Tensio switch
A Tensio switch , also known as a switch tensiometer , is used for watering automation . It is a measuring device for soil moisture measurement with an electrical switching output.
Measuring principle and structure
The measuring principle is identical to that of the tensiometer . Instead of the pressure sensor there is a membrane (4) which is connected to an electrical pressure switch (3).
When the soil dries out, the negative pressure increases until the switching point of the pressure switch is reached through the bulging of the membrane.
The switching signal - usually a potential-free closing contact - can be used directly to control an irrigation pump, a solenoid valve or as an input signal for an irrigation computer. With the entire arrangement, the soil moisture can be kept constant in a horticultural culture under glass. The term “tensiostat” has become established for this.
A common switching point for Tensio switches is for applications in horticulture at −90 hPa, corresponding to a soil moisture of approx. 90 cm groundwater level below the soil surface. The switching hysteresis of the mechanical switch is approx. 10 to 20 hPa due to the design.
Designs
There are also designs with a switching point of −60 hPa, −120 hPa or with an adjustable switching point. For the measurement of the suction tension of thin substrate layers, ceramics are also used, which are designed as a level sensor: there is only an open-pored ceramic surface for measurement on the underside, while the sides and the top are glazed.
For direct reading of the suction tension and for control purposes, there are also designs with an attached pressure measuring cell (manometer). However, continuous measurement and recording of soil moisture is achieved with an electronic tensiometer .
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- G. Bambach: Control and regulation of the pot plant irrigation . In: Closed cultural processes , Taspo-Praxis No. 18, Braunschweig 1990, ISBN 3-87815-030-X