Ensuring Heat Transfer; High Dew Point Measurements - GE Optica Operator's Manual

Chapter 2. Installation

2.5.2 Ensuring Heat Transfer

Be sure the sensor has an adequate heat sink when operating in hot environments. The sensor must never be allowed to
reach a temperature above its rated limit. It is not sufficient merely to ensure that the sensor is in an environment whose
temperature is below the rated limit; a means must be supplied to remove heat from the sensor.
When the Model 1111H or D-2 sensors are used at ambient temperatures of 20° to 24°C, full rated depression can be
achieved by mounting the sensor on a smooth, thermally conductive surface (such as metal), which tends to remain at
the ambient temperature.
If possible, do not operate the sensor continuously at or near full depression. Doing so may decrease the anticipated life
of the thermoelectric heat pump.

2.5.3 High Dew Point Measurements

2.5.3a Using Heated Sensors
When measuring dew points at or above the ambient temperature, the sensor must be heated to a temperature of at least
5 to 10°C above the highest anticipated dew point (but not higher than the sensor temperature rating). Some sensors can
be mounted on a liquid heat exchanger, or a temperature-controlled electric hot plate, or installed in a heated enclosure.
GE recommends closed-loop active control of the elevated sensor body temperature.
The sensor base should be coated with zinc-oxide-filled silicone thermal grease and securely anchored to the heat sink
with suitable fasteners. Allow ½ hour for the sensor to reach thermal equilibrium after adjusting the temperature of the
heat sink.
The GE SIM-12H high temperature sensor is designed for high-temperature applications. It measures dew points above
ambient temperature without condensation problems.
2.5.3b Sample Lines for High Dew Point Measurements
Sampling lines carrying gas to the sensor must be heated and insulated when the dew point of the gas is above the
sample line's ambient temperature. The simplest way to achieve this is to use heater tape (either thermostatically
controlled, or continuously operating, and sized to provide the required temperature rise). At high temperatures, use
stainless steel tubing with adequate insulation to avoid hot and cold sections in the line and to avoid water absorption/
desorption cycling as the heater is thermostatically controlled. Heated sampling lines (HSL) are available from GE.
20 Optica™ Operator's Manual