210-5320 Dew Cell

The Model 210-5320 Dew Cells are improved versions of the traditional lithium chloride (LiCl) sensor. The sensors include a bifilar heater composed of a pair of gold wire electrodes. These are wound over a fiberglass wick treated with LiCl. The LiCl is highly hygroscopic. As it absorbs water from the atmosphere, its conductance increases. This causes additional current to run through the heater, heating the sensor, or dew cell, to the equilibrium temperature at which the LiCl again becomes nonconductive. Equilibrium temperature is measured by a temperature sensor located in the hollow cavity under the heater and is translated to dew point temperature based on a linear relationship.

Two types of dew cells are available, differing only in their temperature sensors. The 210-5320 utilizes a 3-element thermistor, while the 210-5321 features a 100 ohm platinum resistance probe. Both models include a perforated protective shield, temperature sensor leads, and heater leads. The heater requires 24 Vac for excitation, making AC power and a transformer necessary for dew cell operation.

To protect the dew cell from sunlight and the elements when it is used outdoors, it must be installed in a radiation shield or an instrument shelter. The 380-43408-DPT Motor-Aspirated Radiation Shield includes a transformer and a mounting adapter for the 210-5320. It will also hold a temperature probe. The 210-53212 Dew Cell Power Supply is designed for use with a dew cell installed in an instrument shelter. The 210-53212 consists of a transformer, a ballast resistor, and a terminal strip, all in a weatherproof enclosure.

Specifications

Dew Cell
Measuring range: -40° to +40°C
Temperature sensor:
210-5320: Thermistor composite (same as 4480-A)
210-5321: 100 ohm platimum resistance
Accuracy*: ± 1.3°C
*After the appropriate correction, based on relative humidity, is added.
Time constant: 2.0 minutes (typical operation inside 8152-A Shield)
Heater winding: Gold wire
Salt: 8% LiCl solution
Operating temperature: -40° to +55°C
Operating humidity: 17-100% RH at -12°C, 12-100% RH at 30°C
Storage conditions: -40° to +85°C, 0-70% RH
Input voltage: 24 Vac
Power consumption: 2.4 VA
Size: 0.375" dia x 3.75" L (10 mm x 95 mm)
Weight/shipping: 0.5 lb/1 lb (0.22 kg/0.45 kg)

Ordering Information

210-5320 Dew Cell, 3 element thermistor
210-5321 Dew Cell, 100 ohm platinum resistance
210-53212 Stand-Alone Power Supply, 115 Vac
210-53212-A Stand-Alone Power Supply, 230 Vac
380-43408DPT Motor-Aspirated Solar Radiation Shield (holds one dew point sensor and one temperature sensor)
330-0320 Cable to connect dew cell transformer to AC power; 3-conductor, 20 AWG, shielded
330-0420 Cable to connect dew cell to signal conditioning module; 4-conductor, 20 AWG, shielded
M482020 Lithium Chloride Solution, for re-treating the sensor

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