Vaisala WAA151 Installation Manual download pdf (Page 44)

Installation Manual __________________________________________________________________

42 ___________________________________________________________________ M010114en-B

DSU12 employs six blackened temperature sensitive bimetallic

element pairs, arranged in a circle, which track each other thermally

during overcast lighting conditions. When exposed to direct sunshine,

the inner element is shaded whilst the outer element heats and bends

to make a contact closure. In the absence of direct sunshine, the inner

element receives diffuse radiation reflected from the white base and

therefore the element pairs bend uniformly under varying temperature

conditions thus preventing false contact closures.

The element pairs are protected within a clear acrylic dome fitted with

a silicone O-ring seal and restricted ventilation chimney. Due to the

difference in the bend radius of the inner and outer elements, the

contacts close with a self-cleaning wiping motion.

Rain drops and frosting on the outer dome have negligible effect upon

the performance of the DSU12 sensor. The solar heating of the dome

via the blackened element pairs and the restricted ventilation combine

to assist in quickly melting snow deposits and frost. Heavy snowfalls

may reduce the effectiveness of operation.

DSU12 can be used at latitudes between 0° and 65° in either

hemisphere. The sensor is correctly installed when exposed to the sun,

without shading, throughout the entire day. Due to the shape and

geometry of the element pairs, DSU12 does not need any special

alignment for the latitude of the site or the season of the year. The

instrument is equipped with a shielded 2-core cable, two meters in

length, and a connector for easy installation.

Soil Temperature Sensors

QMT103

9901-012

Figure 29 QMT103 Soil/Water Temperature Sensor

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Vaisala WAA151 Installation Manual Page 44