Installing the soil moisture sensors

iMETOS can be equipped with 4 different types of soil moisture sensors. Tensiometers are giving accurate readings in between 10 and 700 mbar of water tension. Tensiometers for this are widely used in horticulture because their measurement range fits very well to the most vegetables and soft fruits. Watermark sensors are returning water tension too. The range of this sensor is in between 10 and 2000 mbar. This sensor fits for all horticulture crops, soft fruits, for all tree fruits and for all agricultural crops. It is easy to use and allows applying a controlled deficit regime for crops which can accept this. Echo probes measuring soil water content in volumetric percentage. They are a cost effective capacitive sensor. The use of echo probes gives the amount of water what has been used by the crop but it tells nothing about the availability of the crop.  Sentek Enviroscan or EasyAg sensors are giving a perfect way to monitor the water use in different soil depths.
On iMETOS we can combine tensiometers with watermark sensors, echo probes and Enviroscan or EasyAg?. The combination of Tensiometer and Watermark will give accurate readings by the tensiometer in the area when water is easily available for the plant and readings for controlled water deficit when this is applied. Please note the tensiometers should be removed in the time of water deficit or refilled after this time. The combination of tensiometer with echo probes will give information about availability of soil water and about the water needed to refill the soil. 

Installing the tensiometer


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The Pessl Instruments Ges.mb.H. tensiometers are delivered in chains of 2, 3 or 6 pieces. They are connected to one of the digital Inputs on the PCB inside the box. The tensiometers are based on the iMETOS bus which allows to line up several sensors in one line of cable. The tensiometers chains are having 15 m cable in between the sensors. The sensors have not been filled by Pessl Instruments Ges.m.b.H. Otherwise they would have wetted all delivery. To fill them follow the chapter below.
The tensiometers are having an outside diameter of 20mm. Use a soil auger to make a narrow hole and moisture the hole with water before you enter the tensiometer. The tensiometer has to have close contact on the side and at the base of the hole. Water tension measurement is very sensible to air gaps below the sensor.  

Filling and Re-filling the tensiometer

To re-fill the tensiometer please place emerge the sensor totally overnight in water filled bucket. The next morning please connect a syringe to the tensiometer and pull it up. Use the syringe to degas the tensiometer. When the syringe fills with water remove it and plug the tube again.  

Installing the watermark sensors



The watermark sensors are connected to the top of the electronic box. The top gives the possibility to connect 6 sensors to 6 pairs of screws. The numeration of the sensors starts in the left upside corner and ends in the right downside corner. To connect the sensors you need a Philips one screw driver to open and close the screws.
The second possibility to connect watermark sensors to an iMETOS is to use watermark extensions on the iMETOS bus. This way extents iMETOS 1 up to 36 watermark sensors on iMETOS 2 PCBs even a higher number of watermark sensors could be possible. This extensions are small boxes with up to 1 km cable in between giving 3 inputs for watermark sensors. The sensors have to be connected inside the box.
The iMETOS bus uses all digital inputs like the tensiometers.

Before installing the watermark sensors in soil they should be prepared. For preparing please water the sensors 2 times for 12 h and let them dry again. The prepared sensors can be buried. Water tension measurement is very sensible to air gaps below the sensor. Therefore we prefer to dig a hole with 8 or 10 cm diameter and bury the sensor in moist soil.

Installing the echo probes

ImageMaximum five echo probes can be connected to an echo probe top of the iMETOS. The echo probe top has PCB with 5 screwing connectors for echo probes. On the lower side of the top there are seven 6 mm screwing to enter the cables. If the probe have been ordered from Pessl Instruments Ges.m.b.H. together with the top it will be already mounted. If not please mount them following this instruction. The echo probes are delivered with 5 m cable with a male connector plus 15 cm cable with a female connector. The short cable with the connector has to be mounted first in the top. The short cable has 3 wires: Bare, white and red. Fix them left to right bare, white red in the connectors on the PCB and close the screwing. Now you will have the top with the connectors hanging down. The electronic is prepared to install the sensors in field.
To install the sensor in field use the specific tool for echo probe installation or something like an asparagus harvesting knife to make a cut of 20 cm depth and 4 cm wide. Insert the sensor in this cut and close the hole. Now bury the cable and connect it to the iMETOS. 


Created by heiner. Last Modification: Friday 03 of February, 2012 13:35:51 GMT by Lena.