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MAS-1 Soil Moisture Sensor

3. Integrating the MAS-1

A 4-20mA system generally consists of a sensor, a transmit-

ter, a power supply, and a device to read the current being

transmitted through the current loop. The MAS-1 is an inte-

grated sensor and 4-20mA transmitter. When the MAS-1 is

the loop that is proportional to the soil dielectric permittivity

and therefore the soil volumetric water content.

In Figure

1, the current loop is shown by the dotted line labeled I=4-

20mA. The arrows indicate the direction of the current.

Figure 1 - 4-20mA current loop diagram

The MAS-1 uses a microcontroller to regulate the interval at

which it takes measurements. It takes one second from the

time it is powered up to take its first measurement and trans-

mit current though the loop. The trasnmitted current will

reach a stable value within four seconds of power up. After

the initial four second startup, measurements are taken every

one second, while the current in the loop is continuously

maintained. Since the measurement intervals are controlled