Campbell Scientific 237-L Leaf Wetness Sensor - Manual (Page 5)

Model 237 Leaf Wetness Sensor
1. Introduction
The 237 Leaf Wetness Sensor is a simple resistive grid configured in a 3-wire
half-bridge. The circuit is completed when water bridges two inter-digitate
electrodes. Response is non-linear with a rapid decrease in resistance relative
to an increase in wetness. The simplicity of the sensor lends it to various
applications, means of preparation, and data interpretations.
1.1 Specifications
Temperature Range: Operational 0° to 100°C; Survival -40° to 150°C
Sensor may crack if temperature drops below -40°C
Dimensions: 2.75" W x 3.0" L x 0.25" D (7.1 x 7.6 x 0.64 cm)
Weight: 3 oz per 10' cable (91 g per 3.1 m cable)
2. Wiring
Figure 1 is a circuit schematic of the 237. Table 1 describes wiring to
Campbell Scientific dataloggers.
FIGURE 1. 237 Sensor Schematic
TABLE 1. Connections to Campbell Scientific Dataloggers
Color Description
CR200(X)
CR800
CR5000
CR3000
CR1000
CR510
CR500
CR10X 21X
CR7
CR23X
Black Excitation
Switched
Excitation Switched
Excitation Switched
Excitation
Red
Resistance
Signal Single-Ended
Input Single-Ended
Input Single-Ended
Input
Purple
Signal
Ground
AG
Clear Shield G
1