Humidity Sensor, digital and analog to measure air and soil moisture
All water movements in the soil are directly depending on the soil water tension, as water will always move from the lower to the higher potential.
Compared to other methods, only with Tensiometer:
the sum of the water holding forces is measured, no knowledge of the soil's pF-characteristic, no soil calibration is necessary and installation disturbances are inhibited as the measured volume is much higher.
A few of many applications:
The type 3503.0000 incorporates a digital signal processing which offers highest flexibility for integrating the sensor in measuring systems, different output signal ranges for data logger applications or possibility for direct PC-readout or networking.
The Tensiometer is optimised for in-the-field use. Signals for soil water tension, soil temperature and filling status are offered. Water tension and temperature are linear voltage signals 0 ... 2 V. Thus, the signals are directly connectable to nearly any datalogger or other data recording device.
The complete electronics of the sensor is integrated in the sensor body. The housing consists of glass-fibre reinforced synthetic. All electronic components are epoxy moulded, thus featuring maximum protection against moisture.
The Tensiometer is calibrated electronically by programmable potentiometers. The calibration is stored in EPROM's. The piezoelectric pressure sensor measures the soil water tension against the atmospheric pressure.
The atmospheric pressure is conducted through a watertight diaphragm (the white, 2 cm long tube on the cable) and through the cable to the reference side of the pressure sensor. A platinum sensor 1/3 DIN B is used as temperature sensor. The platinum sensor has a maximum deviation of ±0.1 K at 0°C. The tip of the sensor dips into the Tensiometer cup's water. Thus, the best possible thermal contact to the soil is achieved. To transfer the soil water tension as a negative pressure into the Tensiometer, a semi-permeable diaphragm is required. It must have good mechanical stability and water-permeability, but also have gas impermeability. This is achieved by means of the ceramic Al2O3 sinter cup. The reference atmospheric air pressure is conducted to the pressure transducer via the air permeable (white) Teflon membrane and through the cable. The membrane does not absorb water. Water will not pass through the membrane into the cable, but condensed water inside the cable will leave the cable through the membrane.