperatures rise above the maximum rated
Chapter 2. Installation
19