HydroSense II Soil Moisture Measurement System
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9.4
Measurements in Special Materials
The HydroSense II and its sensors were designed principally for use in
agricultural soils, but the measurement technique underlying the instrument
supports other potential applications. Other porous media can also be monitored
using the period value shown on the display. The period is strongly related to
dielectric permittivity of the material surrounding the probe rods and can be used
as a relative value to measure changes in the material of interest. Period
generally increases along with water content. For actual water content values, a
soil specific calibration can be performed using an independent measure of water
content such as gravimetric analysis. A calibration equation can then be derived
to relate period measured by the HydroSense II to water content for the chosen
soil or other medium.
10
Maintenance
10.1
Batteries
Under normal use, the life of the 4 AA batteries in the HydroSense II should be
close to a year. The device is designed to continue to provide accurate
measurements until the batteries are completely exhausted. The battery indicator
icon on the
main screen
gives a warning of the battery status and when the
battery indicator shows that the batteries are close to empty (
symbol), it is
advisable to have replacement batteries close to hand. It is recommended to carry
them in the spare battery holder provided in the carry case.
Configuration settings, stored data and zones are all preserved when the batteries
are replaced, however the time and date are lost until GPS synchronisation is
restored or the time and date are entered manually in the
time/date menu
.
10.1.1
Battery Types
Because of the nature of the power supplies used in the HydroSense II, it is
strongly advised to only use good quality alkaline batteries as replacements.
Carbon Zinc batteries (sometimes marketed as “extra heavy duty” or “extra long
life”) are not well suited to this use and are likely to be exhausted in a relatively
short period. Carbon Zinc batteries are also particularly prone to leaking when
exposed to large temperature variations such as those experienced in outdoor
use.
While rechargeable battery technologies such as Nickel-Cadmium (NiCd) or
Nickel-Metal-Hydride (NiMH) may seem attractive, these batteries have a high
self-discharge rate which makes them inadvisable for use the HydroSense II.
Since the device will sometimes remain unused for several months over winter,
it is likely that the batteries will be discharged when the device is called into use
after such a long break.
Despite its design enabling a standby life of many years, it is always prudent to
remove the HydroSense II’s battery pack when the unit is to be stored for an
extended period (greater than 1 year) to guard against the possibility of damage
due to leaking batteries.
